54 replies to this topic

[jdi]

I'm wondering what strategies can be used to minimize turbocharger lag and maximize the usable RPM range of a turbocharger by causing it to spool up at as low an RPM as possible.

Assume that a turbocharger of the appropriate size and design for the desired horsepower level has been chosen, and that changes which would drastically affect the engine or turbocharger's reliability or lifespan are undesired. No WRC-style anti-lag plumbing, for example.

A couple thoughts I had:

- When the driver floors the throttle and the turbo is not yet up to speed, ****** ignition timing to be after TDC and inject more fuel than normal so that the mixture is still burning when it goes through the turbo. Something like the anti-lag systems used in WRC, but only active when the driver is coming back on the throttle instead of the whole time the driver is off throttle. Or would better results be obtained by just using timing and fuel mixture settings that would give the best response on a naturally aspirated engine in that RPM and load range?

- Design the engine intake runners to be most efficient in an RPM range that is just below where the turbo would normally begin to generate boost, with the hope that the extra bit of power generated would help the turbo to spool up more quickly and/or at a lower engine RPM than it normally would. Would this even make a difference?

Any comments or suggestions?

[Andy McCord]

I believe the biggest step to come in reducing lag will come from this angle.

http://www.autoblog....rbine-geometry/

[J. Edlund]

To ****** the ignition is used today in racing to get the turbochargers to spool earlier. To keep the boost up when the driver lifts off the throttle, that a separate issue though. For that an anti-lag valve can be used that bypasses charge air into the exhaust for combustion of fuel from the ordinary injectors. It's also quite simple to bypass air though the engine with an electronic throttle for anti lag. Any factor that affects the working temperature of the turbocharger will reduce its life though.

There are more options. A variable nozzle turbine can decrease lag and increase the range of the turbocharger. The problem so far have been with the temperatures, a modern gasoline engine can have exhaust temperatures of 1050 degC and VNT turbos typically can handle about 820 degC.

Ball bearings are said to reduce the lag, any real difference is however almost impossible to notice given an otherwise identical turbo.

To operate a turbocharger over a wide range requires a compressor with a wide range. Ported shroud is recommended and the impeller blades should be backswept, more than typical. Backswept blades cost you a bit in boost pressure but range is improved.

To improve boost at low speeds the volume of the exhaust manifold can be decreased to a minimum; this will make more energy availible to the turbine. With more than three cylinder per turbocharger, use a twin scroll turbocharger or more than one turbo.

To use more than one turbo have also shown some possibility to decrease lag and widen the performance of the engine.

To reduce lag an extra throttle before the compressor can be used. The function of this throttle is to create a vacuum in the compressor housing when the driver lifts off the throttle. This reduces the losses and the turbocharger will keep spinning longer and lag is reduced when the driver goes for full throttle again. Was used on some F1 cars during the eighties.

Reduce the inertia of the turbocharger rotating assembly. Instead of conventional superalloys like Mar-M 247 and Inconel 713 the turbine can be made out of silicone nitride or titanium aluminide. This will give some reduction in lag.

Use a high compression ratio. This will increase power when the engine is off boost. To prevent detonations with boost lots of fuel, retardation of the ignition and/or water injection is needed. This typically results in high exhaust temperatures.

[ray b]

some drag racers use NOX to boost gas flow at low RPM befor starting the race

a smaller turbo cuts lag and will give boost at a lower RPM
I like my volvo set up that gives very progressive boost
but price is lower power at hi RPM

[NTSOS]

As opposed to a light switch racing application, does anyone here feel unconfortable about placing a throttle in front of a compressor?

Yep, we understand the concept of a Bov...very crude attempt at ham fisted/narrow range pressure control after the fact of slamming the throttle closed.....as opposed to an attempt to control outlet air pressure with a foot control in the face of pre-boost/post boost variable compressor/engine load/speed requirements.

Does it make sense, if you are driving a street machine, to compress air 24/7 when it is not needed? Would it not make sense to throttle the compressor inlet? I know, I know....the time it takes to accellerate the mass air flow volume between the compressor inlet throttle, the intercooler and the operating cylinder.....it could be a problem, but in reality we are talking ms/sec and the motor responds less violently and simply acts like a normally aspirated motor that just hits the camshaft......especially important when you are dealing with close to 900 lb/ft of torque at relatively low rpm's. When cruising down the road normally, the turbine/compressor is merrily spinning away madly at very high rpm's because there is no load..........when you get back on the throttle, it pretty much instaneous.


If you are going to build a low/high range turbo motor....how about using a variable geometry induction system to present the turbine inlet with a docile low rpm pressure producer to spool up the turbine and then as the pressure and RPM increase, open up the manifold and take avantage of the large ports, large turbine A/R and relatively non-standard, long duration/high lift camshaft to produce a very wide power band from off idle to red line.

John

[Stian1979]

This would be my options.
1. Trotle befour compressor.(cheap, you can just go to the junkyard and get a trotlebody)
2. Anti lag valve. (A litle work neded to make it work)
3. Two stepp turbocharging. (find two turbos of diferent size and try to make them work, Maybe it will and maybe it wont, but it can be cheap since ordenary turbochargers can be found in a junkyard and variable nozzle can not)

[Powersteer]

Regular stuff to cut lag is smaller turbocharger, very short distance plumbing or minimal volume between the turbo to the intake port, minimal volume exhaust extractor to turbo exhaust housing all done in a way they still go with the flow, throttle housing in front of blower intake, run higher compression than you might and you can try opening the exhaust valve a bit early like what Saab did. There is a myth about supercharge and turbocharge together which should be interesting to try out.

Better get use to living with turbo lag, they might be more to gain than lose.

[jdi]

I don't think I've seen a throttle used before the compressor except on F1 cars from the turbo era. If putting a throttle before the compressor has the benefit of preventing the turbocharger from stalling during a shift, why isn't it seen more often?

Reducing volume/length of piping between turbocharger and intake port is something that everybody seems to be sure will reduce lag, but has anybody ever done a proper test of this and measured how big of a difference it makes?

[J. Edlund]

Originally posted by jdi
I don't think I've seen a throttle used before the compressor except on F1 cars from the turbo era. If putting a throttle before the compressor has the benefit of preventing the turbocharger from stalling during a shift, why isn't it seen more often?

Reducing volume/length of piping between turbocharger and intake port is something that everybody seems to be sure will reduce lag, but has anybody ever done a proper test of this and measured how big of a difference it makes?

If you place an extra throttle before the compressor, the vacuum inside the compressor during shifts will cause oil to leak by the compressor seal. So you either need a carbon sealed compressor, these increase friction, cost and so on, or you have to use a scavenge pump on the turbocharger oil return.
In F1 i think these valves where first mechanically controlled by later they where electronicly controlled. I'm not sure of the control strategy, but I think it's somewhat offset to the normal throttle.

Reduction of volume between compressor and engine should have very little effect on lag. A reduction in volume of the exhaust manifold will however have an effect.

In WRC they tried an anti lag solution which used a tank for compressed air; the turbocharger fill the tank when the engine is boosted and the air is then used when the driver goes on the throttle again.

[zac510]

J Edlund, above you mentioned a large compressor wheel being required, but nobody has really mentioned using a small exhaust housing/wheel in combination with an oversized wastegate (to bypass the air). It isn't really a technical feat but perhaps we could hear about your experiences with this kind of combination. It should be fundamental to the turbo choice and before you start putting on electronic anti-lag, etc.

[NTSOS]

It just seems to me that I am unfortunately one of a very few people around that has driven a fuel injected/turbo charged motor with the throttle placed at the inlet of the compressor.....and yes, the unit had a carbon seal. If there were more people to have enjoyed the experience....there would be zero critics. Just cruising down the road and listening to the turbine's faint whine as it spools up and down under low load conditions is worth the price of admission. If the throttle was placed after the compressor outlet, the turbine/compressor would not be spinning as fast during cruise conditions and that lovely high pitched wine would not be so pronounced. Since the compressor was not compressing very much, the turbine could drive it at insane speeds with very little input. Putting your foot into the throttle whilst cruising in high gear generated an equal but instantaneous reaction between the boost gauge and tach needle.

I'm not saying it's wrong to place the throttle in other places.....I'm just saying that it really does work very nicely in front of the compressor and you don't need a BOV.

It's ok though, because I'm going to do it again!

John

[Powersteer]

I wonder if this would work. Since it has been mension here about oil leak if the throttle is in front of the turbo intake I was wondering if two throttle body would work, one in front of the turbo and the other behind it. When the one after the turbo closes, a blow off valve would release the pressure rerouted to the intake between the first throttle body and turbo intake. The pressure fromt he blow off valve could spin the turbo blower for a while if designed correctly.

[zac510]

hmm, I can't imagine there would be a large benefit in that.

Has anybody heard of somebody trying to induce a rotation in the air in the same direction as the compressor rotation. The air must be travelling fast enough to induce some controlled motion into it? Maybe a large vortex, but I'm not sure how stable it would be.

[J. Edlund]

Originally posted by zac510
J Edlund, above you mentioned a large compressor wheel being required, but nobody has really mentioned using a small exhaust housing/wheel in combination with an oversized wastegate (to bypass the air). It isn't really a technical feat but perhaps we could hear about your experiences with this kind of combination. It should be fundamental to the turbo choice and before you start putting on electronic anti-lag, etc.

Usually you want to have a certain relationship between turbine blade velocity and impeller velocity so you can't goo to extreme here.

To use a quite small turbine housing is however quite common. The downside is very high exhaust pressures. With high exhaust pressures even a small wastegate will do the trick.

Originally posted by Powersteer
I wonder if this would work. Since it has been mension here about oil leak if the throttle is in front of the turbo intake I was wondering if two throttle body would work, one in front of the turbo and the other behind it. When the one after the turbo closes, a blow off valve would release the pressure rerouted to the intake between the first throttle body and turbo intake. The pressure fromt he blow off valve could spin the turbo blower for a while if designed correctly.

It's better to create a vacuum that try to force the air around in a circle.

Originally posted by zac510
hmm, I can't imagine there would be a large benefit in that.

Has anybody heard of somebody trying to induce a rotation in the air in the same direction as the compressor rotation. The air must be travelling fast enough to induce some controlled motion into it? Maybe a large vortex, but I'm not sure how stable it would be.

Compressed air have been tested in larger diesels to help speed up the turbocharger. All larger trucks are fitted with an air pressure system that can be used.

[Powersteer]

Originally posted by J. Edlund
It's better to create a vacuum that try to force the air around in a circle.

Of course, that idea only came assuming unsolved oil leakage problems.

[Andy McCord]

John, what car do you have ?

[NTSOS]

Hi Andy,

It was a 1970 1/2 Z28 circa 1984 to 1986.....many manifold variations, but always with the throttle before the compressor. I love the cut and pasted polaroids!







John

[jdi]

Usually you want to have a certain relationship between turbine blade velocity and impeller velocity so you can't goo to extreme here.

J. Edlund, can you explain a bit more what you mean here? I thought that turbine blade and impeller both mean pretty much the same thing - the impeller is made up of turbine blades. Also, why is this "certain relationship" desired, and what would happen if it wasn't maintained? Decreased turbocharger efficiency?

[Powersteer]

Sorry for being a bit off topic, NTSOS, you have not sold it have you.



Although I would change the wheels and stripes it could have been this by Foose.

[NTSOS]

Sorry for being a bit off topic, NTSOS, you have not sold it have you.

Yes, I sold it to Ferrari of Los Gatos in 1987 and have only recently returned to hot rodding/car stuff after attending a Barrett-Jackson auction.

I did watch the Overhaulin episode with the Camaro.....I always liked silver and black.

John

[Canuck]

Always loved the split-bumper Camaros.

[J. Edlund]

Originally posted by jdi
J. Edlund, can you explain a bit more what you mean here? I thought that turbine blade and impeller both mean pretty much the same thing - the impeller is made up of turbine blades. Also, why is this "certain relationship" desired, and what would happen if it wasn't maintained? Decreased turbocharger efficiency?

The turbine is driven by exhaust gases, the impeller is part of the compressor wheel that compresses the intake air. Sometimes "impeller" is used to describe the whole compressor wheel, sometimes it refers only to the radial section of the compressor wheel. Both the centripetal turbine and the centrifugal compressor are turbomachines though.

Given equal stage loading the peripheral velocity of the impeller dictates what pressures ratios can be reached. If we have an inefficient compressor we will need higher velocities and vice versa. The needed velocity can also be reduced by reducing the impeller backsweep but this will be at the expense of range. On the turbine side maximum efficiency is reached when there is a certain relasionship between velocity of incoming gases and the peripheral velocity of the turbine blades. With a higher turbine blade speed it is also possible to extract more work per amount of gas. This becomes very important with high boost pressures as the power consumption of the compressor increases with its pressure ratio (also with massflow, but compressor flow + fuel flow = turbine flow).

Say that we want to reach a certain boost pressure, then a certain compressor pressure ratio must be used. To provide that pressure ratio we need to use a certain peripheral velocity of the compressor. Given that we have a certain size of the compressor wheel this will now dictate what rpm the compressor must rotate with. The turbine will rotate with the same rpm so its diameter will determine what turbine blade speeds that can be used. In order to get a low exhaust pressure in relation to the boost pressure and/or in order to run with very high boost pressures we should run with a high turbine peripheral velocity, this means that it must have a certain diameter in relation to the compressor. To operate efficient a larger high velocity turbine will need a smaller turbine nozzle and vice versa.
Say that our compressor needs to operate with a peripheral velocity of 640 m/s and the turbine with 500 m/s, given that these operates with the same rpm you're stuck with a turbine diameter that is 78% of the compressors. These blade velocities are about what you need in order to reach a compressor pressure ratio of 4, about what was used on the turbocharged F1 engines of the eighties.

[NTSOS]

Ok....here is the plan!

I refuse to mount the turbos in the engine compartment....I just don't like the concept of the front end weight, the added heat and all of the associated plumbing messing about with my clean engine. I am going to mount the turbo's low on each side of the transmission and use a scavenge section from the external oil pump. The exhaust system/turbines may lose a little heat/efficient as opposed to mounting them directly on a manifold.....but OTOH, I don't care if it loses a 100 or more HP, there will be more than enough power to scare me and the overall handling should be better.

Since the throttle before the compressor inlet worked so beautifully in the past, that is of course where a throttle will be placed. A slight variation of the original scheme.....another throttle will also be mounted on the manifold in the conventional front mounted TPI position. Here is a hi-tech illustration:



The manifold throttle will provide instant throttle response and I may even use a slightly ******** throttle on the compressor inlet that would allow the compressor/turbine to spool even more wildly during part throttle cruise. In any case, both throttles will arrive at full open at the same time.

A air to liquid intercooler (8 core laminova type) will be mounted on the firewall under the dash in its own little box.....covered by carpet of course.....so the turbo outputs come in through the floorboard, into the intercooler and out through the firewall into the back of the manifold. A water tank/pump in the trunk area, plus some stuff that resides within the tank to help cool the coolant down.

I'll use one or two of these snow mobile units placed between the throttle plate and manifold to complete the system.





As opposed to providing a cool air supply to the front throttle.....I am really tempted to simply place a little air filter on it to screw with unsuspecting minds when the hood is popped.

John

[J. Edlund]

Originally posted by NTSOS
I refuse to mount the turbos in the engine compartment....I just don't like the concept of the front end weight, the added heat and all of the associated plumbing messing about with my clean engine. I am going to mount the turbo's low on each side of the transmission and use a scavenge section from the external oil pump. The exhaust system/turbines may lose a little heat/efficient as opposed to mounting them directly on a manifold.....but OTOH, I don't care if it loses a 100 or more HP, there will be more than enough power to scare me and the overall handling should be better.

What you will lose with this turbo placement is low end torque due to that the turbos will provide boost first at a higher engine speed because of the heat/pressure loss, there are also higher pumping losses associated with this setup. Lag should also increase somewhat.
I haven't seen much info about the high end, but I think any difference here is small.

The loss of low end torque is partly the reason why many new turboengines have such compact exhaust manifolds.

[NTSOS]

What you will lose with this turbo placement is low end torque due to that the turbos will provide boost first at a higher engine speed because of the heat/pressure loss, there are also higher pumping losses associated with this setup. Lag should also increase somewhat.

Perhaps some of the above might be true if you are thinking conventionally, but the distance from the exhaust valve to the turbine inlet will not be all that much different than what is pictured below....maybe 12" longer is all and there are certainly materials available that can help circumvent the heat/pressure loss. I was embellishing the 100 HP loss! In any case.....there are ways to offset a potential problem by producing more low end exhaust flow!



Check out one of terrible Tom's SBC dyno pulls.....please overlook the 1st minute or so of hype/PR.

Killer Street Motor

Actually, from off idle and up to the transistion from N/A to boost (crossover point), low end torque will be increased quite substantially over that of a conventional setup! This is primarily due to the fact that typical turbocharged motors use fixed geometry intake manifold designs as pictured above......with their short/large volume intake ports and large volume plenum chambers.....a high speed design not normally associated with the ability to help generate kinetic port energy, especially at low engine speeds. IOW, this type of manifold is not conducive to producing gobs of low end torque which would be beneficial to help spool up a turbine.

Although it's been 20 years since I last worked on my variably geometry manifolds....I didn't stop thinking about them....I just grew weary of trying to explain its virtues as it relates to a turbo-supercharged street motor.

Oh well....that's the whole point of building one last hotrod before I croake. It will debut with a very nice triple-variable geometry induction system and the turbine A/R housings will go up in size, not down.

John

[Stian1979]

Nobody alse asked so I might ask you myself, what are those snowmobile none-return valves for?
Newer sen annyone use that on a 4 stroke befour and I can not figure out anny resonoable reason for using them. Will they not only desturb and restrict the airflow to the manifoil?
My education is directed towards large two-stroke diesels so I might not get the corect picture.

[NTSOS]

Ok....there are two throttles and two sources of air intake....the one on the manifold has the reed valve and the other throttle is in front of the turbo compressor inlet.

Looking at the hi-tech drawing, the throttle on the left/front of the manifold is only used during normally aspirated transitional use. The air inlets on the right/rear of the manifold only admit air from the turbocharger compressor outlets....no reed valve. When manifold pressure exceeds ambient pressure, the reed valve seals and at that point, the only source of air entering the system is coming from the turbochargers through the rear inlets of the manifold.



John

[Canuck]

Where's the little lightbulb smilie? Was sort of scratching my head but now I get it.

[Stian1979]

I have ben thinking how to make two diferent air suplys on turbocharging to avoid restrictional losses trough a turbocharger that don't deliver positive effect, but I newer thought about a this simple sulution.

When I resume my turbo kadett I gues I have to take a diferent aproatch than I have previously

[Powersteer]

Cool idea and it would work. I had something similar, a throttle that would close when it sensored the boost. Yours is so much simpler with a high tech two stroke reed valve. Compare a direct intake with one that has to go through all the piping, intercooler and a slow blower, its just so much more efficient.

[NTSOS]

Where's the little lightbulb smilie? Was sort of scratching my head but now I get it.

....I think my hi-tech drawing needs some work........maybe a few arrows pointing in the right direction!

In any case.......that is why I think it would be great fun to place a small air cleaner on the front throttle and not say anything about the reed valve.

John

[Stian1979]

If some watercoled intercolers are hiden at the firewall and the turbos beside the gearbox you would defently folled me if I only had a quick look at the enginedepartment.

Hope to see your work here on the forum while you are working on it

[NTSOS]

I had something similar, a throttle that would close when it sensored the boost.

Me too, me too! I was going to do the same as well!

I just love looking at the reeds though.....with the neat carbon fiber petals and all!

John

[NTSOS]

Hope to see your work here on the forum while you are working on it

Hey thanks.....I'm old, slow and retired though, so it may take awhile.

My main job is to replace defective Budweiser cans with good ones.....I *always*
seem to get a bad batch of leakers......well, that's what I tell my wife when she
notices all of the "defective" cans piling up at an alarming rate!


John

[NTSOS]

Kind of an idea what my last manifold will look like....but not really, since I have had 20 years to think about what I am going to do and none of these need apply.

This one was strictly a blower manifold and had to be compromised to fit under an extremely low hood.



Rescued from a shed after 20 years.



Kind of pieces and parts waiting for a modern update!



Various projects that were completed in the 1980's.












John

[J. Edlund]

Originally posted by NTSOS


Perhaps some of the above might be true if you are thinking conventionally, but the distance from the exhaust valve to the turbine inlet will not be all that much different than what is pictured below....maybe 12" longer is all and there are certainly materials available that can help circumvent the heat/pressure loss. I was embellishing the 100 HP loss! In any case.....there are ways to offset a potential problem by producing more low end exhaust flow!



Check out one of terrible Tom's SBC dyno pulls.....please overlook the 1st minute or so of hype/PR.

Killer Street Motor

Actually, from off idle and up to the transistion from N/A to boost (crossover point), low end torque will be increased quite substantially over that of a conventional setup! This is primarily due to the fact that typical turbocharged motors use fixed geometry intake manifold designs as pictured above......with their short/large volume intake ports and large volume plenum chambers.....a high speed design not normally associated with the ability to help generate kinetic port energy, especially at low engine speeds. IOW, this type of manifold is not conducive to producing gobs of low end torque which would be beneficial to help spool up a turbine.

Although it's been 20 years since I last worked on my variably geometry manifolds....I didn't stop thinking about them....I just grew weary of trying to explain its virtues as it relates to a turbo-supercharged street motor.

Oh well....that's the whole point of building one last hotrod before I croake. It will debut with a very nice triple-variable geometry induction system and the turbine A/R housings will go up in size, not down.

John

The effect of a tuned intake port is small compared to what a spooled turbocharger will result in. Some turbo engines also have variable inlets and its effect on the lowest speed are usually very small. The variable inlet fitted to Volvos five cylinder engines did for example almost nothing under 2000 rpm.

A larger manifold volume will decrease the amplitude of the pressure pulses, and with that decrease the availible energy which result in a lower boost pressure. Can the pulses be separated that can increase the amount of availible energy, for example using a twin scroll turbine housing.

In addition to the lower amplitude, there is also an increased heat loss. At low speeds with a small manifold you may lose say 3-4 kW, a large manifold can more than double that, to 7-10 kW. Increased pipe length have the largest effect on the heat loss.

Look at the exhaust manifolds of some new turbocharged engines - BMW, Saab, Mitsubishi and Volvo for example, usually they have a small manifold volume with a very compact design. A manifold volume of half the displacement can be common. The manifold design is infact more important for low end torque than the choice of turbine.

[Stian1979]

Originally posted by J. Edlund


The effect of a tuned intake port is small compared to what a spooled turbocharger will result in. Some turbo engines also have variable inlets and its effect on the lowest speed are usually very small. The variable inlet fitted to Volvos five cylinder engines did for example almost nothing under 2000 rpm.

A larger manifold volume will decrease the amplitude of the pressure pulses, and with that decrease the availible energy which result in a lower boost pressure. Can the pulses be separated that can increase the amount of availible energy, for example using a twin scroll turbine housing.

In addition to the lower amplitude, there is also an increased heat loss. At low speeds with a small manifold you may lose say 3-4 kW, a large manifold can more than double that, to 7-10 kW. Increased pipe length have the largest effect on the heat loss.

Look at the exhaust manifolds of some new turbocharged engines - BMW, Saab, Mitsubishi and Volvo for example, usually they have a small manifold volume with a very compact design. A manifold volume of half the displacement can be common. The manifold design is infact more important for low end torque than the choice of turbine.

Pulse charging has best effect on lov load but constant preshure charging is moust efficiant on high load if I remember corectly, but large comercial diesels and turbines are what I'm normaly dealing with so I can be wrong about this aplying to smal gasoline engines.

I did not think that manifoil volume would have a effect on the torque except heat loss from a increased area, but I would exspect that manifoil volume has a great deal to do with the reaction time on the turbine. Smal volume would defently make it spinn up faster.

From all the forums I'm a member off this is the one with moust brainpower.

[NTSOS]

In addition to the lower amplitude, there is also an increased heat loss. At low speeds with a small manifold you may lose say 3-4 kW, a large manifold can more than double that, to 7-10 kW. Increased pipe length have the largest effect on the heat loss..................etc

Yes, thankyou...we all know how it is supposed to work.....now please click on Nelson's video again, watch carefully and read the results from the dyno sheet....then ask me if I'm going to sweat an extra foot of pipe!

Close to a 1000

The effect of a tuned intake port is small compared to what a spooled turbocharger will result in.

Well, I agree............but first you have to get the turbocharger to spool.....please, one step at a time.

Some turbo engines also have variable inlets and its effect on the lowest speed are usually very small.

You would not be generalizing would you and are those really variable inlets....or simply flapper valves closing off one port and/or another flapper playing around with the plenum volume? Ooooh.....hi-tech!

The variable inlet fitted to Volvos five cylinder engines did for example almost nothing under 2000 rpm.

Now whose fault do you suppose that is?

John

[Powersteer]

Although I'm not a turbo head that is an engine bay to die for. There, better to live with turbo lag
than fight it ;)



Look at those welds. I am suspicious of this one, the welder has to be a massive fan of breakdancing and loves to do the robotics move. Axel F kind of stuff.

Fantastic retirement plan NTSOS...but we can hardly call you old school.

[Stian1979]

Originally posted by Powersteer


Although I'm not a turbo head that is an engine bay to die for. There, better to live with turbo lag
than fight it ;)

Nice job, but I'm not a big fan off crome myself. I like more aluminium, black and silicone hosses.

Originally posted by Powersteer


Look at those welds. I am suspicious of this one, the welder has to be a massive fan of breakdancing and loves to do the robotics move. Axel F kind of stuff.

Fantastic retirement plan NTSOS...but we can hardly call you old school.

[/B]

I have recently ben working on a build off a fast patrol boat 25m in aluminium for the Taiwanese coust guard and the welds there onboard has about the same A-meshurement.

You could lift the weight off the car by those welds

[J. Edlund]

Originally posted by Stian1979


Pulse charging has best effect on lov load but constant preshure charging is moust efficiant on high load if I remember corectly, but large comercial diesels and turbines are what I'm normaly dealing with so I can be wrong about this aplying to smal gasoline engines.

I did not think that manifoil volume would have a effect on the torque except heat loss from a increased area, but I would exspect that manifoil volume has a great deal to do with the reaction time on the turbine. Smal volume would defently make it spinn up faster.

From all the forums I'm a member off this is the one with moust brainpower.

Pulse charging minimize pressure/heat loss and reduces exhaust pumping loss at the cost of some turbine efficiency. The lower pressure/heat loss can be shown on a p-V diagram if turbine work is included (see p20 in "Fundamentals of Turbocharging" by N.C. Baines). Constant charging means there is less energy availible for the turbine but instead the turbine efficiency can be increased. Pulse charging means that the turbine inlet pressure can go from say 10 to 1 bar during the exhaust duration, in an extreme case. Now, you can't design a turbine that efficiently will work with such varying inlet conditions. Constant pressure charging allow an even inlet condition, pressure, flow and temperature will remain quite constant and for this we can design an efficient turbine. Since the volume before the turbine also acts as a buffer transient response will be increased. Which type of setup (pulse or constant pressure) that will result in most turbine power output is disputed; in some tests constant pressure turbines showed the best performance and in other tests pulse charging provided a greater output.

Turbocharged car engines are more or less based on a pulse charging system since car engines operate with a wide speed range and many transients. Many modern turboengines have very small exhaust manifold volumes as this have been showed to increase boost build up at low speed and to decrease transient response. In "Simulation of Turbocharged SI-Engines - With Focus on The Turbine" by F. Westin several exhaust manifolds are tested on a production inline four (I think the test is done on a 2.3 litre Saab engine). The exhaust manifold with the greatest torque output at very low speeds was of a compact 4-2-1 type similar in configuration to what these engines usually are fitted with. The choice of exhaust manifold was shown to be more important than the choice of turbine. To take one example, the smallest turbine fitted with two different manifolds resulted in a torque output at 1600 rpm of 210 vs. 290 Nm.

[J. Edlund]

Originally posted by NTSOS


Yes, thankyou...we all know how it is supposed to work.....now please click on Nelson's video again, watch carefully and read the results from the dyno sheet....then ask me if I'm going to sweat an extra foot of pipe!

Close to a 1000



Well, I agree............but first you have to get the turbocharger to spool.....please, one step at a time.



You would not be generalizing would you and are those really variable inlets....or simply flapper valves closing off one port and/or another flapper playing around with the plenum volume? Ooooh.....hi-tech!



Now whose fault do you suppose that is?

John

To get the power out of a turbo engine is usually not a problem, most engines run with the wastegate open at full power speed so heat loss from longer pipes usually doesn't affect maximum power. It's the low end and transient response that will suffer from long pipes. On this dyno run they also doesn't show torque output at very low speeds (we also have no short pipe dyno paper to compare with). They also doesn't show the transient response of the engine, so it isn't much to watch.

Having a variable inlet manifold is good but to help the turbos spool one set of long runners will usually do the trick. Of course, even long runners won't do much for the very low speeds as the length requirement will be too great.

The variable inlet used by for example Volvo uses runners with two different lengths; a short set for high speeds and a long set for low speeds. The system is actually quite effective, by changing set you can increase VE from about 70-80% to 90-95% and to keep it there from 3000 to 6000 rpm. For example telescope runners may be more high tech but this works quite good.

Turbocharged, the Volvo engine fitted with a compact exhaust manifold also can deliver full torque from about 1500 rpm.

[NTSOS]

To get the power out of a turbo engine is usually not a problem, most engines run with the wastegate open at full power speed so heat loss from longer pipes usually doesn't affect maximum power.

Yes, it's true, it's true.....and about packaging for obvious reasons.

It's the low end and transient response that will suffer from long pipes. On this dyno run they also doesn't show torque output at very low speeds (we also have no short pipe dyno paper to compare with). They also doesn't show the transient response of the engine, so it isn't much to watch.

There would be no point in a short pipe dyno paper, again, it's all about making the whole soggy mess fit within the engine compartment and getting the hood to close without cutting a hole in it.....long/short pipes, whatever!

In any case, if you removed the turbos it is still a 427 with a small duration 230 cam @.050. The small cam allows the very large port/short runner manifold to work quite nicely from off idle to boost transition and it doesn't seem to hurt hp all that much. The manifold is obviously not optimized for low speed work, but I am told that all of his motors exhibit excellent low speed drivability and are quite docile until crossover occurs. The Electromotive Engine Control management system is probably somewhat responsible for the good street manners.....IMO, it's a very competent control system!

The only thing I would do differently is modify their intake manifold to trick the motor into believing that it had a very long runner manifold at off idle to transition and then a large volume/short runner manifold from transition to redline.

This would allow more camshaft timing, a larger turbine housing and more hp using the same or lower boost pressure and no loss of low-end response. Don't ask...motors are stupid, they don't know it's not bacon. I did it 20 years ago and I'll do it again!

The variable inlet used by for example Volvo uses runners with two different lengths; a short set for high speeds and a long set for low speeds. The system is actually quite effective, by changing set you can increase VE from about 70-80% to 90-95% and to keep it there from 3000 to 6000 rpm. For example telescope runners may be more high tech but this works quite good. Turbocharged, the Volvo engine fitted with a compact exhaust manifold also can deliver full torque from about 1500 rpm.

I'm kind of confused....I thought you said in an earlier post that the Volvo variable geometry system didn't work. It's ok....not important!

John

[AndrewD]

long time reader first time poster

im finding it interesting how people rant about other peoples work. although this forum seems better for information than ricer forums, i still cant believe some people can, without consulting the designer, come up with why things were designed are certain way and then make a judgement like, its crap or its only designed to fit within the engine bay.

im also of the opinion for turbocharged engines, a dyno is of little use. turbocharger benefits are found in transient tuning, and aware of it or not, you cant do that on dynomometers (unless you've got $$$$ for the setup like f1 engineers and track map datalog inputs). the most you can achieve on the dyno is a steady state comparison of different setups and a base fuel and ignition map to work off.

as for Stian1979's post, have you ever tried to implement a turbocharger system with a throttle placed before the compressor? what do you think will happen when you close the valve? your compressor maps become useless as pressure before the compressor isnt atmospheric so how do you control boost? increase in pressure ratio and compressor speed? lol i hope you like surge. we are having loads of trouble in FSAE with this. then the question moves to oil leaking via the thrust bearing, so you install a carbon seal which massively increases friction induced lag, so you decide to try antilag which increases heat flux and fuel consumption and you begin to fatigue exhaust valves and manifolds, seize turbocharger vanes and oil deterioration.
it can be done, but not without a **** load of ****ing around

later

[Stian1979]

Originally posted by J. Edlund

The exhaust manifold with the greatest torque output at very low speeds was of a compact 4-2-1 type similar in configuration to what these engines usually are fitted with.

I would exspect a 4-2-1 to give a bether efficensy at low RPM, but if size is so important I would exspect a 4-1 to have smaler volume and surface area even they are know to deliver bether on high RPM and not on low.

Originally posted by AndrewD
long time reader first time poster

as for Stian1979's post, have you ever tried to implement a turbocharger system with a throttle placed before the compressor? what do you think will happen when you close the valve? your compressor maps become useless as pressure before the compressor isnt atmospheric so how do you control boost? increase in pressure ratio and compressor speed? lol i hope you like surge. we are having loads of trouble in FSAE with this. then the question moves to oil leaking via the thrust bearing, so you install a carbon seal which massively increases friction induced lag, so you decide to try antilag which increases heat flux and fuel consumption and you begin to fatigue exhaust valves and manifolds, seize turbocharger vanes and oil deterioration.
it can be done, but not without a **** load of ****ing around

later

I tryed with a draw trough system, but I did not do the researth first so I lost some oil.
I did decide to go for injection instead, but now the project has stranded for 6 year's because off no time. NTSOS has done well in the past acording to himself so why not ask him?

[Powersteer]

How many types of external/internal wastegate designs are there? Here are some pictures from Hotrod magazine.


Slide valve?

[zac510]

As far as I can tell all those designs are fundamentally the same. The bottom one just looks different because it has an enormous diaphragm placed away from the valve to keep it cool.

[NTSOS]

Log vs Tube Headers Test 1

Log vs Tube Headers Test 2

John

[NTSOS]

Below is a slightly edited version of two forum responses from Tom Nelson (builds outrageously powerful/durable engines for well know car fabricators and street rodders) commenting on turbo exhaust systems and the results of years of testing numerous combinations. I simply made the content a little easier to read......he obviously does not like to waste a lot of time writing about stuff that he has already done! Interesting...log manifolds as heatsinks and how that could relate to possible head gasket failure. Typical hot rodder trial and error stuff.....and that's a good thing!
___________________________

I’ve used tubular headers and I've used the Banks log types in the past. I would say the main reason I use a tubular header is I only use tangential exhaust housings and I have found a lot of power in that.

Along with a good intercooler, if you want to make 700/800 hp I think a log is good.....it's surprising how crappy you can make a header or log and still have it work well.

OTOH, when you start making big power, I've seen good gains from a header with the right transition into the turbo and some decent tube length. Also with a header, you can give some room for all 4 cylinders to run before the wastegate picks them up.

The logs are also pretty tight especially if you have a big motor and a lot of turbo. The gate has to work really well and it is hard to control on a log. Also note that most logs have cast in hole sizes and bolt patterns that are way to small for a waste gate. Be careful unless you like variable non-controlled boost. I think lastly, nothing looks as cool as a well designed tubular stainless header.

Exhaust manifolds tend to turn into big heat sinks. Look at a tubular header in a pull.....the collector is always what gets red first, then it works its way through the primaries. The log manifold keeps heat throughout the whole deal and I have found that this kills head gaskets.

There are thousands of things going on and what might work well for one combo won't for another because of all the different motors/turbos, a/r wheel size/housing size and of course camshafts and how they all mesh. It gets crazy......when I first started building turbo motors, I read all of the maps and listened to all of the so-called experts........*90* turbo variations later I figured out at least one thing........rather than drive myself nuts with what I think it might do, I just do it, let the motor eat and see if it's worth a damn.

It’s not always a success.......the hp or torque might be crap but you figure out a little every time. I listened to the experts for too long and figured out they were clueless. Everyone I talked to told me the turbos I was running were too big for the applications, they’ll never spool or they are only efficient in certain rpm ranges, whatever.

I by no means am an expert on this stuff.....I’ve just tried enough combos’ to know what works for me on my applications. I believe the header is the way to go for power and reliability as long as it's designed right with the right materials and supports. I learn with each motor I do and we are just at the beginning of knowing what makes these things killer.

[Full-Race Javier]

Originally posted by NTSOS
Log vs Tube Headers Test 1

Log vs Tube Headers Test 2

John

All of our testing has shown that well designed/built "tubular" manifolds outperform "log" type manifolds . We recently tested two of our manifolds back to back. The first manifold was a bottom mount shorter runner design and the second was a top mount longer runner design.

Bottom Mount


Top Mount


Results
GT30R, Dark trq graph=Top Mount, Light trq graph=Bottom Mount


GT35R, Dark trq graph=Top Mount, Light trq graph=Bottom Mount


One of the grad student that works here (Trian) has also recently finished his turbo exhaust manifold design thesis. The results where very interesting...we should have a digital copy uploaded soon.

Till then, here are a few pics from his testing