64 replies to this topic

[MODE]

many photos and technical datas of the most powerful engine in the history of Formula 1 (about 1300 bhp in 1986 for qualifications)
http://www.gurneyfla...m/focusbmw.html

[Kaiser]

Thanks Mode, nice pics on that site. The con rods look stout on the BMW motor, wow!

[OO7]

Excellent link MODE.
It amazing how far F1 cars have come in terms of technology. Back in the mid-eighties even when racing on high speed circuits F1 cars of that era would run huge rear wings, the cars almost always looked like they were setup to run at Monaco. I understand all that down force was necessary simply to put the power on the track. Consider how far things have come, F1 engines are producing upwards of 850bhp in race trim and due to the mechanical/chemical grip afforded by modern tyres, are able to cope with skinny rear wings. Incredible!.

Obi

[zac510]

Brilliant photos MODE. Satisfying us tech-heads again

[ciaoduc1]

Is that the exhaust on the second row of pictures third from the right??? WOW! Maybe it's a trick of the camera but it looks almost as big as the clutch.

How long have teams been using Carbon Fiber?

[shaun979]

Is the pre-compressor throttle for keeping pressure spikes (while upshifting) out of the manifold and popping off the valve? Champ car style?

[david_martin]

Quote

Originally posted by ciaoduc1
Is that the exhaust on the second row of pictures third from the right??? WOW! Maybe it's a trick of the camera but it looks almost as big as the clutch.

That is, indeed, the primary exhaust, there is also smaller secondary exhaust from the waste gate just above it. The primary exhaust has such a large internal volume so as to maximise the pressure gradient across the exhaust turbine - effectively an expansion chamber.

Quote

How long have teams been using Carbon Fiber?

1974/75. Hesketh and Hill started experimenting with CFRP parts almost simulatenous - drive shafts IIRC. It was a failure of a CFRP driveshaft on Rolf Stommelen's Hill that cause the fatalities at the 1975 Spanish GP, again IIRC.

Quote

Is the pre-compressor throttle for keeping pressure spikes (while upshifting) out of the manifold and popping off the valve? Champ car style?

I suspect the two engines in the photos are both non-pop off valve versions from 1986 - USAC/CART style pop-off valves didn't appear in F1 until 1987 (4bar boost limit for '87 and 2.5 bar boost limit for '88). I think you will find the pre compressor throttles are just there for lag control - stopping the compressor from stalling against pressure build up when the main throttle is closed. I don't believe BMW (or Megatron as those engines became for '88) ever used intake manifold dump valves for lag control, although I may well be mistaken.

[shaun979]

Quote

Originally posted by david_martin
I suspect the two engines in the photos are both non-pop off valve versions from 1986 - USAC/CART style pop-off valves didn't appear in F1 until 1987 (4bar boost limit for '87 and 2.5 bar boost limit for '88). I think you will find the pre compressor throttles are just there for lag control - stopping the compressor from stalling against pressure build up when the main throttle is closed. I don't believe BMW (or Megatron as those engines became for '88) ever used intake manifold dump valves for lag control, although I may well be mistaken.

This picture right here.. isn't it the pop off valve?



To stop the compressor from stalling why didn't they run blow off valves like the turbo engine nowadays?

[david_martin]

Quote

Originally posted by shaun979
This picture right here.. isn't it the pop off valve?

Indeed it most certainly is. Dunno how I missed that photo... The "Upright" version of the engine, which is definitely 85/86 vintage also has a pre-compressor throttle. As for why they didn't run dump valves, I don't know why they didn't.

[NTSOS]

Quote

To stop the compressor from stalling why didn't they run blow off valves like the turbo engine nowadays?

Hmmm, good question! Perhaps, BMW felt that the compressor/turbine lost less speed at closed throttle by preventing air flow to the compressor as opposed to simply using a blow off, but still compressing air.

When the thottle was applied again, you would think that there would be a tradeoff as to which system would regain full manifold pressure in the quickest time frame. With throttles at the port and compressor inlet, but with higher compressor speed, the entire system would have to be pressurized....ducting, intercooler and plenum. OTOH, with the blow off system, air would be instantly available to the port throttles and to the rest of the plumbing since it wasn't cut off at the source.....although the compressor would be running at a slower speed.

IOW, I don't have an answer.

John

[crono33]

i remember reading on some magazines at the time that pre-compressor throttle was for lag control

Quote

Originally posted by david_martin


Indeed it most certainly is. Dunno how I missed that photo... The "Upright" version of the engine, which is definitely 85/86 vintage also has a pre-compressor throttle. As for why they didn't run dump valves, I don't know why they didn't.

[shaun979]

Any idea what lay at the other end of the cable of the pre-compressor throttle? I assume it would close just before a shift, but was it manually or electronically activated?

I don't know what type of transmission they ran at the time, but if they could shift without closing the standard throttles, then would this pre-compressor throttle close at least somewhat, in order to prevent the pressure spike from occuring and popping off the pop off valve? Closing the pre-compressor throttle too much in the case of flatshifting would create a temporary increase in pumping losses (vacuum) wouldn't it?

[david_martin]

Quote

Originally posted by shaun979
Any idea what lay at the other end of the cable of the pre-compressor throttle? I assume it would close just before a shift, but was it manually or electronically activated?

There is little doubt that it is mechanically coupled to the master throttle linkage - the entire throttle system was still mechanical (drive by wire throttles didn't appear until a couple of years later). I suspect it closes in concert with the main throttle, although there might be some offset between the two. It will prevent the turbo from spooling down against the closed throttle. I have photos of the Renault RS02 twin turbo V6 from 1979 - it too has pre-compressor throttles on both turbos, mechanically coupled to the master throttle linkage.

Quote

I don't know what type of transmission they ran at the time, but if they could shift without closing the standard throttles, then would this pre-compressor throttle close at least somewhat, in order to prevent the pressure spike from occuring and popping off the pop off valve? Closing the pre-compressor throttle too much in the case of flatshifting would create a temporary increase in pumping losses (vacuum) wouldn't it?

H-pattern or manual sequential gearboxes. The pre-pop off valve Brabham BT55 from 1986, which the "laydown" version of the BMW engine was designed for ran a fully manual Weismann transverse 7 speed transxale. I think it was sequential, although I can't recall. The other teams who ran the upright engine in the photos (Arrows and Benetton) used longitudinal Hewland FG derived H-pattern gearboxes.

[zac510]

I'm not sure that 'dump valves' were invented back then. the oldest one I have seen (heard) is at the end of INCAR 956 dvd. I can't recall off thet of my head what year that was - 1986? Then they popped up on the Ford Sierra Cossie touring cars in the very late 80s.

Maybe they didn't like losing the volume of air that they needed to stop the compressor spinning.

[NTSOS]

I seem to recall that the 917/30 of the early '70's had a number of automatic valves on top of each manifold that vented the plenums to atmophere when the individual port throttles were closed.

Neat motor, close to 1500 hp for qualifying.

Engine Type: Air Cooled twin turbo Flat12, no intercooler

Displacement: 5374 cc
328 cu. in.

Power: 1100 hp @ 7800 rpm
820 kW @ 7800 rpm

Torque: 1128 lb. ft. @ 6400 rpm
1531 Nm @ 6400 rpm

Horsepower per Liter: 204.7 hp/L

Compression Ratio: 6.5 : 1

Valve Configuration: 2 valves per cylinder, DOHC

Bore: 88.9 mm
3.5 in

Stroke: 71.1 mm
2.8 in

John

[ZoRG]

The reason for the butterfly in front of the turbo is indeed lag, due to the size of those turbo's vs the engine, lag was an issue, while it took some time to initially build up boost, once the turbo got spinning, using the turbo throttle the compressor speed could be kept high and made the motor more responsive. Renault engineers once claimed that their drivers "Don't know what lag is..."

Another alternative when using even bigger turbo's is to run the wastegate on the inlet pipes instead of the exhaust side, this you will find on alot of the drag cars in the US that run huge turbo's on small motors, or extremely large turbo's on big motors.

[ZoRG]

forgot to say, blow off valves will have a hard time not leaking at 4bar, especially the ones they had at the time.

Also, and this is pure guesswork but because of the extremely high boost levels it might have been possible for a bov type system to damage the turbo.

[J. Edlund]

Quote

Originally posted by ZoRG
The reason for the butterfly in front of the turbo is indeed lag, due to the size of those turbo's vs the engine, lag was an issue, while it took some time to initially build up boost, once the turbo got spinning, using the turbo throttle the compressor speed could be kept high and made the motor more responsive. Renault engineers once claimed that their drivers "Don't know what lag is..."

Another alternative when using even bigger turbo's is to run the wastegate on the inlet pipes instead of the exhaust side, this you will find on alot of the drag cars in the US that run huge turbo's on small motors, or extremely large turbo's on big motors.

Wastegate on the inlet pipes??? You mean like a type of pop off valve?

A type of "pop off" valve was used to control boost in for example the early 917/30 before they were fitted with wastegates. These valves (which in the 917 case were butterfly valves) bled the air out of the inlet manifold to limit the boost pressure under boost.
Another method to limit boost was to fit the turbocharger with a very large turbine housing or a inlet restrictor. What all these methods have in common is that they all offer poor results.

When bleeding air out of the inlet the turbocharger must keep on compressing the incoming air and this puts an excessive load on the turbine and exhaust backpressure increases.
When using a restrictor the compressor pressure ratio are driven up and with that exhaust pressure and turbocharger rpm. The later the damage the turbocharger and that also why restricor fitted racing cars such as the WRC or LMP are all fitted with wastegates.

If a large turbine housing is used the turbocharger will spool late, there will be quite some lag and the engine will offer poor driveability. Especially when used with a small displacement engine.

The reasons mentioned above was also why the turbocharger wasn't used on gasoline engines in any larger scale until the wastegate was introduced.

Highly boosted small engines typically use a wastegate, nothing else to control the boost. Sometimes no boost controlling device at all is being used, this since the boost will be limited by the turbocharger and the engine can handle all the boost the turbocharger can deliver. It isn't that common though.

Today, on cars such as the WRC no charge air bypass valves are used. They aren't using any secondary throttles either. Instead the air is forced to the exhaust manifold where it together with fuel will keep the turbocharger up to speed like a gas turbine. A system like this was also tested during the turboyears in F1. Cars such as the Audi R8 doesn't use any charge air bypass valves or other devices with the same function that I know of.

[NTSOS]

Quote

Another alternative when using even bigger turbo's is to run the wastegate on the inlet pipes instead of the exhaust side,

Hey Zorg,

Would you mind pointing me in the correct direction......I can't seem to find any reference to this use.

It would definitely eliminate wastegate creep.......at least on the exhaust side.

Thanks!

John

[Powersteer]

I wonder how much disturbances does a wastegate cause when it comes to flowing the exaust. It must cost some distortionto the main flow of exaust because of the velocities. If there is a turbocharger that is inefficient enough not to use a wastegate it might flow exaust better than one with a wastegate(with current wastegatee designs). Less pressure build up, same boost, more power but far more turbo lag.

Edit: Engine specs say it weights 170kg with the turbocharger and intercooler. It goes to show how mindblowingly amazing todays 3,000cc V10 engines are under 100 kilogrammes.

[shaun979]

Quote

Originally posted by ZoRG
The reason for the butterfly in front of the turbo is indeed lag, due to the size of those turbo's vs the engine, lag was an issue, while it took some time to initially build up boost, once the turbo got spinning, using the turbo throttle the compressor speed could be kept high and made the motor more responsive. Renault engineers once claimed that their drivers "Don't know what lag is..."

I understand how shutting the pre-compressor TB would help keep shaft speeds from falling too quickly, but doesn't placing the TB so far from the cylinder introduce lag to throttle changes? When he is off throttle and gets back on it, the turbo has to re-pressurize (from vacuum) the entire tract from compressor to cylinder. When he is on throttle and shuts it quickly, the engine doesn't respond as quickly as it uses up the air left between the TB and the cylinder. All that pipe, plus the intercooler, would have to have made quite a difference in throttle response.

[ZoRG]

Shaun979: Not really, if you calculate how much air you need to make 1500hp, then calculate the amount of space to fill between the turbo and engine, I think you will find it fills up very quickly if the compressor is running at high enough speed. It fills the vacuum quicker than the time it takes to respool the turbo if you were slowing down the turbo while sending the air out the BOV.

NTSOS: The pictures were posted on this link http://www.honda-tec...hread?id=288262 but they are unfortunately not available anymore, I will dig around and see if I saved any.
EDIT:Try http://gallery.funfordevents.com/

J. Edlund, yes wastegate on the inlet side not pop-off valves, apparently works really well on small engines with big turbo's. Or big engines with massive turbo's, if you follow the above link you will see from the comments 13" compressor housings, thats pretty extreme.

[NTSOS]

Hi Zorg,

Interesting about the throttle placement. I weighed all strategies and decided a throttle before the turbo inlet would just about cover all bases with the minimum of hardware intervention. This was in 1984 with my 70.5 z-28....6.9 liter bosch k-jetronic and variable geometry manifold. Photos are available.

It was an excellent choice as it worked superbly. Cruising down the road at constant throttle angle you could just hear the turbine spooling up because of not having to compress air and in the case of part throttle acceleration the turbine would spool madly and when the throttle was nailed..... absolutely instant response. 30 to 50 and 50 to 70 acceleration times where both slightly less than 2 seconds flat. That was direct drive with a 3.73 rear end ratio.

John

[ZoRG]

Impressive, whenever this discussion comes up people always say to me, the throttle so far away so it must be very laggy, I stopped arguing the point to be honest, they seem to forget about how quick air really moves in a engine and as you pointed out faster spooling due to less work the turbo needs to do in the end. If you don't mind, please post some photos!

[NTSOS]

This is my very first design......the ports eventually got short, large and straight without compromising low end. IOW, I could use a cam with typically longer than normal turbo timing and the largest turbine housing and boost still came in at 2000 rpm.

The K-Jetronic was superb.



John

[ZoRG]

That is one of the coolest setups ever considering the time it was done imo! Even today people are not smart enough to place the TB at the Turbo inlet even though the info is available!

[BRIAN GLOVER]

Outstanding, John. Congratulations. Thanks man. And I thought I accomplished something by adapting a continuous flow fuel pump to a non return rail on a crate LS2.
Hot Rod did a nice story on turbos last year some time. Can't remember which issue.

Quote

Originally posted by NTSOS
This is my very first design......the ports eventually got short, large and straight without compromising low end. IOW, I could use a cam with typically longer than normal turbo timing and the largest turbine housing and boost still came in at 2000 rpm.

The K-Jetronic was superb.
John

[shaun979]

Thanks for the explanation Zorg. I see now how it can be better than the usual blow off valve type systems - especially given the simplicity of it (less parts to fail). I guess the reason we don't see the same system on turbo production cars is because they don't flow the high volumes of air, and their turbos are considerably smaller low inertia units.

[zac510]

NTSOS, looks great, care to share any more photos?

Re your comment on cam specs and exhaust housing size, funny timing as just on Thursday I had my turbo car on the dyno and was checking exhaust manifold pressure pre-turbo after doing a lot of research on the relationship between cam specs (specifically overlap) and turbine sizing. The results weren't what I expected, but did confirm the turbo is an OK match so I am quite happy.

[ZoRG]

Quote

Originally posted by shaun979
Thanks for the explanation Zorg. I see now how it can be better than the usual blow off valve type systems - especially given the simplicity of it (less parts to fail). I guess the reason we don't see the same system on turbo production cars is because they don't flow the high volumes of air, and their turbos are considerably smaller low inertia units.

Also you need a turbo with a carbon seal or a new GT BB turbo that will allow you to shut the trottle and keep the turbo from leaking oil into the inlet.

And then yes you are correct all the OE turbo setups I have seen go in the wrong direction imo and do a very small turbo, short duration cam setup.

[zac510]

Quote

Originally posted by ZoRG
And then yes you are correct all the OE turbo setups I have seen go in the wrong direction imo and do a very small turbo, short duration cam setup.

To curb emissions.

[J. Edlund]

Quote

Originally posted by ZoRG
Shaun979: Not really, if you calculate how much air you need to make 1500hp, then calculate the amount of space to fill between the turbo and engine, I think you will find it fills up very quickly if the compressor is running at high enough speed. It fills the vacuum quicker than the time it takes to respool the turbo if you were slowing down the turbo while sending the air out the BOV.

NTSOS: The pictures were posted on this link http://www.honda-tec...hread?id=288262 but they are unfortunately not available anymore, I will dig around and see if I saved any.
EDIT:Try http://gallery.funfordevents.com/

J. Edlund, yes wastegate on the inlet side not pop-off valves, apparently works really well on small engines with big turbo's. Or big engines with massive turbo's, if you follow the above link you will see from the comments 13" compressor housings, thats pretty extreme.

I've now read the thread, couldn't find any pictures though.

I wonder if it isn't a ALS valve they are talking about because their discussions make no sense at all. Regulating the boost with a pop off valve on the inlet will offer no advantages (see note below).

Below a picture of a Peugeot WRC engine, the valve to the left is the wastegate and the valve to the right is a anti-lag valve and connects the charge pipes to the exhaust manifold.


A similar setup but on a rallycross car.

On the picture one can see a charge air bypass valve (blow off), pop off valves on the inlet manifold, the tubes feeding air to the exhaust manifold and the wastegate behind the turbocharger.

Wastegate creep is simply solved by using a solenoid to control the airpressure to the wastegate, or use pneumatic/hydraulic/electric actuators to control the valve directly.

NOTE: If you place a wastegate on the inlet limiting the boost by wenting air it will become a pop off valve. The HKS Racing bypass valve have for example the same construction as a wastegate (but in light alloys instead of high temperature materials), it can be used as a charge air bypass valve or a pop off valve depending how you connect it.
http://www.hksusa.com/products/?id=761

Regarding engine weight; the BMW engine was probably a little heavy since it was based on a production engine. The Honda V6 was around 146 kg.

[ZoRG]

pop-off valve as I understand is is a device that when it pops lets out more air than you want. It is a pitty that those pictures are not there anymore, because when you see them you will see what I mean.
I have a book here that has a brief moment of discussing it, and the author writes that he knows of a outfit that only uses wastegates on the inlets on all their setups and their clients are very happy, they claim the cars are much more responsive.

I can have a quick look for the books name if you are interrested.

[zac510]

Zorg, is that an Australian book referring to an Australian company?
I've heard about this several times but can't put my finger on how it's done. How would you keep the shaft speed down?

[ZoRG]

You don't really as far as I can tell

Example of how I think it works:
If you are boosting say 10psi but the turbo can do say 30psi, it does not mean the turbo is pumping 20psi out the wastegate and is always supplying 30psi, it might only be pumping enough for say 15psi since when the engine is fed 10psi it cannot drive the turbine to go more than say 15psi, if you up the motor's cold side to 15 psi, it now has more exhaust and so the turbo can now supply 20psi etc

I think turbo selection is quite important though.

Just an idea, not 100% sure if it works like that, alot depends on the turbo and the motor. Personally think the butterfly on the turbo inlet is the best idea.

[McGuire]

In my vocabulary a blowoff valve works/looks pretty much like a popoff valve, but in the inlet between the turbo and the intercooler in high-volume blow-through applications. The idea is to give all that air somewhere to go when the throttle snaps shut. On the fancy rice burners, the part that makes the cool Pssshhht noise during spooldown the kids love so much.

[zac510]

Zorg, I suppose that could work. The pop off valve must be of big size and able to pass a significant volume of air. Most small blow off valves (that McGuire speaks of) probably couldn't do that, so our perception of what they can do is probably wrong.
If sized right, perhaps it can even allow the shaft speed to move up into a more efficient range too.

[ZoRG]

Quote

Originally posted by zac510
If sized right, perhaps it can even allow the shaft speed to move up into a more efficient range too.

Indeed.

[J. Edlund]

Blow off valves, or charge air bypass valves which is the correct name (according to SAE J1930) of this type of valve, is basicly the same as a pop off valve in means of construction. The difference is in how the valve is used. The CAB valve is opened by the vacuum in the inlet manifold, and does thereby prevent compressor surge from happening after going off boost, which would otherwise occur during a high pressure ratio, low flow situations. Compressor surge can damage the turbocharger, but it also reduces turbocharger shaft speed and can also cause misreadings by the airmassmeter. The name "blow off" typically means that the air is vented out of the system instead of being bypassed.

The "vent valve", or pop off valve limits the boost pressure by wenting out charge air. The typical application is as a safety valve in case of a wastegate malfuncion or as a boost limit to prevent higher boost pressures than allowed (cheating) in racing.

The wastegate is in design basicly the same as the CAB valve, and pop off valve. The difference is that instead of venting (bypassing) charge air it vents exhausts, and the amount of exhausts vent ed is controlled by the boost pressure (in some early systems it was however controlled by exhaust pressure).

Say that a given engine wants a flow of .5 kg/s at an absolute pressure of 2.5 bar (pressure ratio 2.5 if the pressure is 1 bar in the compressor inlet). 0.5 kg/s is probably enough for around 600 hp. To provide that amount of boost the compressor will demand the power P=Äh*m where m is the massflow and Äh is the change in enthalpy of the incoming air by the heating done by the compressor during compression. For the situation above, with a compressor being say 75% efficient the typical temperature increase would be from say 0 degC to 109 degC, the power required should then be around 55 kW.
This is the power that must be extracted from the exhaust flow, which is also done by P=Äh*m.
To make it simpler on can assume that the airmassflow is idential to the flow over the compressor and that the specific heat of the gas also is.
So question is what is the change in enthalpy over the turbine? That can be answered by T2 = T1*(P2/P1)^((ã-1)/ã) and by some assumptions. If we say that the turbine inlet temperature is 1200K, and turbine efficiency is 70% the minimum turbine pressure ratio (aka expansion ratio) can be solved by 55 = (1200 - (1200*(P2/P1)^(0.4/1.4)))*0.5*0.70. If we assume that the pressure after the turbine is 1 bar the turbine inlet pressure needed is about 1.6 bar.

If the compressor outlet pressure gets too high the wastegate will open and decrease the turbine inlet pressure and the massflow over the turbine. Doing that the turbine power will be limited to the level needed to reach the compressor outlet pressure set by the wastegate.

So what will happend if we use start to went off charge air to limit the boost pressure?
Say that we have the same conditions as above, but now the compressor flow has increased from .5 kg/s to .6 kg/s (the engine does still get its .5 kg/s though, the rest is wented off). Since the massflow through the compressor have increased we will be one step closer to the choke limit of the compressor and its efficiency has therefore decreased to say 68%. The turbocharger speed is however only slightly higher as turbocharger speed is mainly dependant on pressure ratio, not flow. The pressure ratio over the compressor be like before but now the temperature goes from 0 degC to 120 degC due to the lower efficiency. This togethet with the increased massflos has increased compressor power demand to 72 kW. This means that the turbine must work harder and turbine inlet pressure will increase to 1.9 bar.

The higher the turbine inlet pressure, the higher will the pumping losses during the exhaust phase become. Higher exhaust pressure also have negative effects on exhaust scavenging and therefore volumetric efficiency. Everything being equal, the engine with the lowest exhaust pressure will have the highest power output. In short, any type of "vent valve" have no advantages being used as the primary boost control device.

ZoRG: Note the difference between flow and pressure. The capacity of a turbocharger is usually quite complicated and has to be measured in both pressure ratio (outlet pressure/inlet pressure) and mass/volume flow.

The butterfly on the compressor inlet was first used by Renault and Jean Pierre Boudy I think. They called their system DPV and it did reduce the rpm loss of the turbochargerat between boost conditions quite efficient.

[JwS]

Ok, here is a kind of weird idea that occured to me as a result of this conversation, and current thoughts about hybrid drive systems etc.
Has anyone ever tried attaching an alternator to the turbine shaft as a method of boost control? The system as I conceive it would replace the wastegate, and in the event of a overboost condition the feild coils of the alternator would be energized to bleed energy off of the shaft and convert it into usable electricity. This would only be useful if you had a storage battery etc as in a hybrid to save the power for later of course.
JWS

[Greg Locock]

You could try a patent search on it. Volvo and Lotus have both been active in that field since about 1997. I was involved in an early project to design and build a very high speed alternator/motor. I doubt any patents are active, the idea has been around since the 60s on Naval ships using gas turbines and diesels. Of course, once you have direct control of the turbine's speed, things get quite interesting. Why bother with a shaft connecting the compresser to the expander? why not use a wire?

[McGuire]

Quote

Originally posted by J. Edlund
The higher the turbine inlet pressure, the higher will the pumping losses during the exhaust phase become. Higher exhaust pressure also have negative effects on exhaust scavenging and therefore volumetric efficiency. Everything being equal, the engine with the lowest exhaust pressure will have the highest power output. In short, any type of "vent valve" have no advantages being used as the primary boost control device.

Exactly right. While venting or bypassing inlet charge certainly has merits in controlling surge (depending on the compressor wheel you are trying to swing) as a method of boost management it will always be less efficient. It's throwing away work already performed by the turbo, there's no getting around it.

Go ahead and laugh, but in the early backyard experiments with turbo installations Back In The Day, guys would sometimes use cooling system pressure caps as inlet blowoff valves....they were available in seven, nine, 12 and 14 PSI "calibrations" see, and...

[zac510]

I'm interested to know why the turbine wheel speed is rarely considered significant while compressor wheel speed is often. Is it because the turbine is affected by the exhaust temperature aswell as pressure?

How much can the inlet air temperature affect the pre turbo exhaust gas temperature?

[J. Edlund]

I wonder if not the electric motor in the Garrett e-charger can be used as an alternator using the exhaust energy? I think I read something about that.

As for turbine inlet temperature it can be affected by any increase or decrease in charge air temperature. Another factor is the ignition advance; when ignition is ******** exhaust temperature increase as a result of the lower efficiency of the combustion. Since high compression ratios usually are desirable, ignition must often be ******** to prevent engine knock which results in high exhaust temperatures during load. Air/fuel ratio or the use of for example methanol as a fuel or water injection also affects exhaust temperatures. The methanol driven Champ car engines does for example have exhaust temperatures around 900 degC while the F1 turbo engines ran around 1100 degC. In theory higher exhaust temperatures can reduce the turbine expansion ratio required for a given power output (and thereby exhaust backpressure) and also improve turbocharger response; usually it's however considered a limiting factor. According to a SAE paper by Garrett conventional turbine materials like Inconel 713LC could only survive around 30 minutes at the temperatures encountered in the F1 turbos. Therefore different materials had to be used, the turbines where also aircooled by bleeding compressor air onto them (as used in gas turbines).

Both turbine and compressor speed (blade tip speed) is important if you want to reach high boost pressures. Based upon the Euler turbomachine equation and some assumptions about the turbine and compressor one can calculate the blade tip speed required for a certain compressor pressure ratio. To reach pressure ratios around 6 (needed for a boost of around 5.5 bar absolute) you typically need a turbine blade tip speed of around 500 m/s. With a 63 mm turbine that equals to around 150,000 rpm.

The compressor blade tip speed used was slightly higher (the compressor wheel is also larger), around 640 m/s. For an 82 mm compressor that equals to around 150,000 rpm (the IHI RX6D turbocharger used on the Hondas had a 62.9 mm turbine and a 82 mm compressor and used speeds up to 160,000 rpm). Since the centrifugal stress is proportional to the square of the blade tip speed, this should indicate that the stress was around 60% higher in F1 than in normal turbocharger applications and the compressor wheels where therefore billet machined from a forged piece of high strength aluminium (7075 was used, at least initially).
Since the inducer tip speed is supersonic at some conditions the F1 turbochargers where equipped with a trans-sonic inducer design.

[shaun979]

Quote

Originally posted by ZoRG
Also you need a turbo with a carbon seal or a new GT BB turbo that will allow you to shut the trottle and keep the turbo from leaking oil into the inlet.

Do ALL the Garrett series twin BB turbos fulfill this requirement of no-leakage under vacuum? TIA

[ZoRG]

Quote

Originally posted by shaun979


Do ALL the Garrett series twin BB turbos fulfill this requirement of no-leakage under vacuum? TIA

AFAIK yes.

I am not sure if someone actually said it is a fact that it would be more efficient to have a wastegate on the inlet system, we were merely speculating that if you used a big enough turbo, the engine simply won't have enough exhaust to overdrive it and they do become a bit more efficient at high pressure than absolute low ones, many people disconnect the wastegate to up the boost, this system will not put as much strain on the turbo or engine so you won't be maxing out the turbo, unless it is too small. The writer in the book said the cars are more responsive though, he did not speak of efficiency simply said that the clients all agree about the performance.

Now this is quite interesting, since you are doing exactly the opposite as a turbo inlet throttle where the entire inlet system is emptied. With the inlet wastegate the entire inlet is at pressure(This is not the same as not having a blow-off valve), so if the car is set to 14psi the inlet is at 14psi during shifts as well, so as soon as you hit the throttle, boom instant power, on this setup you would want the tb as close to the head as possible. <- Now does it matter if you are running at 75% efficiency vs. 80 or even 85% on a closed system? In some cases, problably many cases, I don't think it does. The only problem here is that when you stop it will stall the turbo, but since you are stopping it is not the end of the world, emphasis here is on gear change instant power. The main difference between this and the turbo throttle is that the turbo throttle system maximizes turbo response by having the compressor run in a vacuum so it works less and the shaft speed is kept high as a result, while the wastegate on the inlet makes sure there is enough air to imediately get the turbo going once the tb opens up, IMO they are both better than the "average" system with a BOV and a exhaust wastegate.

In cars with anti-lag try and do exactly what a inlet wastegate system does by dumping fuel and firing on exhaust stroke, this has the same effect but destroys the turbo in a short time.

It's all compromise, it depends what you use and what you want to achieve. I can see a inlet wastegate having application at many places, people simply don't use it because they feel they need a super efficient system, but do you really?

What makes more power, a 700hp turbo @ 75% or a 500hp turbo @ 85%? If a wastegate on the inlet allows you to get by with a 700hp turbo while a BOV & exhaust side wastegate system only allows 500hp what would you choose?

[J. Edlund]

In case of Garrett GT models the ones that can be used in vacuum has a carbon seal, if the turbocharger is equipped with a carbon seal this is indicated with an F in the model name.

ZoRG: Many of your theories are quite "off the chart". You have missed the basics of how a turbocharger work and what the wastegate do. Also, if you want to read a book about turbochargers get one where the author actually knows what he is talking about. "Maximum Boost" is a good beginners book, on the more advanced level we have a new book (released about a month ago) named "Fundamentals of Turbocharging".

As I said before the power consumed by a compressor, or given by a turbine equals change in enthalpy over the turbomachine multiplied with the massflow. If you increase the pressure ratio (outlet pressure divided by inlet pressure) or reduce the adiabatic efficiency of a compressor it will increase the enthalpy change over the compressor and thereby the power required by it. If you increase the massflow the power required will also increased. The power required by a compressor should always be kept to a minimum for abvious reasons.

Below is a compressor map for a Garrett F1 turbocharger (twin setup)


On the x-axle, pressure ratio and on the y-axle, massflow. Massflow can be related to how much power an engine fitted with this turbocharger can give. Typically it's possible to get around 1200-1400 hp per 1 kg/s flow.

The percent numbers on the map is adiabatic efficiency, the efficiency line at the right can be considered to be "choke flow". Beyond this point you can't get any increase in mass flow, volume flow can be higher but the heating done limits the mass flow. The line on the left is the "surge" limit, during those conditions the compressor will surge due to the air stalling in the compressor. "Surge" will result in a chirping sound when the air flow backwards in the compressor.
The highest of the rps lines can be considered to be the maximum recommended speed of the compressor, in this case 136,800 rpm (2280 rps).

In a twin setup this turbocharger can flow about .8 kg/s, or for about 1000 hp. The engine it is fitted to (the 1.5 litre V6) does however only produce around 250 hp at an absolute pressure of 1 bar, so to get the 1000 hp we will need to increase the absolute pressure to 4 bar (which will multiply the flow over the engine by four). At those conditions one can notice that we will be at around .4 kg/s and PR 4 on the map. The turbocharger is used at its full capacity at maximum power.

As for the wastegate it's after variable geometry the most efficient way to control boost. Its only function is to regulate boost. It does nothing to improve the spool up. Compared to running a fixed geometry turbocharger without any boost control device it do however make it possible to use a smaller turbine housing and therefore it's possible to get boost at lower engine speeds without overboosting at higher engine speeds.

As for the inlet throttle it reduces lag by reduce the drop in turbocharger speed when the driver lifts the throttle for a short while. As I mentioned above the power required by the compressor was change in enthalpy*massflow, so when the throttle almost stop the flow and reduce the outlet and inlet pressure to an equally low level the compressor will not require any power nor will it surge.

As for the charge air bypass valve it prevents surge by reducing compressor outlet pressure and thereby pressure ratio.

As for the ALS system it dumps air and fuel into the exhaust manifold which causes the turbocharger to operate as a gas turbine (compression in the compressor - add fuel - combustion - expansion over the turbine which in turn power the compressor). By doing this the turbocharger will have full speed, and the charge pipes and intercoolers will be pressurized when the driver again opens the throttle. When used correctly and in a mild degree it isn't that hard on the turbocharger.

As for a wastegate on the charge pipes; when you place it on the charge pipes it will no longer be a wastegate but a pop off (vent valve) or a charge air bypass valve depending on how it's used. If used as a pop off and as the primary boost control valve it will work terrible. It will vent away air that the turbocharger have already spent energy on to compress and therefore the turbocharger can't be used at full capacity limiting the power output of the engine or require a larger turbocharger to get the same power output and thereby offer a slower turbocharger response.
If the system are suppesed to keep the pressure up in the inlet during gear changes it's better to use no valve at all, the compressor will surge but there will be pressure when the driver opens the throttle again. This do however only work under really fast gearchanges and will otherwise offer a poor result. Doing this will in the long run cause turbocharger damage as well as problems with the airmassmeters if used.

[ZoRG]

If you say so, however those guys running 6 second 400m times seem to disagree. Let's leave it at that.

[ZoRG]

Forced induction performance tuning: A Practical guide to supercharging and turbocharging.
A. Graham Bell

Suggest having a look at it, lots of info about the F1 turbo motors as well as other race motors. Also explains how the Renault DVP system worked to some degree, no pretty diagrams about that though.
Page.105

"INLET VENT VALVES
Today, virtually all experienced turbo tuners scoff at the very suggestion of using any sort of inlet system vent to provide boost control, maintaining that an exhaust wastegate is the only way to go. However, I know of one outfit building very high performance road engines (200hp per litre) and competition engines (280hp per litre) who would never dream of using anything but an inlet dump boost control arrangement. Such a system is a fraction of the price of a big external wastegate, but these fellows insist money is not a motive. Simply, their system is more responsive and accurate. They and their clients have numerous tropies to back up their claim, so we should not be quick to dismiss this method of boost control."

I disagree with you saying a wastegate on the inlet side will work as a pop-off valve, this is not the case, a pop-off valve is designed to dump more than it is regulated, for instance if it is setup at 14psi it will lower the inlet pressure to say 10psi as an example, it will not slowly bleed like a wastegate would.

[McGuire]

I can see cases where an intake side blowoff valve setup could work slick...big blower/smaller engine in a drag racing application. Here efficiency is not an issue, just big power and decent response.