38 replies to this topic

[ViMaMo]

Finally a very exciting engine on the market....a supercharged and turbocharged engine. 168 bhp from a 1.4 litre engine, 39 mpg !!! a maximum torque of 240 newton metres in the range between 1750 and 4500 rpm. With this engine, the Golf GT has a top speed of 220 km/h (136 mph) and reaches the 100 km/h (62 mph) mark in only 7.9 seconds.

[Todd]

Considering the likelihood that it would require 1,500 mile oil changes to combat the underhood temperatures and that major mechanical longevity would be a quarter of that of a naturally aspirated engine of similar output, I don't think this is going to produce cost savings for the high mileage user.

[J. Edlund]

The concept itself isn't new, and there have been several versions of it. It's all based on the downsizing concept, increasing load by reducing displacement and recover the lost power by forced induction. The supercharger is of course there to increase the response and torque at low speed since there is som difficulty to make a high boost engine easy to drive for the daily driver.

The problem have been, and still is, that even with a compressor it's not easy to engage it without some loss in torque for a short moment (noticeable for the driver/passengers) and if it's not disengaged when it's not needed it will increase the fuel consumption.

Similar concepts have been used on diesels and there isn't anything that have indicated that it shouldn't work on a gasoline engine. Oil changes for the VW engine in question is probably required every year or 20,000-30,000 km like any other new engine. Engine life will most likely be as good as any NA engine, possibly even better...

[Todd]

Originally posted by J. Edlund Oil changes for the VW engine in question is probably required every year or 20,000-30,000 km like any other new engine. Engine life will most likely be as good as any NA engine, possibly even better...

I don't doubt you can get aways with the oil change intervals you mention, but only long enough to get the car off warranty. After that, good luck. Why on earth would you think a small engine being compressed at every point on it's rpm range and packed in a dense web of heat sources would survive remotely as long as an NA engine of similar performance is beyond me.

[shaun979]

Originally posted by Todd
Why on earth would you think a small engine being compressed at every point on it's rpm range and packed in a dense web of heat sources would survive remotely as long as an NA engine of similar performance is beyond me.

The thermal loads will not be unreasonable if the cooling system is designed to match. I think the main expected gain in longevity comes from the reduction engine speed to attain a given output. Reduced engine speed means reduced inertial accelerations. Also, the smaller the engine, the smaller and lower mass components become. Lower accelerations applied to smaller masses means a greatly reduced load.

[crono33]

i don't think engine longevity is going to be a major issue. there are other cars around with similar or higher specific power. and anyway, with current speed limits and traffic, who will be able to use much of that power for any lenght of time?

what worries me is mechanical accessibility and complexity... as user, i sometimes have serious problems to find any garage or mechanic able to work on these complex (and probably rare) cars.


gm

Originally posted by Todd


I don't doubt you can get aways with the oil change intervals you mention, but only long enough to get the car off warranty. After that, good luck. Why on earth would you think a small engine being compressed at every point on it's rpm range and packed in a dense web of heat sources would survive remotely as long as an NA engine of similar performance is beyond me.

[Todd]

For some reason, most cars that wind up lasting many years and racking up seriously high mileage are relatively unstressed and naturally aspirated ones. I've heard of a few exceptions of turbo cars that made it to highish mileages without massive costs, but they are certainly the exceptions. All the theories do is allow turbos to re-emerge on the market every so many years and burn another generation of people who believe the problems have been solved this time and underhood temperatures aren't a factor in durability. Have a ball. It won't be on my nickel.

[J. Edlund]

Originally posted by Todd


I don't doubt you can get aways with the oil change intervals you mention, but only long enough to get the car off warranty. After that, good luck. Why on earth would you think a small engine being compressed at every point on it's rpm range and packed in a dense web of heat sources would survive remotely as long as an NA engine of similar performance is beyond me.

There is a SAE paper on the subject comparing a large NA engine, a small turbocharged engine and a small high speed NA engine for racing. Engine load is caused by combustion pressure and massforces. A small turbocharged engine will have very low massforces since engine speed can be kept down and the components are small (light); load caused by combustion pressure is however somewhat higher. But in general the combustion pressures isn't a problem if the engine is designed for it, at least it's less of a problem than the massforces. The cooling and oil cooling system would not have any problem with oil temperature. 168 hp is in any case not that much, there are turbo engines today with 120 hp/l which can be used like any other engine. Practical experience from for example Le Mans have also showed that turbocharged engines have suffered less problems than NA engines. Most problems related to turbocharged engines was solved during the eighties with the use of better materials for certain parts, watercooled turbochargers and management system using knock control.

Most oil problem in road cars are also related to low temperatures rather than high temperatures.

[Powersteer]

Maybe a turbo engine can run reliably but thats because of high tech expensive material technology. Fact is a turbo engines Jekyl and Hyde nature producing no torque and then loads of it the next second is a pain to engineer. Low expansion and high expansion rate in seconds. When the torque comes in thats when the exhaust headers start to glow red, heat. So the piston will experience heat change far more drastically than any other type of engine. Also the charged air is hotter than atmospheric engines.

[shaun979]

Originally posted by Powersteer
Maybe a turbo engine can run reliably but thats because of high tech expensive material technology.

No, just proper design and build.

Fact is a turbo engines Jekyl and Hyde nature producing no torque and then loads of it the next second is a pain to engineer. Low expansion and high expansion rate in seconds. When the torque comes in thats when the exhaust headers start to glow red, heat. So the piston will experience heat change far more drastically than any other type of engine. Also the charged air is hotter than atmospheric engine.

Output normalized, a TC engine will produce the equal or lesser amounts of heat, at a lower RPM, versus a similar displacement NA engine. The TC engine can also be boosted further to match larger displacement NA engines. If the NA displacement bump is not large enough to match the TC massflow at similar RPM, then it has to be run at higher RPM to compensate. I would take moderate amounts of boost in a properly designed TC engine anyday, over an NA engine that has to run high RPM.

IAT, underhood temps, water and oil temps, can all be managed with proper design and build. Piston heat change is no different than an NA engine of equal power. You have so much massflow, and only so much time in which to dissipate the heat. It doesn't matter if you are turning 10,000 RPM NA, or 1,000 RPM TC. Heat levels are going to be the same, if anything the heat advantage will go to the TC engine because of its lower friction level at that low RPM. The numbers are just to illustrate - obviously there is a point where combustion loads can exceed inertial loads and overwhelm components, but that is only seen in very high boost or large-shot-lower-RPM nitrous applications.

The other thing is that as you work your way towards higher specific output, the NA engine becomes exponentially more expensive because it has to face really high levels of friction, inertia load, and high rate of consumption of component fatigue life. At a certain specific output the curve goes asymptotic and the NA engine will fail to deliver required power. TC engines have a limit at some point too, but as witnessed in many TC racing classes including the old F1 turbo era, this same limit exists far far beyond the NA's.

IMO high RPM race NA engines more exciting than any turbocharged engine, but I do believe that TC engines very often wrongfully get a bad rep because of the number of poor approaches taken by enthusiasts, aftermarket vendors, and even some OEMs. Most common shortcoming being the lack ability to operate strongly and repeatably and at high load and high RPM due to either focus on different application, banking on the idea that consumers won't run at high load and high RPM for extended periods of time, or just lack of knowledge to match setup to application.

[shaun979]

Originally posted by crono33
what worries me is mechanical accessibility and complexity... as user, i sometimes have serious problems to find any garage or mechanic able to work on these complex (and probably rare) cars.


gm

Totally agree.

For the same reasons you list, modifying stock cars is increasingly becoming an all-or-nothing option. In the lead is the highly intelligent and restrictive stock ECU with all its checks and levels of safe modes of operation, plus how all the the body control, autobox or electronic diffs, and HVAC systems have to communicate with it. And now cars like the upcoming Mitsubishi Evolution X will have a whole lot of electronically controlled differentials and stability systems.

So now instead of having a street car that doubles as a track car, people are increasingly being pushed toward having a stock street car, and a dedicated track car.

[Powersteer]

Shaun, simply put, reliable cars are cars that are well engineered,turbo, atmospheric, supercharged, you name it. Turbo's are more challenging so if it is well engineered then it will be good but no one can take away a turbocharges split personality and those are harder for the psychiatrist.

Reliability and production is the issue here and an NA engine does not hit red line in every gear, everyday. It won't even go pask 5k much. In a turbocharged engine, everyday driving, you get too little power before the boost comes in and then a sudden change of tempreture when boost kicks in, everyday, and when I am behind the wheel, everygear, except maybe at the higher gears.

For the same given power, an NA engine produces more friction heat because of its size and in its size also it takes away this heat, more area to dissipate.On a turbo engine the heat is kept within that size of an engine. Basicly charged engine are well, charged up!and usually experience more heat. Less reliable maybe but also less expensive which is the key point of reliability.

[FordFan]

Won't NA cars tend to last longer just because they are simpler? Fewer moving parts, and all that?!

[J. Edlund]

Originally posted by Powersteer
Shaun, simply put, reliable cars are cars that are well engineered,turbo, atmospheric, supercharged, you name it. Turbo's are more challenging so if it is well engineered then it will be good but no one can take away a turbocharges split personality and those are harder for the psychiatrist.

Reliability and production is the issue here and an NA engine does not hit red line in every gear, everyday. It won't even go pask 5k much. In a turbocharged engine, everyday driving, you get too little power before the boost comes in and then a sudden change of tempreture when boost kicks in, everyday, and when I am behind the wheel, everygear, except maybe at the higher gears.

For the same given power, an NA engine produces more friction heat because of its size and in its size also it takes away this heat, more area to dissipate.On a turbo engine the heat is kept within that size of an engine. Basicly charged engine are well, charged up!and usually experience more heat. Less reliable maybe but also less expensive which is the key point of reliability.

Turbocharged engines doesn't operate at higher speeds than NA engines. Most modern turbocharged engines are giving their maximum torque in a range somewhere around 2000-4000 rpm and often more torque than a NA engine of similar power (unless the NA engine has a very large displacement). However, in the speeds just above idle the torque output is less so you have to wait until 1500-2000 rpm intil the boost comes; and the torque comes when the boost does.

The inlet temperature of a turbocharged engine is usually less than 70 degC since they use intercoolers.

The temperature during combustion is equal to the temperatures of a NA engine and exhaust temperatures are quite similar too (but BMEP is higher and pmax is slightly higher). The difference is that when a turbo engine is boosted there is pressure in the exhaust manifold which means that the gases won't expand on cool in the manifold like on a NA engine but in the turbocharger. Over the turbine about 100-150 degC is lost, and from that point, under boost, the exhaust temperature of a turbo engine is equal or probably lower than on a NA engine. However, today engines are in general using higher temperatures but that's because higher compression ratios and leaner mixtures are used. This of course to reduce exhaust emissions.

That a turbo engine is more challenging to make doesn't need to be true, that depends on how you compare. Say that you have a 2 litre four cylinder engine and you want 300 driveable hp; getting the required power using a turbo will be quite easy but without forced induction it will be quite difficult.

[Greg Locock]

That's a bit of a (common but...) odd comparison. Why use the swept volume as your arbiter of engine 'size'? That is as arbitrary as using the number of cylinders, or the star sign of the designer.

I'd rather see an equivalence formula based on installed package size, or weight, or cost.


Size

I can probably squeeze a V6 into the same package as your turbo I4, or a W4 2 stroke with larger cylinders at least (OK that would be a disgusting engine). I don't think 300 hp is feasible for that engine.

Weight
Turbo plus associated junk probably weighs 15 kg. I can't really do much with just 15 kg, in terms of number of cylinders, but I could certainly increase the swept volume a bit. Again 300 hp seems a stretch.

Cost

In mass production it would be much cheaper to build a 300 hp V8 than a 300 hp turbo I4, and if you had to build a one off from scratch then the V8 would be cheaper as well. I'd guess building your own turbocharger would cost more than the entire V8.

However maybe I'm making too much of the 300 hp turbo I4 2000cc, that is 50% more than a typical WRX, per litre, so that would be a track engine, or at least a very hot street engine.

If you take a standard WRX turbo, that is 200 hp. The engine bay is full. Could you fit a 4 litre V6 or V8 in there ? Would it weigh more? Would it cost more? I don't know exactly, but I think it is a better comparison than the 300hp example.

When I get to work on Monday I'll find the Ward's engine survey, that should add some hard and fast numbers to this line of reasoning.

[bobqzzi]

Originally posted by Todd
Considering the likelihood that it would require 1,500 mile oil changes to combat the underhood temperatures and that major mechanical longevity would be a quarter of that of a naturally aspirated engine of similar output, I don't think this is going to produce cost savings for the high mileage user.

I see you are unfamiliar with VAG products. Would a N/A aspirated engine of similar output last longer? Perhaps, but I would expect this engine to last far longer than the rest of the car, so any additional life would be of no use.

[shaun979]

Originally posted by J. Edlund
The inlet temperature of a turbocharged engine is usually less than 70 degC since they use intercoolers.

For reference, a stock 2L I4 boosted to about 350hp at a trackday at Sepang F1 Circuit in ambient temps of about 35 deg C has IATs logged to be consistently below 50 deg C no matter how many hotlaps were run in a row - really effective IMO. A 1.8L I4 running a larger turbo vs former example boosted to about 450hp in cooler evening ambient temps of around 28 deg C has IATs logged to peak at 58 deg C. Both running FMIC, former coming stock with the car, latter being aftermarket with improper front valence that blocked some 30% of IC surface area.

The temperature during combustion is equal to the temperatures of a NA engine and exhaust temperatures are quite similar too (but BMEP is higher and pmax is slightly higher).

Exactly.

==========

Powersteer, I'm not sure exactly where you draw that the heat rise at boost onset is a large factor or that the piston can't take it. To begin with, the power increase is not sharp at all with most production TC cars. Not much different at all from sportier NAs. I might be able to see that with very large shot nitrous applications, but not much else.

[Powersteer]

The temperature during combustion is equal to the temperatures of a NA engine and exhaust temperatures are quite similar too (but BMEP is higher and pmax is slightly higher).
--------------------------------------------------------------------------------



Exactly.

;)

Combustion chambers is closed section so the more air you put in the more it burns thats why you put a turbocharger there in the first place right? Burn = heat = expansion = pressure. So the longer or stronger you burn the hotter it gets eventhough the heat of the fire is the same, pressure change is about as good as heat change and turbos provide pressure everywhere in an engine. If you leave it burning too long the engine tempreture would be the same as the fire (evacuate vehicle). Also a turbo's intake heat is more than an atmosphere engine, defenately an addition to combustion chamber tempreture.

Now, a turbocharger engine is making a small engine perform like a bigger cc engine. The point first put out here is reliability. Just think having bmep's of a big engine in a small engine, that is like high bmep on smaller engine journals. I don't see this as being reliable. NSX 286 bhp production engine versus the rally replicas 276bhp (nevermind accuracy). The NSX engine has about the same piston weight maybe less but the bmep (the substance that hammers the journals) is spread all over a more surfaced area journals making it technically more reliable. I also can't see a high revving journal getting more torture than a low revving one that has higher bmep.

Do you know a turbocharged engine is built much tougher than an NA one??? Have you ever thought why?

EDIT: Oh I forgot to add, I never said the piston cannot take it. Its just that the drastic heat changes make engineering piston clearance a challenge. eventhough on running tempreture it stills changes drastically daily use.(also clicked check spelling and it does not seem to be working)

[shaun979]

Originally posted by Powersteer
I thought nitrous had good cooling properties as itself.

I'm referring to nitrous-fuel mix combustion - sharp gain in massflow per unit time. Large pressure spike and large energy release with little time to dissipate.

Combustion chambers is closed section so the more air you put in there to burn the more it burns thats why you put a turbocharger there in the first place right? Burn = heat = expansion = pressure. So the longer or stronger you burn the hotter it gets eventhough the heat of the fire is the same, pressure is heat and turbos provide pressure everywhere in an engine. If you leave it burning too long the engine tempreture would be the same as the fire. Add to this the fact that a turbo's intake heat is more than an atmosphere engine. Am I making sense here??

Power for power there is about equal amounts of heat energy needing dissipation. The point about surface area for dissipation is valid but there are other ways around it too than just surface area. Separately, what can be interpreted as lack of cooling capacity in one situation, can be viewed as thermal efficiency in another if thermal control is not varied along with varying parameters.

Just think having bmep's of a big engine in a small engine, that is like high bmep on smaller engine journals. I don't see this as being reliable. NSX 286 bhp production engine versus the rally replicas 276bhp nevermind accuracy). The NSX engine has about the same piston weight maybe less but the bmep (the substance that hammers the engine) is spread all over a more surfaced area journals making it technically more reliable.

Why are you so concerned with combustion loads when inertial loads are far greater and have more effect on longevity? In a properly driven car there is almost never any lugging - high load with little to no engine speed increase, worse if it is operating in a high torque band of engine speed range. That is what really stresses the journals at lower RPM. At higher RPM it is inertia load.

It doesn't help that you are comparing TC 2L I4 to a NA 3.2L V6. Given a lack of packaging and/or weight restrictions for vehicle balance, who wouldn't pick a NA 7.4L V8 over a TC 2L I4?

Do you know a turbocharged engine is built much tougher than an NA one???

If you would specify the areas, we can discuss them.

Have you ever thought why?

What are you trying to say?

EDIT: Oh I forgot to add, I never said the piston cannot take it.

You seem to think it is of major concern though - more so than more important factors.

[shaun979]

Originally posted by Powersteer
Its just that the drastic heat changes make engineering piston clearance a challenge. eventhough on running tempreture it stills changes drastically daily use.

In daily use and at production turbo power levels and power curve characteristics, the temperature change is not major once warmed up.

[Powersteer]

You mean actually thought I was discussing this during cold start?????????? Holy!!!!!

[shaun979]

Originally posted by Powersteer
You mean actually thought I was discussing this during cold start?????????? Holy!!!!!

No, just being clear. You can ignore the "once warmed up" stipulation if you want and the point still exists.

[J. Edlund]

Originally posted by Greg Locock
That's a bit of a (common but...) odd comparison. Why use the swept volume as your arbiter of engine 'size'? That is as arbitrary as using the number of cylinders, or the star sign of the designer.

I'd rather see an equivalence formula based on installed package size, or weight, or cost.


Size

I can probably squeeze a V6 into the same package as your turbo I4, or a W4 2 stroke with larger cylinders at least (OK that would be a disgusting engine). I don't think 300 hp is feasible for that engine.

Weight
Turbo plus associated junk probably weighs 15 kg. I can't really do much with just 15 kg, in terms of number of cylinders, but I could certainly increase the swept volume a bit. Again 300 hp seems a stretch.

Cost

In mass production it would be much cheaper to build a 300 hp V8 than a 300 hp turbo I4, and if you had to build a one off from scratch then the V8 would be cheaper as well. I'd guess building your own turbocharger would cost more than the entire V8.

However maybe I'm making too much of the 300 hp turbo I4 2000cc, that is 50% more than a typical WRX, per litre, so that would be a track engine, or at least a very hot street engine.

If you take a standard WRX turbo, that is 200 hp. The engine bay is full. Could you fit a 4 litre V6 or V8 in there ? Would it weigh more? Would it cost more? I don't know exactly, but I think it is a better comparison than the 300hp example.

When I get to work on Monday I'll find the Ward's engine survey, that should add some hard and fast numbers to this line of reasoning.

Most car manufacturers have inline fours availible with around 2 litres displacement, so to make a turbocharged 2 litre engine is usually quite cheap. Sure you need some stronger rods, pistons and so on, but that is quite easily done for an engine manufacturer. The turbocharged engine will be of similar size of the NA version.

If we wanted to replace the 2 litre engine with for example a larger V6 that will cost a lot of money if we don't have a V6 engine (and if we have a V6 we can use that one in the same way). It can also be costly to introduce a new engine to the car that we have, which we can assume already has the small 2 litre engine. The larger V6 will also consume more fuel than the smaller 2 litre engine during daily driving (as it will be run with less load). Unless there is a specific customer demand for a V6 engine we could use the small I4 engine as well as a larger engine.

For example, Saab has an engine with 305 hp (and with 400 Nm from about 2000 rpm), the engine has a displacement of 2.3 litres and its size is equal to the 2 and 2.3 litre turbo engines producing from 150 hp and NA engine producing from about 130 hp (not in production). As an option a 3 litre V6 engine was offered (borrowed from Opel, also not in production anymore), that engine produced 210 hp, but it was also heavier and consumed more fuel. It was later turbocharged and finally withdrawn being replaced by an inline four producing 220 hp. Don't know the production costs but as a spare engine the V6 was about 20% more expensive. The only reason a V6 engine was ever used was because of the US market where you can sell cars with displacement and cylinders. A V8 (GM compact V8) has also been tried on a prototype car, it produced about the same power and torque like the inline four, there was however a difference; the V8 engine took up all the space under the hood so no AC compressor could not be fitted. The fuel consumption with this engine was also higher.

Originally posted by Powersteer
Combustion chambers is closed section so the more air you put in the more it burns thats why you put a turbocharger there in the first place right? Burn = heat = expansion = pressure. So the longer or stronger you burn the hotter it gets eventhough the heat of the fire is the same, pressure change is about as good as heat change and turbos provide pressure everywhere in an engine. If you leave it burning too long the engine tempreture would be the same as the fire (evacuate vehicle). Also a turbo's intake heat is more than an atmosphere engine, defenately an addition to combustion chamber tempreture.

Now, a turbocharger engine is making a small engine perform like a bigger cc engine. The point first put out here is reliability. Just think having bmep's of a big engine in a small engine, that is like high bmep on smaller engine journals. I don't see this as being reliable. NSX 286 bhp production engine versus the rally replicas 276bhp (nevermind accuracy). The NSX engine has about the same piston weight maybe less but the bmep (the substance that hammers the journals) is spread all over a more surfaced area journals making it technically more reliable. I also can't see a high revving journal getting more torture than a low revving one that has higher bmep.

Do you know a turbocharged engine is built much tougher than an NA one??? Have you ever thought why?

EDIT: Oh I forgot to add, I never said the piston cannot take it. Its just that the drastic heat changes make engineering piston clearance a challenge. eventhough on running tempreture it stills changes drastically daily use.(also clicked check spelling and it does not seem to be working).

Temperature is not the same thing as heat!

The temperature during combustion is similar both in NA and turbocharged engines. The temperature in an engine depends on basicly the air inlet temperature, compression ratio and the energy content in the fuel in relation to the mass of fuel added per amount of air. With a turbocharged engine the inlet temperature is higher but the compression ratio is lower. The energy content of the fuel in relation to the mass of fuel added per amount of air is quite constant which means that during combustion the temperature will increase with about 2000K.

Heat is a different issue, and if we increase the power of an engine it must involve more heat. In the case of the turbocharged engine we increase heat by increaseing the massflow. Massflow is also increased in high speed engines or large displacement engines the difference is only that in a turbocharged engine we increase the pressure not the volume of the flow.

[NTSOS]

Let's review.....it seems that most steet turbo-supercharged motors don't pay particular attention to detail as it relates to off idle/pre crossover performance (period between off idle and and the first appearance of overpressure).....witness the fact that most production intake manifolds designated for turbocharged motors are very short large port/large plenum designs that are ideal for post cross over performance but are counter productive as it relates to generating the all important kinectic energy in the operating cylinder at low RPM's to provide the stuff that spools up the turbines prior to cross over. A simple fix really....a variable geometry intake port that permits a tiger N/A motor from off idle to crossover to spool up the turbing and then opens up the geometry to allow non-restrictive pressurized port flow. This is really cool because it allows a larger than normal turbine housing that provided a more favorable intake to exhaust delta/p......a key incredient that allows a turbo-supercharged motor to excel.

When you have to use a mechanical supercharger at low RPM's to fix the above transitional problem, jeeze.....it's very dissapointing.

John

[Powersteer]

With a turbocharged engine the inlet temperature is higher but the compression ratio is lower.

J.Edlund

Add to that quote that the higher inlet temperature is because of the compressed air. The ratio of compressed air is higher than normal air when compressed because of the nature of it being more compact. So low static compression ratio will end up giving a lot of heat when dynamic effective compression ratio takes over. If you have air charged that is twice the amount of normal its compressing nature will change. This is a reason why turbocharged engines have lower compression ratios to combat detonation.

[shaun979]

Originally posted by Powersteer
J.Edlund

Add to that quote that the higher inlet temperature is because of the compressed air. The ratio of compressed air is higher than normal air when compressed because of the nature of it being more compact. So low static compression ratio will end up giving a lot of heat when dynamic effective compression ratio takes over. If you have air charged that is twice the amount of normal its compressing nature will change. This is a reason why turbocharged engines have lower compression ratios to combat detonation.

At higher compression ratios, you have a larger pressure spike in the PV chart while it doesn't gain much area . Lowering compression ratio you have less of a spike and when you pump up pressure via boost, it is more even.

[Todd]

Originally posted by bobqzzi


I see you are unfamiliar with VAG products. Would a N/A aspirated engine of similar output last longer? Perhaps, but I would expect this engine to last far longer than the rest of the car, so any additional life would be of no use.

That is a good point about it being a VAG product, having owned 3 and a fourth with a VAG engine. Even if it had a total of 9 moving parts, the first model year buyers would still be expected to weather the development process.

[DOHC]

Originally posted by Todd
it had a total of 9 moving parts

Sounds like a 4-cyl two-stroke engine, or did the valves get stuck?

[crono33]

Greg,

i have read before this fact that 8v engines can be very cheap to manifacture, and i do believe you, however here in old europe v6 or v8 usually come in high end, very expensive cars. perhaps in other environments (like USA) where tooling is already available and paid for and these engines are (or were) produced in large numbers, this is true, or there is some other factor i dont know, but in europe and surrounding anything that is not I4 will be rare and cost a lot.

in some countries here, large engines or 6v/v8 are heavily taxed by the greedy states, making thus TC engines more attractive (that explains the ferrari 208 of the 80ies for example).

however some countries are starting to tax by the HP...


i have owned several TC cars, both petrol and diesel.

the last TC diesel was a 1.9 litre fiat tipo. at 200,000km i stopped altogether any maintenance waiting for the car to break down in order to scrap it.
at 300,000km, without having changed oil, timing belt or anything else, i gave up and scrapped the car with a still working engine. so i dont really know about short lifespan of TC engines..

gm

Originally posted by Greg Locock
That's a bit of a (common but...) odd comparison. Why use the swept volume as your arbiter of engine 'size'? That is as arbitrary as using the number of cylinders, or the star sign of the designer.

I'd rather see an equivalence formula based on installed package size, or weight, or cost.


Size

I can probably squeeze a V6 into the same package as your turbo I4, or a W4 2 stroke with larger cylinders at least (OK that would be a disgusting engine). I don't think 300 hp is feasible for that engine.

Weight
Turbo plus associated junk probably weighs 15 kg. I can't really do much with just 15 kg, in terms of number of cylinders, but I could certainly increase the swept volume a bit. Again 300 hp seems a stretch.

Cost

In mass production it would be much cheaper to build a 300 hp V8 than a 300 hp turbo I4, and if you had to build a one off from scratch then the V8 would be cheaper as well. I'd guess building your own turbocharger would cost more than the entire V8.

However maybe I'm making too much of the 300 hp turbo I4 2000cc, that is 50% more than a typical WRX, per litre, so that would be a track engine, or at least a very hot street engine.

If you take a standard WRX turbo, that is 200 hp. The engine bay is full. Could you fit a 4 litre V6 or V8 in there ? Would it weigh more? Would it cost more? I don't know exactly, but I think it is a better comparison than the 300hp example.

When I get to work on Monday I'll find the Ward's engine survey, that should add some hard and fast numbers to this line of reasoning.

[clSD139]

The 1.4 TSI (turbo stratified injection) has 170 HP, and characteristics similar to a 2.3 engine. It is fine-tuned in the VW-Chemnitz plant, it is the first production car with that set-up. The new Golf fills up the gap between the Sport (max. 150 HP) and the GTI (200 HP) versions. Also a diesel with the same (!) power figure will be released under the Golf GT tag. Earlier "GT's" had 1.8 90 HP petrol engine, and eventually a synchro rear-axle.

As mentioned earlier, this set-up requires specialists for serious power. Some years ago a Fiesta with 315 HP was presented in some mag. I think there is wheel spin the whole rev range in highest gear...

[JForce]

I drive a car with a 2.5l V6 Twin-Turbo, and haven't come across any issues at all. It is my second turbo car, and with both being Japanese, I am not expecting any.

[Fortymark]

VW builds an "Diesel Elise"

http://www.autocar.c...sp?na_id=217406

[J. Edlund]

Originally posted by Powersteer
J.Edlund

Add to that quote that the higher inlet temperature is because of the compressed air. The ratio of compressed air is higher than normal air when compressed because of the nature of it being more compact. So low static compression ratio will end up giving a lot of heat when dynamic effective compression ratio takes over. If you have air charged that is twice the amount of normal its compressing nature will change. This is a reason why turbocharged engines have lower compression ratios to combat detonation.

The temperature of the incoming air of a turbocharged engine is usually not that high since intercoolers are commonly used. Also, the temperature increase is a result of the increase in enthalpy required when the air is compressed. The temperature increase is dependant on the pressure/pressure or volume/volume ratio, not the actual pressure of the gas. Hence compressing a more dense gas will not result in a higher temperature than compressing a less dense gas an equal amount.

The reason turbocharged engines have a lower compression ratio is to decrease peak pressures in the cylinders. The higher peak pressures are of course a result in the increase in air and fuel mass per combustion. Today turbocharged engines use higher compression ratios, GM HFV6 does for example use about 10:1 as naturally aspiranted and 9,5:1 with about a half bar of boost. In addition they also tend to run leaner during high loads. To prevent detonation (peak pressures) they instead rely more on ignition timing, using very little ignition advance at those conditions. That does of course also mean that the exhaust temperatures gets high and since the exhaust gases are expanded first in the turbine the turbocharger and exhaust manifold can become very hot during high loads and this is usually what people notice.

"Dynamic compression ratio" is one of those invented engine terms. If we talk thermodynamics there are no such thing as a "dynamic compression ratio".

[Canuck]

I thought compression ratios were reduced to combat detonation as well. Not because there's any change in the nature of compression, but as a means to alleviate heat/detonation issues as even with an intercooler, the cylinder charge is still hotter than a N/A engine. 'course, I got that from Corky...

[Powersteer]

J.Edlund, 20 days I had to wait for you, were you on vacation??? Tango the girl from Ipanema??

[J. Edlund]

Originally posted by Canuck
I thought compression ratios were reduced to combat detonation as well. Not because there's any change in the nature of compression, but as a means to alleviate heat/detonation issues as even with an intercooler, the cylinder charge is still hotter than a N/A engine. 'course, I got that from Corky...

If you reduce the peak pressures the risk of detonation will also decrease.

If we assume that we have 2 naturally aspiranted engines with a 10:1 respective 10.5:1 compression ratio and a turbocharged engine with a compression ratio of 9.5:1, the NA engine has an inlet temperature of 20 degC and the turbocharged engine has 40 degC. Assuming that the compression is polytropic (1.32) the temperature will be as follows:

Temperature at end of compression
NA1: (273+20)*10^(1.32-1) = 612 K or 339 degC
NA1: (273+20)*10.5^(1.32-1) = 621 K or 348 degC
T: (273+40)*9.5^(1.32-1) = 643 K or 370 degC

No larger difference here!

Temperature during combustion assuming no heat loss.
The temperature during combustion will depend on the temperature before combustion and the heat released from the fuel in relation to the total mass of combustion products and their specific heat capacity. Typically the temperature increase is around 3600 K meaning that the temperatures will be:

NA1: 3600+612 = 4212 K
NA2: 3600+621 = 4221 K
T: 3600+643 = 4243 K

No larger difference here!

Assuming a polytropic expansion (1.48) the temperature after expansion will be:
NA1: 4212*(1/10)^(1.48-1) = 1394 K
NA2: 4221*(1/10.5)^(1.48-1) = 1365 K
T: 4243*(1/9.5)^(1.48-1) = 1440 K

A slight increase in temperature due to the lower compression ratio and the higher intake air temperature.

If the boost pressure is assumed to be 2 bar absolute for the turbocharged engine and 1 bar absolute for the NA engine then:

Pressure after compression:
NA1: 1*10^1.32 = 21 bar
T: 2*9.5^1.32 = 39 bar

Maximum teoretical combustion pressure at constant volume:
NA1: T3/P3 = T2/P2 = 4212/P3 = 612/21 => P3 = 144 bar
T: T3/P3 = T2/P2 = 4243/P3 = 643/39 => P3 = 257 bar

To sum it up, a turbocharged engine gives a very small increase in temperatures while there is a large increase in combustion pressures during boost.

[Powersteer]

2000cc turbo sucks 3000cc of air. Air is compressed 1.5 times. Compression ratio of engine is 8:1 so at TDC there is 250cc of space. 8 X 1.5 is????? 12, which, in a very basic way, is the compression ratio of a 2.0T engine that takes in 3000cc of air. Say we have14:1 air/fuel mixture. So thats 214.3cc of fuel to be injected into the 2.0T engine instead of 3000cc engine which should also increase compression but cools down the charge.

So now we have a 2000cc engine on 12:1 compression ratio, taking 30% more heated air (50% without intercooler and assuming the turbo is 100% efficient in compressing the air) and having 214cc of fuel injected to it while just seconds before this all happens this engine was still 2000cc but grasping for air that has to go through the turbo and then the intercooler, is 'cold', took so little fuel, and had 8:1 compression on it. Its quite amazing really to get it to run for really heavy mileage, I have total respect for mechanical engineers today I can tell you that much.

EDIT: Think I'm done with this thread

[J. Edlund]

Originally posted by Powersteer
2000cc turbo sucks 3000cc of air. Air is compressed 1.5 times. Compression ratio of engine is 8:1 so at TDC there is 250cc of space. 8 X 1.5 is????? 12, which, in a very basic way, is the compression ratio of a 2.0T engine that takes in 3000cc of air. Say we have14:1 air/fuel mixture. So thats 214.3cc of fuel to be injected into the 2.0T engine instead of 3000cc engine which should also increase compression but cools down the charge.

So now we have a 2000cc engine on 12:1 compression ratio, taking 30% more heated air (50% without intercooler and assuming the turbo is 100% efficient in compressing the air) and having 214cc of fuel injected to it while just seconds before this all happens this engine was still 2000cc but grasping for air that has to go through the turbo and then the intercooler, is 'cold', took so little fuel, and had 8:1 compression on it. Its quite amazing really to get it to run for really heavy mileage, I have total respect for mechanical engineers today I can tell you that much.

EDIT: Think I'm done with this thread

2000cc would require about 285cc volume at TDC for a compression ratio of 8.
8 = (2000+285)/285

You can't mix volume/volume ratios with pressure/pressure ratios. A compression ratio of 8:1 with .5 bar of boost is not equal to a compression ratio of 12:1. Infact, you can't even do a comparison like that.
Gas turbines just like turbochargers use a pressure/pressure ratio while piston engines use a volume/volume ratio. A jet engine can have a "compression ratio" of 8:1, and in that case it means that the pressure after the compressor is 8 times the pressure before the compressor. Just like with turbochargers compression ratio will also decrease at reduced speeds while it on piston engines remains constant. A piston engine having 8:1 compression ratio means that it has a volume/volume ratio of 8; the volume at TDC is eight times the volume at BDC the volume at BDC being the volume at TDC + displacement (bore area*stroke). With a volume/volume ratio the pressure after compression increase with compresion ratio^ratio of specific heats.

Fuel mixtures are in mass/mass ratio, not volume of air/volume of liquid fuel. If fuel is added with a ratio of 14.7:1 to 3 litres of air, the amount of fuel added is (3/1000*1,2)/14.7 = 2,45*10^-4 kg or 0.245 gram or 0.34cc of gasoline.

[Powersteer]

Oh my god!!! the engine I was refering to actually has 9:1 and not 8:1 compression ratio.