Intercooler ineffective over 100mph!?
08 June 2005, 01:22 PM
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Intercooler ineffective over 100mph!?
I have read several threads regarding the inefficiency of the intercooler above 100mph due to aerodynamics etc.
I realise that WRC cars etc have a front mounted IC for consistant performance, but what are the dangers to the engine from a TMIC?
I can understand the charge temperature, and therefore air density/presure, varying with air temperature/weather conditions, obvious really! but I imagine the engine map has the facility to cope with charge temperatures across a wide temperature range.
How does the reduction of airflow through the IC at high speed due to inefficiency; thereby resulting in the charge temperature increasing, put the engine at such risk? Should the engine map not adjust the fueling/ignition appropriately to compensate?
Cheers.
I realise that WRC cars etc have a front mounted IC for consistant performance, but what are the dangers to the engine from a TMIC?
I can understand the charge temperature, and therefore air density/presure, varying with air temperature/weather conditions, obvious really! but I imagine the engine map has the facility to cope with charge temperatures across a wide temperature range.
How does the reduction of airflow through the IC at high speed due to inefficiency; thereby resulting in the charge temperature increasing, put the engine at such risk? Should the engine map not adjust the fueling/ignition appropriately to compensate?
Cheers.
08 June 2005, 03:53 PM
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Problem is that the ECU only has finite ability to pull the timing back in order to prevent knock, and in some circumstances this can be insufficient. Couple this with the fact that the ECU apparently pays little or no attention to the factory knock sensor at high revs and you can have problems.
Since most places have speed limits of 70-80, and in Japan all cars are fitted with a limiter, the mapping isn't really optimised for continuous very high speed running. Running for a long time at those sort of speeds can give rise to engine load situations that you would normally never see, like full throttle, maximum boost but constant speed. This can send the charge temperature through the roof. When you combine that with the air missing the scoop so the intercooler can't work properly you have a problem.
Really it's just a case of you get what you pay for. A Subaru is cheap for the performance and hardware you get. To deal with things like this, the cost in engineering time, and therefore cost of the car would go up, in order to deal with a problem that only a tiny fraction of buyers will encounter let alone suffer a failure from. If you buy a turbo Porsche you don't get these kind of issues as you have paid for all the development work to sort them out, for instance, Porsches don't need turbo timers because they are fitted with a system that allows the ECU to keep circulating oil through the turbo after you have turned off the ignition until the temperature drops to a safe level. Scoobies don't come with that, but they don't cost as much either...
Since most places have speed limits of 70-80, and in Japan all cars are fitted with a limiter, the mapping isn't really optimised for continuous very high speed running. Running for a long time at those sort of speeds can give rise to engine load situations that you would normally never see, like full throttle, maximum boost but constant speed. This can send the charge temperature through the roof. When you combine that with the air missing the scoop so the intercooler can't work properly you have a problem.
Really it's just a case of you get what you pay for. A Subaru is cheap for the performance and hardware you get. To deal with things like this, the cost in engineering time, and therefore cost of the car would go up, in order to deal with a problem that only a tiny fraction of buyers will encounter let alone suffer a failure from. If you buy a turbo Porsche you don't get these kind of issues as you have paid for all the development work to sort them out, for instance, Porsches don't need turbo timers because they are fitted with a system that allows the ECU to keep circulating oil through the turbo after you have turned off the ignition until the temperature drops to a safe level. Scoobies don't come with that, but they don't cost as much either...
Last edited by AvalancheS8; 08 June 2005 at 03:55 PM.
08 June 2005, 05:36 PM
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...Porsches don't need turbo timers because they are fitted with a system that allows the ECU to keep circulating oil through the turbo after you have turned off the ignition until the temperature drops to a safe level. Scoobies don't come with that, but they don't cost as much either...
So you take what you pay for or more now?
08 June 2005, 06:15 PM
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Originally Posted by JIM THEO
New age Scobies and mainly after 2002 have a similar system that allows oil circulation through turbo after you have turned off the ignition due to high temp oil vapours that push the oil from the pan until temps drop bellow a level.
So you take what you pay for or more now?
So you take what you pay for or more now?
Can you elaborate on this system..?
08 June 2005, 06:25 PM
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Since most places have speed limits of 70-80, and in Japan all cars are fitted with a limiter, the mapping isn't really optimised for continuous very high speed running. Running for a long time at those sort of speeds can give rise to engine load situations that you would normally never see, like full throttle, maximum boost but constant speed. This can send the charge temperature through the roof. When you combine that with the air missing the scoop so the intercooler can't work properly you have a problem.
08 June 2005, 10:45 PM
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Originally Posted by drb5
So when i see some yellow lights on the knocklink, while sitting at a constant 100mph or thereabout's, it's the explaination above, that comes into play?
09 June 2005, 02:16 AM
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There's more to detting Scoobs than just air flow, but that is certainly a factor. Run a search. Every new Scoob seems to have a bigger scoop than the last one so it's safe to assume there is a real issue here. That's why I've fitted an STi8 scoop to my classic, from DR Motorsport (Scotland).
Richard.
Richard.
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09 June 2005, 08:31 AM
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Originally Posted by AvalancheS8
Problem is that the ECU only has finite ability to pull the timing back in order to prevent knock, and in some circumstances this can be insufficient. Couple this with the fact that the ECU apparently pays little or no attention to the factory knock sensor at high revs and you can have problems.
Since most places have speed limits of 70-80, and in Japan all cars are fitted with a limiter, the mapping isn't really optimised for continuous very high speed running. Running for a long time at those sort of speeds can give rise to engine load situations that you would normally never see, like full throttle, maximum boost but constant speed. This can send the charge temperature through the roof. When you combine that with the air missing the scoop so the intercooler can't work properly you have a problem.
Really it's just a case of you get what you pay for. A Subaru is cheap for the performance and hardware you get. To deal with things like this, the cost in engineering time, and therefore cost of the car would go up, in order to deal with a problem that only a tiny fraction of buyers will encounter let alone suffer a failure from. If you buy a turbo Porsche you don't get these kind of issues as you have paid for all the development work to sort them out, for instance, Porsches don't need turbo timers because they are fitted with a system that allows the ECU to keep circulating oil through the turbo after you have turned off the ignition until the temperature drops to a safe level. Scoobies don't come with that, but they don't cost as much either...
Since most places have speed limits of 70-80, and in Japan all cars are fitted with a limiter, the mapping isn't really optimised for continuous very high speed running. Running for a long time at those sort of speeds can give rise to engine load situations that you would normally never see, like full throttle, maximum boost but constant speed. This can send the charge temperature through the roof. When you combine that with the air missing the scoop so the intercooler can't work properly you have a problem.
Really it's just a case of you get what you pay for. A Subaru is cheap for the performance and hardware you get. To deal with things like this, the cost in engineering time, and therefore cost of the car would go up, in order to deal with a problem that only a tiny fraction of buyers will encounter let alone suffer a failure from. If you buy a turbo Porsche you don't get these kind of issues as you have paid for all the development work to sort them out, for instance, Porsches don't need turbo timers because they are fitted with a system that allows the ECU to keep circulating oil through the turbo after you have turned off the ignition until the temperature drops to a safe level. Scoobies don't come with that, but they don't cost as much either...
For further information, what sort of charge temperatures are we talking about? I know there are scientific principles for the compression of air and generation of heat, without going to deeply into those, are these the governing factor; or is it another.
09 June 2005, 08:40 AM
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Originally Posted by jasonius
Hi Jim,
Can you elaborate on this system..?
Can you elaborate on this system..?
I will try anyway...
Engine coolant is cleverly moved through the turbo via a pyphon effect caused by the new age plumbing system. This system is detailed in the workshop manual.
dipster
09 June 2005, 10:10 PM
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Originally Posted by davedipster
Can I.
I will try anyway...
Engine coolant is cleverly moved through the turbo via a pyphon effect caused by the new age plumbing system. This system is detailed in the workshop manual.
dipster
I will try anyway...
Engine coolant is cleverly moved through the turbo via a pyphon effect caused by the new age plumbing system. This system is detailed in the workshop manual.
dipster
12 June 2005, 12:10 PM
#14
About 3 years ago, I was lucky enough to attend a factory visit at Prodrive, whilst on the tour we visited the customer car baywhich had numerous classic shapes. Someone asked about the TMIC duct, I can remember the answer which cast doubt on its effectiveness on any speed over 90 mph, hence the newer cars have a taller duct.
Rent a windtunnel for £3k a day and have a play, I am planning to modify my original classic one taller, basically the windflow misses it at high speeds.
Rent a windtunnel for £3k a day and have a play, I am planning to modify my original classic one taller, basically the windflow misses it at high speeds.
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