True Tech Question

[30psi 4agte]

wow where to start? This question is a bit involved and for the guys in the know will drive you a bit crazy as when you think you have worked out a theroy for the answer you can always seem to come up with another theroy that contradicts your first one! (Being a mechanic I do anyway )

Ill give you a brief run down of the senario ( so bare with me) and then a Q at end.


My car was on the dyno and after numerous runs of 280+kw we had come to the conclusion that that was about it for now power wise. The A/F was in the mid 11s but the ECU was telling us that the injectors were maxing out (550cc @ 55 psi) and the turbo was pumping 30 psi which is a bit past its efficency range and hence the air temps were high even with the large front mount i have ( about 90 deg )
We then decided to let the car cool abit and do a final run

On this final run I sprayed Nos onto the intercooler the car GRUNTED and almost worked off the dyno! ( even on the just cooler that Nos is awsome shit ) Unfortunatly on this run the head let go a 6700 and i only got a half run but still managed to pull out 313rwkw ( who knows what i would have made if it held togther till 8300 where my max power is)

We think the car may ( prob ) drew some Nos through the I/C and radiator into the turbo and leaned out causing the head to go but it hard to say as it happened so quick that the A/F didnt change much at all!.

Now anyone with a boosted car knows all too well what cold can do for you and how much more power can be made due to cooler air being denser and the engine being more efficent.. ( plenty would be guilty 3am drives to take advantage of this fact!)


My question is:
If a car is on the limit of its injectors and making good grunt say 280kw on a warm day then you take it for a drive on a cold night and its now making an extra 20+ kw because of the cooler air/ more efficent combustion process.
If the engine was already at its limits (fuel wise) but you have now made an extra 20 kw albeit through better efficeney DOES the engine now need more fuel for this extra power?

See what you come up with!

[fixeruperer]

you have tuned you car to the currant ambient temp @ this temp the air can only expand so much so it will only need so much fuel to combust so much power.
now if you were to go out on your 3am cold run when the air is alot denser/colder and can expand somuch more you can add more fuel for the air expansion thus creating more power.

[thechuckster]

what ^ he said - by chilling the intercooler you got a much more dense air-charge.

you didn't get any NO2 into the engine unless you had masive holes in the FMIC, in which case you wouldn't get that much boost anyway.

If your Manifold air temp sensor was upstream of this (e.g. pre-turbo) then the ECU had no idea about this much cooler charge of air and didn't compensate by adding more fuel.

If (as you say) the ECU is already maxing out the duty cycle on the injectors then even if the cooler air temps were detected by the ECU, there was nothing it could have done about it. You would want to add more fuel if you massively lower inlet air-temps.

basically, you grenaded the engine. It got too much air an not enough fuel. what did the AFR read just before the gasket let go? It would have been heading towards lean.

[oldcorollas]

i think he meant that the NOS that was sprayed on the FMIC, and thus was floating around the engine bay... got sucked into the turbo's intake.... and then leaned it out....and genaded...

i reckon thats a very likely cause

as for extra 20kw at night.... if the cold temps decrease your manifold air temp, due to better IC or whatever, then it still needs the right amount of fuel..

however.. if you are already maxed out, what could happen is...

originally, for the higher intalke air temp, you had to tune rich (11:1) to prevent detonation.
but with lower intake temp, you can pull some fuel and still make the power, cos it doesn't need to be so rich to prevent det.
which means, in reality, if you have maxed injectors anyway, then with colder air, the ECU can't command any more fuel, and so the mixture goes leaner.. but this lean is btter for power due to colder intake.....

in other words, you have artificially pulled fuel (due to being maxed), and the colder intake temp allows leaner mixture with same advance, so it's all good.... except for maxed injectors



so to answer the Q, if you have to add extra fuel to prevent detonation at a given advance, and then you have colder air going in, then you can lean it out a bit. however, this assumes that the ECU is not poperly compensating for air temp in the first place.

driving around with ambient temps around -10 to -15, i don't notice any extra power from my car, but i bet the intake temps are very very low

[BlackSupra]

driving around with ambient temps around -10 to -15, i don't notice any extra power from my car, but i bet the intake temps are very very low

Drive said car on a 40 degree day and note the difference.

[oldcorollas]

Drive said car on a 40 degree day and note the difference.

there is DEFINITELY power loss on a 20-30 degree day, ie when it's hot (but interwarmer doesn't help) but from 10 to -10, there doesn't seem to be a SOTP difference

[omy]

Well, if all things being equal then it was a lean a\f. As I have seen my ecu change fuel cells depending on the air temp. As 30psi is alot of boost, it would only take 1/10 of a second for the temps to go through the roof. I have had a 4g63T melt the head and not damge the bottom end. The a\f shoot from 11.7 to 17.0 in a flash. Were was the a\f meter mounted? as some times it is delaid a bit when pluged in the back muffler. I mount mine just before the cat.

[30psi 4agte]

Omy same thing happened here . i melted through the head ( like an oxy torch ) had 30psi go into the cooling system and blow the header tank clean off the radiator! when i pulled bottom end apart everything was perfect.

My exhaust sensor is about where a cat should be But the one we were tuning with was on the tail pipe. Like i said though it happened so fast both sensors didnt change much

[omy]

I did not pick the change up at the time but when I went back to my logs it showed up there. Some times the display screens have a slow refresh rate.