FSAEracer03

For us po-boys and our chisel-and-stone Motronic system, it's best to keep boost from creeping up with lower temps. Equal boost still means greater power as the ambient temp drops! It's in the summer time that's ok to turn it up a little to compensate for the density loss.

toddk911

True. At equal boost the cooler charge air will still make more hp. I have always read in here though that it is ok to allow the boost to run at the level the colder air allows since you are getting cooler charge air which drops the chance for detonation. Basically, everything (turbo, IC, intake, fuel) are all running at cooler, more effeciant temps; so your boost gauge reflects that in 1-3more psi in the cold temps. So don't look at it as you are running more boost in the cold but you are getting back the boost you normally loose in the summer. Usually in the 45-55F degree range seems to be the sweet spot.

Again, this leads to why there are such benifts for water injection. Even in 90+ degree the car always runs as if it is 40 degrees out.

I have heard that also about leaning it out in the summer, and it makes sence. But I was always told in here to richen it some in summer to aid in cooling those extra hot charge air temps.

ST, Russell???

toddk911

Russell, I assume the MAXX chips are ok with the cold air compensation??

Actually, even the stock system should be ok due to the IAT sensor making adjustments based on the air temp/density.

FSAEracer03

Your info is sound except for one comment on the summer topic: you are running more boost in the summer. You aren't recovering boost lost, but charge air lost due to density changes. It sounds like semantics... but that's the correct science behind it.

FWIW, I don't decrease my boost levels in the winter. Cold air does reduce detonation, though I don't have the sensors to confirm how much detonation resistance is there due to colder ambient conditions. Theoreticall, you have two-fold temperature reductions in colder weather anyways, so I make the educated guess that I'm in the green to keep it constant.

1) Static temperature decrease before the turbo - ambient air
2) Dynamic temperature decrease after the turbo - IC cooling air

The question I have is how different the differential temperature is over the turbo with relation to ambient conditions... ie, how differently does the turbo heat the air in different conditions? It seems to me there are waaaay too many variables to factor in to make a certain estimate without empirical data.

But in the end, I won't deny it, I just love the way my car runs at 40 degrees!

toddk911

Excellent! Glad you put some science to the issue.

I see your point that the charge air is what is being lost in the hotter ambient as the root cause, and the effect is lost boost.....Correct?

Would the fuel temps injected be an issue for the increased performance also??? As a mild "direct port water injection" in that you have a metal can full of, possibly, VERY cold fuel and if it is not heated up by the time it gets to the injector/cylinder, that it is a cooled fuel/liquid charge going into the cylinder????

Or would that be a hinderance in that the colder fuel temps affect/slow the atomizaiton of the fuel?

FSAEracer03

Almost! The traditional boost controller regulates through pressure. The boost stays the same, but with a lower density, there is less air mass per given pressure. Fuel, as a liquid, does not change density for all intensive purposes. So, to keep a given air:fuel ratio in the summer, as air density decreases, you bump up the boost slightly with your handy boost controller.

The only problem, as you've stated, is the following increase towards detonation. Water injection and intercooler sprayers help push that detonation level a little farther away.


It's basically a moot point. People have tried to sell "fuel coolers" before... but it's effectively useless. The only real benefit these might have is to very slightly decrease knock counts if any knock exists. You'd only gain power with such devices if your motor is having trouble in the first place, otherwise, they're useless.

rberry951

This chips can compensate to a degree, but what you run into is the fact that the MAF voltage does not remain constant in temp changes, and the IAT sensor (if even used with the MAF) doesn't do much to compensate for temps. Until we have a unit to rectify the MAF temp/voltage change issue you need to excersize caution running high boost in cold temps. A person running the AFM does not experience such wide changes in air metering ability as the MAF.

Regards,
Russell

ross255

Anyone have any idea how much boost you could run with stock parts, but using water injection?
Is the problem with higher boost, the detonation, or parts not holding up?

My timing should be OK and my mixture is allways spot on, thanks to vittesse maf.

FSAEracer03

I know of extremely careful and thorough tests on an otherwise stock non-S 951 with a VERY good water injection system. It was tested slightly past 20psi and had no detonation.

ross255

FSAE racer
how much past 20psi? do you know.
All this talk of high octane fuel, and adding xylene to run highr boost, I just think a water injection is a more permanent solution, and a one time cost.

toddk911

+1

But this board has never really been to receptive of water injection. Some on here are running it.

ross255

I think even a simple system, just a pump, and a pressure switch set at 17 psi and a small jet would have some positive effect on temp.
After all some water has to be better than none.
It would just take a while to figure out the ideal amount of water.

toddk911

I agree. and it is easy enough to get several size jets and use trial and error. Starting on the safe side first.

I would consider having it come on even lower; 10-15 psi that way you could still get the benifits of the cooler charge are and also add more timing for better low boost response and quicker spool up.

toddk911

But someone like myself running MAXX chips should be ok with the 1-3psi increase in the cold temps as the chips adjust acordingly. Correct?

ross255

Yes, you could have it at 15 psi, especially if you are pushing a little turbo. But i dont think I will be increasing timing much. You give your self a better margin of safety with water, so you want to be sure your not taking it all away again by increasing timing.
Or perhaps just a little bit more