Turbo boost pressure cold different to when hot - any ideas??

[exfuzzyt5]

Anyone got any ideas why boost pressure would vary when the engine is running upto normal operating temp - basically from cold it will boost 13 psi and when at normal operating temp it only boosts 10 psi - is this normal??

Checked all usual hoses and pipe work for leaks/splits etc all seems ok

Thanks in advance

[ukcb7tuner]

Anyone got any ideas why boost pressure would vary when the engine is running upto normal operating temp - basically from cold it will boost 13 psi and when at normal operating temp it only boosts 10 psi - is this normal??

Checked all usual hoses and pipe work for leaks/splits etc all seems ok

Thanks in advance

Just my 2 cents but u shouldn't be flooring it till its upto full running temp anway :worried:

[cameron]

Agreed

You should let everything warm up before givin it the boot ;)

[exfuzzyt5]

Just my 2 cents but u shouldn't be flooring it till its upto full running temp anway :worried:

Point well presented - however what I mean is if I run from cold and temp would normally go up to just under half hot (so its just under it normal running temp) before I boot it and it will boost 13 psi - then run around for 20 miles or so and boost will drop to 10 psi max - let the car cool for 1/2 hour - rerun and for the first 2 miles it will boost at 13psi and then drop back down to 10 again - hopefully I've explained a little better!!!!

[Johnny5]

Not sure if this may help, but air is less dense when its cold, therefore the turbocharger is able to "squeeze" more air into the intercooler... and therefore more into the cylinders, the more air in - the more fuel is able to be burnt and the more boost pressure will be acheived! The cold air intake for the engine is above and just infront of the radiator (If you have the standard air-box and trunking)
I maybe barking up the wrong tree here, but i always remember my sapphire cosworth boosting better when the weather was cold...........
Hope this helps??????????
Regards
John

[JelT5]

I agree with you John- ambient air temp definitely has an effect on boost pressure. Been in the mid 20s here this wk/end and, similar to you exfuz, peak boost drops after a while. Just one of those things that can't be controlled sadly!

[jez.w]

Not sure if this may help, but air is less dense when its cold, therefore the turbocharger is able to "squeeze" more air into the intercooler... and therefore more into the cylinders, the more air in - the more fuel is able to be burnt and the more boost pressure will be acheived!
John

You got that wrong, cold air is more dense and warm air (hot day) is less dense. Turbo cars run much better on a cold day (air more dense), on a very cold day my gt4 boosts and extra 3 or 4 psi taking it over the safe limit, i therefore have to turn the boost down on the boost controller when its cold so it doesnt boost more than 15 psi. On a very cold day it can overboost at 65%, but on a hot day it can be set at 80% to get 15 psi.
My T5 doesnt have an adjustable boost controller but boost goes off the end of the gauge on a cold day, and stops just short of the end on a warmish day. I dont think the standard dash gauge is very acurate but it gives an indication if its holding boost and roughly what is happening.

[exfuzzyt5]

Cheers guys - this sort of all adds up - had the same issues when racing a normally aspirated car - went better on cold days than hot - would removing the air con rad make any difference too hot running - or just a striaght forward increase in boost pressure via a remap??

[Johnny5]

Damn..... ur right, oops! I got that round the wrong way..... hmmmmmmm or did i? So why did my sapphire cozzy boost better when it was cold??????? ;)

[daveforber]

Because the air was denser! :)

My limited understanding is that the effect may be more marked if you use an induction kit, which will take in warmer (less dense) air from the engine bay.

[Johnny5]

lol..... ok i lost! ;)

[Babybadger]

You got that wrong, cold air is more dense and warm air (hot day) is less dense. Turbo cars run much better on a cold day (air more dense), on a very cold day my gt4 boosts and extra 3 or 4 psi taking it over the safe limit, i therefore have to turn the boost down on the boost controller when its cold so it doesnt boost more than 15 psi. On a very cold day it can overboost at 65%, but on a hot day it can be set at 80% to get 15 psi.
My T5 doesnt have an adjustable boost controller but boost goes off the end of the gauge on a cold day, and stops just short of the end on a warmish day. I dont think the standard dash gauge is very acurate but it gives an indication if its holding boost and roughly what is happening.

Seconded, just take your car out on a damp cold foggy morning and enjoy the boost.....

[jez.w]

Basically cold more dense air = more air mass compared to same amount of volume of warm air.

Therefore with denser air, your turbo is forcing much more air in, so your car puts more fuel in to balance the air/fuel mixture ratio, and this increase of air/fuel produces more power. Its a bit like turning up the boost pressure on the turbo. But if you get too much air in (or too much boost) the mixture will go lean (not enough fuel) as the fueling cant keep up with the amount of air being forced in by the turbo. When the fuel mixture is lean the cylinders get very hot and tops of the piston get over heated, fuel helps to keep the cylinder temperature down. If your car regularly runs lean at high boost or when you thrash it then it will melt a piston or go bang eventually. Also way too much fuel (rich) can cause bore wash and oil to be washed away causing lubrication problems in the cylinder, and poor running and bad MPG. So its a fine balance and its better to be slightly rich than lean.