Boost, generally..

[~Rob~]

OK further to my thread about me hitting 1.3 bar, where Martain stated..


...For maximum boost reading, you need to go for highest load on the car which is highest gear going up a hill.

why can boost only be built up when under load? i dont get why boost could not be built up when say, revving the engine in neutral? surely the same amount of exhaust gasses pass through the turbos wheather youre moving or not at a said point in the rev range?

[Guyver]

This is my guess (before someone turns up with the facts).
With the car in neutral there is no load on the engine (its only got to spin it self up) so it doesn't need to produce a lot of power. Going up a hill in top gear the engine has to move over 1.5 tonnes of car uphill this needs more power (ever tried pushing a car uphill?) as there is more for the engine to react against. A case of equal and oppersite actions/reactions?

Hope that makes sense and is right or at least close.

[Martin F]

I'm not sure of the best way to explain it but i can understand why you may be perplexed.

As Guyver says it's a case of load on the car. If you think of the engine out of the car and no load, then you would only need a certain amount of air and fuel to cause a big enough explosion to turn the crankshaft at say 3,000rpm.

If however the engine is all fitted to say a 1.5ton car and you are trying to drive along, you now need a bigger explosion and hence more fuel and air, to turn the crankshaft at 3,000rpm, as well as the gearbox, axle and ultimately the wheels.

More air and fuel means more exhaust gases which obviously are used to spool your turbos.

HTH.

[~Rob~]

ahh.. (i think)..

so if a car is in neutral (no load) with revs at 3,000, the power produced by the explosion in the cylinder is less than if the car was in gear (under load) and at 3,000 revs?

[Martin F]

Yes, very much so as less fuel and air is required to turn things.

[flyingbrick]

Also guys dont forget that the volume of air entering the engine is more reliant on throttle position than engine RPM.

While cruising at 3,000RPM your boost gauge will be showing vacuum (the air is very thin and expanded) and obviously the more you open the throttle the denser the air in the plenum ( and entering the motor) is going to get.

I'm no good at explaining things. hope this helps.

-Nathan