10 replies to this topic

[Chappb]

Blow through supercharger system, have an Eaton M45 with a 17% reduced pulley, managed to get 10psi of boost when i ran a suck through system but for some reason cant seem to get it to boost any higher than 8/9psi now im om blowthrough....ive pressure tested pretty much everything on the pipework and carb, manifold, etc....can anyone shine any light on this or suggest why it wont boost anymore? Cheers Ben

[Ethel]

Where's your boost gauge plumbed in?

[Chappb]

Right before the ports on the head/after the carb

[Ethel]

Well the carb wouldn't work if there was no depression across it.

[Chappb]

Sorry mate, i'm not following what you're saying?

[Turbo Phil]

You're getting a pressure loss across the carb as it acts as a restriction. You'd see the same if you had an intercooler fitted.

Phil.

[Chappb]

So i have the boost gauge in the wrong place? I have an intercooler fitted also but i have tried bypassing that previously and hardly any difference was made to the pressure reading

[Ethel]

The gauge is in the right place to tell you what's actually going in to the engine, which is what you're interested in, if you want to avoid detonation. The carb needs lower pressure (a depression) above the fuel jet than above the fuel in the float chamber to push the fuel through. The carb has to reduce the pressure in the venturi a bit to achieve that.

 

Phil makes a great point about intercoolers - the reduced pressure is actually a good thing, you want more oxygen molecules (for combining with fuel molecules) to make power. Cooling the air makes it more dense - same mass taking up less volume = lower pressure. Vapourising fuel will also have a cooling effect that wasn't as prevalent in the suck through system.

 

The gauge is showing evidence of the improvement you've made, that's all.

[Chappb]

I think understand now, thanks for the help :)

[HUBBA.HUBBA]

When you tried it without the intercooler dis you use the shortest amount of pipe as possible?

[Chappb]

Yep, bypassed quite alot of pipe along with the intercooler