HIGHBOOST

Hey all,

I have a vacuum leak going on here, I get 15in hg warm idle. I was wondering if this leak is robbing me of any power. I have no boost leaks however.


Thanks

Jared

95Juan

does it feel sluggish?


i always thought vaccuum leaks like, stole power instantly.





you gotta check out the taco run on the 25th. it's on the n/a forums.


ok, that's way OT. sorry, nevermind.

theedge

15 is slightly low, it should be 18 or so on average, 20 is good.

Dal Heger

A vacuum leak becomes a boost pressure leak once the turbo spools up. So, yea you're losing power.

Dal.

HIGHBOOST

Yea, see my friends were telling me that I might be losing power, but I figured that since my gauge registers 16psi like it should, that it is ok. I know 15 is low for sure. The car doesn't feel sluggish at all, just rough idle at cold.

Bill

A vacuum leak might rob power or could increase power. It depends on what is going on in your engine and the size of the leak.

What happens is the leak will introduce additional air into your intake that has not been measured by the AFM/MAF. The DME does not "see" the air to add fuel to compensate. This in turn will give you a leaner mixture. Now if your O2 is not up to snuff, or your custom chips are mapped to run rich, or, or etc. and your mix is a tad rich, then the added air could INCREASE power. Too much fuel (rich mixture) rob power.

Now if everything is functioning as designed, and the leak is a large one, then a very lean mix will not produce the power that a 14.7 mix will. You could also get pre-ignition (detonation). If this occurs then the DME will pull back the ignition timing which reduces power.

But power aside, the worst case with a vacuum leak (lean mix) is you will melt down your engine.

And as Dal says, your intake system is under vacuum during light throttle and transitions to pressure during boost. So you have both a vacuum leak and a pressure leak.

SoloRacer

Bill,

If it's a vacuum leak wouldn't your lean mixture (extra air not measured by AFM) only apply when the car is under vacuum? Under boost metered air would be going out not in. So how much time do our cars stay under vacuum? And how much unmetered air would we be talking about? Is it really enough to make that big of a difference?

Dal Heger

Our cars are under vacuum most of the time. The only time they get into boost is when you accelerate hard, or drive over 120 mph (or so). 99% of the time they are under a vacuum condition.

Just replace the hard, cracked rubber hoses, you will be amazed at how smooth these cars can run when taken care of.

Dal.