Ok I'm real dumb
I took my car to the track, before I got there the car developed a vaccum leak. somehow the cover over one of my vaccum ports came off. I was looking around for vaccum leaks in the pits, but i didn't find it until I got home


I did a bit of tuning at the track, but the car didn't respond well to my changes.

can I expect an increase in MPH with *No* vaccum leaks?
she was running slower than expected at the track

 

Yes!

 

Not really. There's no vacuum when the car is at WOT, so no air will come in through that leak.

A vacuum leak has the most effect on idle, and some but not as much on cruising.

 

RB: But it would also make it harder to tune. You can adjust the carb all day with a vaccum leak and it dont matter... lean and rich the car "sounds" the same. I would fix the vaccum leak and retune it. see if it helps...



-Terry-

 

Im having a vacume leak problem right now also but in my case there is to much air getting in the engine and the carb is running realy lean (ill change that problem 2moro)
When I "gun" it at first the carb gets in 2much air and can not make enough vacume to pull gas out of the carb.

 

Right, but at idle and other high vacuum conditions... but a small leak, up to about the size of a power brake booster line or so, doesn't do a thing to a car at WOT. If the car doesn't respond to WOT tuning changes, one should look elsewhere.

Which of course is not the same as saying vacuum leaks don't matter. They do, just not at WOT.

 

Vacume lines like that will give you problems for the first seckond or 2 at WOT but forsure not in the higher RPMs

 

If you think about it, At WOT, you've got a pair of huge holes open in the throttle bores admitting a whole lot of air so how much difference is an uncapped 5/32" vacuum port going to make?

 

A vacuum leak at WOT will affect performance, but in a very, very, very, small amount. Think about how much can get though that small of a line. FYI, an engine can't have too much air, just not enough fuel.

 

Yea the more I thought about it, I came to the same conclusion, air is going to enter in the path with least resistance.
I just to do more tuning with my carb I guess

 

Vacume leaks can cause a lean condition at idle and at WOT.

The air entering the carb through the top is going past the boosters and taking gas with it.

Any other air entering the engine not coming through the top of the carb is not taking gas with it making the engine run lean.

I dont care if your vaccum leak is the size of a pin hole or the size of a golf ball it is going to make tuning nearly imposible.

A race car of mine developed a vaccum leak on the mating surface of the intake manafold and head. This small leak resulted in a melted piston, scored cylinder and loss of the points chase last year.