-T-

iTrader: (2)

I have a torquer V2 on a 113 LSA installed in my LS6. Calculated 6 deg. of overlap. My vacuum is sitting at 14.5" at idle which is 925-930ish. A quick snap of the throttle gives me a momentary reading of 0" and jumps steadily to 22" at 2500 rpm. Holding throttle at 3K gives me about 24" and a wide open snap gives me about 26-27". Should i worry about a leak somewhere with only 14.5" at idle. I'm looking to install a FAST intake and take it to a tuner soon. But do not wish to spend the money on a tune if I have a leak somewhere... rings/valves. I have PRC dual springs btw. Thank you in advance.

-T-

iTrader: (2)

Any suggestions from the tech's?

garygnu

your vacuum should improve if tuned,you need more timing.get the intake then tune it.

-T-

iTrader: (2)

Can you point me in a direction to understand the theory behind that? I am in no way doubting you. I just don't know much behind the advanced knowledge of tuning, timing and vacuum system. I know basics of timing, just don't know how a spark advance would increase my vacuum.

technicalninja

iTrader: (1)

14.5 seems fine to me for that cam.
Idle vacuum is one of the first things that is effected with increased overlap.

Is it running OK? Changing a cam has a bigger effect on a tune (more likely to need a re-tune) than changing an intake.
If you dont have a way to verify AFR then the tune gets more important.
If you do and the AFR stays good then you might be OK.
Are you running a "tune" now. If so what were the old cam specs?
I wouldn't think a stock tune would work very well with that cam.

-T-

iTrader: (2)

Yes, it is tuned. I did the cam swap in march and towed the car to get it tuned. I started getting irratic rpm hunts during warm start ups. Then went away miraculously. Now with cold starts, she revs to 1500, drops to 750 ish and then to idle. This only happens 1 out of every 3-4 starts. After reading and reading I decided to get a vacuum gauge and check to see what she was pulling. I know it's not dangerously low, but I don't want to take it to a tuner after the intake swap and have "something" covered up that ends up being detrimental down the road.

Motor has 77K on the clock. Rings shouldn't be an issue. But stuff happens. I'm more worried about the valves.

technicalninja

iTrader: (1)

Do a hot compression and a hot "leak down" test.
Never seen that done?
I'm going to try to make a video this weekend and post it on youtube on how a leak down test is done.
This is like having blood pressure test and an EKG for a heart patient. You just automatically do it first.
If it's all good you will not worry about your internals anymore and if you find problems you will end up fixing them before spending money on other stuff.

That vacuum gauge can tell you more than just numbers. What are the needle fluctuations like? Erratic or smooth? leaking valves will sometimes cause a noticable "tick" in the gauge at idle. Sometimes shorting the affected cylinders spark plug lead will "smooth out" the tick. (can be dangerous on a COP ignition system)
Tick at idle or erratic violent swings during load changes would make me MORE interested in what the compression and leak down test would find.

A LIGHT misting of B12 around the intake while running to check for vacuum leaks is a pretty good idea too. If the B12 makes it into the intake tract it will cause idle to rise. You can pin point an external leak using this method.

-T-

iTrader: (2)

I've done a leak down test before, but the engine was on a stand, not in the car. I have a compression tester. Guess I'll swing by the parts store tomorrow and pick up a leakdown tester.

I'll video the vacuum test tomorrow as well. The needle was bouncy... +/- .5" at idle. I just assumed it was because of the cam.