BLOWNBLUEZ06@RKT Performance

The reason the air doesn't go blowing out the exhaust is because all of the exhaust valves are closed or on the cylinders that the exhaust valve is open, the intake valve is closed. "but I have overlap in my cam, so that's impossible for all of them to be closed at the same time" While there is a point which this won't work and all intake rockers should be at least loosened up, the fact is that the plunger in a GM LS lifter can have easily .200" travel. If both the intake and exhaust valves are open at the same time, it won't be long before the lifter bleeds down and at least one of them closes. Still not convinced? Next-level, slightly more technical beginning with a question: How many degrees of cam rotation do you have to have before you yield .200" lift? Where did I get that number? .200 plunger travel minus .080" preload = .120". Multiply by 1.7 (rocker arm ratio)= .204". That is a reasonable number for how much initial lifter travel is absorbed from the lifters bleeding down. Now double that number because you have the ability to have both the intake and exhaust lifters bleeding down. .204" on one lifter and .204" on the other is the equivalent of .408" and 0".
If you have a solid roller cam, forget these numbers and take your intake rockers off. If you have a ridiculously large, high overlap, hydraulic cam, this may not work for you either.
I have performed this test numerous times myself and recommend anyone bringing me a car for tuning do the same. If they don't do it, I will. I have identified so many problems from doing the test that it has become an absolute must on any car that passes through my hands. One recent car I tuned started acting up while I was tuning it. It drove nice and then started surging. It wasn't a jerky kind of cam surge, but this slow, steady surge. The 02's, fuel trims and everything showed this oscillation on the logs. Since I had already tested the car, I kept assuming it was something in the tune. Finally I pulled the car back in and tested it again for boost leaks. I discovered that the little boot adapter that comes with boost gauges had torn lengthwise down the side. This line was tee'd into the same vacuum line that went to the boost reference line as well as the MAP sensor. Fixed the line and the car drove like a dream.

Its Bruce

Screw it, cap the tailpipes and pressure test the exhaust too.

4SFED Z

Two leaks. One beimg the iat sensor location and the other the multi port vaccum manifold. All I found thus far

BLOWNBLUEZ06@RKT Performance

Good work.

BLOWNBLUEZ06@RKT Performance

great idea!!

c5austin

That last part sounds very familiar
and yes it does run like a dream

madmatt9471

Yes! you should in order to really find a leak - you want to pressurize the system to hold air or Boost for us! anywhere from 10-20+ PSI

If you don't then you "WILL" be blowing air OUT the exhaust valves -

If you want the manifold pressurized too then pull the rockers off to close all the valves, this will even show a manifold leak -

IF you do not intend to test the manifold then pull the charge pipe off the Throttle Body and cap it off as well and pressurize it to find a leak

Thanks,Matt

madmatt9471

Wanted to add that it never worked for me either to pressurize the manifold as well.

BUT if you want to be 100% sure then - WHY not pull the roller rockers off - it is quite simple right?

Then the other best way is as suggested above CAP THE EXHAUST TOO! Love it man love it!

Thanks,Matt

4SFED Z

Two other ports on the vac manifold had leak.

Sealed up the iat around bushing and 3 of 4 ports sealed.

Will all these little leaks affect boost?

4SFED Z

They are fixed. The right question.....do lots of little leaks effect boost?

BLOWNBLUEZ06@RKT Performance

Sometimes it's not so much the boost as it is the tuning. It can cause your MAP sensor readings and your fuel pressure regulator (if you're boost referenced) to be skewed. The amount that is is off can vary and drive a tuner bats trying to figure out why your car won't stabilize.

BLOWNBLUEZ06@RKT Performance

It's strange that I haven't had the same experience and have done many, but you're right. When all else fails, pull the intake rockers.

madmatt9471

Let's ask this!

How many Pounds of Boost Loss are you seeing? 1, 2, 3, 4 PSI or more?

I still find it real hard to see no leakage past an exhaust valve as some have made argument for -

It would seem that all rockers would have to be mid point at best to make a seal for the valves - WHY?

I've seen "IT" end on the max lift and if that is the case then you take a .550" lift and subtract the .200" that leaves .350" and an open valve! Or even if it should land at the .300" mark that would still leave .250" - I've tried it and it just don't work for me!

When I pulled my heads off and had to remove the RR's it is apparent that some of the exhaust springs/valves were still compressed despite the bleed down of the lifters!

Anyway "IF" you really want to be 100% sure where your leak is from or not - best bet is to take the time and close all the valves by removing the RR's and pressurize the whole system to 20 PSI and plug all ports exiting the manifold!

Thanks,Matt

madmatt9471

I don't know why! It's gotta be me!

Although I'd rather be 100% as you said and close "ALL" the intake valves No questions of accuracy at all or of not being sure!

Thanks,Matt

BLOWNBLUEZ06@RKT Performance

Just to be clear, I've done the test with an open intake valve and it's pushed the piston to BDC, but with a cam at .550" lift, lifter bled down leaving maybe .350" open on the intake, you had best not have an exhaust valve open with that much opening on the intake unless you're in the top alcohol class or something.

p1bz

OK, Corvette-Chris got me going by calling me a "Internet Mechanic". Lol. I figured that he must be pretty damn sure he's right, so I tested both my boosted cars. With the vette, at 40 psi on the regulator before the throttlebody I was seeing about 4ish lbs boost on my boost gauge at the brake booster line, pressurizing the whole system. Loosened the intake rockers, and the boost gauge was right in line with the regulator. So it was kinda working for me. Now on my Mazda, solid roller 434 SBC with Turbo setup, nada, nothing. So i guess for me it kinda worked a little. Either way, at least i know i don't have a boost leak now.

BLOWNBLUEZ06@RKT Performance

I totally missed that internet mechanic comment. It was RMS-man that posted it though.
I would fully expect a solid roller to keep valves open simultaneously since they don't bleed down like the hydraulics do.

02402ramair

I was doing a boost leek on Z06wanted (Shanes) 434 engine with a Home Depot rubber cap on the SC and the valves backed off. We were running 28psi of boost on his engine so I was wanting to test at 28 to 30. I would creep up on the boost 2lbs at a time and at about 20psi it blew the rubber cap of. Holy crap I thought the world had come to a end! I tried several more times with same result. Could not keep rubber cap on SC. I was able to test up to 20psi but no more. I found several small leaks but did not make any more boost or any more power.

FYI

We did have to loosen his rockers or it would leak out the exhaust. He runs short travel lifters also

EGash

I used to do this procedure on my old Mitsubishi. It had hydraulic lifters and low overlap cams, so no worries about all the pressure blowing out the cyl head. It would always take a higher psi at the compressor regulator than the boost gauge displayed, it was built loose so there was always a lot of blowby, and the escaping pressure would usually come out the catch can breather.

Turbo inlets usually have lips on them, so the rubber boots would usually stay on, to about 25-30psi, but one of those rubber boots coming apart at 30psi is VERY loud! After that (and for checking pressures up to 50psi) I built a metal "cap" with silicon hose couplers. Not sure why, but I haven't used my old DSM boost leak tester on the Vette... maybe I'll do that this weekend.

BLOWNBLUEZ06

The day you woke up in Arkansas was the day your world came to an end!