How many seconds or minutes should the system hold pressure after BLT?

[4gfun]

Say I BLT to 25 psi with a 6 gallon compressor...how long should I expect the system to hold pressure?

My system will hold 30 psi with no issues.

Some say that is a good indicator of no boost leaks.

I am just trying to take a few steps back and figure things out.

Thanks!

 

[99gst_racer]

Mine slowly starts to bleed off as soon as I dsconnect the pressure source. But that's completely normal.

The purpose of a BLT isn't nessacerily to retain the pressure in the intake tract, but to see where exactly it's leaking to. If your test reveals that you have no external leaks and the pressure it simply bleeding past the rings and into the crankcase, then you're golden.

 

[justa4clturbo]

yea just like 99gst racer said it is a main test u looking for like couplers or hoses gaskets cracked or pushed out it will still b going in one cly intake valves and into crankcase and lose pressure that way but as long as u holding 30 psi and dont feel or hear any leaks around pipes couplers and intake then u are set to go

btw paul i love your compund turbo setup hats off to u for a bad ass setup

 

[Jiggalude]

Yea I was going to say, I've done tons and tons of boost leak tests and I've NEVER had it hold pressure after the tester was off. I don't know how people are holding this pressure for an infinite amount of time.

 

[99gst_racer]

Yea I was going to say, I've done tons and tons of boost leak tests and I've NEVER had it hold pressure after the tester was off. I don't know how people are holding this pressure for an infinite amount of time.

He wasn't asking about holding pressure after removing the tester itself. He was referring to after removing the pressure source.

 

[habitatguy187]

It should take it awhile to bleed off once it hits around 5psi (say 20 secs)

 

[rich3389]

For me with no leaks i will pull the air chuck off at 25 psi, will bleed 1 psi every couple of seconds, then slow down at 10 psi(maybe 1 psi every 3 seconds) then once it goes down to 5 psi it will stay there for a minute or two...

 

[pboglio]

On boost leak tests I typically have to rotate the crank shaft so that some of the cylinders have the intake valves completely blocked, and some with the exhaust valves completely blocked. This blocks any and all air from traveling thru any of the 4 cylinders while doing the boost leak test. With radical cams, this MAY not be possible, but on my cams there is a small window where all intake and exhaust valves are in a position to block airflow thru to the exhaust ports. This'll boost leak check the entire intake system including the intake manifold.

 

[AlaskanDsm]

Approximately where is this window? I would love to test my system to see how the rest of my system is doing!

 

[4gfun]

Thanks all...I think that the window is supposed to be 15 degrees ATDC. I can still hear air coming from the crankcase no matter what...some say that is normal some say it isn't but very few answers overall on that. I don't see the problem with it leaking through the crankcase anyways if the oil cap gasket is good.

Mine seems to leak at about the same rate that most of you describe.

 

[VIGILART]

to my experience the higher psi the faster it goes down until it gets to about 14-10 psi and then slows way down and generaly takes a couple of minutes to get down to zero.