Acceptable leak-down rate for the boost system?
08-08-2007, 11:18 PM
#1
Three Wheelin'
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Acceptable leak-down rate for the boost system?
Guys, a friend of mine is troubleshooting a leaky boost system and having some problems. Would any of you care to venture an opinion on what the allowable leak down of the boost system should be? The way Ive done this in the past was to pump the system up (using an test adapter) to about 15 lb. Then time the loss of "boost." Just wondering what you guys would consider normal. Bruce
PS. the adapter goes into the inlet side of the intercooler.
PS. the adapter goes into the inlet side of the intercooler.
08-09-2007, 08:20 PM
#2
Three Wheelin'
If you are testing between the turbo outlet and the intercooler-hose outlet, it should be zero. Technically speaking, there should be zero leaks in between the air meter and intake valve.
Of course, that reading is affected by how good your boost leak tool is...
Of course, that reading is affected by how good your boost leak tool is...
08-10-2007, 01:58 PM
#3
Race Car
Haha, right away the quality of the arnnworx tool comes into question.... Moving on!
I would say that 0 leaks is ideal, but we live in the real world, so don't hold your breath. If mine fell to 0 in under 1 minute I would be concerned, or of course, if I heard any large leaks. There is a lot of volume in there, but then I have heard of some people pumping theirs up with a bicycle pump, so maybe it is supposed to hold nearly indefinitely?...
I would say that 0 leaks is ideal, but we live in the real world, so don't hold your breath. If mine fell to 0 in under 1 minute I would be concerned, or of course, if I heard any large leaks. There is a lot of volume in there, but then I have heard of some people pumping theirs up with a bicycle pump, so maybe it is supposed to hold nearly indefinitely?...
08-10-2007, 02:50 PM
#4
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That is a good question and frankly quite surprising, that it has not been asked and answered many times before, since there are so many posts on how to do the test.
I have posted a number I got long time ago, searched, but can’t find it.
I did the test again a few months back, but only recall that it took “quite some time” (= 5 to 30 seconds) to reach half pressure. The system was pressurized from the IC inlet. I’ll update this post with a recorded number next time I do the test.
So others can benefit, it is worthwhile to define a procedure:
1. Select and note a location for pressurizing the intake system, preferably (for convenience) at IC inlet
2. Get (purchase, make, find old one) a fitting to pressurize the intake
3. Make sure your boost gauge functions reasonably well (OEM or aftermarket)
4. Pump the system up (with shop air) so you or a helper can read the pressure decay from 15 psi (~2 bar abs)
5. Measure and record the time it takes to reach half* the value (about 7.5 psi or 1.5 bar abs)
6. If the measured time is less that 5 sec, crank the engine** very briefly and repeat item 4. and 5.
* The pressure decay is close to an exponential decay, which means that the half pressure time is somewhat insensitive to the start pressure.
** There is a small chance that the engine is “parked” at TDC (for end of exhaust stroke) where there is slight valve overlap.
The engine leak-down also affects the results.
So with this I’ll encourage anybody with actual measured numbers to post here, preferably with a mention of differences from the procedure above and estimate of engine leak-down or compression (bad, good, very good, excellent).
Laust
I have posted a number I got long time ago, searched, but can’t find it.
I did the test again a few months back, but only recall that it took “quite some time” (= 5 to 30 seconds) to reach half pressure. The system was pressurized from the IC inlet. I’ll update this post with a recorded number next time I do the test.
So others can benefit, it is worthwhile to define a procedure:
1. Select and note a location for pressurizing the intake system, preferably (for convenience) at IC inlet
2. Get (purchase, make, find old one) a fitting to pressurize the intake
3. Make sure your boost gauge functions reasonably well (OEM or aftermarket)
4. Pump the system up (with shop air) so you or a helper can read the pressure decay from 15 psi (~2 bar abs)
5. Measure and record the time it takes to reach half* the value (about 7.5 psi or 1.5 bar abs)
6. If the measured time is less that 5 sec, crank the engine** very briefly and repeat item 4. and 5.
* The pressure decay is close to an exponential decay, which means that the half pressure time is somewhat insensitive to the start pressure.
** There is a small chance that the engine is “parked” at TDC (for end of exhaust stroke) where there is slight valve overlap.
The engine leak-down also affects the results.
So with this I’ll encourage anybody with actual measured numbers to post here, preferably with a mention of differences from the procedure above and estimate of engine leak-down or compression (bad, good, very good, excellent).
Laust
