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Old 01-08-2014, 08:40 AM   #1
Scooby Newbie
Member#: 375902
Join Date: Dec 2013
Location: Ontario, Canada
2004 WRXSTi

Default prerequisite for tuning

as I seem not to have much luck with my question in newbies (I'm one) forum, 56 views '0' answers, (but a guy stuck in a foot of snow gets over 1300 and over 51 replies), I'll try here.
I'm trying to bring a car that I recently bought (if interested look here: http://forums.nasioc.com/forums/show....php?t=2586093) to a point that I can book a visit with a tuner.
One of the 1st questions asked as I understand, is:' what are the compression and leakdown numbers;
', so I'm guessing this is the right place to pose my Qs.

did a leak down test yesterday (my 1st in fact), I studied the topic fairly extensively.
Bought myself a tester before I read enough though and ended up with Chinese crap (sorry if my Chinese fellows member feel picked on) Cylinder Leak Down Tester Cylinder Engine Cylinder Compression Lost Tester | eBay (old adage: you get what you pay for)

So I'm trying it and the leak is 100% on 2 cylinders (I tried so far), something's not right, my compression numbers were in 130s psi so I refused to believe it's leaking that bad. Checked my TDC setting methods to make sure no mistake here.

Right away I didn't like the fact that it was around 15psi when the right (% of leak) gauge was referenced to 0% (cw end of the scale) and the set pressure was going down as well when tester was connected. So I took the sucker apart and found globs of silicon sealant floating inside the regulator, cleaned it put it back together but still set pressure was dropping across the regulating valve, much less though.
Out of this crap-of-a-tester plus some gauges that were kicking around and a cheap regulator valve I procured myself a two-gauge-psi-tester .

I must say that a single gauge without restrictor gave a very similar results, I think that an error added at minimal leaks is negligible (and at large doesn't really matter ).
So I did a test on all cylinders using both methods probably 4x over at 80psi, cold engine, and the leaks across are almost the same at around 2.6%
So who could ask for more..
But going through the motion I realized that having comparable results, there must be some standard, because 2psi leak at 40psi is twice as big as 2psi at 80psi.
I read some statements like: 'I did my test at 100psi (I saw some other psi ## as well)
because it's easy to calculate', meaningful (and comparable) results cannot be based on subjective choices,
So this is my question, what is the standard pressure a leakdown should be done under?

I understand that it may vary with the size of the engine, but what it really should be for our Subarus?

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