Leakdown tester??

[BK911]

So what do you guys think about this leakdown tester?
Most of the ones I see have two gauges and some sort of orifice between them.
This one only has one gauge on a regulator.

-Set the pressure @ 50 psi
-Screw rubber hose into spark plug lead on cylinder at TDC
-Connect rubber hose to regulator which was set @ 50 psi
-Read new psi

Difference x2 is leakdown percentage

So for example, checking the SC over the weekend and got pretty consistent 48psi after connecting hose to regulator. Is that a 4%?
Or is the tester / procedure flawed?

[T77911S]

if all you have is a regulator then it will not work.
i think there has been some debate on this in the past. it depends on the orifice size. it does not look like yours has one.


do like i did. get the one from harbor frieght and change out the output gauge for the one you have. i put on a 100psi gauge but your 50 will work.

[BK911]

Bump.
Any more thoughts on this?
I got ~1% leakdown on a 912 engine I am messing with. Too good to be true?

Per wikipedia:
Leak-down tester - Wikipedia, the free encyclopedia
Some manufacturers use only a single gauge. In these instruments, the orifice inlet pressure is maintained automatically by the pressure regulator. A single gauge works well as long as leakage flow is much less than regulator flow. Any error in the input pressure will produce a corresponding error in the reading. As a single gauge instrument approaches 100% leakage, the leakage scale error reaches maximum. This may or may not induce significant error, depending on regulator flow and orifice flow. At low and modest leakage percentages, there is little or no difference between single and dual gauges.