Long story short My brother had his engine built.Motor was machined, balanced, and assembled by Headway Performance. Howards rods, JE 2618 pistons 8.5:1 with upgraded wrispins, arp main studs, l19 headstuds and stainless o rings...anyways car didnt make any power. Did a compression check and got 90/120/95/125.(or something close to that)

With the center two pistons at TDC and pumping compressed air into each cylinder...cylinder 2 holds steady with no leaks but cylinder 3 you can hear air leaking out of the exhaust(enough to even spin the turbine wheel) and out of the valve cover breather hole making me think its a bad valve/valve seal. Same thing is happening to one of the outside pistons at TDC(forget which one) When the engine was built the head was left untouched just had the cams swapped. It has the same dual springs he bought the car with as well as the factory(yellow/brown?) valve seals.


any ideas?

 

You have a couple things going on here. In order to do the leak down test you have to ensure the cylinder you are testing in on the compression stroke. This means that the piston is at the top and all of the valves are closed. You can see if the valves are closed by taking off your valve cover and looking at your cams.

By just putting the engine at TDC and testing every hole, you are going to lose air in some cylinders because the valves are open.

You can also do the test by taking out our cams, this closes all of the valves. It's a lot more work to do that IMO. You have to worry about the timing and bleed your lifters.

If you are leaking our of the valve cover, air is getting past our rings. If it is leaking past a valve it cannot get into the crank case.

 

Maybe they didn't bleed your lifters when they swapped the cams and your valves are hanging open a bit. That will cause very inconsistent compression test.

Just a thought...