ok just finished rebuild started it up and started tuning and just noticed excessive blow by out of valve covers so i just did cimpression test and found the following.
#1=120psi #2=121psi
#3=120psi #4=120psi
#5=65psi #6=122psi
#7=90psi #8=120psi

major problem at 5-7 ?

history: block was reringed and new bearings about a year ago.
so i rebuilt 083 heads with port and polish, ss race valves, 981 springs,cut guides for positive seals, and pinned studs. new roller cam, push rods, 1.6 roller rockers, rpm air gap manifold, holly 750.

did rings give or could i have missed something on heads because all other cylinders are good except 5-7 wich are next to each other ? any more tests to try ?

i spent months rebuilding this thing and really dont want to pull it down to rering again

 

Chances are highly likely that its the head gasket between the 2 cylinders.

 

head gasket, good place to start. also when i removed valve cover to recheck rockers on that side the pvc valve holder wes full of gas so im thinking the vapor im seeing is gas vapor or could have come from tuning when trying to set initial timing and motor spit back up through carb ?

any more ideas ?

 

probably a blown head gasket on that side...pull it to check. Could also be due to non-flat head surface and would need to be machined flat again

 

Looks like the throttle wasn't blocked wide open, and your battery was dying.

I'd recommend re-doing the test properly and see where that leads.

 

sofaking thanks for chiming in. i double checked it twice. motor warm, primary and secondaries open, all pluges pulled and battery fully charged. i was praying my tester was crappin out so i went back to a couple other cylinders and got the same good readings as before. is it possible to pump air in on #5 and connect compresion tester to #7 with rockers pulled so valves are closed to check if gasket is blown in between? im going to bring home new tork wrench tonight to recheck head bolts. i went 65# with 12point hardened bolts. sound right?

xpn, heads and block were checked for flatness before assembly, well within tollerances. i could have messed up and and not torked head bolts correctly in that spot though.

 

Yes, you can do that.

Another tactic that might work for troubleshooting #5 is to stick a piece of tubing into the #7 plug hole while pressurizing #5, and listen for hissing sounds. Remove the headers and the intake, and listen for hissing in the #5 intake port and exhaust port. And of course, stick your tubing into the crankcase (quite easy with the intake gone) and listen for hissing there.

I would not immeditaely suspect a head gasket; it would take a SERIOUS screw-up to wipe a head gasket that thoroughly that quickly.

Why are you doing this in the first place? Is it just for the blowby? If so, a head gasket is highly unlikely to cause that, because there are water jackets all around the cyls, meaning that if a cyl can blow into the crankcase via the HG, then there will be water in the oil, combustion in the water, etc. And, if the HG is blown between #5 & #7, since those 2 are adjacent in the firing order, the engine will be all but undriveable, because the #5 spark will light off the #7 cyl while the #7 intake valve is still open; which will in turn light off the intake charge, which is hard not to notice. So if the engine runs ANYWHERE NEAR smooth, it's not the HG.

 

sofa, the reason i checked compression in the first place was because im just starting to tune this motor, initial timing,carb setting ect. i havent got it driveable yet, waiting on new stearing box. i have got it to idle fine with about 16 advance then set carb float levels and idle for max vac. during this time i noticed alot of vapor coming out of my valve cover breather oposite of the pcv cover, and yes pcv is working. problem is and it might just need more tuning but when hitting the throttle it seems to choke out. ill check oil and water for anything that shouldnt be there. thanks

 

Right...

If it had a bad HG between 5 & 7, your post title would probably have been something about fire or popping noises coming out of the carb when revving; in other words, a little steam or vapor out of the PCV holes would have been VERY low on your list of concerns; so it's probably not that.

I would recommend avoiding letting it sit there and idle for extended periods of time. Also, if you haven't got it out and actually SEATED the rings yet, it might be too early to be worrying about blowby just yet.

Go ahead and get it driving ASAP, then seat the rings by putting it in 2nd gear and doing a WOT run from about 2500 to about 5000 RPM, and take your foot off the gas and let the motor brake the car speed back down to 2500 RPM; do that over and over for a few minutes. Let it get up to a little higher RPM each time. Do it maybe 10 or 12 times. See if the blowby is any better after that.