Bringing Compression Up in 426 Hemi

[jayfire]

I have a blown 426 hemi in my GTX. I removed the blower and put dual quad intake and Snipers on it. It runs good except for some popping out of the exhaust at idle, which may be from the lower compression I’m assuming. The whole build has about 150 miles on it since being built in the late 80’s. Could I just replace the pistons with some bigger domes and be done with it? Can that be done with the engine in the car? Would I need to replace anything else besides pistons and rings? Thanks

 

[davek]

You will need to pull the engine if replacing the pistons.

 

[Dodge Bros]

The exhaust popping would likely not be coming from a change in compression. Probably something on the sniper tune.

 

[1 Wild R/T]

Chances are the new pistons aren't going to weigh the same as the old ones do balance should be checked...
Cam may or may not be selected based on having a blower....

 

[jayfire]

I’ve had the sniper professionally tuned. Still could be an issue. I would say the compression is somewhere between 7.0 to 8.0-1 On a side note, what would a 69 426 Hemi .030 short block with 150 miles on it go for? I can get a 572 hemi short block and reuse a lot of the parts I already have.

 

[steve340]

The popping in the exhaust could be valve or ignition related also. Is the ignition timing retarded perhaps? Bit hard to guess from here.
Yes changing the pistons is the simple answer - but getting that right is harder than it at first might seem.

 

[Geoff 2]

Popping could also be wiped lifter/lobe if a flat tappet cam. Low CR does not cause exh popping.

 

[1967coronet]

1st off I would warm the engine up the do a actual compression test .See what you have for numbers and if they are reasonably close on all cylinders.
Many things could be making the ( pop )
even as simple as a plug or wire.

 

[Bird 426]

Sounds like a valve to me. Compression test isn't going to tell you where, you should do a leak down test. Harbor Freight has them. Then you will know the health of what you have. Rings, int valve, and exh valve. Just listen for the air leak.
I am guessing, but a stock Hemi comp was around 10 1/2? Be prepared to have the valve reliefs in the new pistons cut depending on your cam.

 

[INTMD8]

You should remove/disassemble the engine. Assess what you have, then put together a plan to build what you want it to be.

150 miles or not, the thing has been together for 35 years so who knows what it may need.

 

[Geoff 2]

When you put a blower on an engine, you greatly increase the load on the exh valve as they open under increased combustion pressure. This can bend p'rods.....&/or wipe lobes/lifters.

 

[not so famous bob]

I have a blown 426 hemi in my GTX. I removed the blower and put dual quad intake and Snipers on it. It runs good except for some popping out of the exhaust at idle, which may be from the lower compression I’m assuming. The whole build has about 150 miles on it since being built in the late 80’s. Could I just replace the pistons with some bigger domes and be done with it? Can that be done with the engine in the car? Would I need to replace anything else besides pistons and rings? Thanks

dont mess with it , send it to me , I`ll ake care of it ...