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Hey guys finally got my 390 together after a while it waiting aaaaand it pings. Even a little while idling in gear and cruising!! I've put premium in it to no avail and I've retarded the timing to where it barely runs and it pings worse!!!! Previous owner rebuilt bottom half and I drove it for 2 months with no problems. It didn't have hardened valve seats so I pulled the heads and had those done and put her back together. That's it!!! The pistons aren't in the hole like they used to be they are flush with the deck at tdc by my eyeball so I know it's higher comp than stock. Do I just need more cam??? That's stock too. Has 4bbl and headers and runs like a raped ape but I've only ran it once cause of the ping!
Go back to basics by verifying TDC, cam phasing, and rotor position.
If the engine has been rebuilt, did you calculate the compression ratio? Valve relief, piston dish, crushed head gasket thickness, and cylinder head volume all play a part!
Like I said it ran fine with leaky valve seats. Would by replacing them make the compression to high now since it was leaking compression before? I did not build it just gave it a valve job
Like I said it ran fine with leaky valve seats. Would by replacing them make the compression to high now since it was leaking compression before? I did not build it just gave it a valve job
Ah.. OK.
Like I said, go back to basics and verify the setup.
I know it's 30 over. Completely stock heads and valvetrain. Pistons have factory valve reliefs but don't sit down in the hole like stock. I believe they did the old 360 pistons in a 390 truck to raise the compression
Cast numbers are c8ae-h for the heads. It is a true 390 truck so pretty sure the motor is original. And most 360 pistons don't have different skirts. Only some. It pulls 200-210 on compression tester. This is the best pic I had if the pistons while the head was off
After looking around at pics those are flat top pistons so I guess I just need more cam??? Y'all have any reccomendations on what size to go with? I like lunati and was looking at their voodoo series
You can also cup your hand over the carb as it's idling and if engine speeds up in rpm then changes are your running lean. Also having headers leans your over all gas/air mixture stock Holley's carbs for a fe run around #64-66 main jets.
I'm sure if it's been pinging your spark plugs will be white with little gray beads of molten metal specks from the top of your pistons if you run it long enough to start any damage.
.
Orich
What type of dizzy OEM ? Have you checked for a leaking vac. advances diaphragm or how much it's advancing. Most are advances are adjustable with a allen wench.in the hose nipple.
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