what is the torque for the head bolts for my gm350 ?

[sarantis]

In general i know the head torque for GM350 is 65lbs but the service manual #9 says that some models refered as "performance production" models take 75 lbs.My gm350 has block casting number 10243880 with the 14096217 (64cc 285/300hp for 12bolt intake, the center bolts at 72").I wonder if the additional power of these heads means more torque to the head bolts .If somebody has any idea please help ! I've searched all over the web and i can't find the information i need.

 

[Alpheus]

Re: what is the torque for the head bolts for my gm350 ?

Torque them to 70 lbs and run it...

 

[sarantis]

Re: what is the torque for the head bolts for my gm350 ?

ok thanks a lot

 

[John_S]

Re: what is the torque for the head bolts for my gm350 ?

Merc used that casting number on post 87 350's, before moving to vortec heads. 65lbs according to the SM, but 70 wouldn't hurt them Seeing you mentioned a very early SM, hopefully you are not running these heads with flat-top pistons. That would bump the compression probably higher than you want in a boat.

 

[sarantis]

Re: what is the torque for the head bolts for my gm350 ?

Unfortunately i do have flat top pistons and max compression around 205-210 psi. I know it's a problem but for the moment i can't do anything about it. I'll assemble the engine and see how it works.Thanks.

 

[Alpheus]

Re: what is the torque for the head bolts for my gm350 ?

Unfortunately i do have flat top pistons and max compression around 205-210 psi. I know it's a problem but for the moment i can't do anything about it. I'll assemble the engine and see how it works.Thanks.

That compression is to high. From the parts you are describing your compression ratio is about 11:1

Has your block been bored?

Do you know your head gasket thickness and piston deck clearance?

If so I can get that number more accurate...

 

[John_S]

Re: what is the torque for the head bolts for my gm350 ?

Unfortunately i do have flat top pistons and max compression around 205-210 psi. I know it's a problem but for the moment i can't do anything about it. I'll assemble the engine and see how it works.Thanks.

Find some 76cc truck heads.


OK, I see you are in Greece. They might be hard to find there.

 

[sarantis]

Re: what is the torque for the head bolts for my gm350 ?

In Greece it's certainly difficult to replace the heads. It sounds easier to replace the pistons in the future (will this solve the problem of high compression?)
I am aware that i have to run close to WOT to avoid detonation but i'm very curious to learn if the engine runs good at 5000rpm what changes and may run bad at 3000 or 4000 RPM???
Alpheus the block hasn't been bored, the original gaskets were .027' but even with the thicker ones i've noticed a very slight decrease in psi (around 5 psi), as about the piston clearance i haven't measured it because at the moment i can't afford anything more than to make this setup work.So, any tips on how to deal with boating below WOT is very welcome.

 

[coheej]

Re: what is the torque for the head bolts for my gm350 ?

Assuming your pistons have valve reliefs and your deck height is stock of about .020 to .025" with a .040" gasket you're probably at about 9.75:1. With 93 octane you might be ok if the timing is controled very closely. Dished pistons would bring the cr down to just over 9:1. This would be more manageable.

 

[Bondo]

Re: what is the torque for the head bolts for my gm350 ?

I am aware that i have to run close to WOT to avoid detonation but i'm very curious to learn if the engine runs good at 5000rpm what changes and may run bad at 3000 or 4000 RPM???

Ayuh,... I'd Love to hear the danm thing Screamin' at 5 Grand Too....

I agree,... You'll be plenty Safe at 70ft.lbs...

 

[Alpheus]

Re: what is the torque for the head bolts for my gm350 ?

The valve recess in stock SBC flat top pistons is 8cc. Using that with .040 thousandths head gaskets and a deck height of .020 Im getting a compression ratio of 9.74798752533539:1 (9.75:1).

Just use high octane fuel or octane additive and you will be fine...