What compression would be best for pump gas on a rebuild?

[StockMan]

I have a 68'Charger 383 4bbl/auto and need to rebuild the motor.  I have a 2bbl motor in it now that I'll use for the meantime.  Anyway, the 4bbl motor had the 10:1 comp and I wanted to restore it back to the factory specs.  Is the 10:1 going to give me problems on pump gas?

[speedfreak68]

I don't think it will, it should be ok with 10 to 1. But I'm sure someone else will chime in and correct me if I'm wrong

[Rayzor]

That compression is kinda pushin the pump gas limits if your planning on sticking with the iron heads. It can be done with the right timing curves and camshaft choice to bleed it down the psi. a bit.  But if your going to use the factory cam you might want to stay closer to the 9.0 to 9.5 range on the compression. Also just because you do not here the engine making the pinging does not meen that detonation is not happening. Just my opinion   

[Chatt69chgr]

My understanding is for 93 octane pump gas, you would look at 9.0 to 9.5 static CR for iron heads.  One point higher for aluminum heads.  You have to look at the dynamic compression ratio also.  I think there is a calculator for this on the Keith Black Pistons website.  As I understand it, you can run a higher static CR by choosing a cam that bleeds off some of the compression pressure.  The stock iron heads are open chambered (except for I believe 915's made in 67) so you can't achieve quench with them.  A closed chambered head allows you to achieve quench (approx .045 inch clearance between the top of the piston and the flat surface of the head) and this is desirable as it reduces detonation.  I understand that aluminum heads are inherently better at reducing detonation.  As was stated, you can't necessarily hear detonation and it will destroy the engine eventually.  I know you didn't mention aluminum heads but thought I would mention this with all the interest in the new Stealth heads from 440 Source. 

Ron can recommend a good build for you consistant with your goals and wallet.  I'am sure he will read this thread and chime in.  What little I have mentioned, I have picked up from him and the other moderators and good folks on the forum.

[Nacho-RT74]

if stock late 60s/earliers 70s BB Mopar engines ( and some SB too ) got up to 10.5:1 with IRON HEADS, you figure it

[firefighter3931]

With open chamber heads and pump gas you want to keep the static compression ratio in the 9-9.5:1 range. The speedpro 2315 forged pistons should work fine for your application.

http://store.summitracing.com/partdetail.asp?part=TRW%2DL2315F30&autoview=sku

As for the factory ratings don't believe what you read....most late 60's engines were actually a full point less than their advertised specs.  Factory tolerances were poor and most were nowhere near the blueprint spec. Most 10:1 HP engines were in the 9-9.2:1 range in reality. 



Ron