340 compression reducing head gasket

Hi People,


Looking for a little help here. I have a nicely built 340+.030 with a compression ratio of 10.3: 1 Engine has steel heads. Could a simple head gasket change reduce the CR enough to run pump gas. If so any info re: thickness and manufacturer appreciated.

Thanks MoParts

If the steel gaskets are .028 then yes you can use composite gaskets that can be found in .048 or maybe .051. But, if the motor is a tight quench it may not reduce spark knock by much.
i would also be looking a an aftermarket cam to reduce the dynamic compression.

What Fox said, if you have quench now a thicker gasket will actually hurt you and if you have no quench you will not be able to lower it enough with a change to a composition gasket with the exception of possible a custom thick $Cometic$ one which will then need a custom thick $cometic$ intake gasket(s) to go along with it for intake alignment. Compromising your advance curve will help SLIGHTLY but will SEVERELY hurt your power & make it run hotter. Is that a measured 10.3? A wilder cam will bleed off psi but if you dont want a wilder one then call one of the cam companies & inquire about a custom cam that will lower it but not be lumpier maybe one with a late closing intake valve (dont quote me on that). Myself I'd pull the heads & judiciously hog out the chambers but plug your dimentions into KB's calculator to see how many CC's need to be added to see if chamber work would be practical as you can only remove so much EDIT and we'd need to figure out what SCR we're shooting for

What cam are you running now? You might just think you need to lower your comp. Is it detonating?

Doesn't Fel-Pro have a 0.060" thick "Block Saver" shim?

R.

Thanks for the input folks. I don't have the cam card in front of me but I was planning on a cam change anyway. I want to put engine in a 69 Dart with 3:23's and auto. Car will be 90% street driven with occasional blast down the 1/4.

It may actually be cheaper just to run premium gas.
R.

I agree, Premium pump gas should be fine. Been running it in my 11:1 street 340 for 15 years.
Fel Pro head gaskets are .039", that might help if you still need to.

Thanks again I have no problem using premium gas if that's all it takes. I just don't want to get engine in car and have to pull it right back out to change things. Dave, does your engine have steel heads?

I think anything over 9.5 with iron heads falls into the "might work" range on detonation with pump premium... especialy since OE heads were not designed for quench. Some of the things you might do to make it work like a high overlap cam and slow advance curve will reduce drivability and fuel economy on the street. If you know your current gasket thickness its straight forward to calculate compression with the .060 "head saver" gasket. If that gasket plus possibly some chamber machining can get you in the 9.5 CR range, I'd do it.

If it has quench pad pistons fitted for +/-.040 quench, it might be a different story... as posted above.