Your suggestions please, I am jonesing to build.
You can Cometic gaskets from Don at 4secondsflat.com or direct from Cometic. PM sent
Thanks for the information, and I appreciate the PM. Once I figure out exactly what I am going to do, that may be the best option. Thanks again.
I would take the top end apart on the 340 and get the measurements,cc the heads,pistons,check deck height ect.Once you know these things you can make some decisions.I would ditch that cam and go with something in the 230 range @.050 with a 110 lobe seperation.You can add a few ccs to the heads by properly removing small amounts of material and polishing the combustion chambers and not mess with quench.With those small changes you could loose the 25-30 psi you need to be fine with a good tune.
Hmm, the deck height is 0, and CCing the heads might be a good idea as they could have been milled extensively prior to my ownership. I am on my 3rd cam, this is by far the most radical. I had a real small, almost stock 340 Clay Smith solid, then a 467 Comp solid, I still have it but can't remember the duration, now this one. (Yeah I know, I have a sickness and love playing with these things)
Yes, a thicker gasket is very similar to droping a piston down in the hole the like amount of the increase in gasket thickness. If your head gaskets are .040 and you increase the thickness an additional .020, it's very much so like dropping the piston down the hole .020. While this amount may or may not be enuff, it's the direction I found to be cheapest and very effective in lowering compresion.
If you have a domed piston or rely on a quenched area for the set up, it will take away the effect of the set up/quenched area and the engine would probably run poorer if additinal steps aren't taken. Like reduced timing, which at this point, probably won't hurt the performancve as much as it does now, though, it may. It gets very particular in this area. Engines can be a cranky ting from time to time and this is one of them.
MoPar used to sell (And may still do) a shim designed to be used with the older high compresion piston engines. It was / is .060 thick and can be combined with a head gasket or used alone with Holymar to seal it.
In the past, I needed such a thing and combined it with a .039 Fel-Pro to get a pump gas ratio. At a total of .099 thick minus any additinal thickness from the Holymar sealer, it's quite thick and the intake gaskets may also need to be addressed at this thickness. Multiply intake gaskets may be needed.
I really like the shim idea, will check with Mancini tomorrow, if anyone should have it, they should.
I would try backing your mechanical timing off to 34* and plugging the vacuum advance and seeing if it would run on 93 octane first. That would be a fast and cheap test. You might be down on power, but these other options of lowering compression or building a lower performance engine are doing the same thing. If you can get away with just moving the timing you can have the best of both worlds, streetable but able to be quickly tuned to a race engine if you go to the strip.
I have one of those old MP race distributors, no vacuum advance.
The standard Felpro head gaskets are .054" thick. The performance Felpro head gaskets are .039" thick. If you are running the standard gaskets, with that stroke, zero deck pistons, and those heads, your cranking pressure should not be that high. I am wondering if the intake valve closing timing is causing the high pressure? Was the cam degreed in?
If you know all the specs of the engine and the intake valve timing you can use this tool to compute compression:
http://www.kb-silvolite.com/calc.php?action=comp
Great information, thanks. Yes, I have degreed in all three cams, that I have had in this motor. I believe this one is ground on 107, I think the others were 110 and 112 but I would need to check the cards to verify.
I just assumed it was the .200 more stroke, that was allowing it to take in more volume to compress, the reason for the high pressure. That is actually .400 more travel from TDC to BDC, correct?
But as one poster mentioned, these heads may not still have all the CCs they were born with. We did not check that, we just cleaned them up.