Hi there guys and gals, new to the forum, my names connor, im putting together a 383 i picked up for a great deal.
its .030 over 383 and it was build 20 odd years ago was told it was a high compression engine with only a couple summers of run time. Before dropping it into my car i figured id tear it down, check it out and re seal it.

well it looks fantastic inside, like new.
a 509 purple cam, bearings and cylinders, all look fantastic.has a old eddy Tm6 single plane intake.
i pulled the 906 heads and found old school 7023P domed pistons .020 in the hole.
after doing some math i figured out the compression to be right around 11:1 little too high for the pump fuel of today, especially with iron heads.

So i want to run a thicker head gasket. the ones that were in it are felpro 1009's .039 thick 4.410 bore.
if i ran a felpro 1105 with a thickness of .051 and bore of 4.590 that would bring my compression down to 10.4, a better chance of running this thing on 94 octane. can i get away with running that large of a gasket bore with a 4.280 cylinder bore?

thanks everyone.

You would be a lot better off swapping the heads to a set of aluminum like the Edlebrock 88.0 CC Street RPM heads and use the 1009 head gasket
The aluminum heads act like they lower the compression by sucking heat out of the combustion chambers as well as they flow more air making more power with bigger valves
BTW, I hate the Mopar cams like the one you have There are a lot of better grinds out there now so I would change it while it is apart and make that motor run a lot better What year and body style car are you going to run this motor in and what rear gear ratio and rear tire size?
IHTHs

aluminum heads are not in the budget. trying to work with what i have.
engines going in a 66 charger, 323 sure grip out back, 275 60 15's

thanks
connor

If an auto, don't forget a decent stall converter.

forgot to mention its a fresh 727 with a 3500 stall

I don't think that's a great street combo with 3.23s in a fairly heavy car.
Too much cam & converter, IMO.
Sure, it'll sound nasty, but under 3500 it's gonna be pretty soggy.
10.4 is a lot with iron heads, even with all the overlap in the 484 & 509 MP cams.

Yes you can run a gasket with that large of a bore.

laRoy engines, thank you


connor

Hi Connor...I have a very similar engine combo. It came with the car and I have been making the best of it while trying to build another engine. I have similar pistons that are TRW 2293. It has about a 20cc dome. fast68plymouth suggested that I check the volume of my 906 heads and I came up with a chamber of about 92cc. In all my compression ratio turned out to be about 9.8:1. This is what my numbers looked like in the calculator that I used. Yours might be similar.

not sure what your 94 octane is up there but 10.4 imnho is too high. When done be sure to dial in your timing & A/F ratio. until someone chimes in for sure on it you could take a compass & some paper & do some mocking up & at least see what that looks like. Good luck on it!

The .509 is a lot of cam for a 383 in a heavy car. I'd probably try something milder. My '66 Charger weighs 4150 with me in it.

welcome to the board connor !

The .509 cam is way too much for a mild street 383. Maybe something like Summit's 6401 cam would be a better choice? I'd be very leery of running that much compression with iron heads and pump gas. I would think you'll end up with severe detonation, in which case, you'll end up building another engine. It's kind of like pay now or pay later.

hi

just did a 383 iron heads 9.8-1 with a way smaller cam to run o pump gas .

yes if you truly have 11-1 this must be checked and verified !

with the 509 cam there is a lot of duration to bleed off compression soooo ,

i believe you can run that set up with the correct dist curve and carb afr .


nay sayers jump on this one , but i would run it !

I agree, the combo isn't very good. The engine might run in a higher elevation though... You live in the Rockies... 4000+ ft?

509 is an ok cam, but it like converter and gear. if you have 3.23's it isn't going to be ideal. If the motor is not fully assembled. Try a newer split duration cam on a 112-114 centerline. Or just toss it together and run.

Agree with others... a 383 with the .509 cam and 3.23s is going to be very lazy. I ran a 383 with the TRW version of those pistons, a much smaller "484" sized Comp cam, 3500 converter, and 3.91 gears, and it was a real dog off of the line and a chore to drive around town. FYI, my pistons were 0.005" in the bore and something like an actual 11:1 with the FelPro gaskets, and I ran pump gas just fine.

You weren't asking for advice on the combo, and cam swaps are expensive these days, so just drive it and see how you like it... although it might be an easier time to do a cam swap if the engine is out of the car.