What are stock 68 383 magnum heads?

[MoparMotel]

I searched the forum but didn't find what I was looking for. What heads came stock on my 1968 383 Magnum? Are they 906 or is that 440 only?

My factory heads were rebuilt with new valves seats springs etc. when my motor was rebuilt and he said he ported and polished them a little bit but I have been considering swapping them out for a set of Edelbrock 84cc Aluminum heads.

What heads came factory and also what CC are the factory heads? Would it be worth it to swap them out for the 84cc eddy's if mine already have a minor port and polish and are rebuilt?

Thanks!

[MoparMotel]

Forgot to add one of the reasons I am considering swapping heads is because the guy who built my motor said they were 10:1 pistons but I was looking over the invoice and the part number i found on the receipt came up as 9:1 pistons So I would like to bump my compression back up to the factory 10:1

[Ghoste]

906.

[XH29N0G]

I would wait to see what others say because there are a lot more informed people than me, but my guess is that you will not pick up too much in compression with the 84 cc heads.  I think the 906 were slightly higher 87-92 cc (??) but the different gaskets you would use now 0.004 (??) from the stock stamped steel (0.002 ??) effectively increase the 84 cc heads into that range.  My guess is you will need something in the 75cc range to make a difference.  I found it to be very informative doing a spreadsheet calculation of the compression as a function of cc available heads + (gasket thickness + quench height) *(pi *cylinder radius-squared) divided by the same thing plus stroke * pi* cylinder radius.  You can also do it using an online calculator, but not as much fun in my opinion.

for what its worth, I did the swap to edelbrokcck heads on my 383 because I like to tinker and was happy with it, but do not have numbers to back it up.

James

[Cooter]

I do know Swapping out those open chamber 906 heads for a set of closed chamber heads, like the "915" head provides the end user with about .5 point of compression and the end user CAN FEEL IT IN THE SEAT.

[MoparMotel]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

[Cooter]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

IF your still gonna run the stock low comp pistons then yes. However, if your gonna upgrade to new pistons, with a higher deck height(Not as far down in the hole), then go with the open chambers.

I drank the Koolaid when it came to that .040 Quench bullsh*t and now I have a 440 with Six Pack Pistons (.020 in the holew with stock deck height), and .018 Compressed Steel shim head gaskets (.040 "Quench), that WILL NOT start up hot without sounding like it's got the initial timng set at like 25 degrees. I got another one I cannot get down on without racing fuel. So DO NOT run closed chamber heads with aftermarket pistons that actually have some compression height.

[Chryco Psycho]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

Yes

I have built a number of engine using high comp pistons & closed chamber heads , no detonation even at 10.6 compression & no startng problems either

[Cooter]

Well, I got one with 160 PSI cranking pressure that will NOT start up without clacking the pistons. You musta used some magic VooDoo in yours then.

[BSB67]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

So DO NOT run closed chamber heads with aftermarket pistons that actually have some compression height.

What heads, what chamber size, and what cu.in.?  The devil is in the details.

Generally speaking, a 440, with 0.040 quench (FT piston), and iron heads will not run on pump gas as the CR will be above 11:1.  But with an aluminum head and 84 cc chambers, you would probably be ok.

[BSB67]

Forgot to add one of the reasons I am considering swapping heads is because the guy who built my motor said they were 10:1 pistons but I was looking over the invoice and the part number i found on the receipt came up as 9:1 pistons So I would like to bump my compression back up to the factory 10:1

Do you have the piston part number?

[BSB67]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

Yes

I have built a number of engine using high comp pistons & closed chamber heads , no detonation even at 10.6 compression & no startng problems either

Iron heads?

[Cooter]

So DO NOT run closed chamber heads with aftermarket pistons that actually have some compression height.

What heads, what chamber size, and what cu.in.?  The devil is in the details.

Generally speaking, a 440, with 0.040 quench (FT piston), and iron heads will not run on pump gas as the CR will be above 11:1.  But with an aluminum head and 84 cc chambers, you would probably be ok.

well, mine is a 440 with standard Six pack pistons (Forged aftermarket units), .020 in the hole, with steel shim gaskets (.018 compressed), .040 "Quench"...
150-160 PSI cranking pressure. Yep, Figures, shoulda just stuck with Nitrous and low comp pistons. Damn.

[BSB67]

So DO NOT run closed chamber heads with aftermarket pistons that actually have some compression height.

What heads, what chamber size, and what cu.in.?  The devil is in the details.

Generally speaking, a 440, with 0.040 quench (FT piston), and iron heads will not run on pump gas as the CR will be above 11:1.  But with an aluminum head and 84 cc chambers, you would probably be ok.

well, mine is a 440 with standard Six pack pistons (Forged aftermarket units), .020 in the hole, with steel shim gaskets (.018 compressed), .040 "Quench"...
150-160 PSI cranking pressure. Yep, Figures, shoulda just stuck with Nitrous and low comp pistons. Damn.

What chamber size, and what head?

[Cooter]

"915" heads and stock deck height. Chamber stock less about .005 to clean 'em up.

[justcruisin]

I thought .040" was common place. I run zero deck .039" gasket and 84cc eddy's on a stock stroke 440. 180 psi cranking on all pots, 18/36 timing, runs on 91, no problems, at least none that I can hear or see from inspection.

[BSB67]

"915" heads and stock deck height. Chamber stock less about .005 to clean 'em up.

Yeh, that explains it.  That would not run on pump gas with a typical high performance cam.  Bet it ran good with the race gas.

[BSB67]

I thought .040" was common place. I run zero deck .039" gasket and 84cc eddy's on a stock stroke 440. 180 psi cranking on all pots, 18/36 timing, runs on 91, no problems, at least none that I can hear or see from inspection.

Right.  10.1:1 with aluminum heads.  Generally not a problem.

[Cooter]

"915" heads and stock deck height. Chamber stock less about .005 to clean 'em up.

 Bet it ran good with the race gas.

Ain't even made it out the damn shop. Now I gotta decide if I'm gonna pull the iron heads and swap For some Stealths.

Let this be a WARNING to all in mopardom. (Again) DO NOT RUN IRON Closed chamber heads With Six Pack Pistons in a 440, even with the .040 Quench.
Your sh*t WILL rattle. NO good.

[Chryco Psycho]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

Yes

I have built a number of engine using high comp pistons & closed chamber heads , no detonation even at 10.6 compression & no startng problems either

Iron heads?

Yes iron

[BSB67]

I have access to a set of 915's off a 1967 HP440... Would it be better to have those rebuilt and put on?

Yes

I have built a number of engine using high comp pistons & closed chamber heads , no detonation even at 10.6 compression & no startng problems either

Iron heads?

Yes iron

Like Cooter, mine would not run on pump gas, not even close.