Compression vs flow

I ran into a set of used performer rpm heads with the 84cc chambers. The current heads on my 383 are an early style closed chamber that I measured at 78cc. They have 2.08 1/74 valves with very lite gasket matching. With the steel heads I’m at 10.7:1 and switching to the eddy will drop me to 10:1.

So my question is will the flow of the heads outweigh the loss in compression or should I mill the Eddy’s to get back around 10.5:1

What head gasket are you using? Birdtracker

I’ll most likely stay with the 1009 felpro .039 gasket

Flow is way more important to peak performance at WOT than compression is
I built a 400 pump gas 511 C.I. stroker for my old 1971 Duster, it had a set of iron 906 heads on it that had 2.14 intake valves and 1.81 exhaust, mildly ported and 84.0 CC chambers that flowed around 264 CFM at .700 valve lift. I ran that combination for one summer up here and then put a set of Eddy RPM CNC by Jeff at MCH that had the exact same size combustion chambers that flowed right at 310 CFM @ .700 intake valve lift that winter.
That motor had exactly 9.25 to 1 compression ratio with both sets of heads, it ran 10.69 at 124.3 MPH with the iron heads at Woodburn, OR in October of 2005. I put the Eddy heads on that motor that winter and the car ran 10.49 at 127.4 MPH with no other changes in June of 2006
I ended up doing other mods to that short block later to get the compression ratio up to 10.29 to 1 by installing a .050 longer stroke crankshaft in it(which made it run mid 10.30s with tuning and intake and carb changes also) and then later installing a set of Indy SR M.W. size heads on it that ran a best of 9.993 at 134.7 MPH with a single 1050 CFM Dominator carb. on the Indy 400-3 intake and then again another set of Indy 440-1 CNC ported heads, every time I increase the airflow through the heads or intake manifold and carbs. it picked up power on the engine dyno and went quicker and faster at the track
Buy them heads and enjoy

Yea whatever I choose to do with them they are deffinately going on my car, I’m going to use the old iron heads to put a 383 together for my truck.

A good friend of mine is pretty tight with a machinist and I doubt milling a set of heads costs much, probably a good idea to atleast give them a lite surfacing to make sure they are flat. Apparently they only have 10 passes on them so they should be in good shape. And hopefully my pushrods will work!

Cab is right, flow is much more important, especially in this case where the compression ratio either way is 10 or above.
Compression follows the law of diminishing returns. A point of compression between say 7 to 8, is much more effective than a point of compression between 10 and 11.

R.

Thanks guys, and if it helps any motor is .030 over, .557 mopar solid cam, Holley Street dominator intake, 750 mighty demon, 2” headers, and 4 speed with 4.56 gears.

12:1 would certainly up things a bit and I already run 100ll fuel in it so it wouldn’t be a huge deal.... but pulling up to the pump to fill it with 93 is a very nice thought!

to answer your question the better heads will make up for the comp loss in performance....I went from ported iron w2 heads with 13.1 comp to alum indy 230s with 10.5 comp and ran exactly the same actually slightly faster with the indys with pump gas vs higher octane race/av gas.

Sounds good to me!, I haven’t been able to get it to the track with the iron heads but if the aluminum heads will give it a little more power and pump gas friendly it’s a win win!

From what I’ve seen stock heads flow in the low 200cfm range, and the Eddy’s probably flow in the 260 range at my lift so it should deffinately be an improvement!

Id shave them as well to 10.5 for more comp. it will still be pump gas friendly and you will get a gain from that as well, it would be a win, win, and a win. I would make sure to check your valve clearance though. The wider valves of the Eddys and a small shave will make things closer.

Buddy's 65 Plymouth. 440, bowl ported 906, 11-1,.557 purple, headers, low rise old Weind 2x4 w/2 600 eddys, 4.56, good converter 9x28 slick, race gas. Ran 11.60-70's. we swapped to box stock open chamber Eddy RPM's, 10.0-1. Runs 11.30's on pump gas with gear reduced to 4.10. No other changes.
Doug

I certainly will check, I had a set of fully ported 2.14/1.81 80cc 452 heads I was going to use and they cleared fine but I found a crack in them, so they should work but we’ll see!

Buddy's 65 Plymouth. 440, bowl ported 906, 11-1,.557 purple, headers, low rise old Weind 2x4 w/2 600 eddys, 4.56, good converter 9x28 slick, race gas. Ran 11.60-70's. we swapped to box stock open chamber Eddy RPM's, 10.0-1. Runs 11.30's on pump gas with gear reduced to 4.10. No other changes.
Doug [/quote]

That’s a big improvement, this 383 was in my dads car with stock 8.5:1 compression, 528 mopar cam, 1 3/4 headers , same heads/intake, carb at 3500lb tan mid 12s. With the new pistons little bigger cam, aluminum heads, and a little lighter car I’m thinking it may go high 11s

My old '69 Cuda, 3000lbs, 440SP bottom end, stock 906's, approx 9.8:1, Team G intake, CC.650/.650" sft cam, 850DP, 2" f/well hdrs = 11.23@118>

Bolted on some 2.14/1.81 ported 906's to approx 260cfm = 10.71@124.8.

Lets not forget you have a 383 with a smaller stroke then a 440. It may of not been starving that badly for flow. It does lack torque over a similer built 440. Comp definitely helps that end of it, plus add in the extra available flow of the eddys. Definitely two moves in the right direction. IMO, with the heads Off already, shave them.

I would cut them some to get the comp up also. I run 10.6 comp with aluminum heads and I have good quench. And it runs fine on 92 pump with 36 degrees total advance. Ron