aatkinsonalexdatkinson

Hi guys

Wonder if you can help with some compression / heads related queries.

The motor is a Jensen with a mopar 440. The block is a stock recon block from the US (the company said it was in the range of 9.1 - 9.5 compression). I have just fitted headers and an eddy performer plus cam + a pair of Edelbrock RPM heads(84cc) that I bought on my last trip over state side.
The engine details:
bore: 4.350 (been rebored)
stroke: 3.750
head vol: 84cc
deck clearance: 0.09 - 0.1 (down the hole)
gasket thickness: 0.038

On the summit compression calculator this is coming out as a compression ratio 8.93. However, since my last trip I see edebock have brought out a set of e-street heads with 75cc volume. This would clearly increase my compression to 9.6.

So to the questions (sorry if they sound dumb - I'm not mopar expert)

Do you people think that I should stick with the rpm head 84cc heads or go for the new 75cc (I'm in the states next month and so can pick up a pair). Do you guys think the increase in compression worth the trade off in cc?
I'm not looking for super car, just a decent pull off the line (lots of torque). I also don't have the time to pull the block and change the pistons which I know is the best way to increase compression.

I also have considered fitting a steel shim gasket. I have a pair of 0.016 thick gaskets sitting on the shelf here. Do folks think it is worth the effort? Based on the summit calculator if I went for the small cc heads and steel gasket this would put my compression in the 10:1 range.
That feels quiet a big uplift but would be interested in anyone's views if I what I currently have will hit the mark (the car is stripped of it's interior and paint so wont be drivable for another few months - and therefore I can't test drive.

Appreciated your advice
Many thanks, Alex in the UK

Mr.4spd

I think the block needs to be sorted out, .10 in the hole? Changing heads seems like a band-aid to me. Just my two cents though.

Gorts 5th

well he's still going to raise the compression ratio with the smaller cc heads why pull apart a motor and do all that work when a set of heads will raise the compression also and the edl heads are.... well they speak for themselves
the only concern would be piston valve clearance and i don't think that cam is going to put those valves into the pistons

Chryco Psycho

without changing the pistons either is a bandaid fix
the smaller heads will increase the compression which is needed as you lose approx 1 point of compression with alum so even at 10:1 you have the heat of a 9:1 build , using steel shim gaskets is a must with the different expansion rates between alum & Iron as well , fiber gaskets will eventually tear & leak . the real problem is you will never achieve quench with the piston that far from the head .
As for the "eddy heads speak for themselves" I did a swap from ported 906s to eddy RPMs also ported the tested HP on the same dyno proven net gain at the rear wheels was 3 yes 3 HP...not bad value for $3000 considering we needed different headers , the pistons had to be fly cut to clear the valves that were not in exactly the same position as factory heads etc !

PK1

As for the cam, 440 Performer + cam? as in 204/214.. Can you give me the part number?

I believe that is the RV / Truck cam for 0-5500 rpm power with excellent idle. If so I wouldn't change a thing until you know what your cylinder pressures are with that cam. Did you advance the cam at install? If so where? Run a compression test and post back your pressures.

Garys69RR

Wow Chryco, thats alot, $1000 per hopsepower! Think I will stick with my ported 906s and 915s for now. Besides its kinda fun carving cast iron. There is alot of info on different sites on porting iron heads.

Garys69RR

And Alex, I have heard that raising compression alone wont gain much horse power. Plus the steel shim gasket can damage the alum head since it is a softer metal compared to the steel. I have heard from a respected engine builder to go with the Cometic .027" thick gasket with alum heads.

Chryco Psycho

I agree with the Cometic for alum heads , it will allow for the different expansion rates between alum & iron without tearing the gasket a creating leaks . I have some different thoughts on porting Iron & flow bench proven creating a swirl & better mixing of the Air fuel making decent milage & powr

moe7404

i know for sure the first two years for the 440 it had 10:1 , 1966, 1967,,,,,,,,,,and about 1971or 1972 they dropped the CR

TVLynn

You have a set of eddy heads, why not just replace the pistons rather than get another set of heads. If the bore is good? just hone & replace the pistons. The Keith Black Hypertecitic pistons are a good and you can match them to the eddy heads.. AND it would be cheaper !!

66,67 use the closed chamber heads. they then changed to the open chamber style and the lower compression

Chryco Psycho

if you are going to change piston use forged , the cost difference is minimal but the quality is far better