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aatkinson
10-27-2012, 07:39 AM
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

te.ringer
10-27-2012, 10:04 AM
I don't think you can use steel shim headgaskets on alum. heads unless there the coated type. I could be wrong someone here with more exp.might ring in on this.

JVMopar
10-27-2012, 10:31 AM
First off that steel shim gasket isn't going to work well unless it's a multi-layer gasket. Aluminum and cast iron expand and contract at different rates. So with the head moving around on that shim it would be hard to get a good seal.

The CC of the combustion chamber is only going to determine the compression ratio, has nothing to do with the heads overall performance. The 75cc edelbrock heads listed on summit have a much larger intake and exhaust runners, and have much more flow above 0.500" lift. But with your low lift cam that isn't much of a benifit. Then there is port velocity to think about too.

I don't think your going to gain anything besides compression from swapping heads with your current combo. I think a cam change would be a better choice. You've basicly got a stock 340 grind cam. Which is listed for truck/rv use. The heads you have don't really peak their flow till 0.600" lift so you have alot of room there. Call around and get some cam recommendations. That's going to be the best bang for your buck.

If I were my engine I'd swap a set of multi-layer 0.020" head gaskets and the cam. That should put you in the 9.25:1 range and a cam with a lift of about 0.500 maybe a 0.484. Depending on manual trans or what stall converter you have.

Rich Kinsley
10-27-2012, 12:14 PM
Since you have it all together now and haven't run it, why not just wait till you try it to make any changes. You may be happy with it as is and will save a bunch of money to buy more gas :-) You can always tweak it later.

John Kunkel
10-27-2012, 06:05 PM
There's a common belief that aluminum heads absorb enough combustion heat to alter the perceived compression ratio about a full point...ergo 9.6 becomes 8.6 in theory.

340_GTS
10-28-2012, 12:12 AM
You could always mill the existing heads.

440Ramcharger
11-11-2012, 02:47 PM
Run it the way you have it configured. The 440 makes loads of torque. You will be happy as is. Do you still have the 3.07 gear ratio?

mtdrydock
12-08-2012, 12:15 PM
What are you looking at getting out of it? 9:1 with aluminum heads is pretty low, but have you looked at Hughes Whiplash cam? I have no experience with them but plan on running one on my smogger 440. They have narrow lobe separation, very little overlap, and early intake closing to build dynamic compression.

Dunnuck Racing used a whiplash cam, otb rpm heads, otb performer intake, 1.5:1 rockers and 9.2:1 compression to make 491hp 578lbft.

cudabob496
12-08-2012, 08:54 PM
There's a common belief that aluminum heads absorb enough combustion heat to alter the perceived compression ratio about a full point...ergo 9.6 becomes 8.6 in theory.

Alum removes heat better than steel, so that decreases cylinder pressure I think. I run a higher thermostat to compensate. Pump gas limits
an iron head motor to around 9.5/1 CR, while alum heads allow a 10.5 CR on 92 Octane, assuming your timing is not too agressive, and your cam
has a fairly large duration.

440+6
12-10-2012, 11:25 PM
I would have to agree that since the engine is already together, to run it and see how you like it. However, while the 440 is a torquey engine, I think you're really short-changing yourself with the low comp. ratio. Without getting too involved, I'd say you should at least have the heads milled and use the thinner head gaskets. I built an IRON headed 440 w/ 10.6:1 comp. and 34 degrees of timing and dynoed it on 93 octane pump gas with no issues at all. Though it had a pretty good sized cam, I'd say with yours having aluminum heads and an average cam, you'd want at least 10.5:1 to really optimize your engine.

cudabob496
12-12-2012, 08:56 AM
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

Don't know if its true, but I read somewhere that an old engine will gain about .5 in Compression Ratio due to carbon buildup over time.