Head volume effects on compression ratio

[Bobby Sixkiller]

I have a low mileage 440 from an rv. I’m thinking of swapping on edelbrock heads. I think the compression ratio on this engine is around 8 to 1. The 452 heads have 88 cc chambers if I remember right. The eddy’s are 75 cc. Shouldn’t that put it close to 9 to1 ratio? That with a dual plane intake should be a decent daily combo. Or am I wrong? I didn’t do the math. Just wondering if anyone has tried it

 

[bennydodge]

While I haven't done this myself, you will gain a little over 1 point of compression if you go from an 88cc chamber to a 75cc chamber on a stock stroke 440. The real question is how far below deck are the pistons. If it's an RV motor, I wouldn't be surprised if the pistons are down at least .080 thou.

 

[Bobby Sixkiller]

I haven’t measured them yet. I suspect you’re correct. I was thinking the edelbrock heads would raise compression and flow good. Reasonably cheap upgrade. Add a bit of cam and have a great street engine that should run easy on n 87 octane.

 

[Adam]

The aluminum will save you much weight. A cam with less duration closes the intake valve sooner and can really help build compression; talk to a cam manufacturer.

I’m sure someone on this forum will have performed this exact swap and can tell us what the effect was...

Perhaps having your iron heads milled and massaged might be worth a look.

 

[Chryco Psycho]

Having built a lot of engines & combinations , I actually would not recommend this swap .
First are you Sure the eddys are 75 cc , all the ones I have sen are 84 cc , yes you will gain a point of compression IF they are 75 cc but you also lose about 1 point of compression due to heat loss so I would expect to gain little even if the compression is 1 point higher .
For example my friend did this swap years back , I had ported 452 heads for him & he swapped to Eddy RPM which I also ported for him . we dynoed his car on thurs & made 308 rwhp with the 452 heads did the swap & returned to the same dyno a few days later the next week & made , Hold you breath A whopping 311 rwhp , so total of 3 RWHP for just over $2000 !!
I can think of a lot of ways to make 3 HP for less than $2000+, but it is your $$ to spend .

 

[bennydodge]

If it were mine I wouldn't run Eddy heads either. Their quality control, at least on small block Mopar heads, is lousy in my view. Mine needed a LOT of rework to be right. I'm not as well-versed in big block aftermarket stuff, though.

 

[Chryco Psycho]

A very good cam design will get you a lot further in the pursuit of power , I can help with that if needed .
Eddys heads are poor quality big or small block , I would look at Trick flow first .

 

[bennydodge]

A few years back I did screw together a 440 stroker 493 six pack with 440source aluminum stealth heads="chinesium". Those things needed around $600 to equalize valve heights, fix rocker stand geometry and valve guides but new they cost $995. They might have worked OK out the box..?? I've heard good things about Trickflow but in the OP's case I think I would run a set of mildy ported 452's.

 

[Chryco Psycho]

Even still $1500-1600 for the 440 source heads is reasonable

 

[DrEamer]

If you can find a free trial to Motor Trend on demand, be sure to look over the Engine Masters show. They have several episodes testing different combinations of motorhome 440's. The compression was around 7.2-7.4 to one. With stock heads, a Comp Cams Thumper, Holley Street Dominator intake, open headers, they made a little over 390 HP at the flywheel. The other test was with a worn 440, but with a Magnum 268 Comp Cam, same intake and header, but with Trick Flow 240's and made 445 HP. then for fun they threw a turbo on it to make close to 600 HP .

 

[Bobby Sixkiller]

Around 375 to 400 at the flywheel is all I’m looking for. The engine is pristine at 39k actual miles. I figured it’s around 300 in stock form. Best 30 bucks I’ve spent in a while

 

[fasjac]

I rebuilt one in 89 stock bore, even had a slight ring groove but, budget was tight. I bought the MP 509 purple shaft cam/lifters. Dual plane eddy manifold, used 750 vac sec, with blackjack headers. Found 2 sets of 906 heads but, two had cracks in the plug holes and two had cracks under the valve seats. So, 452’s were what I used. Machine shop straightened em up, valve job, harden seats. Stock valve train. 833 trans. I had more fun with this torquey motor than allowed. Ha.
Love em

 

[Chryco Psycho]

You can do better than Comp cams , lots of better choices including custom ground cams

 

[fasjac]

This Lunati can might be an option to consider?? I’d go a little bigger though

 

[Chryco Psycho]

with a low compression engine I would go 1 smaller keeping the duration @ 50 in the 218 range

 

[Bobby Sixkiller]

What if I have .060 taken off the heads. That should bring compression up a bit I’d think. Without doing the work I’m not sure how many cc’s that would take away from a 452 head.

 

[DrEamer]

What if I have .060 taken off the heads. That should bring compression up a bit I’d think. Without doing the work I’m not sure how many cc’s that would take away from a 452 head.

You could also run thinner head gaskets. There are a number of companies that make ones that are .030 or thinner.

 

[Bobby Sixkiller]

.030 thinner than stock steel?

 

[DrEamer]

No , stock is usually .040, so .010 thinner. There area a couple of gaskets that are .020 total if you don't want to mill the heads, or not mill them as much.

 

[Chryco Psycho]

quick math , milling the heads .060 will remove approx 14.4 cc from what is now 88-90 cc chamber so you would be around 75 cc so it would raise compression over 1 point & put you in the low 9s with a thin steel shim head gasket , if .060 removes the entire open part of the chamber in the cylinder head the volume will drop less than my calculations . You would also have to mill the intake approx .012 for every .010 you remove from the head so the intake will still fit .