I building a 340 stroker with 5cc icon pistons and lunati 60403 cam. I have attached 2 compression calculations: 1 with factory X head and another for the 340 RPM edelbrock head.

[img]https://drive.google.com/file/d/0B9h_hTKK80XMSmo1cWU2dkFaRms/view?usp=sharing[/img]

[img:left]https://drive.google.com/file/d/0B9h_hTKK80XMOEVkaFI0NjVlbU0/view?usp=sharing[/img]

Is it worth the money to purchase the eddy heads? The static compression with those heads will be 11.2:1 and dynamic compression is 9.5. Would I be able to run the engine without damaging it on 93 octane gas?

thanks in advance for any help,
Ray

Why would you pick pistons without knowing what head cc you were going to run??

I think 9.5 DCR will be too much for 93 octane.

91 seems to need very low 8 or very high 7's DCR.

Youre gonna be stuck with an open X head just for compression reasons. I see your calca all use .051 head gaskets. Sound like your realizing the corner you've painted yourself in.

I run a 422 stroker (340 with a 4.00 crank) in my Demon. It has ported closed chamber iron econo W2's and 9.6:1 compression, runs great on pump 91. It all boils down to the piston and chamber details (quench build, hot spots, cam specs, etc.). A proper cam design that bleeds off a bit of compression can help with detonation issues.

That's a good question.

I was originally going to use my X heads and then saw the edelbrock sale for the top end package with free carburetor and thought I may go that route.

Do you think I should just stick with my x heads? I have the lunati valve spring kit to match the cam that I can have installed at the machine shop.

thanks,
Ray

This is your cam:

Advertised Duration (Int/Exh): 268/276
Duration @ .050 (Int/Exh): 226/234
Gross Valve Lift (Int/Exh): .494/.513
LSA/ICL: 110/106
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1800-6200

You'd need a ton more cam to bleed off 11:1 compression. Start asking your machine shop about flycutting your piston tops if you what to run those smaller cc edelbrock heads.

IMHO you are stuck with an open chamber head with 72+ cc's. I think that will be X, J, or W-2.

X heads by your calcs give you 10.2:1. That might work with 93 octane. But you'll have no quench and cast iron heads that tend to promote pinging vs closed chamber alum.

I guess I'll just stick with my stock heads and pay for my stupid mistake.

I was thinking a screwed up and needed someone to confirm my mistake.

thanks for your help.

One other question is do you think I would benefit from a set of dougs headers with this combination or should I just stick with stock manifolds?

I'm planning on an airgap manifold and 800cfm avs.

thanks again,
Ray

With a mild build like that you wont see a huge gain with headers, I'd bet less than 20hp. Personally I'd stick with manifolds.

Before you decide on the heads I would CC a chamber in each heads, that way you will know exactly what your compression ratio can be and not hope it is near stock on the combustion chambers
I've CC a ton of both X.J,U,O and other stock 340 heads, none of them where larger 67.0 CC
I haven't seen a flow sheet on a OEM stock iron 340 head in a lot of years no I have no way to judge the new Eddy aluminum heads are any better or worse than the original iron ones are

what are your hp goals? what type of car are you gonna put it in?

I'm assuming running 93 octane is set in stone. What Cab said I would CC/measure everything to see exactly where you are at for SCR but IMNHO it is way too high from what you posted. Cometic makes thicker gaskets. I would not go with a wilder cam to lower the DCR, keep the cam that suits your driveing style. For manifolds the best are early 340 HP ones & magnums, '92/early 93 ex manifolds which have ~2&5/16 outlets. Holler how it turns out. I would stay with the iron heads (for now).

Go with the Edelbrock package you want, go thinner on the head gasket to get quench back, run it until it pings, then back your timing off 2 degrees.

What about the Eddy Magnum head? If it has the fast burn chamber it might help with you DCR problem. They take a lot less timing to make power and less timing is usually less prone to detonation. Whether that's enough to overcome its even smaller chamber volume .

Kevin

You're kind of in a pickle.
Using the engine size, a zero deck piston, 5cc in the valve pocket and 64cc head, you're right at 12:1.

First of all don't buy the Edelbrock 340 heads. They were made for guys who already had new or nearly new 340 pistons that come out of the bore. By carving out the material where the piston would collide, they eliminate the opportunity to get squish.

For a 30 over 4" stroke 340, to get to 10.5:1 you need 90cc above the piston. Assuming your new head is 64cc, the head gasket is 10cc, there's 5cc in the valve pocket, you need about 11cc more volume. This comes out of the piston top closest to the spark plug. That's with piston at zero deck.

To get to 10.5:1 without machining the piston, it needs to be down in the hole 0.046".

Regarding heads, the consensus opinion for the best flow out of either an X or J head, stock, is 220cfm. The max flow out of a Edelbrock LA head is 251 cfm. Using this as an example you are looking at as much as a 65hp increase.

A 3" diameter circle 0.090" deep is about 10.5cc.

Clear as mud, right?
Rats! I just found out that while I was calculating a 64cc chamber, the LA head is 63cc.

R.

The Magnum heads are only 58cc and would need to have an inverted dome machined into them that matches the chamber's shape. Just slapping them on with a 10cc gasket, piston at zero deck, and 5cc valve pockets you'd see 12.7:1 compression.

While not desired, couldn't he bleed off some compression with the cam ABDC spec?

I have to assume there's no way to return the pistons? ICON makes a 20 cc dish piston that is 10 grams heavier that your current 5 cc piston. I just pulled them out of my motor and went to the flat top you have to bump compression.