440 Edelbrock Top End Kit With 75cc RPM Heads

[magoo426]

Hello.  I am considering getting Edelbrock's 440 Top End Kit #2087, except I'm thinking of using the Eldelbrock's 75cc RPM Heads.  My 1968 440 currently has a compression ratio of 10:1 with factory 1968 steel heads.  Has anyone used this head before, also would this jump my compression ratio up too high that I couldn't run premium pump gas?

Any advice, suggestions, thoughts, opinions are greatly appreciated!

Thank you.

[72cudamaan]

Got a link to the kit? What are the casting #s for the heads? Has the block been decked?

[magoo426]

Hello.  I bought the engine and was told that the heads were slightly milled, like .003" or so just to square them up.  I'm not in the shop right now, but I think the heads are 452.  The block has not been decked as far as I know. 

As far as a link, this is the link to JEGS website with the top end kit I was thinking of using. It specs out 84cc RPM heads.
http://www.jegs.com/i/Edelbrock/350/2087/10002

On Edelbrock's website says they make a 75cc RPM Head.  So I was thinking maybe could I use the 75cc heads instead of the 84cc heads.
http://www.edelbrock.com/automotive_new/mc/cylheads/chrysler/bb_perf_rpm.shtml

I appreciate you taking the time to give your advice.

Thank you.

[Chryco Psycho]

Using the 75 cc heads you will drop the chamber size by approx 14 cc , so the compression will jump to 11.5:1 which is too high for most pump gas combos , you can use the thicker Cometic gaskets to lower the compression back to 10.9:1 or open the combustion chamber slightly unshrouding the intake valve & enlarge the combustion chamber slightly which will increase flow & drop compression

[magoo426]

I checked the heads and they are 906 heads, I was wrong when I thought they were 452.  Even with 906 heads, the 75cc Edelbrock RPM head would make my compression ratio too high.  Are the 906 heads about 88~90cc heads?

So if I decide to go with the 84cc heads that Edelbrock has would that put my compression ratio no more than 10.5?  If so, I should be able to run premium pump gas with that compression ratio, correct?

Once again, your insight is greatly appreciated!!  I don't consider myself to be an engine expert, so that's why I came here to gain some knowledge.

Thanks again!

[Chryco Psycho]

Difficult , the 906/452 headas are 88-90 cc as you said , sothe 84 cc heads will raise the compression to 10.6 approx But you lose a lot of heat to the alum as well so effective chamber heat will drop similar to 9.6 ratio so now you need another .5 compression to retain the heat / power you have now so this puts you between the 2 head choices , if you are using a thick head gasket now you might gain a little back using a thin gasket & retain the quench or use the smaller head & use a thicker gasket to lower compression , , personally I would lean to maintaining quench for pump gas with the thinner gasket maybe getting you back into the 9.8 range .

[magoo426]

I'll need to look up what gasket thickness is being used on the engine right now.  I have the receipts from the previous owner on what was bought and done to the engine.  I'm hoping the gasket thickness is high 0.040" or more.  Then I could get a thinner one, I like that option better than trying to find a thicker gasket to lower the compression if I were to use the 75cc heads.  The only other thing I've thought would be, would it be better to get the 906 heads ported out to get the same flow as the Eddy 84cc heads.  I think that this would cost a ton though to get the 906 heads to the same flow level as the Eddy 84cc. 

Any thoughts?

[Chryco Psycho]

If I was closer I would port your heads , I used to charge about $500 & on the dyno eddy heads ported only made 3 RWHP more than the 452s but I have not been overly impressed with the Eddy for the $$.
You also still want to use a Cometic multi layer head gasket to prevent gasket failure with the different expansion rates I I believe the thinnest is .028 thick

[magoo426]

Has there been any dyno results recently with the Edelbrock Top End Kit with 84cc Heads?  I can't seem to really find any besides what's on Jegs website.

Also what's the highest compression ratio that can be run on pump gas for a normal street 440?

[Chryco Psycho]

I have not seen any results but I have not been looking either .
 Generally 11.1 with alum heads is max , but it depends on altitude , sea level is tougher so you need to be more conservative , cam duration , more duration will bleed off pressure at lower rpm , & fuel quality which is getting worse by the minute .
I got away with 11:1 using iron heads, the same .590 cam  & Sunoco gold 94 octane  20 years ago , ti would ping bad below 2800 if you put a load on the engine but never had an issue 3000 rpm up , very streetable If you kept your foot out of it or were above 3000 rpm