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Discussion Starter #1
I had a complete L-35 BBC to start with. I wound up putting the 702 heads on my 460 BBC to bump the compression up. I later realized that I probably should have re-used the 781's that were on it because they have the biggest runners in the factory oval head class. Too late now. The question is that I'm going to put the L-35 back together and probably put it in a 70 Camaro with a TH400. I'm wondering how those heads (the 781's) will work on a smaller 396 bbc. This will have the factory cast dome pistons. Will it work just fine? Is this the best factory oval head for a 396??....or would the 702's work better for some reason. Lastly, What would the compression be with the 781's (118cc) and the factory 396 dome pistons? Thanks!
 

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As always, it depends.

Stock 325hp/396 was 10.25 to 1 CR.

You start changing heads and you really need to cc them to know what they measure so your calculations come out right.

What head is a -702?? Early closed, semi-closed, open or completely open chambered?

And you have to watch piston dome fitment here when changing heads from closed to open and visa versa too.

pdq67

PS., are the -702's the small peanut port heads??
 

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Discussion Starter #3
The 702 is the oval 65-66 98cc closed 396/427 head. I know I'll drop compression, but coming from 10.25 might not be that bad for the street if it will help the motor breathe? It's not out of the question to get some different pistons to get an ideal CR. I just thought I'd try to build a budget motor.
 

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Try here and run the numbers..

http://www.campbellenterprises.com/Race math calculators.htm

I use a piston DITH of about a stock, .025" and also .020" thick steel shims like stock was back then.

Not knowing the cc of your new heads calculate using 113 cc's and then 118 cc's to see how much of a CR range drop you may create.

Again, "you really need to cc them to know what they measure so your calculations come out right." I say this b/c open chambered heads can and do vary all the way from 113 to above 120 cc's!!!

pdq67
 

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Try here and run the numbers..

http://www.campbellenterprises.com/Race math calculators.htm

I use a piston DITH of about a stock, .025" and also .020" thick steel shims like stock was back then.

Not knowing the cc of your new heads calculate using 113 cc's and then 118 cc's to see how much of a CR range drop you may create.

Again, "you really need to cc them to know what they measure so your calculations come out right." I say this b/c open chambered heads can and do vary all the way from 113 to above 120 cc's!!!

pdq67

I think I need to go back and redo this......it said my CR is about 7.7 LOL

Time for a blower!!!
 

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No, it probably is b/c most stock 454 P/U engines w/ flat-top pistons and -781's are only like 7.9 to about 8 to 1 CR.

I can see 396 closed chamber low dome pistons w/ -781's being way low, CR-wise, imho.

Maybe not that low, but still darn low....

pdq67
 

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Discussion Starter #7
No, it probably is b/c most stock 454 P/U engines w/ flat-top pistons and -781's are only like 7.9 to about 8 to 1 CR.

I can see 396 closed chamber low dome pistons w/ -781's being way low, CR-wise, imho.

Maybe not that low, but still darn low....

pdq67
That makes sense and that's why I put on the 702's instead....wanted to get 9-ish.
 

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You might check K-B's piston pic's and CR tables to see how far off you are w/ the cc heads you want to use just for the check is all.

I think they list by head cc to get CR.......

pdq67
 
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