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Old 07-10-2011, 07:18 PM
SPEED MASTERS CC's Avatar
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383 Sbc Build

MY 1ST. POST!

I am working on a 383 build and have a few questions.

I am using a O.E. roller cam block with a -.005 deck with a Scat internal balance cast crank, 6 inch rods, Mahle flat top pistons with a Comp Cams Big Mutha Thumpr Cam. (I know, poser cam...) Edelbrock Street Tunnel Ram with two 450 holleys. I have two sets of heads, 492 64cc iron heads ported by Joe Mondello's that flow in the 220's on the intake and 180's on the exhaust @ .500 lift and a set of Brodix -10 spreadports which I think are 210's with a 67cc chamber, no porting. This engine is going in my 32 ford coupe street car with 4.56 gears with a 3000 stall.
I do not have headers yet. They will be sprint car type. The cars weight is 2600 lbs.

Thanks in advance.

1st. question: Does any one have a idea what the cranking compression (psi) would be with the above combo?

2nd. question: Will this engine run on pump 93 octane gas with the iron heads and/or the aluminum heads?

3rd. question: I am considering E-85 fuel, any problems with running this stuff on the street?

4th question: Which head should I use?

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Last edited by SPEED MASTERS CC; 07-10-2011 at 07:19 PM. Reason: grammar
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Old 07-11-2011, 08:27 AM
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welcome to the site!

as far as your first question, i can't really answer that one cause i dont know the intake closure point on the cam. it may say it on your cam, or you may have to call up Comp Cams to find it out.

for your second question, that is also hard to answer without knowing what your dynamic compression ratio will be (cranking pressure) but i would give this guess: since the iron heads will have you at 10.85:1 i doubt you will be able to manage that on pump gas. aluminum heads are a bit more forgiving when it comes to running higher compression (they can handle more cranking pressure before detination). the alm 67 cc heads will have you at 10.5:1. (the compression numbers are based on a 4.100" bore head gasket, proper .040" quench, and 7cc valve relief in the "flat top" pistons)

for your third question, i dont know too much about E-85 (it hasn't really gotten to my town yet) but i really dont see it working with compression numbers like what you are looking at. but here is a website that can explain a little more about it and maybe how to convert the carbs to accept E-85

http://www.brokenboltgarage.net/E85.htm

for your fourth question, it's a no brainer. use the Brodix heads. for todays standards 220cfm at .500" lift is garbage those Brodix heads are likley closer to 250cfm @ .500". not to mention the better combustion chamber design it will have over the old "double hump" heads as well as the 30-40lbs weight reduction.
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Old 07-11-2011, 08:42 AM
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If you want to run E85 just be sure to run the proper fuel system, it will run fine with that compression, even more, but then you have to have a starter that can handle the added cranking compression.
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Old 07-11-2011, 01:15 PM
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Thanks for the help!

The Cam in question has an intake closure point of 73 degrees BTDC and a exhaust closure point of 86 degrees BBDC. The Cam has a 107 degree lobe separation.


Quote:
Originally Posted by my87Z
welcome to the site!

as far as your first question, i can't really answer that one cause i dont know the intake closure point on the cam. it may say it on your cam, or you may have to call up Comp Cams to find it out.

for your second question, that is also hard to answer without knowing what your dynamic compression ratio will be (cranking pressure) but i would give this guess: since the iron heads will have you at 10.85:1 i doubt you will be able to manage that on pump gas. aluminum heads are a bit more forgiving when it comes to running higher compression (they can handle more cranking pressure before detination). the alm 67 cc heads will have you at 10.5:1. (the compression numbers are based on a 4.100" bore head gasket, proper .040" quench, and 7cc valve relief in the "flat top" pistons)

for your third question, i dont know too much about E-85 (it hasn't really gotten to my town yet) but i really dont see it working with compression numbers like what you are looking at. but here is a website that can explain a little more about it and maybe how to convert the carbs to accept E-85

http://www.brokenboltgarage.net/E85.htm

for your fourth question, it's a no brainer. use the Brodix heads. for todays standards 220cfm at .500" lift is garbage those Brodix heads are likley closer to 250cfm @ .500". not to mention the better combustion chamber design it will have over the old "double hump" heads as well as the 30-40lbs weight reduction.
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