Advice needed on head swap

flipbro

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I in the middle of putting vortecs 906 castings on my 5.7 block 3970010 with factory flat tops 4 valve reliefs. Original heads were 462624 with 76cc chambers and 76 cc chambers that were cracked. Im worried about compression being a little to high with the vortecs 62 cc chambers to run 87 octane. Pistons are .025 in the hole the victor gaskets I got are .040 thick is .065 quench to much? My cam is 420/443 valve lift 204/214 duration and 107/117lobe seperation. Will this combo work also what should timing be set at? Thanks Flip
 

Scott Danforth

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flipbro

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Scot ive read youre post. What was your quench when done? Im thinking if I can run a felpro 1094 head gasket .015 compressed thickness that would put me at .040 which would be ideal and help with det would I still need 91? We pay any were from 5 ro 6 bucks a gallon for the good stuff lol.. I know if you wana play you gota pay... I do have a set of smog pistons l think 16 or 18 cc would they be a better choice? Im looking for around 300 320 hp. Flip
 

Bondo

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Scot ive read youre post. What was your quench when done? Im thinking if I can run a felpro 1094 head gasket .015 compressed thickness that would put me at .040 which would be ideal and help with det would I still need 91? We pay any were from 5 ro 6 bucks a gallon for the good stuff lol.. I know if you wana play you gota pay... I do have a set of smog pistons l think 16 or 18 cc would they be a better choice? Im looking for around 300 320 hp. Flip

Ayuh,.... Ya gotta do the Math,.... put a number on the static compression ratio, insteada just guessin',.....

smog pistons got the dish in the wrong places for Vortecs to Shine,....
 

flipbro

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Well I got bigger issues. I popped off my main caps to have a look at bearings and cap 2 3 and4 are to the Cooper all the Babbitt is gone but only on the cap side block side looked ok.. by the way it was rebuilt 2 summers ago just a freshen up bearings and rings clevett every thing was plastigaged and was fine .002 to .003. I know not the rite way to cheak .. so could this be a bent crank or is it possible the block wasnt cleaned properly after it was honed?
 

Scott Danforth

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dial indicator will tell you if the crank is bent.

however as Bondo stated, the flat tops are the wrong pistons to really make the vortec head produce power.
 

flipbro

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I believe bondo was referring to the dish piston.. I put some numbers in a cr calculator and come up with 9.72.1 with the flats and a .065 quench.. is this to high?
 

Bondo

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I believe bondo was referring to the dish piston.. I put some numbers in a cr calculator and come up with 9.72.1 with the flats and a .065 quench.. is this to high?

Ayuh,.... I'd rather see 9.5:1, at .043 quench, with an off-set dish,....

Were there any signs of detonation when ya tore it down,..??

The bearin's being hammer in the saddles Could be from detonation,...
 
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Scott Danforth

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I believe bondo was referring to the dish piston.. I put some numbers in a cr calculator and come up with 9.72.1 with the flats and a .065 quench.. is this to high?

yes, Bondo was referring to the factory flat-top 4-relief slugs that you have (as well as I do). while the vortec heads will add some power, the KB d-dished pistons work best with the .043 quench.

depending on your gasket, you will most likely be in the 10.4 - 10.5:1 range using the factory flat top slugs and vortec heads. hence my original comment on not being able to run 87 octane.

however if your motor has had issues with detonation, it may be time to reslug. if that is the case, get appropriate d-shaped dished pistons, zero deck and end up with the 0.043" quench.
 

flipbro

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I dont beleive there was any det problems prior to being pull.. this motor run stronge for the past two years never missed a beat pulled hard and plained the boat very quikly never heard any pinging. I own a 78 corvette that pings if I dont run 91 octane.. The pistons look fine no sighs of detination problems. If I have to run higher octan so be it. Are 906 heads closer to 66cc then the advertised 64?
 

Scott Danforth

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no, both the 062's and the 906's are nominal 64cc, and if you actually measure (cc the head), they are closer to 62-63cc's unless there has been some head work done.
 

flipbro

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Bondo and Scott thanks for the help..I think ive come up with a plan I cheaked the cc of the dished pistons I have they are 12 cc so im going to use them with a .026 victor gasket that will keep me around 9.2 cr. I dont believe my cam would like to much more compression then that. And that should get me up around the 300 hp mark with good torque. Btw I running my stock rodchester with a ebay special dual plane intake speedmaster I believe. . Does this sound resonable. I would love to get a block deaked with kb d dished to mirror the vortecs. But wife kids and morgage come first toys second..
 

Scott Danforth

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if your motor is newer than 1987, it was putting out 300hp at the crank, and 260 at the prop (prop rating).

a set of vortec heads, a good cam, and the flat tops should put you in the 330hp range at the crank (about 280-290 at the prop).

your still going to be more than 9.2. your motor was 9.4 with the factory 76cc heads. you now have nominal 64cc heads. your CR is in the 10.4 range
 
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Bondo

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Ayuh,.... I ain't no mathamagician, but do yer math, 'n be Sure, yer under 10:1,.....

Vortecs are pretty detonation tolerant, but there are limits,...
 

flipbro

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Scott this is what ive got 4 inch bore. 3.48 stroke. 64cc combustion chambers 13 cc dish. .025 in the hole. .026 x4.100 head gasket shows me a CR of 9.19.1..Now I change the numbers to what I was running ppreviously flat tops with 6 cc reliefs and 76 cc heads with a .40 gasket I come up with 8.43.1.. Now if I do the math with the flat tops 6 cc vortec heads 64 cc and a head gasket .041 I get 9.48.1. Are these calculations wrong?? Ideally the flat tops would yeild me 9.48.1 which would be nice but I loose all quench
 

flipbro

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Bondo im no Mathamagichan either.. If I was id magicaly make 9.5.1 with a nice tight quench lol
 

flipbro

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Tail Gunner thanks for the link really helpful. I just pick up a 350 out of a 1990 pickup its a motor buddy bought from napa I guess its rebuilt by ironclad.. only 30 thousand on it. So I geuss im going to be needing a new fly wheel and coupler.
 
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