408 SBC build- compression to run pump gas help - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-18-2012, 12:31 PM
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408 SBC build- compression to run pump gas help

i have a sbc 408 and need help deciding on what parts to get so ill have an pump gas compression rate, i want to get between 450- 475 horse power kinda green on this so bare with me ok.

i have scat 9000 (3.75) kb flat top piston i think there 11-1cc there kb 125, cam i wanna go with is comp cam (282)- 282--286 duration @ 50 230-236 valve lift is 510- 520 ls is 110 ic is106 heads i want to go with the afr 195 cc itake 75 combustion c 2.05/1.6 int/ext block is zero deck any info i forgot let me know this is gonna be a street car.

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Old 03-18-2012, 04:51 PM
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Flat top piston 11-1? What do you mean, that you think the c.r. is 11:1? If yo have a 400 block, .040, with specs you list, your static c.r. is approximately 10.26:1 assuming a .041 head gasket thickness. You don't want to go any higher for a street motor, even with aluminum heads.

KB 125?? What's that? If they're flat tops it's not a volume cc.
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Old 03-18-2012, 05:57 PM
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Kb 125 Is The Piston Part Number. 11-1 Told Ya I Was Alittle Green Doing This But Thanks For Your Reply.
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Old 03-18-2012, 08:01 PM
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BODINE014, I looked up the KB125 piston on KB's website, it shows a 7cc 2 valve relief flat top piston. Using specs of 4.126 bore (400 block .040 over), 3.75 stroke, 7cc piston reliefs, 75cc head chamber, .041 thick head gasket with 4.20 bore on a zero decked block (gives you a .041 quench) I get a static CR of 10.17. With the cam you've listed gives a dynamic CR of 8.03. If by "street car" you mean it will run on pump gasoline, then, YES, it's a street car.

Ed
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Old 03-18-2012, 08:13 PM
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Thanks ed I appreciate that
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Old 03-18-2012, 09:28 PM
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Quote:
Originally Posted by BigEd36
BODINE014, I looked up the KB125 piston on KB's website, it shows a 7cc 2 valve relief flat top piston. Using specs of 4.126 bore (400 block .040 over), 3.75 stroke, 7cc piston reliefs, 75cc head chamber, .041 thick head gasket with 4.20 bore on a zero decked block (gives you a .041 quench) I get a static CR of 10.17. With the cam you've listed gives a dynamic CR of 8.03. If by "street car" you mean it will run on pump gasoline, then, YES, it's a street car.Ed
Might be a typo, since a 400 stock bore is 4.125, which would give you 9.99 using parameters above. you have a 408, stock stroke 3.75, that means your bore is 4.165, which indeed gets you closer to Ed's number, I show it 10.15:1. I mention that so as not confuse you, since you're on a learning curve.
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Old 03-19-2012, 03:49 AM
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68NovaSS is correct, I did have a typo there, I did mean 4.165 for the bore. I did the calculations correctly, just typed wrong when I posted it (I just re-entered all the specs in both the KB-Silvolite dynamic CR calculator and Pat Kelley's DCR calculator to make sure).

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