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Old 09-29-2005, 03:07 AM
b-body-will's Avatar
b-body-will b-body-will is offline
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Default Compression recomendations?

Okey, so I now have my KB 215's. Tomorrow the block and pistons go to the machine shop to be bored/fitted. I will end up with 456 cu. in. and it's going in my '73 Charger with 727 and 3.23 rear. The car has A/C and P/S.

From what I can ascertain the C/R will be in the area of 10.75:1 if I leave the pistons alone and run them with my "213" heads. (according to what I read the 213's have 81.9cc chambers) I am going to install a Comp Cams cam with specs:
Duration @ .050" 224°/230°

Valve lift: .477"/480"

Lobe sep.110°

So the question is... do I machine the domes down to get 9.75:1 or go for the higher ratio? Or, go to something in between? Or do you think I should go even lower than that? Once the heads get back we'll cc them and plug the numbers together (deck clearance, dome, etc...) and come up with the real C/R.

What C/R do you recommend and why? What are you running for your mostly street driven vehicles?
:rolley
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Old 09-30-2005, 08:58 AM
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rumblefish360 rumblefish360 is offline
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Weeeellllllllll, Run the most compresion you can get away with in the given combo. It is free HP and torque. Seeing the cam your running is small, the 9.75 in a iron headed engine is possible. The higher ratio will need more octane. How well the gas burns inside is another story.
I'm used to flat top piston builds. There a little easier to control in there ratio with head milling and gasket thickness.
Closed chambered heads also offer a better quench for higher compresion and burn. This equals less timing. Better power and complete (er) buring of fuel @ a lower octane.
I'd error on a low ratio myself to be safe than sorry or have a problem on gasoline octane. Your builder should be in the know on this.

Wheres the big block guys that been there done that?
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Old 10-01-2005, 09:47 PM
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b-body-will b-body-will is offline
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Thanks man, I am leaning toward keeping it at 9.75:1

I am building it. This is my first BB Mopar. Built a 318 and a 360 in a prior life for my '71 Challenger. (That I no longer have, dammit!) In between I went SB Chevy for a few race cars and was able to extract pretty good power from them. But the siren song of Ma Mopar was strong and pulled me back about 10 years ago.

So while I am confident of building a solid, reliable engine I am not certain about the differences between the BB and the rest of the engines from my past. (getting clearances correct is not the worry... selecting the right cam, CR, etc... is what I am refering to) Been doing a lot of reading and asking questions and for opinions. Been great so far and I can't wait to fire this one up.
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