Keith Black pistons VS Speed Pro for 318

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canner78

canner78
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Any of you guys with 318`s use the keith black pistons. i was looking on their web site and their calculator says that with the flat top pistons and my 58 cc heads that my compression ratio will be 10.3 to 1. and on the speed pro site it says with their flat top pistons that my compression ratio will be around 9.2 to 1. what is the differance in the pistions that can make that much differance in compression ratio.
 
Compression height. That is, the distance from the pin bore to the top of the piston. The KB 167's are taller.
 
Look at the piston specs for the compression distance. This is the distance from the center of the wrist pin to the top of the piston. A difference here would account for the difference in compression ratio. Although the top of the piston still travels the same distance (stroke), the size of the available space in the combustion chamber at TDC changes. I went to Summit's site & compared what I think are the 2 pistons you are talking about & the SP has a CD of 1.755 in. The KB has a CD of 1.810 in. The KB sticks up .055 in. higher.
 
LOL, it's hard to beat the CHEIF!

Also, the little things like valve relief cc's and possible dish or extra quench pad should be noted when looking at pistons. A minor dome can have dramtic effects.
 
The advertised compression is assuming that the block deck height is at it's nominal dimension. Since it hardly ever is the actual compression will be lower than advertised. The only way to know for sure what the compression is to measure the actual deck height of the block (or clearance from he top of the piston to the deck surface and actually measure the chamber size of the heads since they are rarely what they are advertised to be too.
 
i measured the heads buy covering them with a piece of plastic and they were full with 58 cc of tranny oil. so give or take a little bit they are 58 cc and i`m having the block decked to 0. i am also using the mopar performance .024-.028 head gaskets.
 
So with the KB's you should be right around 10:1. Thats about the max for pump gas and iron heads on the street. Even then, make darn sure you deburr and smooth every sharp edge in the chamber.
 
canner78 said:
i measured the heads buy covering them with a piece of plastic and they were full with 58 cc of tranny oil. so give or take a little bit they are 58 cc and i`m having the block decked to 0. i am also using the mopar performance .024-.028 head gaskets.
Click to expand...

based on those numbers you are right at 10.6:1
 
I dunno if this really applies to the topic at hand but...my machinist swears by Kieth Black.His reason is that they are always within a gram or two of each other and this really helps when balancing...

Have no idea about speed pro.
 
Thats a mighty close piston to head clearance!!!!!!!!!!!!
 
Good point. If you are running a closed chamber head (like a 302), thats too close. Use a regular Fel-Pro .043 gasket. If you are more than .010 in the hole, use the MP thin gasket. Besides, 10.6 is pushing it on pump gas. A properly set up chamber with .030 - .060 quench will get you there.
 
would i be better off not decking the block to 0 and still using my mopar performance head gasket. that should lower the compression ratio enough to get me into pump gas and solve the clearance issues. what do you think
 
First thing I would do is measure your deck height with the new pistons installed. Then you can decide which way to go. If you are .010-.015 below, then leave it be and run the thinner gaskets. If you will have to cut the decks anyhow, then shoot for zero and run the thicker gasket. If you have already bought the gaskets, I suppose you can adjust the machine work accordingly, but this is going about it somewhat backwards. Also think about parts availability, you can get a normal .043 gasket from your neighborhood parts store.
 
No need to install pistons to figure deck clearance. Measure how far you current pistons are down in the hole then subtract the difference in piston height between stock pistons and the ones you want to use from the current clearance and you will know where the new pistons wind up.

Plus, the machine shop should tell you what will need to be machined to get to the clearance you want by measuring the block.
 
here is an answer from another site about my setup. He addressed the zero decking of the block and gave the #'s. hope this helps.

If you want a Zero deck engine, and you DO, have it decked to 9.588". That will be just right.

I to agree with others that your cam choice is to big, But i see BJR is talking with you, The Guru of small blocks, so youll be ok
 
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