Hi all, I am planning a build for an all street motor on a car which will probably never see the track. I want low to mid range RPM power. I

What I have so far:

• '91 L98 roller block which I plan to have bored .030 over
• a set of AFR 1040's which were milled to 58 cc when I bought them (I got a good deal)

What I was planning on getting:

• Comp Cams XFI 268
• L2490F30 Speed Pro Flat top pistons which I think have 4 cc reliefs.
• FIRST fuel injection intake set

Using 5.700" for rod length, a 0.029" gasket, and 64* for valve closing ABDC, I get a compression ratio of 11.43 and dynamic compression of 9.112. Did I input wrong variables given the above?

Isn't this too high for a California street motor? I thought dynamic shouldn't be greater than 8.5 for 91 gas. If so, any suggestions on what I could do to bring this into the right range for what I'm looking for?

Any suggestions to bring these numbers into operating range? Any help will be appreciated.

 

You have aluminum heads, so you can easily run 10:1 static, and if you pay attention to detail 11:1 is possible.

I'm not sure where you came up with those numbers, mine are slightly different. One thing to consider is that the pistons will sit below the deck unless you have milled the block, and with replacement pistons they may even sit lower than stock. 0.022 is about what they run stock and using that you're at 10.98:1 and 8.80. Thats on the high side, but may work out. About the only thing you can do is increase the cc of the chamber or piston. I would not go the route of a thicker gasket, that is just going to make things worse IMO.

 

Thanks for the reply, I was using 0.010 piston to deck clearance in the compression calculator. I don't know where I got that number from but it was the only one I could find. My block is unmolested so I will now use 0.022. Now my question is with 0.022" deck height, would I have to run a 0.018 compressed thickness gasket to achieve the golden 0.040" quench height? That sounds like its pretty thin.

There's a LOT of things to consider when building a motor, a lot more than I thought. Hope this is all worth it in the end.