How can I get really close to 10:1 in a L28 without going to flattops? What are the options? There is a lot of unused space in the top of a n42 block that could be used. D crank?

steve77

the simplest way would be the flat-top pistons, why dont you want to do those?

Yeah, I know...I just wanted other ideas. Probably will...With flattops, I will be over 10 and with everything 91 now...well....Maybe go flattop and use 2mm? I just want better than 9 and less than 10.

steve77

I tried it in the calculator and got to 8.9 with an E-31 and dished pistons with a 1 mm head gasket. Could go a bit over 9 if you had to deck the head 10 thousandths to true it.

I think the easiest bet will be the flat tops. Ought to be able to run 91 octane without too much trouble if you keep it close to 10:1. Most of the new cars on the road now are running near to 10:1, but with the old engines without the benefit of the new computer systems running the ignition, injection etc. I think I'd go to 93 octane if possible.

There is always the idea of using a custom piston (pricey) with a lower pin height or a higher dome.

"Most of the new cars on the road now are running near to 10:1, "

I couldn't believe that! I saw a write-up of Q45 engines on Freshalloy.com and the street version is 10.something :1!!!!!!! I couldn't believe it. So I would assume with a 6A or a HI6 a 10+:1 L6 would run better on 91.

steve77

you can get 9.73, but its not easy

L24 rods

L28 crank

Dished pistons Fly cut 1.00

2MM head gasket

E31 head

1.00 over bore

not only does your compression go up though it leaves you with a 3L engine too.

Matt