I am planning on building a new shortblock this coming Fall/Winter.
I have a few "criteria" I'd like to include, but don't know where to begin on the rest of the design...

This is basically a street motor going in a convertible, Richmond 5-speed,headers, dual-quads (low-rise), etc. Currently have a 396 bottom end with ultra low compression ratio...

I have a 454 block (0.030 overbore?), a cast 454 crank (unknown journal sizes), a nice 396/427 steel crank (cross-drilled?, and polished up at std/std on the journals), lots of stock rods (3/8" bolts).

I want to reuse my Edelbrock Performer heads (~110cc Aluminum), and I want to run pump gas (91 Octane max), and I'd really like a mild idle (idle between 750-900 rpm?). And I'd like to use off-the-shelve pistons to keep the cost down. I am leaning toward the 427, as it would allow the contiued use of the new flywheel (internally balanced), balancer, etc


I am leaning toward using the 396 steel crank to create a 427 (plus overbore), but don't know which pistons to use. I am thinking of pistons with a CR of around 9.5:1 (this is what I am unsure of). I know I can put differnet cams in to increase/decrease the DCR, but I want a mild cam. Most "catalog" specs list various "427" pistons with respect to higher of lower chamber sizes.

How do I find other data on pistons (manufacturers websites?)? What's a good static CR to shoot for with my desire for a mild cam? Am I right in assuming I can fine tune the DCR with cam selection and degreeing?

Overall power isn't critical, but naturally I'd like as much as I can and still keep the pump-gas streetability.

How much power loss (roughly) and what DCR to shoot for if I wanted to run 89 octane or 89/91 mix?

I'd shoot for a DCR of about 8.0:1 with your aluminum heads. That should give you plenty of lee-way on octane requirements without making your low end power soggy.

Now that you have a ball park idea of the DCR you need, now you need to pick an RPM range -- once you know what RPM range you need you can try a couple different off-the-shelf pistons with various cams that fit your desire power band and you are there.

Personally, I'd start with pistons that will get you to about 10.0-10.5:1 compression. That will give you lots of streetable cam choices and a DCR that fits the fuel you will be using.

That's how I'd go about it anyway.

I suggest figuring out what cam you want to use taking the gearing, and want you want out of the car into account first. Then optimize the CR for that cam. For max power, shoot for 8.3 DCR. I don't know what DCR is best for 87 octane but under 7.5 should work. Once you get the DCR worked out, plug in the actual stroke and see what SCR to build. I'm guessing you have read the DCR page linked in my sig. I'd be leary of the piston mfg CR claims. They all seem to calculate it differently. The best bet is to get the dome cc and work with that. Although getting that info can be difficult for some pistons. Most of the better pistons have the data but with less expensive ones, like Speed Pro/TRW, it can be hard to find. You should try to get the .035'-.045" quench you hear so much about.

You can "tune" the DCR with the cam and cam timing but it is best to use the cam you want with the advance recommended by the mfg and adjust the CR to get the DCR desired. Any DCR between about 7.8 and 8.3 will work fine. With aluminum you could go .1 of a DCR ratio higher although for long miles on the street 8.3 should be the max.