How much piston - cyl. wall clerance is best on a forged 426 wedge piston? I'll be just south of 12 to one comp. and set to run @ 6200 rpm on E-85. Thanks in advance guys

What pistons?
Some of the Older TRW stuff requires diff clearances than the newer CP, Diamond pistons, they don't expand as much, which requires tighter piston/bore clearance.

I bought theses pistons a while back thinking they were OEM 11.5 - 1. but now I'm not so sure of the origin. They are standard size have a small .065 dome, .085 valve reliefs and TP in a triangle on the under side of the piston. A comp height of 2.055. These old slugs are in pristine condition. I'd like to bore a 413 truck block .070 and race em. If the part # would be helpful I could run to the shop and check.

An 065 dome with a CD of 2.5 will not get you near what you need for E85 fuel. Is there a fire-slot in the dome at all?

But these pistons would be perfect for what I am putting together !!

Those sound like the OEM ("Thompson Products" which later became TRW) pistons for the low compression 1963 415 HP M.W. motors. Before making a choice on using them check the skirts for collapse very carefully and the ring land clearances, if the pistons where used at all Also make sure the 413 block is thick enough(sonic test it) before having it bored out

Thanks Cab "You Da Man" My Machenist miked the skirts and gave them a good to go. I was thinking the low comp MW was 11.5 to 1. Is this correct? I've got a set of milled 915 heads they cc about 70. They should get me where I want to be. The 2.14 1.81 valves will be dang close to the bore If they work at all with the orig. 525 lift. More measuring required!

I don't remember if the 415 hp was advertised as 11.25 or 11.50, either way they weren't what they advertised, they where lower. Bill Jenkins got NHRA to change the dome height on the 1963 415 HP only to .090 or .093, I can't remember which exactly. I used the stock pistons and ran them that way, some guys would take a set of 1964 415 HP pistons and machine the dome down to the .09? spec and get more compression. If your making a street and strip motor on pump gas with a iron head it will detonate like crazy any where near 11:0 to compression ratio and kill the motor unless you use E85 for fuel I have a 9.4 to 1 compression 446 C.I. that I can make detonate by leaning down the primary part throttle cruise AFR to 14.3 or higher That is on Oregon 92 octane at 2500 ft. above sea level

Cab; He needs all the compression and cylinder pressure he can get. I'm loaning him an E-85 carb for this motor. Dave