Hi. New to site. Ive got a 1970 454 LS6 I've been rebuilding. Question. My 1974 motors auto repair manual and three other books I've got show cylinder bore at 4.251", but I've seen 4.250. What is it ? With inside mikes, backed up by my bore gage, I get an average bore of 4.2505-4.252", avg. taper 0.001". Bores looks great. My old 11:1 pistons are worn, 0.007" avg. clear, skirts worn out, need replacing. But I checked on TRW L2399F pistons - they'll give me 9.6 CR with my rect. port heads - but they say their diameter is 4.2465-4.2470" measured at pin, at 90 degrees. That give's max 0.0055" clearance which is right at max wear limit per one of my books. I hate to rebore such nice looking bores that are only 0.001-0.002 (if 4.250 is the right std bore) oversize, but this'll be a performance street engine, and I don't want an oil burner. Haven't owned Chevy engines before, am an old 239 Dodge ram hemi guy, and a previous 389 GTO guy. Any input welcomed. Thanks.

Hi Jeff.:waving: I have no idea what the hell you are talking about,but welcome from a fellow 70 owner.:thumbsup:

Welcome!!

You might ask your question in the General Engine Discussion part of the site.

Hi Jeff! Welcome from Oregon!

Jeff, Welcome to the forum.

Welcome to the site.

Welcome to the site. Fairfield where???

Hi,
I did figure things out and posted my question on the engine site and got some good feedback. Thanks.
Fairfield is in California, North East SF Bay Area. Don't blame me, the geography is beautiful, and it was a civilized place - I'm from Ohio - when I moved here 44 years ago. Go figure. I'm a retired engineer, trying to build my car before they outlaw everything including me. I may be too late.
Thanks, Jeff