cbellamore

I just figured out the compression on my motor
and its way way down,
around 7.5 to 1 which would help explain why it wasnt running like it should have

so Im looking for a set of pistons that came on a 420hp merc BBC motor,

they should help me get the compression up to around 9.25 to 1 with the new heads that I have,

if anyone has a set or something similar,

the TRW number is L-2399F
trying to find something used to help keep the cost down
if you got anything or know someone with anything please pm me or email me at [email protected]

jeffswav

Your old setup with flat tops and 118cc heads you should have been 8 to 1. With the new 113cc heads we talked about before and a 454CI your compresion will probably be 8.65? ish. That is acceptable, I run 8.9 to 1, I thought it was 9.3 until RMbuilder ran the numbers. If you get your cam from Bob he can set the cam up and take in account the low compresion. I hear your motor came out OK. That is good news, keep us updated. If do install new pistons to get the compresion up the piston used on the Mag engine has a slight dome.

cbellamore

Yeah thats what Im looking for the piston with the slight dome to it
the pistons I have now are 50 in the hole,
me and my builder checked them over about 10 times, and kept on doing the calculations and the compression is 7.489 or something like so call it 7.5,
with the new heads going from 118 cc size to 114 cc size (the new heads I have now are 114 cc's) will only bring it up to around 8.1 (actually a little less)
so thats not that good at all,

I can have the block decked .040 and have the heads milled
.020 and that will get me close to around 8.75 to 1 but I would really like to be around 9.25 to 9.5 to 1

Im gonna look around for the mag motor pistons (which from what I have looked into are the same for 420hp BBC Merc motor setups and the early 70's LS7 454's)

if anyone has a set of these that they are not using, in good shape please let me know,
thanks

Jeff I will keep you updated as to what happens
thanks for the reply

getrdunn

so what do your heads cc out at. also what is your bore size?
i have a couple of sets that may or may not work for your application.
john

getrdunn

you would think there would be a ton of those .095 454 dome pistons around. did you post it in WANTED also.
john

picklenjim

[QUOTE=cbellamore;2925091]









Early 70's LS7's were 12:1 CR with 122 cc chambers.Merc at that time had the 370-400-440 which were all 8.8:1 CR.