i thought the ls6 was an open chaimber design.

hay mark,,back in the day we use to take a 454 crank and have it ground to a offset,then have it renitrated,then we would use a 1.980??? small block h beam rods and have custom pistons made for the older bowtie blocks..total cid was 509..

if those are true LS6 pistons they should be TRW slugs. with the closed chamber heads it will be close to 12 to 1 compression. the engine for my Wesco v-drive flat is the same pistons and heads and that is what it comes up to. the original tall deck pistons are are taller and I think had 4 rings if memory is correct. that is why the 4.25 and longer rod is needed to make up the distance. if you figure out the numbers that rod works.

ls6 had 291 closed chamber heads......ls7 was open chamber

the first ones were closed chamber, then they went to open chamber. you have to remember that more of the LS6 motors were sold over the counter than in cars. they started out at nearly 12:1 and then the later ones dropped the compressions. they were sold new into the late seventies at least.

It is but this is how it's built,
Block 340220 .... 427T ...... 4-bolt 1968-85... 427 tall truck
Head 3964291 RECTANGULAR PORT - Valve size 2.19 intake, 1.88 exhaust, closed, 108.9cc
Pistons 3999295 454 - LS6 - 1971 - 9:1
Crank 3963521 454 - 4 in stroke, 5140, raw forged (I guess now it could be a 4.25 until it is measured)
Rods ????
Now I was told that this motor was a 482 and I found it wrote on the crank balancer but that could have been an inventory number for all I know. A lot of the parts say it is but this one also has a roller cam and lifters with the roller rockers that were expected. It also has these rods that are floaters and the way the crank oil holes were chamfered and the rear rod bearings being a different size and the front cam bearing oil passage has a hole drilled through the block into it so oil will feed behind the top timing sprocket so it wont dig into the block with the roller cam.
Did I say I like 454's?

i did a little research it looks to be a 7.9 l 460 trs engine...it mentioned the oil paw was liquid cooled?? found this on the net..see if you can match some part numbers.. http://www.boats.net/parts/search/Me...%29/parts.html

That's what the numbers say it is and it looks like a LS piston. The guy I got it from kept saying it was a compression monster but that didn't fit the 482 profile. It's supposed to be a 9.1 to 1 but I'm starting to think this was not a factory build even though it has a mercruiser oil pan. Never saw a mercruiser come with steel freeze plugs and solid lifters.

Thanks Mike. I've see that but the years are much later and the numbers don't jive.

is the piston a flattop or does it have a dome?i think it is a merc built 482.that was one hell of an engine in its day.