good morning all, technical question for you guys. have a nos set of jahns 12 to l pistons . the box states that they are 4 in. pistons. would like to use these in my 61 truck block with the rods and crank. does anyone know if a 292 block will bore this far without sleeves. if so, what kind of cubic inches would it produce. also  with the new composite head gaskets, g heads , any thoughts as to compression ratio assuming no cutting of the heads or block? thanks for the input.

Deuce:

I have never seen a Y that would go to 4", although Speedpro says he has a block that sonic tested thick enough to go that far.  Head gaskets that don't overhang the bore will be a problem too.  I think the Best big bore gaskets will accomodate a 3 15/16 bore.

John

John - "The Hoosier Hurricane"

Was one of the big MEL blocks 4"?  368?

TC

You gotta have the right tools and know how to use 'em.

TC - Austin, Texas

thanks john, head gasket bore size never entered my mind, but is something to consider. dont know if jahns has an answer for that or no, but will inquire.

double check, make sure of pin size, could be chevy 327  or old 301 chevy stroker stuff, put in another box, I have alot of oversze 312 pistons, 3.900 or 3.920  jahns pop-up stuff. The biggest I have seen,  check pin size, all sbc are .927 pins

Po ol Davie

Sparta , Tn.

There’s been a few four inch bore Y-Blocks built over the years so it is possible.  Most were done by resleeving all the cylinders but there were a select few that got there by simply boring.  Circle track applications are where the 4” bore applications were the most common back in their day.  If anyone is needing composition gaskets for the 4+ inch bore Y’s, I do have them.

Lorena, Texas (South of Waco)

thanks ted, was thinking to be on the safe side, would probably have to sleeve the block. had an hours worth of conversation with my machine shop friday, and will be taking a block to him shortly. will need a set of head gaskets after the machining proves successful, and idea as to cubic inches this 292 will produce or compression ratio? thanks

Displacement for a 292 wih four inch bore would be 331.752, however it you want to get a little more you could use a 312 crankshaft machined to fit the 292 and 312 rods and pistons and get 345.836 CID. Sounds like a lot of money either way.

Jan  Urbanczyk  Major USMC Ret.

                                                                 Bowie Maryland

Compression ratio would be vary depending upon the piston design, installed deck height, and head cc’s.  But here’s a couple of scenarios.  Four inch bore with a 292 crank, zero deck, flat top pistons, and 68cc heads would be 9.88:1 static compression ratio.  Similarly a four inch bore with a 312 crank, zero deck, flat top pistons, and 68cc heads would yield a 10.26:1 CR.

Lorena, Texas (South of Waco)

do you have a number from the piston box???????  dont pistons usually have a part number somewhere on the undersie of the piston??????? Id verify those pistons first before you do any machine work.