Best way to lower compression ratio down to 18:1 on the 6.5 diesel

[6.2 turbo]

On my 6.2, I made a chamber between the valves,down to the valve seat. The heads were cracked between the valves,but I think they were that way. My 6.5 got the pistons shaved .045. It needs 30 sec of glow plugs to start cold. I think its lower than 18-1. Pistons are in the hole .035 .

 

[turbonator]

Back in the day we went for 50 thou piston to head clearance on the Chrysler wedge engines. The "squish" generated worked great allowing us to run higher CR's on the crappy gas of the day. Humm, oh yea we still have that crappy gas.

Un shrouding the valves on the 6.2/6.5 has the additional advantage of you dont have to touch the pistons, even pull then out of the engine. IIRC someone here has already tried this on a 6.5, remember reading it don't remember who.

The thread that I think of is a build for a suburban......the engine builder was Maxpf. Did a lot of work to the heads, then girdle and studs on the bottom end. Nice build, not sure if it is running yet though. Might be able to find it with Max's name, or the sub belonged to "Mikeyvon". Try a back search through the threads started by Mike. It is a good build, well worth the read.....

 

[L98TPI]

I like this idea of Unshrouding the valves but have actually never heard this term before. Any "quick" description of what this entails? 6.x engines arent know for their high qualtity heads so I would like to know where the metal would be taken from.

It involves opening the area between the valve head and the line the cylinder bore defines (gasket line). Generally three ways to do it.
1. All hand work with a grinder, takes forever. hard to be consistent (kinda important on a diesel), easy to screw up.
2. Use a fly cutter piloting on the valve guide to rough in, like cutting (not grinding) valve seats but all the work done above the valve seat, finish up with a hand grinder.
3. CNC mill them. Requires special equipment and programming skills, very accurate and fast once setup.

you're welcome!

 

[J.Peart]

I was under the impression they stopped making those 18:1 pistons

I tried to get a set for my rebuild and the supplier ended up coming back to me saying that the mahle 18:1 pistons were discontinued. I later talked to mahle, and it turns out the supplier had misunderstood. the 18:1 pistons weren't discontinued, just the .040 over ones i ordered. i dont know if that is all .040 over, or if they replaced the model. and this was a couple years back so i dont know what they are making now.

i ended up getting ones for a .010 decked block just to drop comp a bit. also have diamond precups. i found out later that they still made the 18:1s.