6.9 rebuild time

[trapper]

Well ive decided to rebuild my spare 6.9

currently i am breaking down the block to take to the machine shop
i will have it hot tanked magnaflux and Pressure checking
then i will aline hone the main bores and camshaft tunnel
followed by decking the block

the heads will be checked and rebuilt along with some port and polishing
new push rods ,valves, and lifters along with 7.3 rockers

i will be getting a new set of pistons looking for the low compression pistons, which will be ceramic coated

Ive been looking into hypermax rings, main bearings and rod bearings and pins

set of head studs and coated gaskets along with a turbo

Would you boar the engine 20 over ? or leave it alone ?

 

[icanfixall]

A 6.9 can safely be bored 20 over easily but don't do it if its not required. No sence wasting a bore on a block that does not need it. I don't see a reason to bore the cam bearing bore in the block but I would deck the block to true it up. Use either Victor Rienz or Felpro gaskts and do not install an oil pan gasket. These never came factory but some gasket makers sell them to unsuspecting customers anyway... That is something we need to stamp out fast. Use a quality rtv like permatex ultra copper plus. It has never leaked on any of my builds.

 

[86truckpull]

I would bore it to drop th compression even more so you can run more boost

 

[trapper]

im looking into getting the low comp pistons and also having them shaved i just dont know what the compression will be then

 

[86truckpull]

I'm not sure either but ik the more you can drop the composition in these the better so u can running hire boost the more forced air and fuel the better

 

[trapper]

which is why im watching bio's twin turbo ideas lol

 

[86truckpull]

That would be swee looking personally iv built cummins pulling trucks and I love the look of a big compound turbo but I doubt we could run 100psi in our trucks lol

 

[trapper]

id be happy with 25 psi

 

[hesutton]

Remember when dropping compression you certainly could lose power unless you compensate with significantly more fuel and air. Chris (diesel4me2) dropped his compression and was disappointed with his dyno results (in the FAQ's) with a hypermax turbo and with moose fuel.

How much of a drop is a good thing? How much and what fuel pump is needed to compensate and overcome the drop in compression? What turbo is best for low compression IDI? All good questions, but we don't really have the answers to them yet.

Eric's build with lower compression pistons, hypermax C-Ringed block, studs, and a huge S400 turbo with a 75mm inducer is a good test for these questions. But, he's not gotten the fuel sorted out yet and he's not put the truck on the road yet, much less on a dyno.

Just a few things to consider when dropping the compressoin ratio....

Heath

 

[trapper]

with the lower comp pistons what is the cpr without shaving them ?

 

[bike-maker]

What is the actual gain in lowering compression ratio?
I am fully aware this would allow more boost, but that would just be compensating for the loss of compression. The cylinder pressure is what shoves the piston down and makes power, right? I'm starting to think the limiting factor on these motors is the head gaskets. You can lower the comp. ratio, then gain the loss back by shoving more boost into it, but at a certain amount of cylinder pressure, the head gasket is going to let go.
So to the diesel guru's out there, what are the effects of having too much compression on a diesel engine? I know what happens on a gasser (pre-ignition), not sure about the diesels.
I think if there were a set of copper head gaskets available, and one was to have the block O-ringed (can't O-ring the heads because of the prechambers), these things could survive a whole lot more boost.
If the Cummins guys can run over 100psi boost, we should be able to at least get away with 25psi.

 

[88 Ford]

One thing to remember is that if you drop the compression you have to have the boost to compensate for it. What boost level is diesel4me2 running? But anyway 25 psi sounds like a good level to me. You just have to have a turbo (or 2) that will push that boost level for you.

 

[88 Ford]

What is the actual gain in lowering compression ratio?
I am fully aware this would allow more boost, but that would just be compensating for the loss of compression. The cylinder pressure is what shoves the piston down and makes power, right? I'm starting to think the limiting factor on these motors is the head gaskets. You can lower the comp. ratio, then gain the loss back by shoving more boost into it, but at a certain amount of cylinder pressure, the head gasket is going to let go.
So to the diesel guru's out there, what are the effects of having too much compression on a diesel engine? I know what happens on a gasser (pre-ignition), not sure about the diesels.
I think if there were a set of copper head gaskets available, and one was to have the block O-ringed (can't O-ring the heads because of the prechambers), these things could survive a whole lot more boost.
If the Cummins guys can run over 100psi boost, we should be able to at least get away with 25psi.

The limiting factor are the head gaskets for sure! I remember a thread that talked about this topic, but I can't quite remember what was said. What is the best way to go as far as head gaskets that are actually manufactured or are available?

 

[Knuckledragger]

While you are having the block aligned, honed and others, have the shop check the bore for runout. If it is within specs, no need for a bore job, unless you have already bought the pistons. These engines are cast from a special iron with high nickel content, it wears very well. I took apart an engine with 100,000 miles on it and there was no bore taper at all.

Also be careful when decking the block. The pistons already protrude and any more exposure can mean collision with the valves or head surface. If you deck the block, you now are obligated to cut the pistons, and if you are cutting them to reduce compression already, you run into low material conditions on the piston head. EGTs run up a little high and you have see through pistons with no compression at all.

 

[trapper]

well i am looking at the lower comp pistons without shaving them they will also be ceramic coated