A question about compression ratios...

Extended Power said:
Deffinetly.
The more overlap you got, the more compression you can run, because you will lose the cylinder pressure when both intake, and exhaust valves are open at the same time. To a point, I guess...

Stock cams don't have near the overlap as a "Puller" cam, and can run higher compression, but in a competition engine, the boost isn't only 30-40psi....its 100+ psi.

.....just guessing:hehe:
Click to expand...
it's more like the more compression you have the less overlap you need.
 
The non IC pistons in a tight engine yield slightly over 18:1. Mine calculated to 18.2:1. Ran great. But the first time down the track, I blew the head gasket at 5 different cylinders. That was at 85-90psi. Engine makes somewhere in the 900s.

Upgraded to 625s and a second set of O-rings. So far, so good. But it hasn't been back down the track again yet.
 
.035, .050

Block was decked, and everything in the combustion chamber was ceramic coated about .003 thick.
 
Drothgeb said:
The non IC pistons in a tight engine yield slightly over 18:1. Mine calculated to 18.2:1. Ran great. But the first time down the track, I blew the head gasket at 5 different cylinders. That was at 85-90psi. Engine makes somewhere in the 900s.



Upgraded to 625s and a second set of O-rings. So far, so good. But it hasn't been back down the track again yet.
Click to expand...



286210 piston? Not sure exactly if that's the right number.
 
Those are about my exact measurements. Good to know it's still pretty high.
Also what all was coated in the combustion chamber ?
 
Maybe I missed which thickness head gasket was used? Thanks for sharing the info!
 
rightwinger said:
The article never mentioned a deck plate, and I think if my memory serves me right, the pistons were stock pistons that were milled down, this is probably where such high CR came from.
Click to expand...

jimbo486 said:
Ahh, I assumed a deck plate being a 6.4L. But if pistons were milled, then that's where it came from.
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Pretty sure milling the pistons down would lower the CR, not raise it. Using a thicker head gasket or cutting the pistons will lower it and decking the block or installing taller pistons, or pistons with a smaller bowl will raise it.
 
lowering the deck height and machining the pistons brings the bottom of the bowl up higher in the bore.. think of it that way.
 
I've noticed with mine going bfrom 16.8 to 17.5 everything has improved. Especially part throttle area... Been thinking about building a 20-22:1 Dmax... Though I'm pretty sure stock rods will have a lower hp limit aka bend sooner. Figure I'd have to build a mild 1000hp block to live at sustained 500hp
 
97rada said:
Those are about my exact measurements. Good to know it's still pretty high.
Also what all was coated in the combustion chamber ?
Click to expand...

Everything, head, valves, pistons.

95cummins5.9 said:
Maybe I missed which thickness head gasket was used? Thanks for sharing the info!
Click to expand...

That was with the .079" gasket, the engine is .020" over too. Just ran the numbers through the calculator, 18.21:1.

You could get 18.8:1 with the .010 over gasket. But that's really tight with a 188/220.
 
Drothgeb said:
Everything, head, valves, pistons.







That was with the .079" gasket, the engine is .020" over too. Just ran the numbers through the calculator, 18.21:1.



You could get 18.8:1 with the .010 over gasket. But that's really tight with a 188/220.
Click to expand...



Any pictures of the coating?
I didn't coat anything in this build. I stayed standard with .009 PTW and a .020 over gasket with 194/220 cam so sounds pretty similar. The block was decked .006. What pump are you using?
 
97rada said:
Any pictures of the coating?
I didn't coat anything in this build. I stayed standard with .009 PTW and a .020 over gasket with 194/220 cam so sounds pretty similar. The block was decked .006. What pump are you using?
Click to expand...

I did take pictures while coating. But the only thing I could find on Photobucket is of the head in my oven. I'll look around for the card with the coating pictures. The coating I used on the head didn't require oven curing, but I had it in the oven for a few hours at 200 degrees to speed up curing for handling it.

I switched to 13MM pump this year.

P1070391_zps76d5d77b.jpg


Smokem said:
Is that what you measured it to be?
Click to expand...

I measured them out to ~ 5 1/2 ccs, but it was hard getting it to within .2 ccs. Calculating based on dimensions came out pretty close though. I rounded down to 5 cc to allow for injector protrusion into the chamber.

Below is a screen shot of the numbers I used in the Wallace calculator. Bore is .020" over plus an extra .002" for clearance. I knocked .2 cc off the piston bowls because they were coated. Also, the deck clearance is -.038 due to .035 piston protrusion and .003 coating on the surface of the head.

P1090007_zpszvwfhbto.jpg
 
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