Milling off top of stock pistons to drop compression??

BigYellowIron said:
Why would you take .100 off the top, especially on a CR? I would think (after looking at the spray pattern on a CR piston) that you would be getting close to spraying out of the bowl and on top of the piston. Then you add programing with timing. Looks like trouble to me, but thats just my thought.

What would the benefit be to cutting the whole top as opposed to just making the bowl a little bigger? I don't know, thats why I am asking.
:thankyou2:
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The 04.5 does not spray the fuel into the bowls edge like the 12, 24 and 03 engines do, but rather more into the center of the piston. The 04.5 and up pistons are not a classic re-entrant design. The fuel travels down the center of the piston like a skier going down a slope. Cutting material from the tops wont make the fuel spray outside the bowl, but does shorten the time the spray will be on the ramp up.

Its is a reverse design to the older engines that spray fuel toward the wall at the edge of the bowl that ends up re-entering or swirling backward toward the center. The 04.5 and ups spray in the center and swirl toward the outside.

This does not include the 6.7. It is back the other way like the 03-04 engines before.
 
There is a point you need to cut compression, thats for sure, that 900-1000 and up is around there.

Pumping losses get huge at high rpm/high boost/pressure ratio.

Bring the heat down, cylinder and egts.

Longer life for the head seal.

Spraying lots of water at a high CR motor will be another way to join the bendsy rodsy group.


Like Don said, the 04.5 sprays the fuel down the bowl, and it curves back up, towards the head.

The older-newer sprays the fuel at the outer part of the bowl, fuel curving down and back in.

Figured this out the hard way with diesel RK software, then the easy way with the can of brake cleaner and 04.5 piston/nozzle combo and the older cr piston/nozzle combo.

Was trying to figure out how my steel monotherms would like the 04.5 nozzle.
 
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Soup Nazi said:
The 04.5 does not spray the fuel into the bowls edge like the 12, 24 and 03 engines do, but rather more into the center of the piston. The 04.5 and up pistons are not a classic re-entrant design. The fuel travels down the center of the piston like a skier going down a slope. Cutting material from the tops wont make the fuel spray outside the bowl, but does shorten the time the spray will be on the ramp up.

Its is a reverse design to the older engines that spray fuel toward the wall at the edge of the bowl that ends up re-entering or swirling backward toward the center. The 04.5 and ups spray in the center and swirl toward the outside.

This does not include the 6.7. It is back the other way like the 03-04 engines before.
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Don, that explaination of the 04.5+ spray design sounds like the Exact reason that we have this aweful rattle!! Is it?
 
Big Swole said:
Don, that explaination of the 04.5+ spray design sounds like the Exact reason that we have this aweful rattle!! Is it?
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My opinion is its due to the large quench area above the piston created by milling down the top and adding a thicker gasket.

It will be interesting to see how Bean likes his pistons, quench tight, larger bowl. IMO thats the way to go, BUT 60cc's is a fair bit with one charger.

Seen a paper a while back the asians were doing some testing on compresison ratio, lowering it by cutting the top created rattle, lowering it by a larger bowl, no rattle.
 
Ya I am not thrilled with the 60 cc's but to get the bowl shape an diameter needed that was as small as we could get it. I am shooting for north ward of 1k hp but still on a single charger. I dont like super low cr on a single but its kind of a damed if I do damned if I dont deal.
 
We are all damned with internal combustion engines. The best we have is a silk purse from a sows ear in any of them. Every time I build a IC engine I always say: "One silk purse coming up" They are a joke! Probably not what everyone wants to hear I suppose.



Also, I "might" have a rattle fix. I might not. Still working on it.

So far I have an 03 Cummins and a 04 DMAX that sound like gassers. It was troubling to not hear the engine idle. They sound like Honda accords. Scary almost
 
Dang if it would have been a snake, it would have bit me. Look at my avatar for a visual explaination of the 04.5 and up engine's diesel spray configuration. The top portion of the avatar is a side view ( cross section ) of a modeled injection event of said injection system design. You can visually see the fuel sprays as they travel down the center of the piston toward the outer edge of the bowl for vaporization.
 
Soup Nazi said:
Dang if it would have been a snake, it would have bit me. Look at my avatar for a visual explaination of the 04.5 and up engine's diesel spray configuration. The top portion of the avatar is a side view ( cross section ) of a modeled injection event of said injection system design. You can visually see the fuel sprays as they travel down the center of the piston toward the outer edge of the bowl for vaporization.
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Wow, this whole time I figured your wife must be pregnant and you were really proud of the ultrasound. LOL

Interesting thread though.
 
How close is a stock engine to the advertised compression ratio?

Anyone ever take measurements as you tore down the engine and then compare the calculated compression ratio to what it was advertised at?
 
Joesixpack said:
My opinion is its due to the large quench area above the piston created by milling down the top and adding a thicker gasket.

Seen a paper a while back the asians were doing some testing on compresison ratio, lowering it by cutting the top created rattle, lowering it by a larger bowl, no rattle.
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I would want to agree with you, but there are members here with Stock Pistons that have the rattle like us decompressed guys...
How do we explain this, if it about lower compression???
 
GOT-Torque said:
How close is a stock engine to the advertised compression ratio?

Anyone ever take measurements as you tore down the engine and then compare the calculated compression ratio to what it was advertised at?
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yes , and the CR is in the 17.2 to 17.4 range
 
GRotman said:
Wow, this whole time I figured your wife must be pregnant and you were really proud of the ultrasound. LOL

Interesting thread though.
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Im with ya :hehe: I always did wonder what that was.......Just didnt want to sound stupid by asking LOLLOL
 
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