A question about compression ratios...

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rightwinger

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I was reading an article in "Trucktrend" about Brent Lorencza who had a VP powered 6.4 Cummins, and if my memory serves me correct he was running a 64/80 for compounds. The part of this article that really caught my attention was that his CR was 21:1......The article went on to say the truck is producing around 900HP, and the turbo set up makes 80psi of boost, and the only thing he has is 13mm head studs, no O-rings or fire rings. He said his low end power is great, and I would imagine so with that kind of CR, but my question would be, is that high of a CR going to limit how much timing you can give the engine? I just wonder how this setup would do on a P pump with static timing. If you want to read the article, just Google 6.4 Cummins Black sheep. I plan to build a 6.4 in the next year and am just trying to get some ideas and thoughts before I start buying parts. I'm still surprised that his head hasn't lifted with that much boost and that high of a CR, but maybe the variable timing with the VP makes this possible......
 
It's a stroked 5.9 (more that likely with a deck plate) so I wouldn't doubt the compression ratio increased accordingly.
 
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was not a deck plate engine.^

the engine that was in brents truck was the brain child of mike. he liked the higher cr. the turbos were another of mikes favorites, a k31 over an s4t. engine was torched a couple years ago with a bit too much nitrous.
 
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.
 
JlBayes,

Do you see anything wrong with running that high of a CR on a street driven truck? I would have no plans for Nitrous. Do you think timing would have to be significantly less than a 16 or 17:1 ratio?
 
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.
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Ahh, I assumed a deck plate being a 6.4L. But if pistons were milled, then that's where it came from.
 
I've got a VE'd 12V sitting here that's 21:1. I need to finish the head and pump and get it on the engine dyno this summer.
 
I'd be curious to hear how it runs for you and how you like driving it. I like the idea of having a higher CR, but don't like the idea of spending a lot of time and money building an engine, and then have to repair a blown HG......
 
It seems like combustion pressures would increase with a higher compression ratio, wouldn't they? If so, you'd certainly want to keep timing on the lower side to minimize even higher combustion pressures. You'd certainly want good studs or bolts torqued up well and maybe even an MLS head gasket to help seal off the cylinder.

Or am I way off and bass-akwards in my thinking?
 
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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mike makes his own pistons. not sure if this was a set of his welded up pistons or not. this was a vp based block, not a common rail.


rightwinger said:
JlBayes,

Do you see anything wrong with running that high of a CR on a street driven truck? I would have no plans for Nitrous. Do you think timing would have to be significantly less than a 16 or 17:1 ratio?
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i do not see a need for the ridiculous high compression ratio. i do see blocks and cylinder heads being an issue. brent broke a few blocks over the years. i can put you into contact with him if you'd like. he built the current transmission in my truck.
 
I just wonder if that high of a CR would hold up with with moderate boost and lower timing? It sounds like he was pushing this engine pretty hard. I would think fuel milage would be better on a higher CR engine like that as well. I'm also thinking if I did mill some factory pistons down, I could save a boat load of money as opposed to buying the stroker pistons for 1600 bucks.....
 
We deal with some farm tractor engines that were originally designed as a military engine. The compression ratio options were 16:1, 18.5:1, and 22.5:1. The 16:1 was military only, I've never dealt with them. The farm tractor pistons were the 18.5:1, and the military multi-fuel was the 22.5:1.

I've overhauled countless 18.5:1 engines and installed 22.5's in them. My experience is there is a huge improvement on every level with the higher compression. We've run them up to 7-800 hp like this. Better starting, more torque, better fuel economy, reduced smoke, you name it, it's improved.

Pretty much every 5.9 I've overhauled was originally 16:1 ish and I've put 17.5's in most and 18.5's in one. They've been better on every level also.

I realize that when you get to a point you have to have lower compression to make things live, this is all relative to less than 1000hp I would say.
 
Hasn't Zach Hamilton been playing with this as well? I've been thinking about pulling mine back apart as I've hated it ever since I converted to p pump and lower compression.
 
16:1 at 60psi is equal to 21:1 at 42 psi. Head gaskets, blocks, heads, ect do not scare me a bit. The biggest place the high compression shines is low end driving the charger.
 
cetanefreek said:
Hasn't Zach Hamilton been playing with this as well? I've been thinking about pulling mine back apart as I've hated it ever since I converted to p pump and lower compression.
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He did. I got the opportunity to ask him about it in his forum. Explanation is in the thread. Unfortunately the project was derailed by parasites. I know at least a few 2.6 engines run raised compression as well. It's something I wish I had some experience with. I'd like to try it at a modest level.
 
The cam used could be a factor no?


Lurking at this point but didn't see anyone mention it
 
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9724VF350 said:
We deal with some farm tractor engines that were originally designed as a military engine. The compression ratio options were 16:1, 18.5:1, and 22.5:1. The 16:1 was military only, I've never dealt with them. The farm tractor pistons were the 18.5:1, and the military multi-fuel was the 22.5:1.

I've overhauled countless 18.5:1 engines and installed 22.5's in them. My experience is there is a huge improvement on every level with the higher compression. We've run them up to 7-800 hp like this. Better starting, more torque, better fuel economy, reduced smoke, you name it, it's improved.

Pretty much every 5.9 I've overhauled was originally 16:1 ish and I've put 17.5's in most and 18.5's in one. They've been better on every level also.

I realize that when you get to a point you have to have lower compression to make things live, this is all relative to less than 1000hp I would say.
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Who makes the 18.5 pistons and is there higher cr pistons for the 5.9.
 
f6jbob said:
Who makes the 18.5 pistons and is there higher cr pistons for the 5.9.
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At one time Zach Hamilton had some 18-1 04 1/2 to 07 pistons. I wouldn't think he'd have any left. From there, most others are going to be forged, and not have the cast in ring groove.
 
REALPOWERSTROKE said:
The cam used could be a factor no?


Lurking at this point but didn't see anyone mention it
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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:
 
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