Oval Chamber Pistons

moparkxracer

moparkxracer

Well-known member
Jun 25, 2010
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Agree

If you plan on or are thinking abt going with different stuff latter down the road, just save and do it the way you want it to begin with. You will save a lot of money and extra labor in the long run. Mine has been a work in progress for along time.
S Phinney said:
Every time you tear into the motor you will spend 1000 bucks even if you don't change a thing. Not many people start out and stay there. They always want more. So it is wise to build around growing and you will save money I the end. Lower compression helps protect the piston from damages. Too low and there is problems when used daily driving. Street use 16 to 16.5 is a good place to be.
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K

Kramer

Member
Sep 3, 2014
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Hornell, NY
Mark, what were you seeing for fuel mileage with these pistons and your 72mm vgt? Most of this trucks life will be daily driving, also a lot of highway driving. I don't plan on drag racing a lot, probably never going to sled pull. I guess I'm more worried about fuel mileage and engine manners at 550 to 600 hp on a daily driver tune rather than longevity at 1k+ since the truck won't see high horsepower tunes very often at all.

This is a lot of great info, thanks again guys.
 
duratothemax

duratothemax

<--- slippery roads
Aug 28, 2006
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S Phinney said:
Every time you tear into the motor you will spend 1000 bucks even if you don't change a thing. Not many people start out and stay there. They always want more. So it is wise to build around growing and you will save money I the end. Lower compression helps protect the piston from damages. Too low and there is problems when used daily driving. Street use 16 to 16.5 is a good place to be.
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Couldnt have said it better myself Shane! Especially that first sentence. :thumb:
 
H

Hot COCOAL

May the farce be with you
Jun 9, 2012
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Kramer said:
Mark, what were you seeing for fuel mileage with these pistons and your 72mm vgt? Most of this trucks life will be daily driving, also a lot of highway driving. I don't plan on drag racing a lot, probably never going to sled pull. I guess I'm more worried about fuel mileage and engine manners at 550 to 600 hp on a daily driver tune rather than longevity at 1k+ since the truck won't see high horsepower tunes very often at all.

This is a lot of great info, thanks again guys.
Click to expand...

The guys Mark is talking about aren't worried about fuel economy
;)

If you're planning to have a hot street truck and maintain economy, you tow and want to keep the power band closer to or in a stock more street friendly RPM range, I'd suggest you stick to 16.5/1 CR for under 750whp goals. If you are wanting to make 750-1000whp I'd suggest to use a 16.0/1 CR or even a bit lower if you're using it at it's max potential frequently. If you're going to be racing allot and going for big power and lots of boost with twins, I'd say 15.5/1 CR or lower is what you're after

Basically, the more power you wanna make and faster you wanna spin the engine, respectively the lower the CR you should pick.

For your goals and usage at 600whp you'd be fine with a stock compression ratio of 16.8/1 but most guys will suggest to drop to 16.5/1

Just keep in mind that CR is like free horsepower and relative to your throttle response, so if you're looking for a more streetable tow friendly rig running a single charger I wouldn't go too low on the CR
 
rgullett83

rgullett83

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Oct 27, 2008
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I should have mine up and running in the next few months. 16:1 with reliefs. I will update my other thrread as i progress.
 
Fingers

Fingers

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Apr 1, 2008
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The biggest thing against higher CRs is the beating it puts on the bottom end. IMO

I'm not worried about the pistons. They have been proven to be fine so far. Seems we have moved the weak link to other parts of the engine.

However, you get into leak-by increases, pumping losses and a lot of other things that take away from the theoretical efficiency gains of the higher CR. If you are going to lean on the engine, you better back off what you can stand in the compression ratio department.

I like to see the street warrior around 16.5:1 for their builds. They don't run stupid boost and they then don't have to tune around the compression ratio for the daily commute. Anything higher is a waste. Noisy too. Lower requires a deft hand in the tuning department. 16.5 is a good compromise.

I currently have way too much compression in my engine. Some day, I plan to tear it down and re-cut the pistons. (Oval set #1 BTW)

Finally, this is all my opinion. YOU the builder have to decide what specs to build your motor to. No one else makes the call, no one else lives with the result.
 
Cknight199

Cknight199

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Aug 23, 2012
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So tell me this about c/r. I heard sled pullers use a higher compression ration because they can make more power with a higher compression rather than a lower one. But I have also heard that a looser compression will let the motor live longer? My question is are these myths, or facts? Stock is 17.5:1 correct? If someone were to say run a HUGE single turbo and go for big hp, would a lower compression ratio help, or rather not help. And does compression ratio have anything to do with egt's and spooling?
 
H

Hot COCOAL

May the farce be with you
Jun 9, 2012
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Stock CR is 16.8/1 for the duramax.

Well the rule of thumb is the higher you can run the compression, the easier it is to make power... But at some costs.
Cylinder pressure is one
Exponentially greater force to the bearings as CR goes up
Noise...
Engine heat usually increases from the greater CR

I'm not sure if your EGT's would be much different in boost or at peak power cuz fuel is the power source and it takes a certain amount to make the power, so 1200hp is 1200hp from my understanding.
I bet you'd have a greater EGT spike coming on boost with a lower CR

Running a lower CR is fine as long as you can stuff enough air in the cylinder to make up for the AFR needed. So as long as you've got a turbo(s) that produce the air volume and "boost" you can make good power with a lower CR

Higher or lower, you can make power both ways. I think you'll get longer engine life at a lower CR than higher because there's less stress on all the parts.
I also think you can make more power on a lower CR because of this. Meaning it's easier to cram more air into the cylinder than it is to up the CR.
 
S

S Phinney

Active member
Aug 15, 2008
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Cknight199 said:
So tell me this about c/r. I heard sled pullers use a higher compression ration because they can make more power with a higher compression rather than a lower one. But I have also heard that a looser compression will let the motor live longer? My question is are these myths, or facts? Stock is 17.5:1 correct? If someone were to say run a HUGE single turbo and go for big hp, would a lower compression ratio help, or rather not help. And does compression ratio have anything to do with egt's and spooling?
Click to expand...
Higher compression will help with spooling characteristics and will make more power. There is the point of reliability so cast pistons tend to Crack easier under higher c/r. Higher boost does the same to cast pistons. With Fingers oval design he has made a more reliable piston than has been on the market. In pure competition trucks most go with forged for two reasons. They are substantially lighter and are less likely to break.
 
MarkBroviak

MarkBroviak

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May 25, 2008
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Dyno sheet

Here is the dyno sheet for you guys to see. The highest we have dynoed the forged was 1,2xxhp in 2.6 truck. We haven't had an open opportunity to push them in the forged state, been more so trying to see how far the cast version will go before they fail. My personal goal with them is 2,000hp on the cast pistons. We will see if we can get there at some point hopefully soon.:thumb:
 

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Fingers

Fingers

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There are very few Forged Ovals out there. Besides none breaking, there isn't anything earth shaking to tell....yet.

Still waiting for someone to break a cast Oval piston. That will at least set the HP mark for when to switch to the Forged.
 
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