So, Why Oval?

[CurtisEmery]

I do understand what he said and no there would not be any benefit of that much clearance for a quench. It would create big problems for you.

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This is an interesting topic. I have done a few engines with loose quench and no valve reliefs in the last couple years. The latest build had .120" piston to head 14:1 compression. Hasn't hurt performance in the least. The engine is more responsive than it ever was at 16:1. I should also add that the bowl design changed drastically from previous pistons to accommodate the increased quench clearance.

 

[Chevy1925]

This is an interesting topic. I have done a few engines with loose quench and no valve reliefs in the last couple years. The latest build had .120" piston to head 14:1 compression. Hasn't hurt performance in the least. The engine is more responsive than it ever was at 16:1.

What did you do for bowl design? Leave it alone? Widen it?

 

[CurtisEmery]

Quite a bit wider and shallower.

 

[Chevy1925]

We're these street motors or just competition?

 

[CurtisEmery]

We're these street motors or just competition?

Competition.

 

[Fingers]

If you made the bowl wider, you reduced the quench area significantly. Add to that, you were over the .075" that I have observed and I would understand it working.

The $50 question is how much fuel is getting to the cylinder wall.

 

[Chevy1925]

..

 

[CurtisEmery]

If you made the bowl wider, you reduced the quench area significantly. Add to that, you were over the .075" that I have observed and I would understand it working.

The $50 question is how much fuel is getting to the cylinder wall.

Exactly. I have a hunch that getting rid of the valve relief is gaining us some low lift flow as a side benifit. Last disassembly showed the fuel plumes we'll inside the bowl. How much is reaching the cylinder wall I can't say for sure. I haven't seen any signs of bore wiping or fuel dilution. I would love to try it on a higher comp Street set up and see how it reacts.

 

[S Phinney]

This is an interesting topic. I have done a few engines with loose quench and no valve reliefs in the last couple years. The latest build had .120" piston to head 14:1 compression. Hasn't hurt performance in the least. The engine is more responsive than it ever was at 16:1. I should also add that the bowl design changed drastically from previous pistons to accommodate the increased quench clearance.

My post was in regards to a quench change alone. It does not consider changing the whole equation to counter the big quench that you ran.

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[Fingers]

Exactly. I have a hunch that getting rid of the valve relief is gaining us some low lift flow as a side benifit. Last disassembly showed the fuel plumes we'll inside the bowl. How much is reaching the cylinder wall I can't say for sure. I haven't seen any signs of bore wiping or fuel dilution. I would love to try it on a higher comp Street set up and see how it reacts.

But, keep in mind that the ovals were about strength first. The wide flat bowls were/are weaker.

Everything is a compromise.

 

[Chevy1925]

But, keep in mind that the ovals were about strength first. The wide flat bowls were/are weaker.

Everything is a compromise.

even if you add material back into the bowl (or dont machine out as much from a blank) to flatten it out some and then cut the outer lip area down .130ish or so?

 

[CurtisEmery]

My post was in regards to a quench change alone. It does not consider changing the whole equation to counter the big quench that you ran.

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Sorry I should have been more clear in my original post. What I am getting at is I think getting rid of the valve reliefs altogether and adjusting bowl volume to reach desired compression is a plus. 1 it requires less machining and 2 I think it promotes more uniform combustion.

 

[CurtisEmery]

But, keep in mind that the ovals were about strength first. The wide flat bowls were/are weaker.

Everything is a compromise.

Definitely nothing comes without compromise.

 

[Verlon at ATP]

I will be pulling my ovals out of the race truck and running them in the LLY tow truck. Never saw any decrease in mileage with the ovals versus stock and race cast in prior motors.

These ovals have around 60k miles on them with never less than an 800hp tune. I will get some pics when they come out of the motor. I expect them to last a lifetime in the lly as they will live life at 650hp.

They were in the "Race" truck for 3 full years. 300+ 1/4 mile passes and a couple hundred dyno run's. They also have around 20k miles of towing on that 800hp tune. They are by far the best piston for the guy that wants the daily driven 1000hp truck.

 

[1slomax]

just ordered a set of these pistons for my lbz i cracked a set of mahle race casts and another set of the mahles in another engine, getting pretty excited after seeing all the goodluck with them hopefully they hold up for me i have bad luck with pistons lol

 

[Fingers]

I will be pulling my ovals out of the race truck and running them in the LLY tow truck. Never saw any decrease in mileage with the ovals versus stock and race cast in prior motors.

These ovals have around 60k miles on them with never less than an 800hp tune. I will get some pics when they come out of the motor. I expect them to last a lifetime in the lly as they will live life at 650hp.

They were in the "Race" truck for 3 full years. 300+ 1/4 mile passes and a couple hundred dyno run's. They also have around 20k miles of towing on that 800hp tune. They are by far the best piston for the guy that wants the daily driven 1000hp truck.

Glad to hear they are doing you well. It is kicking my business plan in the butt though. I rarely get to sell a customer more than one set.

 

[Fingers]

even if you add material back into the bowl (or dont machine out as much from a blank) to flatten it out some and then cut the outer lip area down .130ish or so?

It has been a while since I have run the analysis, but it is like you have to add 5-6 times the material in the bowl to make up the strength for what you take off the top. And then where you add it back is a big deal.

That is why the depth of the bowl varies on the oval bowls. High across the pin and deep at the ends. I have kept the material amount the same across the pin for all compression ratios.

 

[malibu795]

Glad to hear they are doing you well. It is kicking my business plan in the butt though. I rarely get to sell a customer more than one set.

Coming from the last 3 years been hotshoting.. And experience... And a guy that split a piston making less then 300hp...
Engine gets oval pistons before being put on the road.. Along with keyed crank/cam

But yeah.. The down fall of making a product that last... They only buy one...

 

[MarkBroviak]

I hope we help offset this issue Jon for you sir! 99.8% of our engine builds have your pistons in them and don't plan on that changing anytime soon! Side note, saw my first 5K+ psi reading on a set of them recently during a tuning session on the engine dyno. Will be very interesting to see what the pressure reading is on Brett's motor considering the setup it is on cast pistons. Will post the info as soon as I know for you. Thanks again Jon for the great job you have done, we really do appreciate it sir!:thumb:

 

[Chevy1925]

It has been a while since I have run the analysis, but it is like you have to add 5-6 times the material in the bowl to make up the strength for what you take off the top. And then where you add it back is a big deal.



That is why the depth of the bowl varies on the oval bowls. High across the pin and deep at the ends. I have kept the material amount the same across the pin for all compression ratios.

Oh I see! Thanks for the info Jon!