Updated/Current Oval Piston Roll Call!

[DieselDemon18]

Hello All!

Rather then try and bump up 5 year old threads if figure id start a fresh one (delete if not allowed please) and get some insight one these pistons.

Im getting ready to build my LB7 and was thinking of going with a set of cast ovals but im just wondering how well these are holding up to use and abuse? Information on them seems to be fairly scarce (which i hope is in a good way) now my truck is going to be a all in one package: daily driver, tow pig, fun toy, drag racer on weekends etc... now its only going to be 550-600 hp but just in case id like to have the capability to go up to 750-800 if i get i wild hare and decide to change it up but mostly i want the reliability and longevity and the ability to thrash on it when i want to without having to worry about it much.

In short, how are your setups doing? Getting good miles and reliability out of these pistons?

Thanks in advance.

 

[Ne-max]

Great pistons. Only thing I would run in a truck 800 plus hp. Some guys say the oval dish design hurts performance. Witch is hard to say. Buddy of mine made 1700hp with cast fingers.

 

[Chevy1925]

Great pistons. Only thing I would run in a truck 800 plus hp. Some guys say the oval dish design hurts performance. Witch is hard to say. Buddy of mine made 1700hp with cast fingers.

agreed. had them in quite a few engines as well as my personal truck.

 

[Bdsankey]

Great pistons. Only thing I would run in a truck 800 plus hp. Some guys say the oval dish design hurts performance. Witch is hard to say. Buddy of mine made 1700hp with cast fingers.

agreed. had them in quite a few engines as well as my personal truck.

3rd, they're the best cast piston for a high hp street truck. That said, at the ~800whp mark a set of Mahle motorsports cast pistons would do just fine.

 

[N2BRK]

Can't wait to find out! We bought a set for my buddy's build... waiting on machine shop for a few more weeks!! :woott:

 

[MarkBroviak]

Been north of 1700hp with them and deep in the 5's in the 1/8th with them. The only major thing between them and a round bowl is at low engine speeds/low airflow they are smokier, engine dyno testing has shown a too close to call on power differences to decide one way or the other. If you aren't going past 1300-1350ftlbs(this is far more important than HP) than the Race cast from Mahle will live for quite a while. I have more faith in these pistons than the factory block and crankshafts!:thumb:

 

[WolfLMM]

Around 10,000 miles on my ovals. 1200whp LMM. Sees 700-800hp everyday. I’m not easy on my daily. Plus I love the exhaust note from these pistons!

 

[JoshH]

I second 100% everthing Mark said. They are hell for stout, but they tend to be a little dirtier than a traditional round bowl. I also haven't seen anything to suggest they hurt overall performance though. If you are a primarily street driven truck that doesn't see a lot of competition and are making less than 1000 HP, I would look at the Mahle race cast pistons, but if you want the absolute strongest cast piston available that you have to make a few small concessions for, the oval bowls are the way to go. Just to be completely fair, they do clean up pretty decently with some time in the seat of the truck doing tuning, but they are difficult to clean up when the tuner can't see exactly what is going on (such as the typical email tunes).

 

[Harbin_22]

18,000 miles on mine 1,200+HP, kill tune is the only tune, goes wot at least once every time I drive it.

 

[KRODMAX/KS]

I have over 90k on my "fingers" Pistons at over 750/14xx ftlbs. They are dirty down low but clean up quick. Not easy on them either. Daily driver, run coast to coast draggin my wagon @ 7k lbs w Marks 68R/tuning.

 

[N2BRK]

If you wanted them to clean up a little, would you perhaps spec a little more CR? Just wondering out loud as I dream of a "someday" build.

 

[Chevy1925]

If you wanted them to clean up a little, would you perhaps spec a little more CR? Just wondering out loud as I dream of a "someday" build.

Nope, Adam tried that. Made no difference. Honestly it’s not that big of deal if you got a good tuner that can sit in the truck. I really don’t think my truck runs any dirtier on 100% overs lly and fingers compared to delipped lb7 and 45% over lb7 injectors.

I had more rattle issues with rail pressure and pilot fueling than I had with smoke

 

[juddski88]

The bigger the injector and closer to tdc you can inject with less duration, the more efficient these pistons will be. Just like any of the other pistons, but with less margin for error, in my opinion.

 

[Ne-max]

Tuning plays a huge part on smoke. Half of the well known tuners out there can't clean them up.

 

[MarkBroviak]

The haze/smoke down low has to do with the difference in swirl created in the cylinder and the fact that the piston has less surface area so there is less heat available in the cylinder. On a 1400hp engine fuel only we didn't see any appreciable difference from the cast ovals to forged round bowls other than the sound coming out the pipe! I built a 17.5:1 compression motor(In my ProMod currently) and it didn't help on the lowend smoke compared to my old 15.25:1 motor I used to run back in the day. Cylinder heads help/hurt this also.

 

[juddski88]

The haze/smoke down low has to do with the difference in swirl created in the cylinder and the fact that the piston has less surface area so there is less heat available in the cylinder. On a 1400hp engine fuel only we didn't see any appreciable difference from the cast ovals to forged round bowls other than the sound coming out the pipe! I built a 17.5:1 compression motor(In my ProMod currently) and it didn't help on the lowend smoke compared to my old 15.25:1 motor I used to run back in the day. Cylinder heads help/hurt this also.

That's an interesting take on it Mark. I'm trying to wrap my head around the less surface area part of that, but I can definitely envision the difference in swirl. It would be fun to machine a PC model and run some smoke through it.

 

[Fingers]

What Mark said about surface area is true. Depending on CR and a couple other factors, 10%-15% less surface. This makes them run cooler, especially at low load.

As far as CR is concerned, You don't get the bump from higher ratios in the Dmax for a number of reasons. The two biggest being heat exchange and the ability of the rings to hold back the pressure.

The Dmax, with it's aluminum heads and oil cooled pistons, tends to suck a lot of heat out of the combustion chamber into the cooling system. What drives this is the temperature differential between the hot gasses in the chamber and the hard metals. The higher the delta, the more energy the metals pull out of the chamber. When you bump up the CR, you increase the delta, and it eats up the efficiency gains from the higher CR.

For whatever reason, all the ring packages that I have seen for the Dmax are not exceptional at holding back the higher chamber pressures. So more CR means more blow-by.

 

[juddski88]

So the surface area being discussed is just the surface area inside the bowl, correct? And Jon, from a piston reliability standpoint in general, a higher Delta T is not optimal, correct?

 

[SickLL7Crenshaw]

From my experience on tuning ovals I agree with what’s stated above, CR really doesn’t seem to make that BIG difference on haze like you would think. Several other factors being played into it like Jon said, it just take a little of effort to get them clean. Haven’t had an issue though. Love how they hold up for a cast piston. I have several happy customers at 1k+ that daily them with 150%+ injectors as well.

 

[Fingers]

So the surface area being discussed is just the surface area inside the bowl, correct? And Jon, from a piston reliability standpoint in general, a higher Delta T is not optimal, correct?

The whole crown of the piston.

Delta T is a factor. How much the piston material absorbs is another as is how much area is exposed at a given time.