LB7: Cracked Piston

[sickdiesel]

I run forged in my white truck and street drive it pretty regularly.

My builder has a LLY with over 45k miles on mahle forged and still no blowby. has dynoed over 1000 many times.

I have around 85 passes on mine at this point and around 2500 miles

I did forged so I wouldn't have to worry about them. we ran the same set of mahle forged in maxd out for 4 seasons in a row which goes round after round in the 9s

 

[Stingpuller]

Pistons

Going to try this.ROSS has one of the most complete selections of general purpose and specific use forgings in the entire custom piston industry. We make pistons from 2.283" (58 mm) through 6.190" (157.2 mm) diameter for hollow dome, flat top and dish top applications.

As can be seen in the photo, the lack of external features on the ROSS forging allows us complete freedom in machining special features for your pistons.

All ROSS Racing Pistons (since 1985) have been forged from 2618 billet bar stock and have been heat treated and aged to a T61 condition (2618-T61). 2618-T61 is the material that is used when fatigue resistance and durability are of prime importance by all premium racing piston manufacturers. This material has less than 1% silicon particulate content. High silicon content pistons (forged from 4032 or MS75) will not stand up to the most extreme stress placed on many racing pistons. If a crack starts to form in a high silicon piston it will continue until the piston experiences a catastrophic failure. Simply stated, adding sand to the aluminum only makes it more brittle. In the rare instance of a 2618-T61 piston cracking, the crack will continue to an area where the stress is not as great and will then stop. Another advantage of 2618-T61 over the high silicon pistons is the ability to keep its shape under extreme pressure and high RPM's. "Skirt Shrinking" is not a problem with ROSS Racing Pistons

 

[Stingpuller]

Pistons

I just used Ross so I wasn't being brand loyal. They each have there use. As a end user you need to pick what you think will best work for you.

 

[S Phinney]

Going to try this.ROSS has one of the most complete selections of general purpose and specific use forgings in the entire custom piston industry. We make pistons from 2.283" (58 mm) through 6.190" (157.2 mm) diameter for hollow dome, flat top and dish top applications.

As can be seen in the photo, the lack of external features on the ROSS forging allows us complete freedom in machining special features for your pistons.

All ROSS Racing Pistons (since 1985) have been forged from 2618 billet bar stock and have been heat treated and aged to a T61 condition (2618-T61). 2618-T61 is the material that is used when fatigue resistance and durability are of prime importance by all premium racing piston manufacturers. This material has less than 1% silicon particulate content. High silicon content pistons (forged from 4032 or MS75) will not stand up to the most extreme stress placed on many racing pistons. If a crack starts to form in a high silicon piston it will continue until the piston experiences a catastrophic failure. Simply stated, adding sand to the aluminum only makes it more brittle. In the rare instance of a 2618-T61 piston cracking, the crack will continue to an area where the stress is not as great and will then stop. Another advantage of 2618-T61 over the high silicon pistons is the ability to keep its shape under extreme pressure and high RPM's. "Skirt Shrinking" is not a problem with ROSS Racing Pistons

That is kind of the same ideas that i got when I read the article Fingers posted. The differences it noticed where the high silicon could excell were above 625 degree F. The 2618 did seem to be superior for the most part from how I understood it. Conversation like this does allow for us normal people to gather a better understanding of how things work. Thanks for the posts guys.

 

[Fingers]

There is more to my pistons than just the material. You need the additional 12% in material strength to handle the weaker bowl design. Actually, you need 30% to 50% more material strength.

I've thought of applying my design to other manufacturers, but have not made much headway on that. Ross, Arias, Mahle and the others all make quality products IMO.

 

[matt78]

I saw your oval bowls up close at josh h shop. Very nice

 

[Fingers]

Thx

 

[matt78]

Stupid question, sorry to the op its not my thread, I have .040 over pistons on a stock cam so does that lower compression somewhat? Again, I dont know so I am asking, thanks.

 

[Fingers]

Exact same chamber volume in the piston, it increases the compression.

With about the same .020" piston-head clearance, 17.5:1 becomes ~17.71:1

 

[Cknight199]

I just read through this thread and my mind is blown. Too much info to take in, so what would you guys recommend for an 750 hp build? It would see 700-750 as a daily driver and occasionally 1000+ hp or whatever I can get it to for a dyno run or two... I have always liked the finger pistons but haven't really researched in depth what to go with. It's my daily driver truck and I don't want to tear back into the motor... Ill be using my 72mm VVT turbo and prolly 60 or 100 overs.

 

[S Phinney]

I just read through this thread and my mind is blown. Too much info to take in, so what would you guys recommend for an 750 hp build? It would see 700-750 as a daily driver and occasionally 1000+ hp or whatever I can get it to for a dyno run or two... I have always liked the finger pistons but haven't really researched in depth what to go with. It's my daily driver truck and I don't want to tear back into the motor... Ill be using my 72mm VVT turbo and prolly 60 or 100 overs.

Most recommend to not use cast pistons for more than 800's on HP. As a daily driver that creates a problem when making more HP since you want a more durable piston. It is a catch 22. I will have to go forged but would prefer a better option. Every time you go into one of these it is going to cost more than three grand. Fingers cast pistons have shown promise for sure but I am not willing to chance it again on cast pistons. The turbo you listed should not make enough HP to get you into a problem cracking pistons unless you have a problem (aka extreme Philosophies) with your tuning. I would use Fingers pistons on a build like yours. Going into the 1k areas I would use forged or wait for steel monotherms which are not ready yet. I originally didn't think I would be in the 1K plus area. There really are not that many guys that regularly drive their truck and can make that kind of power. I do regularly drive mine but not everyday.

 

[MAXX IT OUT]

Hey fingers, could you get better blanks like Arias? I mean I see the strength in your design, but if people don't like the metal composition of the mahle piston, they could get the higher quality piston with the better bowl.

 

[yellowchevy]

For a daily driver/tow vehicle towing at around 500-600 hp, max of 700-800 hp would I be better off using delipped LB7 pistons or fingers piston? Or is there other options?

Sorry for the derail.

Yellowchevy

 

[S Phinney]

For a daily driver/tow vehicle towing at around 500-600 hp, max of 700-800 hp would I be better off using delipped LB7 pistons or fingers piston? Or is there other options?

Sorry for the derail.

Yellowchevy

Having to do this more than once now I would not use stock cut pistons. I know plenty guys do it trying to save a few bucks but usually in the end they spend more on replacing the failed ones.

 

[Fingers]

Hey fingers, could you get better blanks like Arias? I mean I see the strength in your design, but if people don't like the metal composition of the mahle piston, they could get the higher quality piston with the better bowl.

There are a lot of market reasons why I have chosen Mahle and the 4032. First, and most importantly, Mahle will play, and make their pistons available to me in a form I can use at a reasonable price. Second, Forged is less than 5% of the market. I cannot commit to 500 pc minimum orders or get someone to pay enough to cover the one off prices to get blanks to work with.

But really, there just isn't enough difference in strength at operation temperature between the alloys to matter. The Mahles 4032s ARE quality pistons.

I'm still waiting for someone to crack an Oval cast. I'm much less worried about the forged.

 

[yellowchevy]

Having to do this more than once now I would not use stock cut pistons. I know plenty guys do it trying to save a few bucks but usually in the end they spend more on replacing the failed ones.

I take it cast pistons would be better than cut stock ones?

Yellowchevy

 

[S Phinney]

I take it cast pistons would be better than cut stock ones?

Yellowchevy

Yes the aftermarket cast are better. If I were going cast I would straight to Fingers for his cast with his bowl design. It shows a lot of promise and is the best cast alternative out there.

Sent from my DROID RAZR using Tapatalk 2

 

[Cknight199]

Yes the aftermarket cast are better. If I were going cast I would straight to Fingers for his cast with his bowl design. It shows a lot of promise and is the best cast alternative out there.

Sent from my DROID RAZR using Tapatalk 2

X2! No one has cracked a finger piston yet, seems the right option IMO.

 

[TheBac]

X2! No one has cracked a finger piston yet, seems the right option IMO.

Just b/c nobody has yet, doesnt mean someone wont. Dont confuse those.

Nothing, and I mean nothing, in these engines is infallible. Everything has a breakage point. Luckily, nobody has found that point with Jon's pistons yet...and thats a good thing. But eventually someone will. Does that mean the parts are "crap"? Hell no.

 

[gmduramax]

I think Jon is onto something with the oval bowl, but his pistons haven't been proven. When there is a set that lasts 100,000 miles, has had 600 1/4 mile passes in the 10's with a truck that weighs 7000lbs that's when they will be proven. Until then a forged piston from arias is what I think is the best option for anyone going for 1000hp.