Best coyote piston for 12.5 to 1 compression

[twistedneck]

Looking for a piston that clears the valves without any machining. Goal is light weight for high spinning NA applications.

Looks like most builders have a preferred piston supplier.

What are the important options to get for rings, coatings, pins, etc..?

The only advertised 12.5 Cr piston is the Mahle cobra jet piece but I can't find that for sale.

 

[twistedneck]

Manley makes a +6.75cc 11.5:1 piston with the beter 2618 alloy, 4130 pin, very nice.

for a bit more money ($700 vs $500 a set) Diamond makes the +10cc 12.5:1 and +15cc 15.0:1 pistons. Same material as the Manley. Here are some cool pics form Livernois of the 15:1 setup.

15-1 coyote Photos by LivernoisMotorsports | Photobucket
Mahle makes a 10cc 12.5:1 piston also but i can't find any part numbers or information, it does use the same 2618 alloy. Not sure on pricing.
JE, CP, wiseco HD, how do those stack up?

 

[Modular Racing]

We offer 12.5 to 1 in the MMR/Manley Version, the Manleys are truly the highest quality piston, the same piston off the shelf from Manley is used in our 2000HP twin turbo coyote!

Let us know how we can help, we keep most bore sizes in stock but can custom order anything you need!

MMR
www.modularmustangracing.com

 

[twistedneck]

Here are some pics of the stock piston, MMR can you describe what is better about the Manley pistons? Why you guys choose Manley not Diamond, Wiseco, CP, Mahle....

Edit - more info on the stockers: Our pistons are a Mahle Al-Si hypereutectic alloy, low pressure cast with minimal after heat treatment apart from the coatings. Very similar to cast aluminum wheels alloy but stronger and more brittle due to the silicon, they don't need the heat treatment due to the super saturated silicon. they expand less when hot so they fit tighter and are more efficient, they also are lighter because you can cast an optimized shape vs. extensive machining needed on the forging (and a heavier Boss rod to hold on to it!).

The weight of the stock coyote 11.0:1 hypereutectic cast piston is a mere 361 grams (no pin or rings). That's about 40 grams less than a forged piston.

Dome is about 7.8mm thick, this application is clearly optimized for N.A. with a positive displacement dome and short top ring land. The big issue with a stock coyote piston is not strength, its plenty strong (hard), and it was superior wear resistance.. the difference is a lack of fracture toughness that leads to easier cracking and fracturing during detonation. Also, our cast piston cant cool itself well because the same silicon that helps make it a tighter fit insulates it from heat transfer. that's why the oil spray nozzles really help the cast piston and are not needed on the forged. finally, for huge rpm or cylinder pressures when temp is under control, the flow lines in the casting, poor distribution of silicon, clumps of silicon in some areas, metal front internal weld lines, these create stress risers in the metal and a fracture can occur that would not under perfect conditions of a forged piece.

Boss guys wanted a new piston mostly due to heat build up from excess friction at high rpm and the huge duty cycle, greater forces and accelerations from heavier weight, combined with less cooling with no sprayers to save on windage losses. Another reason why we should limit the rpm on piston sprayer coyote motor. or just go E85 and solve all the problems at once!

One thing I do not understand. On all the coyote pistons the valve reliefs are the same, about 33mm in diameter. Yet the intake valve is 37mm in diameter - so it must be the exhaust they are worried about only. that's got me a bit confused.

 

[by9468840]

as far as I know, in every blown up engine case, it was the rod that gave away first.
as long as the tune is spot on, the stock pistons never seem to fail.

 

[96lasersvt]

mahle pistons

The part number for the mahle cobra jet pistons is 930049901. They are for a 3.7 bore and with a .040 gasket the comp is 12.3:1.

 

[twistedneck]

the Mahle piston is for the larger bore NA cobra jet I believe.

for the boosted cobra jet i'm not sure what piston they are using or what compression ratio. my plan is a higher compression e85 boosted coyote, possibly 11.5 or 12.5 to 1. using the MMR block and manley pistons..

MMR, what are your thoughts on static compression ratio and 15+lbs of boost on e85?

 

[grnenvy]

I would go at least 11.1 unless u plan on running more then 15psi.

the Mahle piston is for the larger bore NA cobra jet I believe.

for the boosted cobra jet i'm not sure what piston they are using or what compression ratio. my plan is a higher compression e85 boosted coyote, possibly 11.5 or 12.5 to 1. using the MMR block and manley pistons..

MMR, what are your thoughts on static compression ratio and 15+lbs of boost on e85?

 

[Livernois Motorsports]

Coyotes LOVE compression, we can get you whatever your after compression wise. Power adder combo's or compression's over 12.5:1 really should be a 2618 slug.

 

[twistedneck]

Livernois, do you guys sell any NA only pistons with the short ring lands, thinner lighter body, etc.. i ask because all of the pistons except the 12:1 Mahle seem to be tanks built for FI.

 

[Livernois Motorsports]

We do not have a shelf stock N/A piston. We do however offer custom pistons based off of our years of mod engine experience.
"twistedneck" We can do a custom set for you with a bunch of N/A specific features.