ptuomov

In case someone is interested in looking at some sub-par quality photos of nice turbo pistons, here they are. These are from Pure Performance Motorsports, the same firm that made my conrods.

These are forged 4032 alloy pistons, which will allow me to run really tight piston to bore clearances when combined with Nikasil coated aluminum cylinders.

The piston crown, the combustion chamber, squish area, etc. were sketched by me. PPM did the design and technical drawings, and of course made the pistons. The squish area should match the cylinder head pretty well, and the valve reliefs are deep enough for good cams. The piston top is symmetric, so I can use the same piston on both banks despite the 1mm piston pin offset.

The skirts have moly coating and are intended to be run on Nikasil cylinders. [edit: the rings are thinner than stock] I am going with Japanese rings from NPR. (More about those rings on a later date.) The top ring land is 8.75mm and second ring land 5.50mm. The second ring land has an accumulator groove which I didn't sketch there -- I am not sure the benefits in slowing down the pressure wave outweigh the cost of slightly weaker second ring land.

Top of the piston. Because of my Blackberry camera, you can't see the PPM Racing logo carved on the piston dish.:


The piston pin fasteners weigh 18g/8 per assembly:


The piston rings weigh 273g/8 per assembly:


Piston pin is 145g. The piston pin is heavy but extremely strong/rigid. It has 24mm OD, 14mm ID, and 5mm wall thickness, and 60.5mm length:


Piston itself is 502g. Of the 60.5mm piston pin length, about 2x16mm = 32mm is inside these rather massive looking piston pin bosses. (By the way of coincidence, my Nissan VK45DE also has 16mm active length for the piston bosses.) There are eight oiling holes, four on both skirt sides and none on the side of the piston pin holes, presumably to increase strength. Finally, I had them offset the piston pin by 1mm and plan to be running it the noisy Smokey way ;-) :



Altogether the weight cost is 18g/8 + 273g/8 + 145g + 502g = 683g. I couldn't go Sterling-light or anything since this is for a turbo engine, but I think this is a nice weight loss gain (not an oxymoron) over or more accurately under stock. The stock piston is 575g vs. PPM 502g and the stock pin is 180g vs PPM 145g. Making the assembly light wasn't the sole consideration, strength and detonation resistance was important as well. Altogether, I am expecting about 17% weight reduction and much improved strength from forged material located mostly in all the right places.

Next stop for these babies is under the hot spray of thermal barrier coating...

RicerSchnitzzle

Very nice. 100mm? What compression ratio will you end up with?

Ballpark cost?

ptuomov

100mm. I am trying to keep all key design parameters stock so that if something doesn't work, I am not SOL with all the custom parts.

The compression ratio will be somewhere between 8:1 and 8.5:1 depending on what happens with the heads. I'll cc the piston dishes tomorrow.

Why don't you make a guess about how much these cost? ;-) Forged steel 4340 conrods, ARP rod bolts, 8.3:1 forged 4032 pistons with moly skirt coating, and NPR piston pins, locks, and rings?

Lizard928

I am curious as to why you are offsetting the pin hole by 1mm?????

My guess would be between $3-4k USD for what you got.

ptuomov

I offset the wrist pin by 1mm to get a better rod angle on the power stroke. Kinda like the OEM but the opposite...

USD 2,500 plus shipping for the items listed (rods and piston assemblies) if you contact Thomas at sales@ppmrace.com.

Lizard928

That is a damn good price!

Though the only thing that I dont like about these pistons is that really fine edge around the intake cut out. That is going to get hot and work as a great ignitor.

ptuomov

I was thinking about the same thing.

It's so close to the wall and the head surface that it doesn't get particularly hot assuming the engine doesn't detonate. That's a big assumption... In other words, it's not going to cause pre-ignition but it may be a victim of pre-ignition or detonation.

The good news is that if after a couple of true expert opinions it's deemed not to be safe, it's really easy to just cut that wall down. With the huge top ring land width, that's not going to cause issues I believe. The minimum thickness between the top groove and the dish is also large, so the whole "eyebrow" is not going to break of no matter what. It's just that thin wafer at the edge that I may have to worry about.

In any case, whatever the decision, it will be made before thermal barrier coating.

entropy_engineering

Man I'm jealous. How much boost do you plan to run (or do you know)? Your Smokey Yunick reference is to running the pin offset the "wrong" way so the pistons are noisier from rocking but better on the cylinder walls right? I need to get some progress picks of mine soon.

ptuomov

More is never enough and too much is just right! My plan is to run more and more boost until the engine grenades and then back off a couple of psi. ;-)

entropy_engineering

Hey that's the right attitude! I bet you blow the driveline before the motor. Too bad you don't live closer I could have your gearbox cryo'd. (and axles....etc.) I've been cryoing cranks for these mitsubishi's I build and the output shaft for the transfer case with pretty good results. Hell, do the rotors too they won't warp slamming on the brakes from those high speed runs.

slate blue

Don't get the crown coated, it is on the way out that particular coating, Mahle has experimented with many coatings and in particular so have the teams they supply in Nascar and F1 and they don't recommend it. I have this on good authority and it is not just from mahle but another coater of F1 pistons.

Your pistons are 4032 as such your need for a coating is reduced anyway. Where you might go wrong is that if you hammer the engine when it is cold that might play havic with the clearances, I know the coating is supposed to help this issue, but just take it easy and properly cool the piston.

Greg

123quattro

That is not bad at all. Best case I would have expected $150/rod and $200/assembled piston.

ptuomov

I don't know about F1, but I think TBC coating of the piston tops is still a good option for a turbo conversion engine putting out 2.5 x the stock power levels. TBC coated combustion chamber makes more power in a turbo engine.

With TBC coating, 4032 pistons, and Nikasil I can run tight clearances so that really shouldn't be an issue.

Here's a question to you. They sent me what looks like wrong piston wrist pins with the pistons. I say they are wrong because they look too short. The piston wrist pin length is 60.6mm. The space between spirolox grooves is about 63.5mm. It's my understanding that a floating piston wrist pin should only have maybe 0.1mm free play betweent the spirolox clips. So the wrist pins should really be at least 63.4mm long and probably longer such as 2.5". Do you agree with me?

I did send them an email asking them about what the correct pin specs are about six hours ago but they haven't gotten back to me yet.

slate blue

Yes I agree with you, you have the wrong pins, don't use them under any circumstances, as to the coating it is not an F1 thing, the reason they don't use them is that there is a poor benefit risk ratio, they are also not used in Nascar. If the coating doesn't come off you wont have any troubles with it, in racing they did have problems.

Greg

entropy_engineering

I'm sure their are many many circumstances involved, but I've always been a big fan of coating pistons for turbo engines for the reduced crown temperature. You have me wondering about long term longevity now. I just had a 500hp mitsubishi engine sustain pretty healthy damage because the moly skirt coating came off really quick (like 50 miles) and clogged the little oil filter so quick the bypass opened and the bearings got torn up. Not my car, didn't have an oil pressure guage. No oil light no bad noises (till it was too late). I changed the oil once already before it happened. Teardown inspection made it look like the pistons weren't blasted before the coating was applied and it didn't bond properly. I plan to have a "discussion" about it soon.