The Lightest Pistons, Hands Down

[gotsomegetsome]

I'm doing a rebuild of my 7mgte engine
plans:

800ish HP
new rods, pistons, oil sump, valves, springs, camshafts, headgasket, studs, thats for now off the top of my head

anyways, I've been reading up on pistons, and seems as though probe pistons are the lightest on the market for the 7m

can anyone chime in on this and either confirm or otherwise?

[honestabe]

Talk to Duane (UpgradedSupra). He can tell you what it takes to do 800 on a 7M.

[IJ.]

From memory the JE's are the lightest, make sure you're comparing the same sizes. ie: All std's from each brand or all +40's.
(some don't make std's so list their OS weights other list the std as it's usually the lightest)

[Keros]

IIRC, Doward never designed the Probe pistons to take 800hp.

[Zumtizzle]

Manleys look the lightest?

but they're rare.

[honestabe]

Edit, I was thinking of Duane's connecting rods.

[Supracentral]

Also guys, there's more to pistons than weight.

Silica content determines how much the pistons expand. Some forged pistons contain almost no silica. Other can have up to 11%. This changes the expansion rate and how much clearancing must be done for the skirts.

Ever wonder what makes a hypereutectic cast piston hypereutectic? Silica content over 12%. In fact most are 15 to 21%

Silica hardens the alloy the piston is made from. This increases durability. It also allows the top ring groove to be located closer to the top of the piston to reduce emissions.

But that comes at a price. The more silica, the more brittle the metal. Less silica? Higher expansion and more clearancing is needed in the build. This is why some forged piston motors sound like diesel engines when they start up cold. After they warm up and the pistons fully expand in the bores, they quiet down.

It's a balancing act. You've got to determine what you want out of your motor, the types of power adders you're going to use (turbo, n02, etc.), determine the RPM range it's going to operate in, and then select the piston that best suits the job.

Do you know that many manufacturers make pistons slightly elliptic rather than round? Some are up to .035" shorter across the wrist pin axis than the major axis to compensate for the different expansion rates in the area that has thicker piston mass by the wrist pin.

So to really work out what you want to do, if you want to truly "design" an engine rather than just "throw one together", you need to know not only your power goals, but how you are going to get there. What turbo will you use? What speed will you have to turn your little 3.0 liter motor to boost that big ass turbo enough to hit the goal. Will you use nitrous? Will you be able to live with the high boost threshold without it?

Get all of that together, then you'll be able to calculate things like mean piston speed to determine how much stress you're putting on the rods. You'll be able to tell if you need a piston that's more forgiving of detonation (low silica pistons take it better, but are softer overall).

What's the use of the car? Daily driver? Lots of cold starts? You might not want a low silica piston. Just a weekend driver? Maybe a loose bore with a more forgiving piston works better for you.

There's a lot more to this than just weight.

[Mk3runner]

my buddy who used to build engines for some place called toe performance. he always tells me when we build your engine you want your 7m loose on start then once warmed up drive it like you usually drive, this motor wont be for getting milk. as for expansion rates from hypereutectic pistons that we used on his 350 build they wont really move. kinda freaked me out when we were putting them in. far more stiffer feeling going down the cylinder than a forged would.


I'm not 100% today....what i typed seemed chopped up..

[Supracentral]

What luxury you have in the break in has a lot to do with how you build a motor.

I covered it here:

http://www.supramania.com/forums/showpost.php?p=182731&postcount=23

[gotsomegetsome]

i was thinking hypereutetic pistons would be smart considering their durability and that fact that this engine will be in an occasional weekend warrior but mostly drag car. But it seems JE pistons would be to my best interest.

so just to be safe, this is what I came up with

8000rpms, 45.5mm radius = 3261.45 G's ( units in terms of gravity in relation to radial acceleration) multiply that by 300grams for JE pistons, and thats one hell of alot of stress.

....i say 8000 rpms, just to be safe. This is why I wanted to figure out what the lightest piston would be for these uses. It seems like a forged alloy piston, non hypereutetic low silicon would be optimal. I dont think i would be too worried about warmup time, seeing as I would have plenty of time to do that on the weekends.

So lightest forged piston at 83.00mm bore?
probe? maybe not then

[Doward]

I think JEs are where you need to be looking.

[IJ.]

His criteria was "lightest" ;)

[Doward]

Ian, are you thinking of the Ross pistons? ;) I think the JEs are in the neighborhood of 293 grams, aren't they?

[IJ.]

Can't remember John but they were one of the lightest available back when I was doing research and decided on the Ross.

I knew I was going to break parts and wanted something "solid" then when I got a handle on what the 7M needed and had a clue about setting up my ECU I changed over to the JE's.

[Supracentral]

JE's are advertised at 293 grams.
Ross are advertised at 357 grams.

Either way I find the JE to be a better piston overall. Without going to the expense of something like Arias, JE is almost always a good choice.

[gotsomegetsome]

does anyone know the skirt length on the ross's?

[Adjuster]

Light pistons are good, but just buy the best rods possible, and don't worry about it. ;)

Pauter rods will work with any pistons available, regardless of the weight, or your planned RPM goal for the 7M based engine. (Within reason of the bore and stroke possible on this motor.)

I have 84mm bore ROSS pistons and the Pauter rods swinging on 97.5mm crank throws at the stock ECU RPM limits, and it's worked great so far.

I think if I was going to do it all over again, I'd just build a 7.0L twin turbo LS6 engine at 9:1 static CR, and two T70 Masterpower's with a goal of 1100rwhp on pump gas.

In the end, it would be cheaper.. LOL (And allow for an easy hook up to a 4 or 5 speed auto trans built to handle the power etc.)

But then again, building an ultimate 7MGTE based engine has been a learning process that I'll soon not forget. (There are some expensive things learned along the way, that is for sure.)