Piston Choices

[miekedmr]

Is there a comprehensive comparison anywhere between the different pistons available for the 7M? IE stock, wiseco, JE, ross
I know how they compare as far as compression, but I'm concerned with weight, length of the skirts, and any other differences that might effect their durability and/or the longevity of the motor.
I will put info here as I find it. Please correct/add anything, anywhere you can.

Weight:
Stock pistons.... 366g without
JE................... ~293g depending on bore
Ross................ 357 Grams
Arias(??).......... 310 Grams
Affects bottom ends ability to rev without snapping a rod/excessive wear. Reduction in mass also equates to a little bit of power and efficiency.

Skirt length:
Stock.............. long
Wiseco............ longest of forged
JE.................. short
Affects wear on bores, shorter causing more bore wear, usually not a problem within reasonable mileage.

Material Strength:
JE.................. stronger (21% stronger material than Ross, negated somewhat by having less material)
Ross............... strong
Stock............. stock...

Heat tolerance/expansion:
Forged pistons tolerate more heat in general. Forged pistons (usually?) expand faster than cast/hypereutectic pistons. Faster expansion means you need more piston-to-cylinder clearance (meaning faster wear + more noise, especially when cold. allows more blowby as well)

(hey this post is old but i just noticed a typo.)

 

[Justin727]

JBLmk3.com iirc. I'd go with wiseco because of the skirt is longer then ross, JE.. Not as much piston slap

O and They come coated

 

[souprat]

thats good info miekedmr.

 

[rakkasan]

I chose JE because they're the lightest of them all. Not only does it help with engine response, it also reduces wear & tear on the rotating mass too (especially the crank & rod bearings). Something not often thought about when choosing pistons......

 

[Justin727]

Key thing to do when you go with anything besides stock if its lighter which they all are. Is to get the motor BALANCED. Very smart thing to do. I went with different rods and pistons. All lighter then stock. Had everything balanced.

 

[rakkasan]

Key thing to do when you go with anything besides stock if its lighter which they all are. Is to get the motor BALANCED. Very smart thing to do. I went with different rods and pistons. All lighter then stock. Had everything balanced.

Werd! My machinist sent my entire rotating assembly (harmonic balancer to the pressure plate) to a guy in North Carolina so he could balance it. Skipping the balance would be suicide.

 

[brad92t]

just to add some info to this thread,

wiseco pistons, .020" oversized (.5mm) are right around 322-323 grams

 

[Supracentral]

I'm kind of tied up at the moment so I don't have time for a long post, however, in the post below towards the end there's some data about pistons that might be helpful:

http://www.supramania.com/forums/showpost.php?p=180719&postcount=18

and motor builds overall:

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

 

[Justin727]

good links Mike!

 

[spoolint78]

i went with ross pistons, because at 469usd i couldn't go wrong.

I got them coated as well.
In my opinion all the aftermarket ones are good.

Never really heard any problems.
And if you did, its in the build, not in the actual piston.

 

[ross1]

supracentral: i just read the first link and was wondering a few things about what you said, is there a way to i guess destroke the 7m yet bore out the cylinders and have it change numbers to match the 2jz (not necessarily match) but become higher revving and still reliable?

thanx,
ross

 

[miekedmr]

supracentral: i just read the first link and was wondering a few things about what you said, is there a way to i guess destroke the 7m yet bore out the cylinders and have it change numbers to match the 2jz (not necessarily match) but become higher revving and still reliable?

thanx,
ross

The HKS drag supra was destroked and overbored. Using a 5M-GE crankshaft to make the motor 2.8 liters has been mentioned. There is not a lot to be gained from overboring. Theres not much meat around the cylinders. You certainly couldn't match a JZ's bore.

Edit: Guess I'm wrong..

 

[Justin727]

not true. I know of a 7mgte with 2jz pistons in it. Bored out as much as you can. If something screws up in the block then thats it. Gotta get a new one!

 

[ross1]

so our block doesn't take to overboring very well i guess, obviously .2 and .4 over are fine but not too much bigger than that? so the destroking and overboring to create a higher RPM redline isn't a viable option... not seriously considering this just what the first link in supracentrals post said made me think if we could do this and create a higher redline and still be reliable.

thanx,
ross

 

[Adjuster]

Ok few points to consider.
1) The 7M block is different from one to the next. The only way to be sure your not going to have a bore size problem if you go larger than "stock" reccomended bore is to sonic test each bore to see how much material is there, then cut away to your chosen piston diameter.

2) RPM increase is not always the best way to increase power. (The head has some flow resistrictions, and higher RPM will just make them more obvious.) If your going to replace the valves with larger ones, and port the head, you might get more from the higher RPM ability.

3) The stock stroke and bore is not a disaster waiting to happen. (Contrary to what the 1JZ guys will tell you. There are many engines with larger bores and longer strokes than the stock 7M design, and with higher RPM limits.)

4) The larger the bore, the better you unshroud the valves, so you do get some added benefits from this besides the increase in displacement.

I've done both. Increased the stroke, and the bore. It runs fine, and I've spun this puppy up to 7150 with no parts flying off. (Of course I'm using forged pistons and billet forged custom rods, but it can be done.)

To get more flow from the head, you need bigger valves. There are a few ways to go about this. you could get a set of used 2ZJ valves and fit them to your head. (The stems have to be ground down to the right height, but this makes doing the valve job lash clearance easy for a good shop.) Or you can buy aftermarket valves that are larger. If you go 1mm or even 1.5mm oversize, you should be able to use the stock valve seats, but your going to have to port the head quite a bit to make use of the 1.5mm valves. (That would be the stock 2JZ valves BTW.)
I used 1mm OS stainless valves from some dude on Ebay, and they have been great so far.
I had the seats cut, then went back and very carefuly ported the runners and bowels to remove all sharp edges, and open up the exhaust ports as much as possible. (The valve guides are gone where they stick into the runner, and I opened up the runners to the size of the gasket almost. IMHO, you want some small sharp lip where the exhaust port dumps into the exhaust manifold as a anti-reversion point just like Toyota designed. (My tourqe numbers reflect this was a good choice, and guys who have completely port matched the exhaust side say they lost tourqe as a result.) to enhance the effect, I further ported the exhaust manifold to open up and create more turbulence after the gasket too.

So, back on topic. Bore/stroke/displacement or reductions of same and increases of RPM to get more power? (I'll take the larger engine any day of the week 99.9% of the time.)

This engine is so much fun between 3500rpm and redline it's scary. (Many times I'm bouncing off the rev limiter it's so smooth.) I really should get the TCCS re-clocked to raise the limit to 7500rpm or so and enjoy more power since I belive it's there.