Greetings!

We are assembling a project that is a 85.5 mm bored Evo 6 block. It does not have pistons/rings.

Highest target crank horsepower is likely ~450.

There seems to be a wide range of piston availability in this size with OEM rod length (150 mm) and 93 octane (max of 9 to 1 CR).

What forged piston offers tight piston to wall clearances (for low oil consumption/quiet operation) for street use. I do expect some road course use down the road, but street manners is priority.

Thanks.

Tim

 

Basically forged pistons are available in 2618 and 4032 alloy.
the second one allows tighter cylinder wall clearances, and are more Closer to in respect with your goals.
you may find easily more info about 2618 vs 4032 with Google help, or youtube vidéo by Mahle.

 

Mahle sells a 4032 allyo piston you can go with. But I don't have oil consumption issues with Wiseco 1400HP pistons with appropriate clearance and ring end gaps.

 

I use Mahle 4032 and so do few dear friends, I think it's wonderful option.
Quality is superb, light, quiet, robust.

 

Appreciate the responses.

It appears an appropriate Mahle is referenced here...one of the few that I could find piston to wall clearances too:

http://www.us.mahle.com/media/usa/mo...2-2020-web.pdf

I've never used Mahle and based my experience on domestic V-8's.

I see Summit has 930130066 and currently a $100 rebate...hmm. Give that some thought and discuss with the machinist to confirm these are acceptable (fit the already bored block, etc...)

Thanks!

 

I run CP pistons and have done 5 track days, run 15w 50 and have no excessive oil usage. The motor was built well

 

Another thought is a gapless 2nd ring like I have on my Wiseco 1400HP pistons
Max 2% blow by, No E85 etc gets into the sump. 2nd ring is the oil scraper
Many used gapless on the 1st ring, but that's not the choice by my eng builder

 

Oil consumption isnt really an problem regarding pistons and rings. Noise will be more an issue for the first 30-60 seconds after cold start.

Main problem is always the final honing.... and hard to get it right here in Germany. Too many here doing the honing like they did all the time.
We tried that different honings over the years...
Qiuck summary. Oil used is 10W-60 Liqui Moly
CP pistons with rings of the shelf in an brand new Mitsubishi block 85mm didnt had any oil consuption like an stock shortblock !
same of the shelf pistons in 85.5 in an bored and honed block ( 240 / 400 grid 2 step hone, std Stones for cast iron, Plataeu cleaning ) had app. 1Liter oil consumption for 1000 KM.
same of the shelf pistons in 85.5 in an bored and honed block ( 240 Std Grid, 600 Diamond grid soft, brushed final Diamond ) resulted in no Oil consumption like an stock engine.

The stock Mitsubishi hone is a lot finer and not as deep as an std. Hone aftermarket.

same as above with JE´s...

@Tim M you can send me an PM if you need any more information..many things are easier by PHONE...
BTW: there is something wrong in the Mahle PDF:
The very same piston is listed for Eclipse and Evo... but there is an difference in HEAD CC between these engines resulting in an different CR. ( 2G =47cc Evo = 43cc ) afaik

Example for an CP Piston: CP Pistons CP7228: 85mm, Eclipse 2G CR = 8.5 , Evo CR = 9.0

 

Correct, the head cc makes the CR difference, but pistons are still the same. Like the CP example, you will get the higher CR with the Evo head.
in the chart seems they use 47 cc for head, but also 1.3 mm head gasket whereas the OEM 3 layer is about 1mm.
I’ve created an Excel spreadsheet on my own to re evaluate CR.
In my case (94 mm stroke, 85.5 bore), I get 9.4 with 43cc head and 1.3 mm headgasket.
this is in line with the 0,5 CR gap advertised between DSM and Evo head.
I plan to CC my head to Check the commonly used 43 cc value for Evo.

Basically I would say you add 0.5 with 1.3 mm headgasket to the chart value, and 0.7 with 1mm headgasket

 

Yep, thats right thats its the same Piston... ( installed reversed )
A quick calculation for the Evo CR will be:

Piston 930130066:
2G = CR 8.62
Reduced headgasket 0.93 ( 5 Ply ) vs 1.3mm 2G
Head cc 43 vs 47 for the 2G
Final Evo CR 9.40

 

Lots of great information!

Believe we will lean toward the supplied ring package - as the costs to restore this vehicle are rising! We do plan to file fit the rings, if they allow (not too wide out of the box)

Today the machinist confirmed the bores are exactly 85.50. Unsure of the surface finish. Is there a surface finish rating (RMS) to relay to the machinist for the final hone?

My last location had E85 2 kms from the house...not now so 98/93 octane fuel it is.

Thanks a ton!

 

We visited the machinst and he had already progressed! Went and ahead and decked the block...ack. I wanted this to happen as there was an imperfection near the fire ring (from it getting bumped!)...but also just to start with a flat surface as I've read on this forum. He took off .1 mm. Surface finish is undetermined although he reiterated it was a fine finish - better than Mitsubishi. As were the bores (he did not touch).

Machinist agrees on Mahle so will get those ordered...of course Summit shows backordered 1 Dec. The package may come with additional instructions that I can relay to the German expert.

Thanks again.

 

Careful, Mahle pistons are not longer available in plenty of shops, some sales support said to me these products are discontinued !

 

AlexEvo26: Good to know. The Summit order is holding steady, but it is 5 weeks delay. Will have to keep a close eye on the status. Thanks.

 

I hope you’ll get them, in my case I have to switch to another option.