4032 Pistons for RB30 with 25 Neo head

[lolhax]

I am in the early stages of planning my RB30/25 Neo build - still trying to find a good RB30 block, they seem to be getting a little harder to get these days.

This will go into a ER34 which currently has a (tired) RB25DET NEO; but I won't be touching the engine that is in it until I have completed the new engine.

This will very much be a daily driver/gokart and would be quite happy making 350-400rwkw (even that's overkill), full boost at or around 3500rpm (max) would be my preference - I'm considering something like the EFR 8374 or perhaps the next step down.

I've read many of the threads and while there is some talk about these pistons I still have not managed to find a definitive answer for my preferred choice of piston material, 4032 pistons - smaller tolerances - ideally for the longevity, (slightly) improved detonation tolerance (over raw cast) and the fact that I would rather bore out that 25+ year old bore and replace the 25+ year old pistons, it seems logical to go with brand new pistons/rods... well aware of the general consensus that that the stock pistons and rods are good for 300rwkw.

For rods I will probably go with spool import conrods, for pistons it appears only Wossner and Mahle do a piston in 4032.

So my question being, using the RB25DET Neo head (we'll have to assume the head cc at this stage) and having a preference for around 8.75 - 9.0:1 compression ratio - does anyone have any recommendations on exactly which pistons would be required and exactly what work would need to be performed to the block - ie deck height (more so I know what I'm in for, ideally I would like to not have to mess with the deck height significantly more than a skim if avoidable)

Looking at the various catalogs it's very confusing in so much as I often cannot even find the pistons being listed on various retailers sites in the manufacturers catalogs.

 

Edited September 7, 2019 by lolhax

[Murray_Calavera]

I'm in a similar boat as you, I spoke with Supertech recently and they advised that around that power level their 4032 forged pistons would need about 4 and a half thou of clearance. 

I'm still looking into other options... I was hoping to run less clearance if I was going to be using 4032 pistons 

[Meathead]

Seems rather excessive for a high silicone piston. 

[lolhax]

Mahle specify a clearance of 0.0016" to 0.0024" (1.6 to 2.4 thou)

Wossner only appear to specify 0.07mm. (2.755 thou)

 

2 thou seems like an acceptable compromise, 2.755+ is getting a bit loose I rekon - what you can't gamble on is.... is this their accuracy confidence or them being excessively cautious. 

Stock clearance for a RB26DETT appears to be 1.377 - 2.16 thou and 0.59 - 1.377 thou for RB25DET... still quite the difference, also not sure why there is the difference between RB26DETT and RB25DET... more margin due to different piston composition or due to known higher factory PS rating?

 

Mahle Source: https://www.mahle-aftermarket.com/media/media-global-&-europe/products-and-services/engine_components/2016-app-guide-final-rev1-compressed.pdf

Wossner Source: https://www.woessner-kolben.de/fileadmin/Downloads/Kataloge/Automobil_Automotive.pdf

 

Edited September 8, 2019 by lolhax

[CowsWithGuns]

Hey mate, what path did you end up taking here and how did it go? I'm in a similar position.

[Old man 32 GTR]

7 hours ago, CowsWithGuns said:

Hey mate, what path did you end up taking here and how did it go? I'm in a similar position.

My rb30/26 was built using supertech pistons, was done a while ago, motor did around 50k making 350kw and 5k making 500kw. 
Had a health check done on the motor this week and came back perfect. 
Motor has little to no blow by and is insanely strong. 
Even on E85 I never got any noticeable contamination in the oil. 
And supertech rate them to 800hp I believe 

 

[Murray_Calavera]

What piston to cylinder wall clearance did you go with when it was built?