Pistons For Your Rb30

[WMDC35]

Maybe better off to look for a good stocker?

[AngryRB]

you guys have a lot of confidence in 26+ year old engines, this engine I have was supposed to be a 1 owner 120k motor, so its a lottery finding that "good one", not sure where you

pick them up for a slab cause all wreckers want $700 for a motor.

[Glynn82]

I got mine for $150, it was running in a vl and pretty much ready to go. I have just finished rebuilding it, in

hindsight I should have just shimmed the oil pump and dropped a twin cam head on

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[Simon-S14]

can buy whole R31's for 400 bucks... driving and all. take motor out, sell r31 shell for 200... laughing

thats how you find a good ish one

[WMDC35]

you guys have a lot of confidence in 26+ year old engines, this engine I have was supposed to be a 1 owner 120k motor, so its a lottery finding that "good one", not sure where you

pick them up for a slab cause all wreckers want $700 for a motor.

Yes we do

[AngryRB]

pulled a piston out today, measured it and it has 21thou of wear on the top side plus 1.5thou on the bore, so that makes about 23thou piston to bore clearance,

why would someone sell a good R31 for $400 if it had a good motor in it? I think I must be in the wrong state, need to move down south for the goods..

[Glynn82]

23 thou is massive, I've never seen a running engine with slop any where near that! Mine had over 300,000 on the clock and I only rebuilt it for piece of mind and so I could ceramic coat everything

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Edited August 3, 2014 by Glynn82

[AngryRB]

If going forged, is it ok to go 88mm pistons if limiting power to 350kw's or will the block crack? would be extra torque for free

thinking about wisecos with the coated skirts, theres a few threads with mention of

tightening the piston to wall clearance down to as small as 2thou without issues, so maybe 2.5-3thou for a street application might be doable and the slap might be very

minimal. Using E85 the piston would be running cooler than 98, and not being on a track the pistons would have chance to cool down between floggings as you cant be drive flat

out on the street anyway or even at the drags for long.

Edited August 3, 2014 by AngryRB

[Glynn82]

Anything under 350 and I'd be using stock replacement with a piston to bore clearance of 1.3 to 2 thou. Remember it's the tune that kills engines.

I would seriously be listening to Simon-s14 though, he has had great success with rb30s

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Edited August 3, 2014 by Glynn82

[XKLABA]

Use as small pistons as possible, do not put 88mm pistons in a RB30, 86.5 or if you have to 87 after that get another block

I'm using the RB25 Wisecos and I tightened them up from recommended specs due to knowing it will be mostly on E85

[iruvyouskyrine]

How does E85 affect what piston to bore clearance you want?

[XKLABA]

I figurd the engine would run cooler, I also used a lower temp thermostat to keep temps down

Its just what I figured and worked to for my build, right or wrong who knows, but it seems to be working ok for me

[iruvyouskyrine]

You mean lower cylinder temps so less thermal expansion of the piston? I'm just curious, never built an engine or anything i just like knowing how things work.

[Glynn82]

I wouldn't go straight to 88mm but I wouldn't throw out a 88mm block either. Not ideal but for approx 300rwkw should be fine IMHO

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[XKLABA]

You mean lower cylinder temps so less thermal expansion of the piston? I'm just curious, never built an engine or anything i just like knowing how things work.

Yeah that was the idea

I've had a long day and not used to doing them so a little slower then normal on details tonight

The idea of the lower temp thermostat was to keep head temps down to try and reduce hot spots, I also found places where air could get trapped in the head water pocket and modified it to let it out

[XKLABA]

I wouldn't go straight to 88mm but I wouldn't throw out a 88mm block either. Not ideal but for approx 300rwkw should be fine IMHO

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Every one has a different idea on what's "safe" I personally would not use a 88mm bore in anything other then an N1 or RRR block

Given you can get a whole running original bore RB30 for between $0-500 I personally wouldn't risk it, but that's just me

[AngryRB]

There is a lot of forged piston designs and shapes , is there a shape of piston that is best suited to an RB engine, eg flat top compared to the stock design, and also with a neo or non-neo head?

Would a flat top piston be less likely to get detonation due to being more uniform with no valve cut outs and more efficient due to being flat?

Some pistons have the top ring landing closer to the top, is this preferred, and what about the silicon contents of the latest pistons on the market.

Apparently some BMW's have forged pistons and they are designed to be quiet and smooth due to the increased silicon content which is quoted to be 14 percent compared to old days of 7percent, and compared to stock pistons having 12.5 %.

Just like with turbo's, HTA's are getting a name for the design and effectiveness, what about pistons and the head design of the RB, which piston is the HTA version for the RB.

Edited August 20, 2014 by AngryRB

[iruvyouskyrine]

RIPS use flat tops in MGAWOT I believe so there is that. Must be some reason.

[Endless26/30]

im currently in the process of building a RB30DET (Forged 3.0l Bottom end, RB26 Head, GTX45, E85, Built C4). My engine builder has told me we want a 11.5:1 compression ratio because we are using E85. ill be looking to run 30+psi with this. Ive contacted Brad @ Spool Imports to see what pistons he can get his hands on that would get close to this CR. He reckons that they (CP Pistons) wont be able to fit enough Dome on the piston to achieve that. Another issue im looking at is, ill be running fairly high lift cams (between 9-11mm lift) so with such High compression im assuming ill have to fly cut the pistons which would lower the compression again surely. So what CR have people running high boost and E85 run and how did you achieve that CR (original CR of piston, work to block, HG thickness etc)?

also any hints on how to get as close as possible to my 11.5:1 CR?

[Ben C34]

im currently in the process of building a RB30DET (Forged 3.0l Bottom end, RB26 Head, GTX45, E85, Built C4). My engine builder has told me we want a 11.5:1 compression ratio because we are using E85. ill be looking to run 30+psi with this. Ive contacted Brad @ Spool Imports to see what pistons he can get his hands on that would get close to this CR. He reckons that they (CP Pistons) wont be able to fit enough Dome on the piston to achieve that. Another issue im looking at is, ill be running fairly high lift cams (between 9-11mm lift) so with such High compression im assuming ill have to fly cut the pistons which would lower the compression again surely. So what CR have people running high boost and E85 run and how did you achieve that CR (original CR of piston, work to block, HG thickness etc)?

also any hints on how to get as close as possible to my 11.5:1 CR?

Isn't the point of having an engine built by an engine builder the fact that they figure all that stuff out?