Pistons For Your Rb30

[ahh 33 s2]

what is considered too high of a comp ratio in a turbo motor

[Alf]

what is considered too high of a comp ratio in a turbo motor

Depends what fuel is being used.

For 98 pump fuel in Australian climate anything over 9.4 is getting a bit exxy with decent boost pressure.

I bought Arias 9.4 forgies before cc'ing the 25 head which was a mistake coz the volume of the bowls were smaller than std brining the comp up to 9.6

I've had to stuff around trying to source a thicker head gasket to bring it down to 9.2.

Tip of the week, get ur bowls in the head checked before you buy pistons.

[gtst25]

we just got a new set of mahle 40 thou oversize forged pistons from hi octane. They look very schmick!

Will be the first set of pistons used in one of the many rb30 builds weve done that hasnt come from CP.

Judging by the specs on the piston box i imagine it will net a comp ratio of about 8.2:1, same as the flat tops CP provide for the conversion.

Have you had any headway with the Mahle's?

Cheers

[The Ant]

Very good idea to put this thread up...1 question is, which is the better shape piston to use...dish top, flat top or crowned top pistons?

When I was building Cooper S engines 20 plus years ago I was lead to believe that dished tops were better because they captured the explosive combustion better not allowing as much blow force to spill over the outside diameter of the piston...(a bit like an upside down parachute) therefore producing more downward force on the piston creating more power...probably only marginally, but every bit helps. Also the shape of the dish helps keeps the piston more balanced and even under combustion load preventing less piston skirt wear on the bore. As I said, this is what I was lead to believe.

And Mahle pistons were the ducks nuts (the best) of pistons to be used...then.

Edited May 11, 2008 by The Ant

[richie$$$rich]

wisco's 8.5.1

Stock GTR Head gasket , stock head , cams and intake manifold

520hp on 20 PSI (street @ 8500rpm) , 637hp on 32psi C16 (race @ 9500rpm)

see for yourself. (I know its a VL not a skyline , but I also have a R32 GTR)

Behind a 2 speed power glide.

[unique1]

ok i am looking around for piston options at the moment and thought i better keep piston info in the one thread instead of starting a new one again.

I am loooking for a fairly cheap option in forged pistons, firstly i was thinking cp pistons but havent got great confidence in there rings at all and have these in my other rb26 motor and rings are causing some minor blowby issues i dont like. Ive been told the rings have been updated but still abit uncertain.

other options are the Mahle pistons and ACL Race Series pistons.

does anyone have the part no. for the 2 brands of pistons above to suit a rb26/30 and what sort comp ratio do they work out too.

ACL Race Series

Ive found part no. 6MKRY9608 from the ACL race series website and they qoute 8.5:1 cr on rb30et engine so i assume its gonna work out too low using a rb26 head?

anyone with suitable part noumbers of pistons to suit rb26/30 engines and have a reasonably good cr ratio can u post them up.

Mahle Forged Pistons

Mahle i found a link on ebay qouting this info...

Part#: NIS264425I05

APPLICATION: NISSAN SKYLINE GTS-T RB30DET TURBO

RB30DET 87.00 Bore, 85.0mm, 152.5mm, 21mm Pin, 32.1mm, 4.5cc dish, 312g, 8.5:CR

does that info sound correct or do u think they are qouted for a rb30et instead?

anyone running Mahle pistons besides R33_Racer? any opinions on them?

[TiTAN]

Using either the RB25 or RB26 head on the RB30 block you need to use RB30E pistons the RB30ET pistons will result in a far too low compression ratio to be much use as a street car.

[unique1]

Using either the RB25 or RB26 head on the RB30 block you need to use RB30E pistons the RB30ET pistons will result in a far too low compression ratio to be much use as a street car.

i realise that i was qouting the mahle website which said rb30det so i assume it might mean with a double overhead cam head setup, maybe it was a typing error from the ebay seller. The acl ones also had 2 versions for the rb30et, one being a 7.5:1 cr and the other a 8.5:1 cr.

[Sydneykid]

Mahle Forged Pistons

Mahle i found a link on ebay qouting this info...

Part#: NIS264425I05

APPLICATION: NISSAN SKYLINE GTS-T RB30DET TURBO

RB30DET 87.00 Bore, 85.0mm, 152.5mm, 21mm Pin, 32.1mm, 4.5cc dish, 312g, 8.5:CR

does that info sound correct or do u think they are qouted for a rb30et instead?

anyone running Mahle pistons besides R33_Racer? any opinions on them?

Pistons with a 4.5cc dish sounds about right for 8.5 to 1 using a 62 cc combustion chamber. We run flat tops for 9.0 to 1.

Cheers

Gary

[Stealth-Z]

What is everyone using for a compression ratio calculator? Perhaps I am using the wrong formula?

I have been using the four stroke version on Wiseco's website.

http://www.wiseco.com/Calculators.aspx

Here are the specs on the Wiseco pistons I have.

3.046 inches (86.5mm)

1.260 inch (32mm) Comp Height

16cc dome

The RB26 head I have measures out at 64cc's. The head gasket being used is a Cometic MLS 87mm. Cometic rates the thickness at .051 inches (1.295mm). My block has been decked and the pistons sit at a zero deck.

When I plug these numbers,

Bore Diameter = 3.046

Engine Stroke = 3.346 (85mm)

Head Volume = 64cc

Gasket Bore Diameter = 3.425 (87mm)

Compressed Gasket Thickness = .051

Deck Clearance = 0

Piston Effective Dome Volume = 16cc

With these numbers I get a CR of 9.69:1

My plan is to shave nearly 11cc's off the piston dome to bring the dome volume to 5cc. According to the calculator this would give me CR of 8.490:1. I have to face the reality of 91 octane premium fuel in my part of the world.

[xsv_32]

RB30e block, Factory 25de head, Wiseco gudgeon pins and forged pistons (40 thou oversized), Eagle rods. Wanting 9:1 comp ratio as running big boost but still want good response. Any suggestions on headgasket thickness?

[TuneR32]

i am running Mahle pistons in my 26/30 hybrid. i think they are 8.5:1 - no idea on kw output from them yet, as during the run-in my turbos went pop and meant my rebuilt engine had to get re-rebuilt.

on the good side, the pistons were completely undamaged despite the bore getting damaged, so i can vouch for their construction.

on the bad side, new rings had to be ordered from the USA as there are none available here (apparently).

will post again once it has had a tune for power.

[Spoolup]

3.046 inchs = 77.3mm

86.5mm = 3.4 inchs

that could be a problem

What is everyone using for a compression ratio calculator? Perhaps I am using the wrong formula?

I have been using the four stroke version on Wiseco's website.

http://www.wiseco.com/Calculators.aspx

Here are the specs on the Wiseco pistons I have.

3.046 inches (86.5mm)

1.260 inch (32mm) Comp Height

16cc dome

The RB26 head I have measures out at 64cc's. The head gasket being used is a Cometic MLS 87mm. Cometic rates the thickness at .051 inches (1.295mm). My block has been decked and the pistons sit at a zero deck.

When I plug these numbers,

Bore Diameter = 3.046

Engine Stroke = 3.346 (85mm)

Head Volume = 64cc

Gasket Bore Diameter = 3.425 (87mm)

Compressed Gasket Thickness = .051

Deck Clearance = 0

Piston Effective Dome Volume = 16cc

With these numbers I get a CR of 9.69:1

My plan is to shave nearly 11cc's off the piston dome to bring the dome volume to 5cc. According to the calculator this would give me CR of 8.490:1. I have to face the reality of 91 octane premium fuel in my part of the world.

[Stealth-Z]

3.046 inchs = 77.3mm

86.5mm = 3.4 inchs

that could be a problem

Ops, I transposd that one in to the post wrong. It should be 3.406 for the bore diameter. Inputing that number would give a 8.174:1 CR.

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.046 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume -16.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 3.399

Swept Volume 24.382

Compression Ratio 8.174 :1

Thanks for catching that error.

Not counting the typo in my copying, my numbers entered into the calculator still yeild the same 9.969:1

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.406 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume -16.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 3.399

Swept Volume 30.485

Compression Ratio 9.969 :1

I am still not understanding how it is possible to get around a 9:1 CR with flat top pistons.

Changing the Piston Effective Dome Volume to 0 will yield a 7.968:1 CR according to the calculator.

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.406 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume 0.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 4.375

Swept Volume 30.485

Compression Ratio 7.968 :1

What am I missing here?

Edited July 12, 2008 by Stealth-Z

[ahh 33 s2]

perhaps a different pin hieght is used

[Spoolup]

A flat top piston with a 1mm ( compressed head gasket - as in a std OEM ) will achieve 8.1:1 - 8.2:1 with your combustion chamber size. As does the CP flat top piston.

To achieve around 9.0:1 you will have to have an around 6 to 7cc dome on your piston.

Ops, I transposd that one in to the post wrong. It should be 3.406 for the bore diameter. Inputing that number would give a 8.174:1 CR.

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.046 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume -16.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 3.399

Swept Volume 24.382

Compression Ratio 8.174 :1

Thanks for catching that error.

Not counting the typo in my copying, my numbers entered into the calculator still yeild the same 9.969:1

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.406 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume -16.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 3.399

Swept Volume 30.485

Compression Ratio 9.969 :1

I am still not understanding how it is possible to get around a 9:1 CR with flat top pistons.

Changing the Piston Effective Dome Volume to 0 will yield a 7.968:1 CR according to the calculator.

Comp Ratio Calc For 4-Stroke Only

Bore Diameter 3.406 Inches

Engine Stroke 3.346 Inches

Head Volume 64.00 Cubic cm's

Gasket Bore Diameter 3.425 Inches

Compressed Gasket Thickness 0.0510 Inches

Deck Clearance 0.0000 Inches

Piston Effective Dome Volume 0.00 Cubic cm's

Gasket Volume 0.470

Deck Volume 0.000

TDC 4.375

Swept Volume 30.485

Compression Ratio 7.968 :1

What am I missing here?

[Phobic]

is anyone on here actually measuring the static compression of their motor or just using a calculator or what the specs say you should get?

[r33_racer]

when we get a motor that holds together long enough to inspect after a season of racing ill let you know how the mahles look....but after the last quick blow up with them in it, they seem like brand new, considering the amount of bearing material that was being rammed up its clacker!

[Stealth-Z]

is anyone on here actually measuring the static compression of their motor or just using a calculator or what the specs say you should get?

Mine has been apart for some time now. I have measured the parameters for the compression calculators. My first set of custom Wiseco pistons were flat tops with -5cc valve relief cuts. They were suposed to produce a CR of around 9:1. After measuring, the CR came out to less than 7.

[daisu]

Pistons with a 4.5cc dish sounds about right for 8.5 to 1 using a 62 cc combustion chamber. We run flat tops for 9.0 to 1.

Cheers

Gary

If your pistons are flat top then that means no dome/dish correct? Using the engine compression ratio calculator I'm having to enter values of -1mm deck clearance (piston sitting 1mm above deck at TDC) to get comp ratios of 9:1.

Does that sound right to you?

Is there a preferred choice in pistons in regards to dome versus compression height?

flat tops with higher compression height or domed pistons with lower compression height.

I've been looking at other possible sources of pistons, the SR20, 3SGTE, 1J and 2J series engines also share 86mm bore. Is it just a matter of finding something with the same wrist pin diameter? Or can that be overcome with use of different bearings?

I'm aiming for somewhere between 250 and 300rwkw, which I think forged pistons are overkill. I'd use the factory RB30 pistons but I want higher compression ratios. Would it be simpler to just deck the block and/or shave the head to remove approx 1mm?

Also, ceramic coating the pistons/combustion chambers, is that going to affect the combustion chamber volume or is the amount of change negligible?

[/so many questions]