Rb30 Whorethread

[StevenCJR31]

does anybody have the part number for the (CP?) pistons that increase the CR up from normal the 8 point 3 to 1 (25/30)

[Gerg_R31]

You do know its not just the pistons that contribute to compression ratios? Head cc's gasket thickness x gasket bore, piston top to deck height piston domes / dishes/ valve reliefs

for example

bore 86.5mm stroke 85mm

Gasket 1.5mm x 88mm

0.004" piston above deck

5.1cc piston dome

62cc head chamber

all this equals 8.49:1

[zebra]

Still no Word on the 3.4 Stevo

[StevenCJR31]

You do know its not just the pistons that contribute to compression ratios? Head cc's gasket thickness x gasket bore, piston top to deck height piston domes / dishes/ valve reliefs

for example

bore 86.5mm stroke 85mm

Gasket 1.5mm x 88mm

0.004" piston above deck

5.1cc piston dome

62cc head chamber

all this equals 8.49:1

of course your right, everybodys engine would have a slightly different CR, i remember reading on here (somewhere!) there was a piston that increased CR to over 9 to 1 (or more)that would fit in better with my intention to run E85

[TiTAN]

they were posted in the RB30 thread.

[TiTAN]

I updated my piston list from P221

Added a new p/n for a flat top piston from Arias and added compression ratios for the Arias pistons. Two are quite high for a turbo engine!

CP

All compression ratios are based on zero deck height, 1.2mm head gasket (7.13cc), RB25 @ 62.5cc, RB26 @ 64.5cc. They assure me they have done alot of work to make sure the facts are correct.

p/n= CP-RB30/26-.20

Flat top with no valve pockets

8.2:1 COMPRESSION RATIO with RB25 head and bit less with RB26 head

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize but can be custom ordered in any size.

p/n= CP-RB30/26-.20-9.0

6.0cc dome top,

9.0:1 COMPRESSION RATIO with RB25 head and bit less with RB26 head

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize but can be custom ordered in any size.

*Care must be taken when using on RB26 with more than 11.5mm valve lift*

ARIAS

Suit RB30/26

p/n= AP332103

flat top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 8.4-8.6

Suit RB30/26

p/n= AP332104

10.6cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.2-9.4

Suit RB30/25

p/n= AP332105

13cc dome top

21mm pin

1.280" compression height

Only stocked in 0.20 thou oversize (86.5mm).

COMPRESSION RATIO 9.5-9.8

WISECO

Skyline RB30 w/ DOHC RB25det cylinder head

1.260" compresion height, 66.5cc head chamber, Dish top -11.3cc, 7.0:1 compression ratio, 21mm pin, 1mm gasket thickness, 1mm deck clearance.

K577M865 86.5mm

K577M87 87.00mm

ACL

6MKRY9608 (VL turbo)

87mm, -4.5cc dished top, 1.261" compression height, 21mm pin,

Standard RB30ET pistons are 7.8:1, with RB25 head it is 7.1:1

These are bumped up to 8.5:1 so with the RB25 head it may give about 7.5:1??

Using http://www.csgnetwor...m/compcalc.html I came up with 8.5 for VLT (spot on) and 7.6 with twin cam head with 64cc chamber.

I entered: 2, 87, 85, 87, 1.2, 64cc, -4.5cc = 7.6:1

BUT these have a lower compression height than the CP/Arias and im sure it stuffs up my calculations but its late and im too tired to look at it any more...

[StevenCJR31]

thats the info im chasing,will print it off at work today, thanks Titan!

[Gerg_R31]

Titan's info states what was used to achieve the ratio's with that brands piston,

If you put them pistons in without checking everything else matches there is a strong chance the ratio WILL be different.

The example i used with the piston sitting above was done without even machining the block which is common. machining everything to suit the pistons manufactures specs wwith the piston above would have equaled 8.75:1

[StevenCJR31]

Titan's info states what was used to achieve the ratio's with that brands piston,

If you put them pistons in without checking everything else matches there is a strong chance the ratio WILL be different.

The example i used with the piston sitting above was done without even machining the block which is common. machining everything to suit the pistons manufactures specs wwith the piston above would have equaled 8.75:1

fair enough, will make sure chambers are cc'ed and everything else is checked before the pistons are ordered, just looking for a build where i have good off boost response by having a reasonably high CR, will be using a R32 RB25DE head on a series 3 R31 RB30E block and would rather buy the correct pistons without having to excessively machine the block and head

Edited September 20, 2011 by StevenCJR31

[R32Abuser]

fair enough, will make sure chambers are cc'ed and everything else is checked before the pistons are ordered, just looking for a build where i have good off boost response by having a reasonably high CR, will be using a R32 RB25DE head on a series 3 R31 RB30E block and would rather buy the correct pistons without having to excessively machine the block and head

Just put the CP 9:1 pistons in my R32 RB25DE head with 30 bottom end.

Still yet to drive it or do a reasonable power run. Will post results as soon as they become available.

Either way, make sure EVERY SINGLE measurement that can be taken is carried out. My builder/assembler didn't measure the head cc and we had issue with pinging. Hence we didn't know for sure whether its was too higher static CR. Turned out it was timing (or base timing) and CAS. Pays to make sure and check things before its too late!

Edited September 20, 2011 by R32Abuser

[StevenCJR31]

Just put the CP 9:1 pistons in my R32 RB25DE head with 30 bottom end.

Still yet to drive it or do a reasonable power run. Will post results as soon as they become available.

Either way, make sure EVERY SINGLE measurement that can be taken is carried out. My builder/assembler didn't measure the head cc and we had issue with pinging. Hence we didn't know for sure whether its was too higher static CR. Turned out it was timing (or base timing) and CAS. Pays to make sure and check things before its too late!

bugger . . hope you had words with the builder, when i ve got my 25/30 together im making sure the tuner will have every scrap of info i can provide on the motors specs so i get the best tune possible, dont plan on spending the $ twice

[Gerg_R31]

My biggest issue with working in a machine shop is "can you organise pistons with a 8.5:1 compression ratio" "what head CC's do you currently have? "oh no, i don't want any head work done"

then they come back saying they had issues and their mechanic says that their comp was too high too low cause problems etc we organised the wrong pistons, we don't know how to do our job, we owe them a new motor etc

if measurements are done right or to match the figures the piston manufacture suggested there won't be an issue and the job will be done right the first time and everyone is happy

[zebra]

My biggest issue with working in a machine shop is "can you organise pistons with a 8.5:1 compression ratio" "what head CC's do you currently have? "oh no, i don't want any head work done"

then they come back saying they had issues and their mechanic says that their comp was too high too low cause problems etc we organised the wrong pistons, we don't know how to do our job, we owe them a new motor etc

if measurements are done right or to match the figures the piston manufacture suggested there won't be an issue and the job will be done right the first time and everyone is happy

This is exactly why Many brands of pistons for V8's dont give comp ratios, all they give is dome/dish volume pin height and bore.

Its then up to the builder to work out what the chamber volume is with head gasket fitted /deck height etc. and then order pistons to suit the desired comp ratio

[zebra]

Just put the CP 9:1 pistons in my R32 RB25DE head with 30 bottom end.

Still yet to drive it or do a reasonable power run. Will post results as soon as they become available.

Either way, make sure EVERY SINGLE measurement that can be taken is carried out. My builder/assembler didn't measure the head cc and we had issue with pinging. Hence we didn't know for sure whether its was too higher static CR. Turned out it was timing (or base timing) and CAS. Pays to make sure and check things before its too late!

The tuner should be the one setting timing, not the engine builder, bit hard for an engine builder to set timing when he cant run the engine.

[StevenCJR31]

does anyone know the CC (chamber) is for a 32 25DE head ? this one hasnt been faced at all, still has factory machine marks on the cams!

[R32Abuser]

Steven

62cc +/- 1 cc depending on what has been done to the head. As sated previously- always check.

Zebra

I was referring to the base timing. This was done incorrectly during the motor assembly. Hence the overall timing was then out. The tuner stopped the run and told the builder to re check the timing etc. After a couple of runs- detonation disappeared but it now doesn't make the power it should. I still believe it is timed incorrectly as per my post in the forced induction section. Motor is currently being re timed with new cams. Hopefully it makes some decent power!

[Gerg_R31]

i think r32abuser is talking about cam timing

i can garrantee not every engine builder knows, that with the rb25/26-30de( t ) the cam timing is not right if they are lined up with the timing marks on the cam gears backing plate, or if they go off the degree wheel or the valve lift at TDC as them values are more suited to the rb25/rb26 blocks

this is even out of my experience, best thing i did with my motor was line up the dots, measure piston to valve clearance, gave it to my tuner, told him i lined the dots up and what the piston to valve clearance was, he then told me he knows what to do and he can sort it out

[zebra]

Cam timing makes sense,

Either way a timing light should be brought out on the first start no matter what. even if the exhaust cam is out, the bas ign timing should easily be brought back to spec, its a 10 sec job on an RB

[R32Abuser]

Post should have read:

Steven

62cc +/- 1 cc depending on what has been done to the head. As sated previously- always check.

Zebra

I was referring to the cam timing. This was done incorrectly during the motor assembly. Hence the overall timing was then out. The tuner stopped the run and told the builder to re check the timing etc. After a couple of runs- detonation disappeared but it now doesn't make the power it should. I still believe it is timed incorrectly as per my post in the forced induction section. Motor is currently being re timed with new cams. Hopefully it makes some decent power!

Base timing is a name which can be confused easily.

[StevenCJR31]

Steven

62cc +/- 1 cc depending on what has been done to the head. As sated previously- always check.

Zebra

I was referring to the base timing. This was done incorrectly during the motor assembly. Hence the overall timing was then out. The tuner stopped the run and told the builder to re check the timing etc. After a couple of runs- detonation disappeared but it now doesn't make the power it should. I still believe it is timed incorrectly as per my post in the forced induction section. Motor is currently being re timed with new cams. Hopefully it makes some decent power!

Thanks David