R33 Rb30 Conversion

[Dahtone Racing]

the CPs i have are flat too and they reckon they are good for 8.something:1

[N I B]

The one we just did with CPs with a minor machining of block and head faces for reco using a stock Nissan head gasket ended up at 8.3-1 using an RB25 head.About as low as you would ever want for a street engine but higher comp would be easy.

[sky30]

The CP's im using have no dome in them..they are flat tops. So i dont believe that part is in my calculations.

Are these VL turbo pistons? to get a comp ratio of around 8.3:1, you need some dome tops dont you??

[R31 POWER]

Excuse my ignorance but what will the cr be with a stock R32 RB25de head,stock head gasket and stock non turbo bottom end?Lots stock there lol

[Cubes]

My calcs show 8.07:1 comp ratio running the 86mm n/a rb30e -1cc dished pistons (due to valve reliefs), 85mm stroke, stock headgsaket, 63cc combustion chamber.

According to a bloke on ct.com who measured the n/a and t pistons, the stock n/a pistons are 1cc dished due to the valve reliefs

Doing the calcs they do appear to return roughly the expected comp ratio.

Maybe mine is running more comp and the measurements were stuffed up. I do doubt it though as Ash's R32 runs the same ignition timing as I and had an almost identical power curve (except for top end where his developed a strange power loss). He runs the n/a pistons, so the 14cc dome pistons I run MUST be damn close to the same sized dome as the rb30e pistons.

I have done a comp test BUT the motor was cold, I had the injectors out so I thought I would check for variation.

All cylinders were suprisingly exact apart from number 3 that was from memory 1 psi down. I think from memory they came up around 158psi. I made a post when I did the comp ratio, I should dig it up. Either way ~158psi with the cams and head I'm running is what the n/a piston rb30det's achieve. *According to RIPS in NZ (SDU)*

[R31 POWER]

That sounds like shit cr i dont like that.I dont really wanna pull the bottom end down thats all Should just get the head faced hahahaha.

[platinum]

yeah the CP pistons in mine were supposed to create about an 8.3:1 c/r as well, from memory they were flat

[r33_racer]

alrighty.

Well the cp's state that with std headgasket and their 25/30 coversion pistons you will get about 8.3:1 and so far from what ive heard it seems to be at least half accurate. So then i guess my calcs worked out right if others are using same parts and getting the cr stated. Either way around that CR is all we are aiming for for the race car. So things are looking good so far.

[Cubes]

The CP Pistons.

Run a 1.280" compression height.

I've double checked the wiseco catalog and it states with a comp height of 1.260" you will achieve a deck clearance of 0.040".

The 1.260" piston will sit 0.040" down the bore. + the headgasket it will give you a sloppy 2mm (0.040") quench.

The CP 1.280" comp height piston will sit 0.020" down the bore.

So what does this mean.. The STOCK RB30 N/A piston must run a 1.260" compression height (piston sits 0.040" down the bore) to achieve its 9:1 compression with the sohc head.

I swear the rb30 block in the shed 'looks' as if it has zero deck clearance. hrmm maybe not.

Does any one have a picture of the top of a CP RB30 flat top piston or know if they run valve reliefs, I would assume so.

If so does any one have their spec sheet laying around on the dish cc?

Providing the CP has no valve reliefs they will achieve a comp ratio of 7.9:1.

Should you deck the block 0.020" for that 0 deck clearance it will raise the comp to around 8.2-8.3:1.

Thats using my head cc measurements of 62.2cc's and a gasket thickness of 0.040".

Wish I knew this earlier... Looks as if the CP's specs are the better suited pistons that I know of.

Nice comp ratio for some good boost + a really nice quench.

8.2-8.3:1 ... As Mr. NIB said.

[r33_racer]

I have the cp spec sheet with me here...and like ive said before there is zero intake and exhaust valve relief, dish depth is nothing and dome height is 0. as you said cubes they run a 1.28" comp height.

Hmm ok...looks like more research is needed to double check this again.

[FORZA-MOTORSPORT]

Has anyone who has left there engine mounts as per standard in there rb25/30 conversion been able to close there bonnet using the standard intake plenum?? Mine will click in the first notch but thats it which i think will be usafe to drive over 60k's. I dont want to go for an aftermarket bonnet as i want to keep the car looking as stock as possible, perhaps a small bonnet scoop, got to find one that would appropriate. The other way i was thinking was of chopping the support bars from the underneath of the bonnet where they are fouling on the inlet plenum, is this a bad idea??

[sky30]

My calcs show 8.07:1 comp ratio running the 86mm n/a rb30e -1cc dished pistons (due to valve reliefs), 85mm stroke, stock headgsaket, 63cc combustion chamber.

According to a bloke on ct.com who measured the n/a and t pistons, the stock n/a pistons are 1cc dished due to the valve reliefs

Doing the calcs they do appear to return roughly the expected comp ratio.

Maybe mine is running more comp and the measurements were stuffed up. I do doubt it though as Ash's R32 runs the same ignition timing as I and had an almost identical power curve (except for top end where his developed a strange power loss). He runs the n/a pistons, so the 14cc dome pistons I run MUST be damn close to the same sized dome as the rb30e pistons.

I have done a comp test BUT the motor was cold, I had the injectors out so I thought I would check for variation.

All cylinders were suprisingly exact apart from number 3 that was from memory 1 psi down. I think from memory they came up around 158psi. I made a post when I did the comp ratio, I should dig it up. Either way ~158psi with the cams and head I'm running is what the n/a piston rb30det's achieve. *According to RIPS in NZ (SDU)*

Joel,

So are you saying the RB30e pistons are 1cc dished?? Arent they normally dome tops?

so what comp ratio do you work out with the RB30e pistons, and RB25n/a head?

Are tht CP pistons that are made for the conversion the same dome as a RB30e piston?

[SirRacer]

The CP Pistons.

Run a 1.280" compression height.

I've double checked the wiseco catalog and it states with a comp height of 1.260" you will achieve a deck clearance of 0.040".

The 1.260" piston will sit 0.040" down the bore. + the headgasket it will give you a sloppy 2mm (0.040") quench.

The CP 1.280" comp height piston will sit 0.020" down the bore.

So what does this mean.. The STOCK RB30 N/A piston must run a 1.260" compression height (piston sits 0.040" down the bore) to achieve its 9:1 compression with the sohc head.

I swear the rb30 block in the shed 'looks' as if it has zero deck clearance. hrmm maybe not.

Does any one have a picture of the top of a CP RB30 flat top piston or know if they run valve reliefs, I would assume so.

If so does any one have their spec sheet laying around on the dish cc?

Providing the CP has no valve reliefs they will achieve a comp ratio of 7.9:1.

Should you deck the block 0.020" for that 0 deck clearance it will raise the comp to around 8.2-8.3:1.

Thats using my head cc measurements of 62.2cc's and a gasket thickness of 0.040".

Wish I knew this earlier... Looks as if the CP's specs are the better suited pistons that I know of.

Nice comp ratio for some good boost + a really nice quench.

8.2-8.3:1 ... As Mr. NIB said.

the block in my shed also looks like it doesnt have any clearance whatsoever

[mr_rbman]

Has anyone who has left there engine mounts as per standard in there rb25/30 conversion been able to close there bonnet using the standard intake plenum?? Mine will click in the first notch but thats it which i think will be usafe to drive over 60k's. I dont want to go for an aftermarket bonnet as i want to keep the car looking as stock as possible, perhaps a small bonnet scoop, got to find one that would appropriate. The other way i was thinking was of chopping the support bars from the underneath of the bonnet where they are fouling on the inlet plenum, is this a bad idea??

why didn't you do the engine mounts? Surely you've been through this thread and Joel's PDF before you did the conversion so you must have know they needed doing!

[FORZA-MOTORSPORT]

why didn't you do the engine mounts? Surely you've been through this thread and Joel's PDF before you did the conversion so you must have know they needed doing!

Shifting the engine mounts down will cause problems to the gear box, drive shaft, cv's and basically the whole drive line...

[Cubes]

Foolboost is running the motor in a GTS4 so as I remember Sky30 saying the only way it can be done is by lowering the subframe some how.

I envy the Attessa + rb30 package.

I don't know the particulars.

Sky30.... The 1cc dish measurement was by some bloke on calaisturbo.com.

I do see it as being feasible as sure they are slightly domed looking BUT they have quite large valve reliefs.

+ it works out when you do the comp calcs.

The CP pistons as stated have NO valve reliefs so they are a true flat top.

The RB30e piston with a 53cc sohc head, 1cc dish (due to valve reliefs) and 0.020" deck clearance (1.280" same as CP) is required to achieve its factory 9:1 compression.

Thats taking in to account the std headgasket squashing .2 of a mm..

I have no idea if this is correct but its the value that returns a 9:1 comp ratio.

IF the std headgasket doesn't squish by .2 of a mm then if you remove the 1cc dish from the piston it drops the comp ratio smack on 9:1.

Any one know how much the std headgaskets squash by?

Either way.. its very close.

If I change the heads cc from 53cc (SOHC) to the DET head of (62.2cc in my case) the std comp ratio 'should' be 7.98:1.

A little lower than the expected 8.2-8.3:1.

Then if I dial in my piston specs, deck clearance and headgasket it shows myself as running an 8.9:1 comp ratio. wtf.

I have NFI.. its too hard.

Here's a good little Java calculator if any one wants a fiddle.

http://www.csgnetwork.com/compcalc.html

A quick run down on the specs for those that are unsure.

Bore - 86mm

Stroke - 85mm

Headgasket Bore - 86mm (same as bore)

Compressed headgasket thickness - 1mm (headgasket thickness once torqued up.. what does the std squish?)

Piston dome - std RB30e (0cc to -1cc), rb30et (-11cc), CP (0cc), Wiseco rb25 (14cc), Wiseco rb30 (-11.1cc)

Deck clearance - std rb30e (possible .5mm), CP (.5mm), Wiseco rb25 with decked block (1mm)

[2BNVS]

i had clearence issues with fitting my rb30 block but not on the plenum, coz i got a vented bonnet the cam gear cover left corner hits the bonnet so thats getting trimmed down to fit, but in terms of hitting the plenum i was fine, although the piping coming across the radiator area had to be made to go down a little bit... when i 1st saw the motor in i thought theres no chance in hell ill get close to closing my bonnet it will hit everything ( i now have a custom plenum though so its no longer an issue anyway)...i didnt want to change any mounts either

ben...

[FORZA-MOTORSPORT]

i had clearence issues with fitting my rb30 block but not on the plenum, coz i got a vented bonnet the cam gear cover left corner hits the bonnet so thats getting trimmed down to fit, but in terms of hitting the plenum i was fine, although the piping coming across the radiator area had to be made to go down a little bit... when i 1st saw the motor in i thought theres no chance in hell ill get close to closing my bonnet it will hit everything ( i now have a custom plenum though so its no longer an issue anyway)...i didnt want to change any mounts either

ben...

Sounds good Ben any pics of the vented bonnet? Mines an r32 so a little diff, i might have to go aftermarket bonnet but they do seem a bit to chunky for my liking, or else scoop from either a mustang cobra or a holden manaro have crossed my mind and i think would suit the 32 quite well, what do you guys think?

Edited May 1, 2006 by FOOLBOOST

[2BNVS]

heres just a couple pics,

[Cubes]

Here's a little quote from the calaisturbo bloke that did a little measuring.

Measurements i got were

63cc for twin cam head

55cc for single cam head

21.3cc for 86mm bore, piston 3.5mm from TDC, cyc vol,

and head gasket 87mm bore, 1mm thick.

With these figures i got 20.33cc displacment of piston from 3.5mm down to TDC with measured at 21.3cc the piston is 0.97cc dished.

Head gasket makes up 5.94cc.

So add the head volume, 63cc with the piston @TDC volume and gasket volume together to get a total combustion chamber of 69.91cc.

Then the compression ratio is the cyclinder volume at BDC compared to volume at TDC, BDCcc/TDCcc.

BDC volume is for 86mm bore and 85mm stroke is 493.7cc piston displacment + CC of 69.91cc = 563.61cc.

and 563.61cc / 69.91cc = 8.06

8.06:1 comp ratio.

If you do all the same calculations with a 55cc head volume (SOHC head) you get 8.98:1, which verifies the results/measurements!