R33 Rb30 Conversion

[FORZA-MOTORSPORT]

Yes so whats the deal now the 8.3:1 compression ratio is thought to be 8:1??? Nothing wrong with the 8:1 anyway just run more boost and timing and there shouldnt be a problem...

[Cubes]

One more reason to measure everything up with the motor you have on hand. As should be done anyway.

[specialk]

A bit off the topic but

if anyone is after a rb25/30 sump adaptor i have one for sale, as i am no longer going through with the rebuild. PM me.

cheers

gif

[N I B]

We have an Ex Zoom GTR from Vic in bits now that has RB30ET pistons,

Now this has to be a nastie low comp ratio.Worst part is we have to re use the pistons as the owner only wants to replace the bearings.

Its going to be interesting to see how laggy this thing is.

If you use the CP pistons its easy to get your machine shop to get you 8-1-8,4 to1 comp.

[Cubes]

NIB,

Be sure to keep the thread posted with how it affects spool and off boost torque.

[r33_racer]

well as soon as i get the block and head from machining i will mock fit the bottom end and check the measurements and see how much i want to deck the block, if at all. but 8:1 or 8.3:1 will be fine either way.

[N I B]

The car will be going early next week so ill post the dyno graphs,It has HKS 2530s i think thier the only thing that may save it.

[sky30]

joel,

So were did the 8.3 figure come from that everyone used to say was the comp ratio using std n/a pistons?

[Cubes]

I'm unsure exactly where it origionated, but it is fairly close to the mark.

Using my 62cc combustion chamber, 86mm pistons, 85mm stroke, 1mm headgasket, 0 deck clearance, -1cc dish - the calc shows a comp ratio of 8.175:1.

Same figures with the 55cc rb30 sohc's combustion chamber and I get 8.988:1. Nissan claim 9:1 so close enough for me.

If I then directly enter my specs.

87mm pistons

87mm h/gasket bore

1.397mm head gasket

62.2cc comb. chamber

14cc dome

1mm deck clearance

= 9.09:1

--

If I were to dial in the stroke, 1mm headgasket and deck clearance those pistons run in the rb25 (according to wiseco) it returns the comp ratio of 8.2:1 as indicated by the wiseco data sheet.

So... I must be running a 9:1 comp IF the engine builded did as he said and pulled 0.020" off the block.

Even if he didn't I would still be running an 8.7:1 comp ratio.

Interesting.... It still returns damn good economy considering it runs such a large quench gap. 'Maybe' the higher comp negates the larger quench area vs a lower comp nice quench.

Andrew, you wouldn't have a 240rwkw dyno sheet laying around? I'm interested to see how the low end torque as you initially jump on the throttle responds.

Its difficult to compare with a gt35r slapped on the side of yours.

If I am indeed running a 9:1 comp ratio it always leaves the door open to drop a 1mm headgasket in there that will bump comp ratio up to 9.4:1 and run a turbo such as the xr6 item. The higher comp will work well with the free flowing hotside, how well. No idea.

I'll have to check the deck clearance when the head is off. I have not pulled the head off for the springs and restrictors yet.

No time during the semester.

[Sydneykid]

On the very first RB30E / RB5DE we built (5 years/80,000k's ago) we decked the block and the cylinder head to get ~8.3 to 1 compression ratio. No big deal, the blocks are always skimmed for the o'rings and the head to check flatness. I chose 8.3 because of the standard RB30E cast pistons and using 1 bar of boost maximum.

Our later RB30's have all had 9 to 1 compression ratio and they are much more torquey off boost and built boost noticeably faster. Some of that is compression ratio and some could be attributed to the better quench. Which also helps with the detonation problem.

cheers

[Cubes]

A quick question to those that may know.

Is there a problem with decking the block too much?

0.020" may be fine but is 0.040" too much?

[Cubes]

Decking the block is fine and has been done since the dawn of time.

Its most definitely NOT a big no no.

However decking too much... I can't see any problems with it UNLESS the blocks design causes problems with quench, water and or oil galleys.

So block dependant I would say.

I really don't know for sure, which is why I asked some one in the know to clear it up.

With regards to the vg30 pistons. I can't see how you have achieved such a high comp raito with a piston that runs a 9cc dish and sits 0.040" down the bore.

The CP's run flush with the top of the block, and no dish yet achieve around the 8.2-8.3:1 ratio.

[sky30]

On the very first RB30E / RB5DE we built (5 years/80,000k's ago) we decked the block and the cylinder head to get ~8.3 to 1 compression ratio. No big deal, the blocks are always skimmed for the o'rings and the head to check flatness. I chose 8.3 because of the standard RB30E cast pistons and using 1 bar of boost maximum.

Our later RB30's have all had 9 to 1 compression ratio and they are much more torquey off boost and built boost noticeably faster. Some of that is compression ratio and some could be attributed to the better quench. Which also helps with the detonation problem.

cheers

Gary,

How do you achieve a 9:1 ratio, what pistons?

[Cubes]

Sky30,

I've been looking through the specs of various piston manufacturers.

It appears the JE VG30DET pistons are suitable. (22mm pin vs rb30's 21mm)

4.8cc dome, 1.255 compression height, the only down side is they are only available in 87.5mm.

http://www.jepistons.com/pdf/2006-sportcomp3.pdf

Without decking the block it 'appears' they will achieve an 8.2:1 compression ratio with a 0.045 deck height and 1mm headgasket.

IF you were to bring the pistons up flush with the top of the block (rip 0.045" off the block) compression will raise to 9.06:1.

I do know Gary has used JE's in the past. So I assume this is how they get their 9:1 RB30's?

I'm also assuming the pin dia. issue is sorted with a nice set of rods.

87mm CP flat tops grab an 8.4:1 comp ratio with 0 deck height. (Requires 0.020" off the block)

87.5mm JE 4.8cc domes grab an 9.06:1 comp ratio with 0 deck height. (Requires 0.045" off the block)

[FORZA-MOTORSPORT]

Having just finished my 25/30 conversion and having to modify the exhaust side to suit a bigger turbo and external wastegate, i have decided to make a few more systems if people are interested to bolt straight onto your stock r32,r33 exhaust manifold with the 25/30 engine. This will be an adaptor plate which allows a bigger turbo t04 or gt3540 to sit lower, looking stock as well as clearing everything while also enabling the use of an external wastegate. Now i can offer these adaptor plates which cost me $200 to make in all stainless steel as thats what they cost me to make, also if people are interested i can make the adaptor plate and dump/ front in one with a tial 44mm external wastegate all attached so all that would have to be done is a turbo bolted on, let me know what you guys think i have attached some pics below.

[Cubes]

What is it with Black R32 RB30DET's in Adelaide.

[FORZA-MOTORSPORT]

LOL , how many black r32 rb25/30's r there in adelaide??

[Cubes]

I believe there are 5 now

[SirRacer]

Decking the block is fine and has been done since the dawn of time.

Its most definitely NOT a big no no.

However decking too much... I can't see any problems with it UNLESS the blocks design causes problems with quench, water and or oil galleys.

So block dependant I would say.

I really don't know for sure, which is why I asked some one in the know to clear it up.

With regards to the vg30 pistons. I can't see how you have achieved such a high comp raito with a piston that runs a 9cc dish and sits 0.040" down the bore.

The CP's run flush with the top of the block, and no dish yet achieve around the 8.2-8.3:1 ratio.

my error was not increasing the bore size with the vg running the 87.12 and not putting in the - for the cc's of the piston

gary has mentioned to me a while back he uses the JE as his first pick and has also used acl pistons, im one whos very interested in getting some part numbers for both

i think the vg's will have a similar problem to the rb30et pistons with horribly low compression. it seems we really need something with a positive cc to get a nice comp ratio.

Edited May 3, 2006 by SirRacer

[mr_rbman]

I believe there are 5 now

haha, think mines the only silver one!