Questions about RB30DET build

[R32 GTSTT]

Ive brought all the gear needed to do a RB30DET build, just have a few questions though.

1. Ive been told i can use the vl rods, just need to heat treat them, would this be alright for 400hp appications. Is it possible to use the rods out of the R32 rb25DE block which i have. Are they the same length as the vl rods? (haven't pulled engine apart yet)

2. Do you think it is worth while sticking a 240degree exhaust cam out of my old Rb20DET, and replacing it with a 232 exhaust cam which is in the R32 RB25DE head. Is this possible because i know the lifts are different and proberly need to change springs aswell. Can it be done?

3. The vl's use a 87mm piston. I know i can use a 87.5mm piston to give me about 3067cc. Would a bore of 1mm to 88mm giving a capacity of 3102cc be to extreme for a high horsepower engine. I was looking to put a set of Arias pistons in.

Any feedback will be great, as i want to get it running soon.

[rb20-calais]

try this thread

http://www.skylinesaustralia.com/forums/sh...ead.php?t=15420

[Sydneykid]

Ive brought all the gear needed to do a RB30DET build, just have a few questions though.

1. Ive been told i can use the vl rods, just need to heat treat them, would this be alright for 400hp appications. Is it possible to use the rods out of the R32 rb25DE block which i have. Are they the same length as the vl rods? (haven't pulled engine apart yet)

2. Do you think it is worth while sticking a 240degree exhaust cam out of my old Rb20DET, and replacing it with a 232 exhaust cam which is in the R32 RB25DE head. Is this possible because i know the lifts are different and proberly need to change springs aswell. Can it be done?

3. The vl's use a 87mm piston. I know i can use a 87.5mm piston to give me about 3067cc. Would a bore of 1mm to 88mm giving a capacity of 3102cc be to extreme for a high horsepower engine. I was looking to put a set of Arias pistons in.

Any feedback will be great, as i want to get it running soon.

Short answers.

1. VL rods are 6" (152.5 mm) while RB25/26 rods are 4.8" (121.5 mm). If you want your pistons 15.5 mm down the bore, then I suppose you could use RB25/26 rods in an RB30, but the comression ratio would sure be low. RB30 rods will handle up to ~500 bhp standard, just use a set of ARP rod bolts.

2. I don't understand the question. Simple answer though, spend a coupla hundred bucks and stick a set of RB26 cams in the R32 RB25DE head, they fit straight in. No VVT on R32 RB25DE's.

3 Standard VL bore is 86 mm, with the standard 85 mm stroke, that gives 2,964 cc's. Personally I wouldn't go bigger than 87.5 mm bore which gives 3,068cc's. Some people reckon even that is too far, you should only go to 86.5 mm (2,998 cc's).

I think I covered all I could understand anyway.

[R32 GTSTT]

Ive read the first 23pages of the R33 Conversion thread, and it hasn't covered some questions i need answers to.

1. Is it possible just to use the R32 RB25DE inlet plenum for the conversion, with a R32 RB20DET wiring loom, or do i have to use the R32 RB20DET inlet plenum.

2. Does the R32 RB20DET inlet plenum bolt up to the R32 RB25DE head without any issues?

3. What size injectors are the R32 RB25DE, and R32 RB20DET?

4. If the R32 RB20DET inlet plenum bolts up to the R32 RB25DE head, what size and type of injector can be used that will fit the RB20DET fuel rail, to make 400hp+?

[Sydneykid]

Ive read the first 23pages of the R33 Conversion thread, and it hasn't covered some questions i need answers to.

1. Is it possible just to use the R32 RB25DE inlet plenum for the conversion, with a R32 RB20DET wiring loom, or do i have to use the R32 RB20DET inlet plenum.

2. Does the R32 RB20DET inlet plenum bolt up to the R32 RB25DE head without any issues?

3. What size injectors are the R32 RB25DE, and R32 RB20DET?

4. If the R32 RB20DET inlet plenum bolts up to the R32 RB25DE head, what size and type of injector can be used that will fit the RB20DET fuel rail, to make 400hp+?

1. Yes

2. Yes

3. RB20DET = 270 cc's, RB25DE = don't know, try Meggala's web site

4. Any top feed injector, Rochester, Denso, Jecs, Bosch etc etc. Around 450 cc's will be plenty. The only thing is to make sure you match the impedance with the ECU you are using, standard is high impedance. If the ECU will handle low impedance, then GTR injectors will just about make 400 bhp.

Hope that answered your questions

[Bl4cK32]

Here's 2 pics. The first is the rb25de inlet manifold with the inlet/head gasket on top, showing port size to gasket shape. Notice its a good fit.

The second shows the same rb25de gasket sitting on top of the rb20 inlet manifold ports that go into the head. Note the size difference.

I used the top rb20 collector (part tb is on) and the rb25de lower half to bolt to the head.

edit/ rb25de injectors are the same as the rb20 ones...

edit 2/ straight drop in replacement injectors are rx7 series 5, part # 195500-1370. These are 550cc injectors, but require tuning to use properly...

[R32 GTSTT]

thanks thats great help.

[R32 GTSTT]

How do i go about geting the right compression ratios?

If i use a set of 86.5mm Arias pistons i'll get a capacity of 2998cc. Ive heard the RB25DE heads have between 62-64cc combustion chambers. Also a 0.5mm head gasket will give an extra 17.6cc to the combustion chambers.

So if i compress 499.7cc into a 66cc combustion you get a ~7.6:1 ratio which is low.

What would i have to do in order to get a more desirable ratio of say 8.5:1 ??

[Bl4cK32]

Well this is a job for a proper engine builder (cos i didn't even attempt to assemble it )

All i know (which isn't much) is that we had our blocks bored 40 thou (twice) oversize to make it the 3.1 Lt. It had 20mm? (or thou?) decked off the top of the block, with a 3 layer metal head gasket. The engine buuilder said it was the ones used in the Group A racing, and also diesel engines....i think it has inbuilt o rings. As for cc of the head, the pic below shows what Joel's head worked out to be.

If -Joel- was here he would tell you about the squish band to work out....he knows more on that than i do.

Oh yer the pistons we used were Wiseco forgies, Part # K578M87, and i think Joel said compression worked out to be 8.2 - 8.4 : 1 somewhere in there. Also clearances were setup to run larger amounts of boost, ie 24 psi +

[Sydneykid]

How do i go about geting the right compression ratios?

If i use a set of 86.5mm Arias pistons i'll get a capacity of 2998cc. Ive heard the RB25DE heads have between 62-64cc combustion chambers. Also a 0.5mm head gasket will give an extra 17.6cc to the combustion chambers.  

So if i compress 499.7cc into a 66cc combustion you get a ~7.6:1 ratio which is low.

What would i have to do in order to get a more desirable ratio of say 8.5:1 ??

Almost right, but You have to add the combustion chamber volume to the cylinder volume to calculate the compression ratio, so.........

499.7 + 66 = ~566

566 / 66 = 8.5 to 1

Other slight correction, a standard head gasket is ~1 mm thick (6cc's at 86.5 mm bore).

So the correct calc is..........

499.7 + 68 = ~568

56 / 68 = 8.4 to 1

Hope that helps

[Cubes]

What you want to aim for is a piston that gives you a 0 deck height (flush with the top of the block)

Then use a 0.040"-0.050" headgasket, this will give you the optimal well close enough squish / quench height. Generall the closer the clearance the better but you also have to allow for rod stretch and high rpm and piston rock. Set it just that bit to close and you will have your piston kissing the head at high rpm.

Do a google on quench / squish and have a bit of a read.

Go for a set of custom pistons to suit your motor.

[R32 GTSTT]

Im thinking about puting a set of Arias Pistons in. What do you guys think of these pistons.

Im not sure if i should put 86.5mm or 87mm in. Any one else used these in there RB30?

[R32 GTSTT]

The Dayco Cambelt, part number 94407, is 25mm wide. Is this right or does it need to be 30mm wide?

[Bl4cK32]

Joel did a lot of research on the topic of which pistons to use. All are good, as long as correct clearances, and run in procedures are followed. If anyone tells you to use any particular brand, ask them why? I like to hear good reasons why people use certain brands...not just that someone said "these are the best"

Saying that Joel and myself chose Wiseco. Do some research on the net and you will find that Wiseco supply most major piston companies (yes, including Jap companies) with their blanks, and or rings. These companies then machine the piston blanks to whatever design they want. Why not buy the pistons from the place that makes them?

Yes the 94407 belt is the correct one.

[Cubes]

When selecting pistons make sure they have a 0mm deck height (come up flush with the top of the block when at TDC)

Thats all you really have to worry about. Then as I said previously with the headgasket it will give you a good squish/quench gap.

I havn't been able to find any information on the Arias pistons (deck height, compression height etc) Wiseco have their specs listed. Arias don't.

[Sydneykid]

Joel did a lot of research on the topic of which pistons to use. All are good, as long as correct clearances, and run in procedures are followed. If anyone tells you to use any particular brand, ask them why? I like to hear good reasons why people use certain brands...not just that someone said "these are the best"

I agree there is no such things as "the best" when it comes to pistons. But there is "a best" for my requirements. So if you truly know your requirements you can easily choose. Some examples;

I want 22 mm gudgeon pins (standard is 21 mm), this give a larger bearing surface area on the pin for the little end bearing. On a high power engine this spreads the combustion load over a larger area, so less wear and higher power tolerance.

I want to use Total Seal Gapless rings, so I need a piston with the right sized ring grooves. I could machine any piston to suite, but that just adds unnecessary cost.

I want to be able to set up the compression ratio to wherever I think I need. So the piston crown has to be substantial enough to be machined if necessary. Plus it has to have a piston crown that gives good squish at the same time.

I want to choose the bore size, not just have 1 or 2 choices that may or may not suite my requirements.

I want consistency, I don't want to have to change the maching process and redo the calcs for every different brand of piston.

So I stick to one brand that satisfies me, but most likely not for everyone else.