Pistons For Your Rb30

[daisu]

Guys, VG30DETT rods are 2mm longer than the RB30 rods. And the RB25DET pistons have the shorter compression height, if I use both of these should give the correct height depending on combustion chamber volumes.

Does this sound like a viable option?

[Dale FZ1]

Probably firstly depends on the crank journal sizes - how much difference is there between the VG and RB rods? You'd need things side by side to measure up, and maybe look at a dummy assembly if you can get the bits at low cost.

Alternatively, why not look at just using RB25 pistons and deck the block by the required amount? Sure you might be retaining cast pistons and stock RB30 rods, but gets the result you want.

There should be a number of viable ways to achieve a similar outcome. It takes $$ to put in the parts that make for a stout 30DET, but the lower spec pistons and rods would still make for a good street build IMO.

[daisu]

Given the options, I'd rather install a longer rod (from an engine that was factory turbo) opposed to decking the block to compensate for the lower height pistons. Also, I'm aiming to get a comp ratio approx 9:1 so I think there would be a fair bit of block decking to reach that with just the 25DET pistons, apparently the galleries start widening once you take off 2mm off the block.

From what I've read the VG30 rods fit in the RB30 block/crank, might need to organise something different for the gudeon pins/bearings depending on the piston used.

But this all depends on combustion chamber volume, if the block and/or head need shaving to ensure it's true, from the rough calcs I did, the VG30 rods and RB25 pistons could result in compression ratios over 10:1, in which case I may need to use RB26 pistons (lower compression height again). Also, another thing I need to factor is if the block is worn and needs boring out I'll need overbore pistons, which may prove difficult to find 2nd hand.

Basically, I see it the similar as using factory RB30 rods and pistons, instead the rod happens to be longer and the piston a bit shorter. The parts are going to be balanced and new bearings etc installed either way and the VG30/RB25 parts can be obtained relatively easily and cheap.

Just want to know if it's stupid idea in theory.

Edited August 19, 2008 by daisu

[R32 Driver]

why not just order off the shelf pistons and rods?

arias, cp, wiseco, ACL all make them

not very expensive either

[daisu]

7. SPOOL RB30 conrods and CP Forged Pistons $2050

Direct from their page

As opposed to picking up a set of VG30 rods/pistons for about $100 and haven't looked at RB25 piston prices but I'm assuming they would be similar priced.

Considering alot of people are making good power figures using standard bottom ends in both RB30's, VG30's, and RB25's I don't see the need to upgrade to aftermarket pistons/rods.

[4drfts]

Direct from their page

As opposed to picking up a set of VG30 rods/pistons for about $100 and haven't looked at RB25 piston prices but I'm assuming they would be similar priced.

Considering alot of people are making good power figures using standard bottom ends in both RB30's, VG30's, and RB25's I don't see the need to upgrade to aftermarket pistons/rods.

I can tell you for a fact that vg30 rods fit. thats what im using. However i got custom JE pistons made to suit and eagle rods. VG30 rods are 154mm (6.070in) and rb30 are 6in or 152.5mm thereabouts. so vg30 are 2.5mm longer, i havnt bothered trying to find out if they work with std. pistons etc. VG30 DOHC rods from 300zx etc have a 22mm rod bush, SOHC use a 21mm rod bush, same as all RB engines, so to start with youd need SOHC 300zx rods from something like a maxima. both VG rods use the same bottom end as RB so use the same bearings, even the acl website use the same partnumber

[Spoolup]

vg30 rods are about 1.5mm to 2mm thinner across the rod ( thickness ) than RB30 rods - so when using VG30 rods you end up with a rod that slides back and fourth on the big end journal.

I can tell you for a fact that vg30 rods fit. thats what im using. However i got custom JE pistons made to suit and eagle rods. VG30 rods are 154mm (6.070in) and rb30 are 6in or 152.5mm thereabouts. so vg30 are 2.5mm longer, i havnt bothered trying to find out if they work with std. pistons etc. VG30 DOHC rods from 300zx etc have a 22mm rod bush, SOHC use a 21mm rod bush, same as all RB engines, so to start with youd need SOHC 300zx rods from something like a maxima. both VG rods use the same bottom end as RB so use the same bearings, even the acl website use the same partnumber

[daisu]

I can tell you for a fact that vg30 rods fit. thats what im using. However i got custom JE pistons made to suit and eagle rods. VG30 rods are 154mm (6.070in) and rb30 are 6in or 152.5mm thereabouts. so vg30 are 2.5mm longer, i havnt bothered trying to find out if they work with std. pistons etc. VG30 DOHC rods from 300zx etc have a 22mm rod bush, SOHC use a 21mm rod bush, same as all RB engines, so to start with youd need SOHC 300zx rods from something like a maxima. both VG rods use the same bottom end as RB so use the same bearings, even the acl website use the same partnumber

Ah yes, I saw those pistons you had for sale on trademe.nz, question for you, with the pistons you had and using the VG30 rods you said it would give approx 8.3:1 compression ratio. Can I ask what was the compression height of the piston and whether how many CC's if it was dome top or dished?

If the VG30E(T) rods have the correct bush size then this would be easier than machining pistons to suit 22mm pin or having bushes made to suit 21mm pin. Only problem is knowing how strong/reliable they are. The factory power output of the engine is very similar to the ratings of the RB30. We'll see if I can find some people pushing decent power through these engines on standard bottom ends.

[R32 Driver]

Part# K577M87

WISECO Rb30/26 head piston

[rockabilly]

cp flat top,3.5 thou bore clearance, nice pistons, 26 head, gt4094r, 530kw @ 1.9 bar with more to come no problem shell v-power, see thread.

[daisu]

K577M87 - NISSAN RB30 GTR DISH 6577M87 - $852.12 That's US dollars without shipping.

And I'm not making anywhere near 530kW. I really don't see the need to use aftermarket pistons in my application.

The rods being thinner could be a problem though.

[R32 Driver]

K577M87 Wiseco Pistons Rb30 GTR, Used by UK owners and proven to work

$648.84 USD from No limit motorsport be around $120 usd ship

$770 USD delivered + Spool rods $750 AUD= saves u around $500?

since they sell CP pistons + rods for 2k

[daisu]

$1500 is still much more than I want to pay when standard items have been proven more than capable in the power range I'm aiming for.

[daisu]

vg30 rods are about 1.5mm to 2mm thinner across the rod ( thickness ) than RB30 rods - so when using VG30 rods you end up with a rod that slides back and fourth on the big end journal.

'Spoolup', do you know how this issue is overcome on the VG30 engines by any chance?

[ahh 33 s2]

i dont no for sure but i would presume that the crank is just sized/designed differently to accomodate the thinner rod.

[Spoolup]

yes that is exactly corret - on the VG30 there are two rods per journal ( being a V6 ).

So the width of the journal is just different to the RB30 and that is why the VG30 is different

i dont no for sure but i would presume that the crank is just sized/designed differently to accomodate the thinner rod.

[Spoolup]

for your power - just run a set of std RB30 rods and NA RB30 pistons - they will handle it and obviously a direct fit with no issues.

$1500 is still much more than I want to pay when standard items have been proven more than capable in the power range I'm aiming for.

Edited August 27, 2008 by Spoolup

[ahh 33 s2]

this may be a stupid question for sum, but do you get your block work done and then purchase your pistons and bearings so forth or do you just get over sized pistons and then got the block done to match. or does it not really matter what way you do it

[daisu]

Yeah, I was contemplating just using standard rod/pistons, but as said before I want higher comp.

I guess I should start by CC'ing the head and having the block checked first. No point in figuring out I can use X pistons only to find out the block needs to be bored out and the pistons won't fit anymore.

I'll just have to go with decked block/shaved head and thin head gasket.

I would assume you'd have the block inspected first and then decide if oversize pistons are needed. Or if you had already planned on oversize pistons I guess it wouldn't matter which way you did it.

Clarification please?

Edited August 27, 2008 by daisu

[R32 Driver]

assuming its a stock block

just oversize it to 86.5 (stock 86)

that way you have 1 bore left incase you f**k up

and the engine builder has new bores to work with