Ive been doing some research lately on the RB motors. I am going to be building an RB25DET motor to put into a S14 very soon and was exploring different build possibilities. I have come to learn that theRB25 and 26 blocks (shortblock) are all but identical. They both share the same 188.5mm block deck height, they both have 122mm rods with 21mm wrist pins, the pistons are the same 86mm bore. The only differences I was able to find are the crankshafts and compression heights on the pistons. The RB25 uses a 71.7mm stroke, 122mm rods and a pistons compression height of 31.5mm. The RB26 uses a 73.7mm strke, 122mm rods and a pistons compression height of 30mm. The only differences being, from a numbers point of view... are, the 2mm larger stroke (RB26) and the lower compression height of 30mm (RB26) to accomidate for the slightly larger stroke.

Now from what Im seeing you can bump your RB25 up to a 2.6 by just dropping in the RB26 crank with either stock RB26 pistons or a set of forged aftermarket RB26 pistons. Im always hearing a lot of talk about the RB26 crank and rods being swapped into the RB25 block but from what Ive gathered it looks as if you need the just the crank and a set of RB26 OEM or Aftermarket pistons.

Are there any differences in the RB25 and RB26 rods that I havent been able to find? Are the rod widths different? Are the rod Journal bore sizes different?

What are the Crank Specs for the RB25 and 26. What is the big end bore size? What is the rod Journal width?

The reason Im trying to gather info is because Im trying to possibly develop products for the RB motors, ie Stroker kits, rods, Turbo upgrades, etc, etc. Im pretty sick of seeing hyped Japanese companies rebadging other companies parts and selling them with a 300% mark up. I have worked for several major Honda performance related companies companies here in the US and have developed several products for various Honda race aplications over the years. I just recently got into the whole Nissan scene and after doing a little research have come to love the SR and RB motors. I have a very good relationship with Wiseco and JE, the company I have most recently worked for is the number 2 Wiseco distributor in the US for Imports and number 3 for JE. I also have several strong, long term relationshps with many crankshaft and rod manufacturers, Crower, Cunningham, Saenz, Pauter, Eagle and Scat just to name a few.

I want to get as much info together as possible. I need the serious info, I need the block heights, crank specs (journal width and diameters), rod specs (big end bore, rod width, length, pin sizes) and pistons specs (Bore, compression heights, pin diameters). If there are websites that have all of this info or if some of you know please feel free to post it up.

Im also going to look into the similarities of some of the domestic (US, Rod/Chevrolet) rods out there. I have modified rods from several different mitsubishi and Toyota models to work with various other makes so I would like to explore the possibility of using inexpensive, high quality Ford/Chevrolet rods. There are rods out there for those motors that can handle in excess of 6000HP and cost less than most big name Japanese companies sell their rods for.

I would like the progression of the SR and RB motors to grow in the US, the major issue I am finding is the lack of aftermarlet support. I, along with a few others am going to start pushing some of the big name US manufacturers to start producing parts for the RB and SR motors. So any help from you guys is greatly apreciated.


Thanks

 

You might want to ask some of the Austrailian or Kiwi guys about those specs. There aren't enough people in the US modifying RBs for companies to care too much. As for SRs, you might be onto something. Don't one of the companies you list already make pistons?

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