stroking the rb20det

[bmarley5780]

What's up everyone? I have found a set of rb25det crank and rods for a decent price. I want to buy them a stroke my rb20det that is going to be here any day. What is involved in doin this? I believe I heard that all that was needed was to shave the crank somewhere and that was it. Is this true? If so, can this be done by me?

[YamaOni]

You might need to relieve the block at the bottom of the cylinder so the crank can swing freely.

I know you have to do it when using a 26 crank.

[bmarley5780]

so your saying that the block will need to be shaved, and not the crank. does the rb26 crank have the same dimensions as the 25?

[YamaOni]

the 26 has a longer throw.

[roundrocktom]

What are you building?

RB20 78 x 69.7 bore x strokeRB25 86 x 71.7 bore x strokeRB26 86 x 73.7 bore x stroke

Little write up about the "stroked" RB20's can be found here

Taking the RB25 crank, and putting it into the stock RB20 will give a 2000 * 71.7/69.7 engine = 2060cc (roughly 3% increase). I'd assume you'd use some oversize pistons....

Tom

[bmarley5780]

Yes, that is the page I am going off of. Wanting to build the 2.3. It does not say anything about oversized piston. Is this something that is needed but not mention in that write up?

[bmarley5780]

Yama- I guessing you have some knowloedge of this when using the rb26 crank. How much does it cost to shave the block? DIY ?

[roundrocktom]

Yes, that is the page I am going off of. Wanting to build the 2.3. It does not say anything about oversized piston. Is this something that is needed but not mention in that write up?

To get up to 2.3 liters, my guess is a 82 mm piston. 4mm overbore. Seems like you would sonic test the block walls, as that is a pretty good size overbore!

Quick math:

disp = 6 * PI * (bore)^2/4 * stroke

with the 82mm bore and 71.7 stroke (RB25 crank)...just about 2.270 liters.

To "clearance" and crank... you take the block, installed the new crank and rods. As they spin you'll discover the hit the walls of the block. Yep, you strart grinding away until you have a good 0.050" clearance between anything rotating and the block.

Given the price difference between a RB20DET and RB25DET... you are ahead of the game by starting with a RB25 engine....

Tom

[bmarley5780]

Yeah, i realize that starting with a rb25 there is a huge starting platform then the rb20. but I got the rb20det engine swap for 950 shipped so i really cant complain...Thanks for the math..bc i have no idea what you did:)! About the pistons, is there any 82 mm ones out they that i can buy second hand from a different car? Although i would probably buy new?

[YamaOni]

Yama- I guessing you have some knowloedge of this when using the rb26 crank. How much does it cost to shave the block? DIY ?

I have yet to it, But I have a friend at a tuning shop that can hook me up with the info when I get a crank.If I had to figure it out myself I would set the 26 crank in and see where it hit, take some block away and try it over and over till it cleared and the I was happy with the gapas for pistons Tomei makes them but I plan on sending one piston to Wiseco and saying make it bigger.An off the shelf piston that might would work is the 4Ag supercharger piston.

[bmarley5780]

Are you referring to the adds in SUper Street. Race Engineering? The forged pistons and rings? They say the prices is 599 for 6 cyl. You think that they have to custom make them?

[YamaOni]

Are you referring to the adds in SUper Street. Race Engineering? The forged pistons and rings? They say the prices is 599 for 6 cyl. You think that they have to custom make them?

I am going to look into it more, Pin height might be a problem with just a 82mm piston from lets say the 4AG, It would be bad to drop 600$ on a new set of pistons and put the lower end together, spin the crank and find out that the top of the piston is sticking out 2mm from the deck.

That would suck A$$

[themadscientist]

Igor, the belt sander!

[YamaOni]

Yes master, and the hammer?

[spec-v5150]

Yeah, i realize that starting with a rb25 there is a huge starting platform then the rb20. but I got the rb20det engine swap for 950 shipped so i really cant complain...Thanks for the math..bc i have no idea what you did:)! About the pistons, is there any 82 mm ones out they that i can buy second hand from a different car? Although i would probably buy new?

Where the **** did you get an rb20 for 950 shipped????

[bmarley5780]

some guy in Ohio! Needed to get rid of asap! He even sent me pic's of papers the go with it....very luck I was!.....