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Do I Have An Rb24?

D-limo

By D-limo,
in Engines & Forced Induction

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D-limo Veteran

D-limo

Posted
Posted (edited)

Okay the auction sheet for my Cefiro stated it had a 2.5L. When it arrived it was found to have an RB20 head.

We've since pulled this engine down and discovered 83mm bores. Stock cast pistons of some form and what I'm pretty sure are RB26 rods. Can someone confirm these please.

Also is there an easy way of identifying a GTR crank?

post-15238-1200966252_thumb.jpg

Edited by D-limo
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D-limo Veteran

D-limo

Posted
  • Author
Posted
O5U = RB26

Check the stroke of the crank, slip it back into the block and measure it, RB26 = 73.7 mm

83 mm bore X 73.7 mm stroke = 2394 cc's

Cheers

Gary

66mm :) What does that make it like an RB22??

I thought GTR rods could only be used with GTR cranks?

Sydneykid Grand Master

Sydneykid

Posted
Posted
This is interesting :D

So what block's it got for that stroke? Someone know?

It's like a hot-pot of every RB engine all in one!

The RB20, RB25 and RB26 blocks are all the same height, the RB30 block is 38mm taller.

66 mm stroke x 83 mm bore = 2,143 cc's

I seriously doubt the 66 mm stroke, an RB20 is 69.7 mm standard, so I see no reason why anyone would destroke it. Plus you would run into low gudgeon pin height problems. The 69.7 (RB20), 71.7 (RB25) and 73.7 (RB26) strokes can all be accommodated with the right choice of gudgeon pin height in the piston But 66 mm would require a very low gudgeon pin height to get the piston to the top of the bore. I don't think so.

Cheers

Gary

murrayis Mentor

murrayis

Posted
Posted

RB20 + rb20 rods + 83mm bore pistons is a rb22

RB20 + rb26 rods + rb26 crank + 83mm bore pistons is a rb24

if the strokes different they could be 4agze pistons because they fall short of the deck by 3mm so the stroke may be shorter because the blocks been decked to suite 4agze pistons.

My 2 cents

D-limo Veteran

D-limo

Posted
  • Author
Posted (edited)

The pistons have UNISA stamped on the so I think that rules out 4AGZE??

It was running an East Bear 1.8mm HG so is it possible that pistons have a high gudgeon pin height?

I didn't actually measure the stroke myself but the guy who did has built Ferrari engines so I think he got it right..

The crank is still installed btw

Sydneykid whats next?? Is there even a next lol

Thanks for the input gents its much appreciated :)

Edited by D-limo
Sydneykid Grand Master

Sydneykid

Posted
Posted
RB20 + rb20 rods + 83mm bore pistons is a rb22

RB20 + rb26 rods + rb26 crank + 83mm bore pistons is a rb24

if the strokes different they could be 4agze pistons because they fall short of the deck by 3mm so the stroke may be shorter because the blocks been decked to suite 4agze pistons.

My 2 cents

Pistons have no effect on stroke. Stroke is the distance the piston travels up and down the bore. Whether it has high or low gudget pins makes no difference to the stroke.

Cheers

Gary

Sydneykid Grand Master

Sydneykid

Posted
Posted
The pistons have UNISA stamped on the so I think that rules out 4AGZE??

It was running an East Bear 1.8mm HG so is it possible that pistons have a high gudgeon pin height?

I didn't actually measure the stroke myself but the guy who did has built Ferrari engines so I think he got it right..

The crank is still installed btw

Sydneykid whats next?? Is there even a next lol

Thanks for the input gents its much appreciated :rolleyes:

Measure the stroke again, if you didn't use a dial guage last time, then use one this time. Rotate the crank such that the piston is at the top of the bore (TDC), and zero the dial gauge. Then rotate the crank 1/2 a turn until it is at the bottom of the bore (BDC). The distance the piston travelled is the stroke.

The previous engine builder would have fitted the 1.8 mm had gasket to lower the compression ratio. The same sized combustion chamber with more capacity (bore and stroke) means higher compression ratio. The 1.8 mm head gasket effectively increases the capacity of the combustion chamber and hence lowers the compression ratio. Personally I am not a fan of thick head gaskets, for one they stuff up the squish and cause detonation.

Cheers

Gary

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