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Which connecting rod for B21ET 1981

T

TurboDutch

Active member
Joined
Aug 5, 2019
Location
Nieuw en Sint Joosland
I was looking for rods to rebuild my B21ET.
But I've found two types, they are all 145mm long and big and 58mm small end 24mm.

But big end and small end width seems to have two options.
Either;
- big end width 29.75mm, small end width 24.8mm
- or big end width 29.73, small end width 29.73.

I understand that this is for either crank or piston steered rods, but which one to buy?
Will both rods fit my engine and is it just my own choice? Or are there differences in these engines? Most websites sell only the 29.73 / 29.73 rods.

Some advise would be welcome, thanks!

I tried searching but didn't find the answer till now.

Didn't open the engine yet... would like to have parts in first :) (I'd like to use stock pistons)
 
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The vaunted "M" rods in the B21/23 are pretty stout. I think Towery bent his ~ 24psi.

How much boost will you be running? I believe the B21/23 design is crank steered and floating piston.... but I'm also on a half cup of coffee. I have some B23 rods (stock) I can measure if you can't find the data.
 
Yes I know that the M rods should handle some forces but I have K24 (borg warner) with 71mm compressor and 9 blade turbina.
So I don't like to open up the engine again to change bend rod (been there).

Stuff should be running on efi kdfi 1.4.
Combined with ported 531 head and IPD cam, should be able to generate some horses :)

So my idea was to overhaul engine with new rods and keep original pistons if ok ofcourse.
I found some king racing rod bearings etc already.

@ DET17
If you'd be so kind to measure original B23 rods I'd be very pleased thanks! :)
I found data but I'm not sure which is original and whether there are differences, maybe from year to year changes or whatever.
It seems difficult to find data about he correct width of conrods.

Does anyone else knows if there are differences in these B19 B21 B23 rods?

Thanks again!
 
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I just measured a B23 M rod with my harbor freight digital calipers 29.8 small end 29.7 big end, definitely crank steered. B21 M rod measures 29.77 on both ends, they appear identical, I would attribute tiny measurement differences to the calipers or operator. I was running 25psi on the B21 with M rods when a piston seized from a fuel pump failure and the rod chopped 3 holes in the block. I think any other rod would have failed in that situation.
 
Those are what are commonly referred to as "china-bay" rods. As they come from china, and are only sold on ebay.
Nothing wring with them at all, and they are usually substantially stronger than a stock rod. Sometimes the small end bushing is a little tight and might have some sharp edges. Some sand paper or a hone easily fixes this issue.
 
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