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Have been out of the hobby for about 18 years just now getting back into it.

Looking to swap the top tranny shaft in a B4.2 with a B3 top shaft. Can this be done?
If this can be done I will buy a B4.2
Thanks for any help.

You'd have to mod the B4.2 trans case and figure out a new way of holding one of the the bearings in the case. The shafts are the same diameter though.


The B4.2 has a better slipper so why do you want to swap it for a B3 shaft?

I had a B3 back in the day and installed an 8201 HPI 2 speed in it. It would RPM out w/ an 18 turn mod motor. It was very fast and run time on 6 cells was around 35min. Motor would barily be warm and the LRP speed control same barily warm in the summer.
I lightened it with aluminum blue screws lowered it and used foam tires graphite everything.
Now I planned on doing the same with a B4.2 with a brushless motor and gear it to the moon.
If someone has the rc calculator maybe u can run the gearing.
It is 19/25 pinions and 87/81 spurs.
The 2 speed comes with a B2 B3 top shaft.

The correct formula would be

2.60 ( S/P ) = FDR for the B4

Forgot to include the drive wheel roll out. But the foam wheels/tires are shorter than the factory wheels and pin tires. Not at home at the moment to get the roll out.
Was trying to get an idea how fast my buggy was I think the B3 is a 2.4 tranny.
Don't have a B4 yet and don't know if the B3 foams would fit it. Would have to get new ones for the B4 so don't have wheel roll out for the calculation. Also there is no balloning with foams.

Roll out is easy too, but in most cases for a runner it's really overkill unless you like the math motor temps with a gear reduction are more important, unlike direct drive.

I thought the RC calculator needed the roll out of the driven wheels for the calculation.
Voltage
Motor
Gearing
Tranny ratio
Roll out
then theres drag and frictional losses but in this case there was very little or can be excluded as the B3 was rpming out and motor temp was slightly warm.

Charlie don't surf wrote:Roll out is easy too, but in most cases for a runner it's really overkill unless you like the math motor temps with a gear reduction are more important, unlike direct drive.

TA driver wrote:I thought the RC calculator needed the roll out of the driven wheels for the calculation.
Voltage
Motor
Gearing
Tranny ratio
Roll out
then theres drag and frictional losses but in this case there was very little or can be excluded as the B3 was rpming out and motor temp was slightly warm.

Charlie don't surf wrote:Roll out is easy too, but in most cases for a runner it's really overkill unless you like the math motor temps with a gear reduction are more important, unlike direct drive.

What's the RC Calculator?

Im refering to the RC speed calculator I believe theres different ones for brushed motors for brushless and problably more.

For a transmission (reduction) vehicle

(T x Pi) / (S/P x TR)

I believe it's a Microsoft Excel program but I could be wrong.

Cool, not familiar with it, but Excel is a simplified Algebraic calculator

I did it the other way round so I could run a B3 with a B4 slipper for a brushless setup. It was a straight swap so I can't see why you couldn't do it the other way.....