This past weekend I ran a track day and used the stock 60 series 5 speed. I'm going through ultra close 56 4 speed so this was a chance to experiment.

Note I use a 4.38 rear gear with a 20.6 tire which equates to 111 mph at 8000 RPMs.

On our 18 turn 3.4 mile course I make 14 shifts with the close ratio 4 speed but on the 5 speed it can be few as 10. I didn't take any lap times mainly becuase I wanted to see how bad a stock box would be.

The biggest two issues were the 2nd to third shift and the issues such huge gaps cause in shifting. In one particular corner the car is down to about 38 mph and so the revs in 3rd drop below 4 grand, using 2nd has the motor at 6500-6600 so by the time you come off the corner the motor has revved to 8100 or more. This brings on the shifting issue; with a 14lb flywheel and a 2800 rpm drop between gears, you have to wait an eternity to shift. Some of this is due, I'm sure, to the synchro likely being worn. I use the tach as my guide and my shift into 4th gear occurred in the same spot regardless of buzzing 2nd or lugging 3rd. Not ideal.

I can likely solve this by changing to the 4.62 rear gear that I have (a 5.125 would likely be better). Although this may cause an issue with over revving in 3rd in one of the other corners.

The final issue may not be the box but once I get to 7600 in 4th the car as this weird harmonic growl a rapid ra ra ra ra ra ra. The real weirdness is that if I shift up to 5th at 7200 to bring the revs down it does it even worse and under braking all the way down to 45 mph. If I stay in 4th the noise isn't there under braking.

So overall with a low enough final drive ratio the stock 60 series 5 speed is an OK compromise but make no mistake it's a compromise. It's a shame the 56 series 4 speeds won't hold up behind my built A15. The reality is I'll either need to suck it up and buy a proper box or live with the compromise.

I'm leaning toward living with the compromise as if I spent the $3000+ on the motor that would net a faster lap time than the proper box. The current motor is around 105whp and another 10-15hp is way more likely to close the 2-3 second gap I need to get from the 5th overall to 1st.

Tom

Nice read Tom. All I can say the it's not best choice for drag racing but I would say it was stronger and outlasted the H145, H150 and H165 rearends. Which I broke every one of them.
The 60 never made it to the H190 because that's when I put the 71 series transmission in. Which the 71 outlasted the H190. Didn't see the 71 break until I went to the the narrowed Ford 8.8.
I finally found a good combination when I installed the 2 speed Powerglide. Wonder what I could do with it on your track?

So my fabricator pal keeps harassing me to put a Ford 5.0 in the car; a 2 speed power glide would work just fine. Actually with another 50 horsepower I probably could get away with it.

There is one plus of the street box, the low first gear makes it easy to put on my tilt trailer.

Tom

You don't need a low first gear when you have a Powerglide and Nitrous.

Here is a Glide and Nitros
https://www.facebook.com/jesse.r.ferguson/videos/10210056618283609/

Tom have you considered a 63 series 5 speed out of the B210. They appear to have a better step from 2nd to 3rd, though my practical experience was behind a stock L18 & most corners were taken in 3rd. I'm sure someone will find a set of ratio's to proof me wrong, but I can remember a rally type guy lamenting that the gearbox wouldn't live behind a worked L20B, as it had the best ratios available stock. Worth a look in my opinion, anyway.

The 63 series box is on my list; if you use the B210 case with H10 Z20 63 series gear set you get a mid close box in effect. It's just a matter finding the parts.

Tom

The Z20 gearbox (63A) can be used behind an A-series by swapping the front case. It uses the same input splines, so just use the 180mm clutch disc (clutch disc from L14/Datsun 510 or the B210/A14 5-speed disc). As the input shaft pilot is larger it can be turned down OR you can machine the crank for the larger bushing. There is an off-the shelf bushing that fits

Another alternative is to swap the gearset into the A-series 63A gearbox. It appears that only 1st and 2nd differ, all the other gears are the same

It may not seem like it but the slightly taller 2nd gear (1.9 versus 2.013) in the Z20 box results in 200 rpm less of a drop when shifting up to 3rd. That is just enough to keep it in the powerband.

Tom