Regearing T-9 for autox

[RedbeardRacing]

Good morning all. 

 

I have finally got most of the kinks worked out on my birkin s3 and have done a couple autox events. My current setup is a zetec with a t-9 that has a tall first and close ratios after that. I hit 59/60 at 8k rpm in first and close to 80 in second. For autox I'd like to be in the 48/50 range for first and 66/68 range in second. My current rear gear is a 3.90/1.

I do occasionally street drive the car and in 5th @ 80 I'm turning 4k rpm so going with a higher ratio gear isn't ideal but that all depends on how hard it is to find gears and parts to change on the t-9. 

any info or suggestions are greatly appreciated. 

The previous owner sent the trans somewhere in New England to be built years ago, but he doesn't remember where. I am currently in Texas. 

 

Cheers

John

 

 

[S1Steve]

Hi John, You have Taylor Race Engineering in Texas. If their still in business, they are gearbox specialists…

[RedbeardRacing]

Thanks a bunch I will check them out! 

[7Westfield]

Taylor has been closed for several years

Scott Young (former employee) took over the Hewland part of it, don't know if he works on anything else

sy-gearboxes.com    ---I think

Edited July 11, 2022 by 7Westfield

[MV8]

What rear tire size?

[RedbeardRacing]

225/45/15 I believe. 

[MV8]

That would be a very unusual 1st ratio of 2.37 with a 3.9:1 diff and a 22.97 tire od at 8k. There is a close gear set available with a 2.97 1st (51 mph) and the domestic production Merkur T9 has a 3.36 (41.7 mph).

[JohnCh]

BGH has a few different ratios available that can be viewed here.  First gear options are 2.98 (what I have in my BGH box), 2.83, 2.75, or 2.66.  I've never heard of a 2.37 in a Type-9 before, but my math matches MV8's.  Are you sure the diff ratio is 3.90?

 

-John

[RedbeardRacing]

I attached what info was given to me by previous seller. It has a full belly pan so I can't spin the wheel and count drive shaft rotation. I'll see what I can do. 

[RedbeardRacing]

I believe all this work was done when Gary slutz owned the car. And I've called and spoke with him, he doesn't remember much. 

[JohnCh]

That helps!  I just looked up the Quaife gearset and they have some pretty extreme options as shown here.  

 

-John

[MV8]

I just stumbled across these chaps: https://www.3jdriveline.com/webshop/gear-kits-and-boxes/ford-type-9-5-speed/gear-kit/ford-type-9-straight-cut-close-ratio-gear-kit/

 

Looks like you may have 2.39 1st. I'd find a used merkur box and try it out, then go through it if you're happy with the ratios.

[RedbeardRacing]

That 2.98 first looks to be the ticket! @JohnCh what's your speed at the top of second with that combo? Do you have similar rear gear and tire size? 

@MV8 really appreciate the help. 

[JohnCh]

I have the BGH E2 HD gearbox with a 3.62 rear end and 205/60-13 tires.  Using the same 8000rpm limit as you do with your engine, my speed in gears are as follows (and no, it won't hit 8000 rpm in 4th or 5th  )  Your 225/45/15 tires are only 1.3% bigger in circumference than my tires, so inconsequential.  Happy to plug any information you have into my calculator so you can compare.

 

 

-John

[RedbeardRacing]

So what would that be with the 3.90 rear. And do you have a good source for rear end gears. I'm assuming you have the same hi lux rear end, with a quaife diff. 

[JohnCh]

This is 3.90.  I believe Birkin uses a Subaru rear diff vs. the Sierra diff installed on Westfields and older Caterhams (they moved to BMW diffs when the Sierra supply started to dry up).  I have no idea what options are available for the Subaru unit.

 

 

-John

[RedbeardRacing]

Thanks again for the help. I'll be reaching out to those vendors and making a plan! 

I was 15th out of 180 cars on raw time this past Sunday at autox, so I'm real excited to see what I can do whenever it's setup right. I had no power coming out of lower speed corners in second, and you don't have much time to be shifting up and down around an autox course. 

[panamericano]

A lot depends on the club you run with.  If the course designer aims for street cars to be under 60 mph it is quite a bit different to a course where you might get a little over 70.  Either way, a shift to 3rd is usually a waste of time, but how long do you want to bang the rev limiter in second.  On the other hand, if it is a fast course, like we run at Eagles Canyon, I spend 1/2 the run in third.  Something to consider.  Have fun.

[CarlB]

The transmission shop he probably used was Quantomechanics. The owner is John Esposito and the number is 203-463-8299.

[bball7754]

I just had my Rocket box refreshed by Scott Young,  and give him a AAA rating.

 

Website is: https://www.sy-gearboxes.com/

 

Steve