Transaxle.
First specs, then reasoning on ratios and why 4 instead of 5 para mi.
All transmission decisions were made after I new what the engine specs were, wheel&tire data, and then use along with personal aesthetics. I think that if one doesn't know these things first you're eating your sandwich from the wrong end.
This is a type 1 four speed built from all new parts by Rancho, I started with their Pro-Suby build as a template. The case is a new Rhino case with added gusseting. Internals are all Weddle: ring and pinion, gears, shafts, and synchros with the normal welding on 3rd and 4th gear hubs, plus steel shift forks and hardened keys. It also has a Peloquin planetary torsional diff. Torsen diff is the common term and this one is much like a Quaife except made specifically for type one cases and made in America. Add heavey duty side plates and type2 stubs to complete the package. The idea here is to craft as bullet-proof a 4 speed in type one packaging as is possible.
Gearing. Here's where the real fun begins, and Stan had a great post on this recently with his reasoning on gear selection to match his use and how he saw his use for his speedster changing (I also thought I heard hints of a project X, but I digress). Rancho made their suggestion, and then in my own inimitable fashion I researched the heck out of it, plotted gearing charts against rpm, horse power and torque curves, ran scenarios in my head, etc. etc. etc. I managed to chase my tail back around to what they suggested in the first place. 3.88 r&p and 3.11-1.93-1.22-.82 1st through 4th. I had played with the idea of a 3.44, but though the ring gear cold be modified for this limited slip diff, Rancho was strongly against it. This winds up being so close to what Stan has specced out on his that they would be hard to tell apart behind the wheel. I think I have a slightly higher 1st and a slightly lower 4th? His big difference is that he has a real clutch pack limited slip (lucky bastard) while I have the Torsen style. I wanted limited slip and a clutch type is near impossible to find plus with a very few exceptions I prefer the torque sensing type for this use. At 10/10ths the clutch type will handle corner entry better but if I get to do more than a track day or two it'll be a wonder. The gearing chart is attached, apologies for the weird way it formats for export. Hey @Stan Galat, what calculator are you using that makes those nice plots?
This all results in an rpm drop in each gear that's pretty close to the same with the biggest drop in the 1st to 2nd shift. I think for performance this is good because there's more torque multiplication in the lower gears. At max acceleration a shift at peak hp would drop to just before peak torque in the 1-2 shift and in subsequent shifts it would drop right into peak torque. The relative qualities of the motor will allow for putt-putting about in town without the air cooled concerns about fan speed. A cruising rpm of 3,000-3,500 at highway speeds will be fine. I'm used to that even in my 6-speed MINI Clubman S. Again, I've hit what I think is a sweet spot for a four speed set-up.
So why 4 speed? Well there were packaging concerns, but those weren't paramount. Reason one for me was I didn't want a cable shifter. A Suby 5-speed would have probably (ok..definitely) been cheaper and not hard for Greg to do. I just wanted to get back to the feel of an actual rod going into and actual transmission and moving real shift forks. With a Vintage shifter, new bushings and everything mounted properly this will have a vintage feel. I'll have to do a good job to make clean shifts. I'll need to do a proper heel and toe to snick off crisp downshifts. THAT'S WHAT I MISS. I also miss long pulls as the revs build, too. I'll be getting that again. This motor should have a nice torque curve to surf and these ratios should do nicely for that. I want the vintage experiences I miss, but with a touch of modern for both usability and so my wife will ride with me. Fun things are fun, but fun things shared are funner.
Now I'll get some flack from some quarters for not going 5 speed, either Suby or Berg 5. It's so nice to row gears they'll say, and they're not wrong. With a nice broad torque curve and a safe 7,000rpm red line I can row if I want. With this set-up I'll have to be good at it, though. I watch some in car footage folks post up on youtube and what-not and most of the time it makes me cringe, shifts for no reason, over revs and bogs and clearly upsetting the car just because Ayrton Senna would shift there (no he wouldn't).
About rowing gears. There is something interesting I discovered in my motorcycle racing days. I learned it when teaching and control riding. On teaching weekends we would start everyone off by letting them out on track in their relative skill groups equipped with transponders to do a 20 minute session. They couldn't see their lap times, but we were recording them. Then after a little classroom time we'd let them back out, but they weren't allowed to shift or brake once they got to 3rd gear: 3rd gear only, no braking, ride as fast as you want. Then another break followed by another session where they were allowed to shift and brake again. Then it was leathers off for a longer break where we'd ask them what they thought their fastest session was. Everyone would say the the last session was their fastest. ALL of the street riders with no race experience (and about 50% those with race experience did) actually set their fastest lap times when we made them circulate in 3rd gear with no shifting or braking allowed!!! In most cases they were a LOT faster. This was true whether we were at a track with long straights like VIR's north course, or tight places like Summit Point's Jefferson Circuit. I was lucky enough to control ride sessions on the school's Aprillia RSV Milles. God what torque monsters. If I added only braking I could still pace the expert group in third gear (not the race group, though!). What a feeling coming out of a tight corner, rolling on the throttle and having the front wheel gently lift about a foot and slowly come back down as the motor crossed the curve from torque to hp. Mmmmmm.
Oops, sorry, I got lost for a moment. Where was I? Oh, yeah. Lunch time. See you later
-M