One thing I've been putting off for some time is the transmission. Hernia operation (minor, umbilical, no biggie, thanks for asking) in November precluded my lifting anything too big so this has been hibernating under the bench for a while. The plan was, originally, to put in the car and see how it shifts, but this project has evolved to be a nut and bolt sort of affair. Am I going to stick a used, tmu, unknown transmission in this car, after all the work I've done? Nah.
So somewhere along the way I started Autocrossing the Rot Rod and changed out 2nd and 3rd for shorter ratios. The thing is an absolute beast now. This little experiment was a success, and a learning experience, and it only reinforced my opinion that a gearing change to better suit a car for it's intended use is absolutely one of the best things you can do. Yes it seems a little pricey (more on that later) but it's such a huge advantage!
I called my trans for the Rot Rod an SC/RS/Carrera hybrid which is pretty accurate, as the final drive, 1st, 2nd, and 3rd are the same as the SC/RS and 4th and 5th are stock 3.2 Carrera ratios. changing just 2nd and 3rd meant it was a budget friendly proposition, and while I was in there I replaced the 1st gear dogteeth, the 1/2 shift collar, and the 1/2/3 synchros (remember the new gears come with fresh dog teeth). It was previously reluctant to upshift, downshift, or go from neutral into 1st at a full stop, but now it shifts like a dream instead of a nightmare.
One thing that I (predictably) don't love about the stock 4th gear is it's a bit doggy compared to third and the upshift does have a fair RPM drop but for the usage the Rot Rod gets it's a good compromise.
For this car I decided to go slightly longer for 2nd gear, with a 1.933 ratio compared to 1:2.000 for the SC/RS, the same 1:1.381 for 3rd, and a 1:1.08 for 4th (compared to the stock 1:1.000). The 5th gear for the late SC transmission is 1:0.8241 so it's a bit lower than the Carrera (but still geared for 165mph at 7000rpm!!). The 4th gear change gives me one more "good" gear for higher speed backroad driving, and retains the long 5th for cruising between special stages and driving home from the track
The results, in graphical form:
Comparing the before and after on the graph might make you thing there's little enough change that it's not worth the trouble, but after trying this out on the Rot Rod I know it's going to be fantastic! Nice close ratios from start up to 135mph, and a long fifth for relaxed highway cruise. Should be fun!
I should note, this is nothing groundbreaking, in fact pretty familiar territory for many on the forum. Bill Verburg and Matt Monson come immediately to mind for their tireless contributions to any and all gearing related discussions, gliding_serpent for sharing his though process in selecting gear ratios for his track car, Gordo2 did a 2nd gear swap with good results, and I am sure there are many more.
Of course let's not forget Peter Z. and his classic, the 915 tutorial, and Gordo's transmission rebuild thread. Thanks, guys!!!