1 Nov 2016

Something I’ve wondered about for a long time is transmission longevity when running a turbocharged engine. The stock gearbox handles about 170 ft-lbs torques (as Clarkson calls it), but add a turbo and torque can be double that. 1st-4th isn’t an concern since they were upgraded to PPG straight-cut gears; the concern is about 5th and 6th which are still OEM helical parts. Certain tracks like Autoclub Speedway are set up for NASCAR and track day events run half the oval, a billiard-table smooth freeway where you go flat-out. Fast cars can easily do 150-165 down the front straight and with fourth gear at 0.909, it results in 139 mph at 7500 rpm. 8000 rpm is 149 mph but I’d rather not (regardless of what my engine builder says) since the K24 has a piston-rod geometry that isn’t as friendly to high rpm like the K20 is. Okay, part of my reluctance has to do with popping the first engine and wanting this one to last*.

Anyway, I asked on a Honda forum what the guys with turbocharged cars had found and unsurprisingly, several had stripped the teeth off 5th and 6th. The gears will still be used for cruising, but for longevity, boost will be reduced on those gears. I don’t want to spend $$$$ on a very nice sequential Quaife transmission because I have to draw the line somewhere on cost.

Somewhat related, the new engine is noticeably smoother, even with the stiffer engine mount. Just yesterday I wound it out in second gear and got surprised by the rev-limiter. Normally I can tell what rpm it’s at by feel but not so with this engine. It’s more “Swiss watch like” over the old one. I guess that’s a good thing!