[Xyebo]

Any V6 manual drivers who autocross?


I've been to an autocross event at Santa Maria Airport, CA where there were two tight hairpin turns where my speed dropped to as little as ~20 mph. Since M6 tranny in the V6 engine tops out at 40 mph, I thought that heel-and-toe downshifting into 1st before the apex of these tight turns would make my run times faster.

However, it was exact opposite: no matter how well I nailed the turn or how fast I could do a 1->2 shift, I would lose 1.5--2 seconds to keeping it in 2nd gear all the way (on a 65 second course).


What gives? And do any other V6 drivers keep their cars in the 2nd gear all the way?

[Scargoes]

Mine isn't a v6, but generally going to first isn't going to help you if you already have momentum in the vehicle. The V6 should be able to pull away pretty good from 20mph. Unless you are coming to a stop and restarting, shifting into 1st and back into 2nd usually takes more time than the slower acceleration from low speed in 2nd gear. And then there is always the increased chance of missing a shift that will cost you much more time.

[Silent_H_]

I plan on doing my first AutoX with this car next month. I'd bet leaving in 2nd will be faster as you can be smoother, but maybe it depends on just how tight the course is. Way back in the day when I used to AutoX regularly with a Subaru Impreza, it was always faster to leave in 2nd. Those had much shorter gears but also less torque than this V6, so I'd imagine it'll be similar.

If I do get out there I'll try to remember to report back!

[foshjowler]

It's almost certainly better to leave it in 2nd. The time to shift is rarely made up by the faster acceleration. Then you have to factor in the change of on/off throttle balance and any imperfections in your shifting.

In the 4 years I've been autocrossing, in 4 different cars, I've used 1st on one run, and that was more just to do it than actually needing it.

[Roostie]

I've autocrossed my LGX for the last three years and I don't find it beneficial to downshift to first. I doubt it would usually cost you over a second, but I do think it's counterproductive.

If you downshift to 1st, that tight corner becomes much more difficult. A 1st gear downshift is the most difficult downshift, particularly in race conditions when you're managing heavy braking and turn-in to a very sharp corner. It will be difficult to put power down in 1st exiting the corner - so your brain has to calculate throttle modulation, and you'll be delayed by a shift on the next straightaway. All that work will distract you from smooth application of the brakes and steering.
The only car I autocrossed that needed a 1st gear downshift was an old-school 4-speed Porsche 930, that had turbo lag and such tall gearing (IIRC, 50 in first, 90 in second), that it usually needed a couple 1st gear downshifts on an auto-x course.

[Xyebo]

Thanks for the advice, gentlemen. I will keep it in 2nd.