Hello fellow GRMers. I am getting my co-driver back after about a 9 month absence. Due to some medical and life issues, we are debating building a new autocross car with an automatic transmission and a bigger backseat than our current Mini. My default choices would be the VW GTI or the E90 M3 with a dual clutch gear box.
In an attempt to broaden my car horizons a bit, I am looking into RWD American cars. CAM looks fun and bumping up into a populated Hoosier class (ESP/CP) is a nice bonus. What does it take to build an automatic transmission that will cruise at 80 mph on the way to the event, then handle an autocross course without a fuss?
Looking around at some C-Prepared cars with automatic transmissions, it looks like they launch in first gear, and shift to second at the first corner. It seems pretty close to the plan for a manual transmission. I am guessing I need a manual valve body, a big trans cooler, and to strengthen 1st and 2nd gear. What else needs to be done to the transmission? I have read a bit about locking the torque converter but I don't quite understand when it should lock and what should control it. Is a solenoid controlled transmission like the 4L80E more or less of a headache than the old school version? After the transmission is set up, is it still reasonable to drive on the street?
In reply to ojannen :
I don't know if it's any different than any other GM transmissions but my 96 Impala SS had a nifty little trick that it did. If you put the shifter in 1st and left it there it would shift to second at redline but wouldn't shift up to third, you could bounce it off the rev limiter in second. However if you slowed and the revs dropped enough it would shift back down into first. IIRC, that happened at about 3500rpms. The first time it happened I was in a decreasing radius sweeper and the tail stepped way out, it was an eye opener. Once I got used to it however I got pretty adept at using it to my advantage to walk the big car through some pretty tight elements.
I like my 4L60e. I can put it in 2 and it will 1-2 shift then stay in 2 which is perfect for the whole course
For a gm car a call to Art Carr transmission's for a 200 r4, If you didn't drive it to and fro... a power glide for a dedicated car.
but then again if you did the big tracks go 200 r4,
Why then would I say a 'GLIDE, because you can beat the snot out of them. they can be built with out a torque converter so the heat isn't a killer and the mass is Gone.
My dads 69 427 corvette th400 was one of the top autocross cars up here back in the day with both the original l36 390 427 and the 427 tri power race engine.
and he was 2 ice dice championships here with a 66 corvair 95 Hp powerglide.
WHat Patrick said. I autocrossed automatic C4 Corvettes by starting in first, upshifting to 2nd and leaving it there.
conesare2seconds said:
WHat Patrick said. I autocrossed automatic C4 Corvettes by starting in first, upshifting to 2nd and leaving it there.
That's pretty much how I run the Jeep in rallycross. Throw the shifter in 2, it starts in 1st, grabs second like it's in D and then stays in second unless I get on it hard enough to force a downshift back to first (which will only ever happen in a pretty much straight line, so the shift isn't a traction problem). With enough power (and ideally a wide torque curve) and enough converter, you won't get the winding it out to redline satisfaction of a manual, but it'll be more like driving a CVT that has the ability to shift its gearing range.
Id run the 700r4 in my el Camino by putting the column shifter in 2nd and leaving it the hell alone. Stock 200k mile junkyard trans. Big aftermarket cooler from a motorhome. Never had an issue, and that thing was treated wirse than a rental.
A TH350, a 2.93 gear and a willingness to use 6200rpm will allow you to run almost every autocross course in first gear.
A 700r4 with 3.73 will do a very similar deal, but on second gear. First is very steep in a 700.
In reply to Streetwiseguy :
Which is why the 700-R4/4L60 sucks.
You can now get a gearset for them now that upgrades them to the same ratios as a 200-4R. Still not as "good" as a TH350/literally every other 3 speed automatic, but better. I think even the JATCO 3-speed automatics are 2.45/1.45/1.0.
Jeff Ellerby uses a race prepped 2 speed Powerglide in his DM Lotus clone and it shifts super fast. I don't know all the details but it sure looks like it works well and would be easy to do in a CAM car
If I use a powerglide or a TH-400 with second gear setup for about 70 mph at redline, how do I get the revs down for the drive to the event? I know Gear Vendors makes overdrive units but they are all over $2500.
The built 200-4R transmissions look like a pretty good fit with an overdrive and a better 1st gear ratio than the more modern transmissions.
How does engine braking work for these transmissions? Can you lift to get more weight over the front wheels like you can on a manual? Most of the manual valve bodies I have found say there is no engine braking at all.
If you want to drive it to the track and be able to cruise then buy a 200r4. Get a good one though. Art Carr no longer owns Art Carr transmissions and their quality over the years seems to have slipped. The real Art Carr owns Califormnia Performance Transmissions and if you pay the money for a good one and use a good cooler they will last a very long time. The 4l80 is an awesome trans but they require a controller or a manual valve body and they use a ton of HP to opperate.
ojannen said:
If I use a powerglide or a TH-400 with second gear setup for about 70 mph at redline, how do I get the revs down for the drive to the event? I know Gear Vendors makes overdrive units but they are all over $2500.
The built 200-4R transmissions look like a pretty good fit with an overdrive and a better 1st gear ratio than the more modern transmissions.
How does engine braking work for these transmissions? Can you lift to get more weight over the front wheels like you can on a manual? Most of the manual valve bodies I have found say there is no engine braking at all.
Well that will also depend on what you are planning for a engine or car combo. Going to short of a gear even in autocross can result in running out of gear on the straits. Some corvair guys have found this with the 3.89/4.11 vs the 3.55. Now if your running an engine that’s making plenty of power and torque a shorter ratio can potentially hurt performance and traction as those engines need less gear.
https://www.facebook.com/Malibeast/
This is what an automatic autocross car can look like. (Any of the white helmet videos are me driving, black helmet is the cars' builder/owner)
Streetwiseguy said:
A TH350, a 2.93 gear and a willingness to use 6200rpm will allow you to run almost every autocross course in first gear.
A 700r4 with 3.73 will do a very similar deal, but on second gear. First is very steep in a 700.
The short 1st, run in 2nd thing works great if you've got enough power to avoid dipping far enough into the throttle for a 2-1 downshift except in a straight line. It means you get the short gear to scoot off the line, grab 2nd before the first corner and then run 2nd through pretty much the rest of the course.
Ford transmissions like the c4 and aod non E lock into whatever gear is selected. If you put it in 2nd that's the only gear you get it will not up or downshift. My c4 engine brakes fine but it's a stock unit.
ojannen said:
How does engine braking work for these transmissions? Can you lift to get more weight over the front wheels like you can on a manual? Most of the manual valve bodies I have found say there is no engine braking at all.
There are manual valve bodies that allow engine braking. They are aimed at off roaders that want to crawl down the hill using engine braking.
18+ Mustang GT with the 10spd? It's supposedly a brilliant transmission and shifts like a dual-clutch box.
19x11s with 305s fit as long as you're willing to run spacers up front.
I think we were thinking this might be 'on a budget'. I did.
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