Has anyone done some documented testing on what behavior of the switch pitch is optimal for acceleration and drivability?

I'm aware of the stock behavior, which is to have it stay in high stall until just off idle, then go to low stall as you press the gas, then go back to high stall somewhere in the mid/upper range of throttle. This seems pretty alright, but also not really.

I'm also aware of the electronic gizmo someone made with delays and sensors. It makes a lot of sense to me, to have high stall any time your foot is on the brake or when vacuum drops below a certain point. The delay business I'm not sure sure about.

I'm seriously thinking of setting it up to react to vacuum and brake switch, since (1) the stock behavior seems not optimal, (2) its toggling the stall every time you ease on and off the gas in light cruising, and (3) my switch is a little on the flaky side at that off-idle engagement point.

 

Years ago I ran a switch pitch 66 442 trans using a 65 442 switch pitch torque converter. I used to start off in high stall and while still in 1st gear I would used a toggle switch to change to the low stall before going to 2nd. I would finish the run normally in 3rd gear low stall. People would always check out the car and would comment to other people saying that I was running nitrous. I was only ever asked by 1 guy what the switch was for, when I told him it was to control the torque converter. He didn't believe me until he looked the car over and after not finding a bottle or injectors. He stated that he was watching the car launch and while in 1st gear the car just seemed to jump ahead of other cars.

I still have the transmission but not the car that I was running it in. It was definitely the best junk yard find years ago. When you set the transmission up to control the pitch with a toggle switch you are basically creating a 6 speed transmission lol.

 

'I'm also aware of the electronic gizmo someone made with delays and sensors.'
That would be the device developed and sold by Bruce Roe, who I believe occasionally posts here. It is a well thought out and tested device that bypasses the pesky throttle switch. I fooled around with vacuum switches adapted to a rebuilt, tested-good throttle switch. The delay relay on the vacuum signal is a necessity, as without it you will have annoying oscillations - low to high to low stall around the vacuum switch setpoint at some cruise conditions. Roe's device has another timer to protect from overheating ATF with extended climbs in high stall, another nice feature for most applications. The Bruce Roe device is designed around optimizing the switch pitch control experience for regular and spirited around town driving. For race/track or hell raising you would design it differently, or maybe even keep it simple with a full manual switch.

I believe only Olds used the rotary style switches with the multiple sets of internal contacts subject to wear. Other GM makes controlled the switch pitch differently. The brake switch was one of the primary control methods for the switch pitch converters installed in Pontiacs. It seemed to be more reliable but the Pontiac brake switches may be harder to find than the olds style switches now.

It is possible to DIY a control system for the switch pitch that has more tailoring for a particular application (rear gear, cam, high stall point, low stall point, etc). But as somebody who did such a DIY, I probably paid for the Roe device 3 times over in my time/materials.

 

So I ran a wire to the brake switch and set up a relay to go to high stall on brake application. I adjusted the rod for the existing rotary switch, so the high stall on the low end is eliminated, and the high stall on wider throttle comes in a little bit sooner than originally. This got rid of the oddity of the off-idle behavior, and gives me a satisfying "downshift" without a gear change when I really lean into it. Very happy with how this is working now!! Excellent point above made about the apparent lack of hysteresis in a vacuum switch and long hauls with high stall. I will not be adding any vacuum input, since the behavior based on aggressive throttle position is very intuitive and satisfying now. Total time about 2 hours and the cost of the relay.

 

Sounds like it would be REALLY fun to set up a rpm-controlled switch so it would change from high to low ambear the top of 1st, and back to high stall for 2nd, then low again. Of course by then we're going too fast to really be marveling at the six-speed simulator I may toy with this idea, when I run out of other hairbrained schemes I thoroughly enjoy cooking up.

 

edited, posted in error

 

An RPM switch working in conjunction with a rebuilt stock rotary throttle switch is where I ended up. You need to use a high end RPM switch as the simple Summit and Ebay stuff I went through first were not robust enough for the application. Specifically you need an RPM switch with an accurate hysteresis adjustment for setting the RPM band between open/close/open/close cycling of the switch. You need this for the same reason that the vacuum switch needs a delay relay.

I have found that the Lingenfelter RPM-003 from Summit ($132) works well. I set the RPM switch to keep the high stall engaged up to 1600 rpm and that works well with the governor and vacuum modulator tuning I did to the TH400 (Transgo #2 shift kit). The shift kit and TH400 tuning is set for firm part throttle shifting but the switch pitch in high stall will soften them considerably when you are putting around town at low throttle in high stall. The additional control over the switch pitch at tip-in and low rpm also works well with more aggressive cams and idle tunes, as the high stall mode will soften up the creep and engine drag at low rpm as you drop it into drive. This low rpm switch pitch control would be difficult to replicate with a combination of brake and vacuum switches. I put the RPM switch hysteresis setting on the Lingenfelter at the max setting of 350 rpm as this provides the best switch pitch performance for my engine/drivetrain.
In my heavy wagon (.342 rear gears, Olds 468 torque build), under light throttle around town it will launch in high stall and stay in high stall under 1600 rpm where I get a softened 1-2 shift within a few seconds. Crossing 1600 rpm I get the feel of another gear change as it drops from high to low stall before finally a more noticeable 2-3 in low stall. With more aggressive around town driving, a firmer 1-2 will happen above 1600 rpm in low stall.

When I hit the gas pedal hard, the stock rotary switch will engage high stall again to help acceleration with the pedal just past half-way to the floor. Keep mashing the throttle and the kick down energizes on top of the high stall and you drop down 3-2 or 2-1 for all the noise and fun. I decided that once you rebuild the stock switch, and combine it with the RPM switch, I didn't need the vacuum switch with all the delay electronics and relays.

For most trying to bring a switch pitch TH400 back to life, I still stand by my original recommendation regarding the Bruce Roe controller: if you have a more or less stock build, and you want to get the switch pitch working better than it did from the factory, he has done it all for you. You don't have to rebuild 60 year old junkyard switches that weren't designed to be rebuilt and you don't have to home brew alternative controls.

 

This is basically what you can do when you use a toggle switch. I was running a 3.91 rear gear with that transmission and absolutely love it. It was a low stall of 1800rpm and a high stall of 2800 to 3000rpm. I ran an external transmission cooler fan to avoid overheating the fluid. I kept the 3.91 rear-end as well.