Turbo 400 challenge question.

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utahvette
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Turbo 400 challenge question.

Post by utahvette » Tue Feb 02, 2016 11:44 pm

OK gang, This is the Turbo 400 Challenge. This is the transmission out of my Corvette. I built this 25 years ago and did some mods that I thought were pretty trick at the time. It has worked flawlessly all these years so the mods worked the way I intended. Can you figure out what I did by looking at the pics? Maybe it's more obvious than I think. I'll give the answer in a couple of days.
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John Wallace
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Re: Turbo 400 challenge question.

Post by John Wallace » Wed Feb 03, 2016 6:39 am

Is the yellow wire going to a micro switch by the shifter quadrant?

Possibly using the downshift pressure to be regulated by some gear position and pressure reading?

:?:
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utahvette
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Re: Turbo 400 challenge question.

Post by utahvette » Thu Feb 04, 2016 11:30 pm

This is a "switch pitch" or "variable pitch" turbo 400. Simply put, the torque converter has 2 available stall speeds that are achieved by hydraulically changing the angle of the stater vanes. Controlled by an electric solenoid. In stock form they only give about 1000 rpm difference between low and high stall, this one however, has been modified to give a low stall of about 1600 rpm and a high of 4500 rpm. It's wired to the brake light switch so when the brakes are applied the converter is in the high stall position and the engine doesn't struggle against the trans. It is also connected to the kick down switch to provide high stall during full throttle. When just cruising around its in low stall and therefor doesn't have all the slippage and heat build up that a loose converter would have. That's all pretty standard for the way these operate, the part I came up with is that I wanted the converter to change from high stall to low automatically after the car launched under full throttle. The solution I came up with is tapping into the governor pressure line with a pressure switch. It turns out that on this transmission governor pressure at 40 mph is 40 psi. So it was a simple matter to run the power through a 40 psi switch and then to the converter solenoid making the converter switch from high stall to low at 40 mph at full throttle , tightening up the converter for less slippage going down the track. It all works together seamlessly. The only thing that is noticeable driving the car on the street is when leaving from a stop, the converter is in high stall and as soon as you take your foot off the brake it switches to low stall and you can feel the car surge forward as the converter tightens up. Its really a kinda cool feeling. All this goes a long way in making the car comfortable to drive on the street and getting reasonable fuel mileage.

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Re: Turbo 400 challenge question.

Post by dave brode » Fri Feb 05, 2016 5:20 pm

Interesting. Wiese or PAE converter?

Stock pressure reg spring in the pump?

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Re: Turbo 400 challenge question.

Post by utahvette » Sat Feb 06, 2016 12:11 am

Its a pae converter. I think they are out of business now.

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Re: Turbo 400 challenge question.

Post by peejay » Sat Feb 06, 2016 5:09 pm

utahvette wrote:The only thing that is noticeable driving the car on the street is when leaving from a stop, the converter is in high stall and as soon as you take your foot off the brake it switches to low stall and you can feel the car surge forward as the converter tightens up. Its really a kinda cool feeling.
Sounds like it feels like a twin clutch automatic, they don't "creep" against the brake since that would burn up the clutch, so the cars don't start to engage the clutch until after you let off the brake all the way. A lot of people hate this feeling because it's not what they expect from an automatic.

What you did sounds really trick and in hindsight an obvious modification to make.

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Re: Turbo 400 challenge question.

Post by Speedbump » Sun Feb 07, 2016 4:04 pm

I have the stuff to do a switch pitch 400 if you want. I ended up going with a 4L80 in my project. I had A-1 redo the converter from PAE.
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Re: Turbo 400 challenge question.

Post by rfoll » Tue Mar 08, 2016 6:55 pm

I had a switch pitch in my 455 65 GTO with a KB V6 converter. I did the brake light switch thing and it worked flawlessly. When the car launched, it was in the fat of the torque curve and the car would really leave hard. With a tightened up converter, second gear was a serious yahoo. The difference with the converter left on high stall was about 1/4 second slower. I have one in my C20 pickup, low stall 800, high stall 2200.
So much to do, so little time...

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Re: Turbo 400 challenge question.

Post by GLHS60 » Sat Apr 16, 2016 3:39 am

I built some many years ago and it took me a while to find out where to put the restrictor.

I ran mine off a toggle switch for fun, stall in high, switch to low without moving and the tires would spin.

Your idea is great, they sure are a cool feature!!

Thanks
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Re: Turbo 400 challenge question.

Post by rfoll » Sat Apr 16, 2016 10:22 am

The one in my pickup is on a switch. it's useful backing the trailers around the driveway slowly, and pulling the boats up the ramp after loading. I used it for a gear splitter on hills when I used to drive fully loaded up hills at high altitude
So much to do, so little time...

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Re: Turbo 400 challenge question.

Post by BBCFAN » Thu Sep 08, 2016 11:17 pm

rfoll wrote:The one in my pickup is on a switch. it's useful backing the trailers around the driveway slowly, and pulling the boats up the ramp after loading. I used it for a gear splitter on hills when I used to drive fully loaded up hills at high altitude
Can you explain this?

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Re: Turbo 400 challenge question.

Post by rfoll » Fri Sep 09, 2016 10:22 am

When the converter is in high stall, the engine has more rpm at any given speed. When pulling a hill with a heavy load, rpm at high stall was somewhere between 2nd gear and drive. You wouldn't want to do this for very long as the temps start going up. When everything is cold, the high stall is handy to take the stumble out of the engine, and to soften the high rpm from the fast idle with the choke on. One of the main reasons I wanted the converter is the low, (800 rpm), stall feature's effect on the highway. Engine speed at 60 mph was noticeably less, and economy improved.
So much to do, so little time...

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