I'm swapping a T56 into another car and need to know what the output of the VSS is.

I've been told that the '94-up T56 and 4L60E VSS output is 40 pulses per rotation, and read that the '93 G92 VSS had a 17 tooth reluctor, but I'm not sure if that means 17 pulses per rotation, or even how many rotations of the driven gear on either happens in a single driveline rotation.

My problem is that I can easily calculate driveline rpm at a given vehicle speed from tire size and differential ratio. Figuring out what's coming out of the VSS (I'm going to use a '93 T56, but assume that I might be able to use a '94 sender, if necessary) at that speed when you don't have the car running is difficult, obviously.

I was under the impression that the driven gear rotated once per driveline rotation, but is this a correct assumption? If so, then the output of the '94-up VSS would be 40 pulses per rotation and the output of the '93 VSS might be 17 per rotation.

Once I know what the output of the VSS is at 60 mph, then I'll know how to recalibrate it. My speedometer was calibrated to 8,200 ppm @ 60 mph, but has been reduced to 8,000 to make calibration easier. The GM PCM (which I'm not using, unfortunately) apparently puts out 4,000 ppm @ 60 mph. If I weren't using a stand-alone SEFI-8LO engine management system, this would be a little easier. Without the PCM to "buffer" the input of the VSS and output the correct number of pulses (after tweaking gear ratio and tire size with LT1 Edit, for example), I need to convert the "raw" signal of the VSS to something useable by my speedometer.

Any help would be greatly appreciated!!

BTW, I have a Camaro (Chilton's) manual, and it is extremely vague on the VSS except where it's located and how to replace it. The Mazda manual, by comparison, tells how many AC pulses per driven gear rotation, and how many pulses at given speeds, in 20 mph increments. Wish this information was readily available for the Camaro.

Thanks!!

 

There are four types of VSS signals required by the engine computer (ECM):
1. The two-pulse (2000 pulses per mile) square wave (D.C. current or direct current) used on all TBI engines through 1992, all computer-controlled-carbureted engines, and on 1985–1989 TPI engines.
2. A four-pulse (4000 pulses per mile) sine-wave (A.C. current or alternating current) signal is required by the 1990–1993 TPI, 1992–1993 LT1 engines, and 1990–1993 Camaro 3.1/3.4 V6 engines.
3. A 40 pulse per driveshaft revolution speed sensor used on 1993 and newer trucks with automatic transmission, 1994 and newer rear drive cars (Camaro, Corvette, and Caprice) with the automatic transmission.
4. A 17 tooth per driveshaft revolution speed sensor used on 1993–1997 LT1 engines with the Borg-Warner 6-speed transmission. An 11 tooth reluctor ring is used on 1993 LT1 engines with the Borg-Warner wide ratio (3.35 First gear) 6-speed transmission.

 

I've seen that information on the Jags That Run web site, which is where I found the 17-tooth reluctor information. However, I was told by someone else on this forum that the '94-up T56 does not use a 17-tooth reluctor, and is instead (#3) 40 pulses per driveshaft revolution.

Dakota Digital's SGI-5 is no help in that situation, because I need to divide the signal by about 5.4 and the maximum resolution of the DD SGI-5 is 2 (double) or 0.5 (half).

If I were using a GM PCM with an output of 4,000 ppm @ 60 mph (according to Ken Kelly), then doubling it would equal the 8,000 ppm @ 60 mph that I need. Without the PCM, I need a signal in the 4,000-16,000 ppm range or I'll need to use a different calibration device to "condition" the raw output of the VSS.

My driveshaft rpm at 60 mph is 2,578 (2.37:1 gear, P275/35-18). At 17 pulses per driveline rotation, the raw signal should be 43,831, which is why I'm hoping my math is wrong and the VSS doesn't output 17 pulses per driveline rotation (if indeed it is 17 at all). I'd have to divide that signal by 5.48 to end up with the 8,000 ppm @ 60 mph that I need.

Any ideas?

 

Jim:

I replaced my 1994 T-56 with a TH400. The TH400 has a 40-pulse output. With the stock PCM (M6) programming, my speedo read approx 2.3X actual speed. That would seem to confirm the 94 M6 PCM thinks that the 94 T-56 puts out a 17-pulse signal.

It was sort of cool to be able to peg the 155mph speedo at 66mph..... .

 

Thanks Fred. Well, that answers one question, at least.

 

http://www.sallee-chevrolet.com/Borg...bwt56pics.html

Another option that both JTR and Sallee chevy offer is a cable drive setup with a/m tail housing, you can run either a cable for the speedo or a after market VSS that will work with the 90-92 F-body speedometer. the JTR set is like $350.00 yikes!!! I dont know what the Sallee cost?

kingslam

 

Unfortunately my stock speedometer is electronic, and it's a '95 RX-7, not an F-body.

 

Go here and talk to this guy, he was an engineer for GM, worked on the electronic fuel injection and digital controls for GM.
http://www.howell-efi.com/

Send him an e-mail in tech support. He has helped a lot of my friends out in earlier years of swpping MPFI engines. Hey you sound like a cool swapper like me, I have done Datsun 240Z LT1 swaps, I have a 1996 LT1 I just swapped into my 95 4x4 S-10
here it is>> http://mediaservice.photoisland.com/...6659252037.jpg

and I am doing a Porshe 944 LT1 swap next, then maybe a 86 Jag. I own a custom swap shop and am building a brand new paint facility right now, I have a link here some place for swapping RX-7's with LT1's.

kingslam....

 

Thanks Kinglsam. I was the one who started the 3rd gen. RX-7 V8 conversion kit with Grant Robbins of Granny's Speed Shop. He's one of the largest suppliers of 1st and 2nd gen. RX-7 V8 swap components, and it was a natural place to start.

3 years later and my project is still in progress, partially because I haven't dedicated that much effort to it, but also because my 396 LT1 build-up has taken over a year and a half, and because I still haven't received all of my conversion components from Grant, which is another story.

The electricals are all worked out, and weren't any big deal. I had originally planned to use a GM PCM but the 7,000 rpm limit meant that I needed an aftermarket controller, and I went with the FAST SEFI-8LO. There was no use in having a GM PCM in the car just for speedometer conversion duty, so I sold my PCM, LT1 Edit, and the ALDL harness to someone else.

I had originally planned to connect the GM PCM directly to the speedometer, and Ken Kelly programmed the PCM to output 8,000 ppm @ 60 mph, which is what I then had my speedometer calibrated to when I had a new gauge face printed and the speedometer recalibrated.

Without the GM PCM, I'm left with the "raw" output of the T56 and converting it to use by the speedometer, which still expects 8,000 ppm @ 60 mph. The two are too far apart to use Dakota Digital's SGI-5, and one of their tech people said they had a "retired" device (SGI-1) that would handle it, but that's as far as I got. I've called and e-mailed and they either don't seem to have it or be willing to build one. If I can get my hands on one of those, or something that can "divide" the VSS signal by a resolution of up to 6 times, I'm in business.

So that's where I'm stuck, but I wanted to be absolutely sure what the output of the VSS was before going about finding a solution to reduce it to the levels I need. I plan on using a '93 G92 T56, so it's definitely the 17-tooth reluctor, but I need to know exactly how many AC pulses it puts out per driveline shaft revolution. The reason I'm using 60 mph for all calculations is that it's a mile per minute, and the ppm calculations are much easier.

Thanks for your help.

 

OK, simpler question (maybe). Does anyone know the number of teeth on the drive gear (transmission tail shaft) and driven gear (VSS shaft)? How about the number of pulses output per rotation of the driven gear?

It's too bad GM didn't document their system as well as Mazda did, or this would be a walk in the park...

 

Jim,

From what I can tell the 17 tooth reluctor also means 17 pulses per driveshaft revolution.

Now I'm not 100% sure on this but after doing the math and looking at the stock ECM file for my car its either a reasonable assumption or an incredible coincidence

Here's my reasoning...

A stock 245/50/16 tires is 25.65" tall so that means it rotates 786.5 times per mile. Now given the stock 3.23 axle ratio the DS needs to rotate 2540.12 times per mile. If each revolution generates 17 pulses then that means the VSS sensor generates 43182 pulses per mile. Looking at the stock ECM file it has a "Road Speed Constant" variable which is set to 43886 pulses/mile. Not a perfect match but taking into account rounding and tire wear its probably close enough (its within 2%).

Hope that helped...

 

The 93s use a simple gear configuration. Available Drive gears are 15 tooth and 17 tooth.

Available Driven gears are somewhere in the low 30's to max of a 45 tooth driven gear. The lowest mechanical combination is the 15 tooth drive gear and a 45 tooth driven gear which would correct for a 3.75 ratio gear set in the diff. the 44 tooth driven gear would correct for a 3.70 ratio. The stock setup (for 3.42s or was it 3.23s) was 15 tooth with 37 tooth driven gear. The 17 tooth drive gear only is used for the 2 series rear end.

Go to the TPIS web site or catalog. They have a full page of text on the available ratios and how to calculate the gear sets you need. They also have all the GM oem gears and their part nos.

For 4.10s or greater a 13 tooth drive gear is needed. LPE makes it for around $150, but it is noisy as Hell! Trust me I tried it and ended up pulling it and throwing it away.

Perry

 

But all that is for an Automatic (4L60/700R4) right? Jim is using a 6 speed and I didnt think it was possible to change the speedo gears in a T56.

 

jimlab contact me at grape@adelphia.net and i will talk with you about my lt1 in a 944 that passes smog with a working vss.

 

Thanks Jason. Ken Kelly confirmed that it is 17 pulses per rotation (which makes a solution more difficult), and I didn't notice the distinction of the VSS having a reluctor, which means no driven or drive gears, so I won't get out of this as easily as changing the number of teeth.