I was doing some research for a prom I might need for my project and found 2 different RPO codes for a T5 in a 91 firebird with 305 TPI VIN F. The same thing is under 90s and 92s. These are from the thirdgen rpo decoder. M39: transmission, man 5 spd borg warner, 77mm, 2.95 MK6: transmission, man 5 spd borg warner, 2.95 1st, o/d Anyone know what the difference are if any? What is the 77mm?

77mm = the distance between the center lines of the mainshaft and the countergear

One of them would be the grocery-cart (CAFE sacrificial lamb) version with the stupid .63 OD, found in L03 cars. The other will be the one with the more sensible and useful .73 OD, found in the performance cars. IIRC the MK6 is the one that came in the better cars. But I don't pay any attention to any of that, I just look at the parts. They are what they are, all "codes" aside.

I'm finding 3 different proms for 91 VIN# F with a T5 with a huge price difference. Since this is a Speed Density TPI and the prom has nothing to due with rear end gears does anyone know why there are 3 different prom part numbers?

I know why there would be 2: 5-spd, 5-spd w/G92. Can't guess why there would be 3.

Why would you pay money for a stock PROM? That's crazy talk.

Transmission ratio & rear gear affect engine loading, calibration will be different. There is also Calif vs Fed emssions standards.

RBob.

90-92 Speed density proms are not programmed with rear end ratios like 85-89 proms so the G92 should not have anything to do with it from what I've read and from what companies that program chips have told me. Some of the prices for a new prom are cheap.

G92 = dual cat exhaust, in addition to "performance gear ratio"

Changes the engine's air flow requirements, which DOES change the PROM.

Don't buy a stock PROM. HUGE waste of money.

N10 = dual exhaust
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G92= performance rear end

G92 cars got N10

Read this link to understand what I'm doing and its all stock: http://www.thirdgen.org/techboard/df...2-350-l98.html (90-92 350 L98 TPI SD with a T5, prom question??)

As far as the price issue is concerned, just recently GM decided that they weren't charging enough for SD proms apparently. They used to be about $60 about a year ago, and now they've skyrocketed to like $175 or so. Probably one of your most economical/practical solutions would be to just get any used 90-92 SD prom, send it in to a chip programmer, and have them tweak the settings for your application. Besides, it'd be the perfect time to have other things changed or eliminated, such as EGR, VATS, injector size, speed limiter, etc.

Here is the problem I'm having sending it to a programmer:

Fastchip wants $350 and I send a V8 SD PROM to do a 91 350 TPI with a T5 all stock and he has a 90 listed for $159 on his site.

TPIS wants $150 and says just send any V8 SD PROM.

Street and Performance wants $185 and its best to start with a V8 SD T5 chip.

All the above are for a 91 350 TPI with a T5 and I send them a SD PROM.

TPIparts said they don't do want I want but some programmers will just take a 350 SD PROM and just uncheck the A/T box when you are reading it.

That price from Fastchip is pretty outrageous, especially considering you're not really needing a chip tuned for a heavily modded motor. And yeah, tpi parts really doesn't do much for the money. It's like you said, all they really do is change the flag switch in the prom from auto to manual. The two places I've heard a lot of good things about are PCM For Less, and LS Racing Chips. Might want to check with those two places before committing.

I found PCM for less but nothing for LS Racing chips. Fastchip was crazy, Street and Performance would do it for right at $300 and they supply a new Prom. Honestly the guy at Fastchips didn't really sound like he wanted to do it and was not very helpful. S&P was the most helpful and really sounded like they knew what they were talking about. TPIS was also helpful.

The PROM itself is like $2. That's not where the money is.

No mail-order tune is going to be right for your car. For what you spend on that, you can buy the equipment and learn to do it yourself; and that way when you decide you don't like whatever programming you have, you can just change it.... WITHOUT another $300 mail-order.

That's why it's not good common sense to buy a stock PROM.

I have a AUJP (90-92 350 SD TPI A/T), ATNX (90-92 305 SD TPI M/T) and a AWFY (90-92 305 SD TPI A/T) PROM, MEMCAL or CHIP whatever the name is for the assembly that clips into the ECM like memory in your computer. I really don't want to program my own chip at this time. Its is hard to believe that a mail order tune can't set a TOTALLY stock 91 350 SD with a T5. Why is it so hard to take the AUJP and copy the engine settings to the ATNX PROM or visa versa? BTW, how much would it cost me to get everything I need to program my own proms?

http://www.thirdgen.org/techboard/diy-prom/ Don't be surprised if you have to copy and paste it into your browser... seems like the message board has gotten farkled about that, again. Maybe it will work and maybe it won't.

Everybody always says "totally stock"; except that their cars NEVER are. Just the fact that it's a 350/T-5 already puts you out of the possibility of any stock bin working right.

I can't answer for the "hard to believe" part. I'm sure it was hard for people to believe in 1630 that the earth orbited around the sun, and not the other way around. Doesn't change the facts. If the facts are hard to believe, the facts aren't at fault.... the "believer" is where the adjustment has to be made, not the facts.

But if you want to spend however much of your money on a mail-order tune, that's your business; don't say you weren't warned.

[quote=Pat Hall;3588196]As far as the price issue is concerned, just recently GM decided that they weren't charging enough for SD proms apparently. They used to be about $60 about a year ago, and now they've skyrocketed to like $175 or so. QUOTE]

The word I got is that GM is discontinuing most of the proms and that why the prices have skyrocketed. No wonder GM can't make any money

I took your advice and bought the equipment to burn my own. Due to all the different advice, prices etc. from program companies I think I will be better off doing my own programming.

Excellent! Now YOU have the power to make it like you want it. I think you'll be MUCH happier with that in the long (and maybe even the not-so-long) run.

My info is AXXD for a 90-92 305 5-speed with G92 (dual cats), AXXC for 90-92 305 5-speed without G92 (single cat). If ATNX is the third chip, I have never heard of that one.

I have compared an AXXD and AXXC and there are differences in the chip, but they are pretty minor.

The ATNX chip is from a 91 Formula 305 TPI 5 speed with dual cats and a 3:42 gear (G92). Pulled it my self from a running parts car I have, all stock. I had 2 of these cars but just sold the other one about 2 weeks ago.
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Here is a link I have for proms: http://www.3rdgenformula.com/91/promcodes.htm Do you have a good link for broadcast codes?