3spd/3.90:1 cars ??
 

I have been wondering this for a couple days;

Are there any 3spd/3.90:1 cars out there still?

I was re-reading Rock'y (70-81) Firebird book when I (re)read that in 1971 a Formula 400 could have had the "performance gears" opted (3.73:1) with no transmission option;
I stopped there for a moment because this is something I am going to be trying in my car, and I thought to myself that I don't recall reading this for 1970.
I then looked in my 1970 Firebird literature and found no evidence of the being able to order performance gears for 1970 Firebird Formulas with no transmission option - namely the assembly manual seems to show limited gear sets available for Muncie three speed cars - even though I couldn't find any idication in my ordering info about limits for option
Then on a hunch, I pulled out my copy of the 1970 Pontiac 'Performance catalogue' and saw (well really looked closely at for the first time) this:

https://forums.maxperformanceinc.com...1&d=1571762669
(Full sized image HERE.)

... and there I saw it, GTO's (or others) could have had the 'base' HD 3 speed teamed up with 3.90 or better gears.

Does anyone know how many cars were ordered like this?
or if any survive?

As a side note, does anyone know if, like the Firebird, opting for the 'performance' axle required an upgraded cooling system?
My car currently has it's original 3 core rad (mine is a 3.55:1 car), and I am wondering if the 10% extra rpm for a given speed might require better cooling.

Bill Nawrot (YNOBIL) is the original owner of his '72 GTO.

He ordered it with a 3 speed, because that's what his previous '67 GTO had. I'd have to do some research to see what rear gear he had in it (or he might join us here).

http://oneownercollectorcar.com/inde...to-bill-nawrot

K

Rear Axle 9799168 XH

that was a great read;
I can't help but feel I've read that before, was that an article from Smoke Signals or another publication?

But to bring this back on track, it appears as though Bill's GTO wasn't ordered with a 'performance axle' (RPO 368):
http://www.gt-37.org/gallery/i.php?/...bad7a62-xl.jpg

I actually don't see the option for a performance axle spelt out in the accessorizer for 1972:

http://www.gt-37.org/gallery/index.p...y/193/start-15

Thanks for chiming in!

I believe on the GTO 3.90 or numerically higher called for mandatory HD cooling which basically got you 4 core vs 3 core, seals around the rad support etc.

Looks like the "XH" rear axle is a 3.55 locker.

Sorry -

K

Very very few '71 Pontiac A-bodys were ordered with 3.90 gearing. Have records on over 1/6 of all '71 & 71 1/2 GT-37's profuced, & only 2 400 4spd cars have shown up with 3.90 (opt ratio rear) with the HD 4spd (M22). Have noted invoice copies on three 71 GTO's factory equipped with 3.90 HD STT. No factory 3.90 gears for the new for '71 model 8.5 F-body axle.

Have never ran across evidence of anything lower ratio than a 3.55 STT factory installed behind the LS5 engine in a '71 A-body. The 71 GM service manual was printed way before actual production. It has a listing & for years there have been internet sites showing charts which list a code for a 4.33 HD STT rear in a '71 400 A-body. Didnt happen, was never actually offered.

For '72 models 3.55 was as low a ratio as was offered in A-body's, no factory optional 3.90 HD STT rear.

In the magazine roadtests of '70 T/A's there is a roadtest which notes 3.90 ratio rear, whether someone at Pontiac Engr set up a 3.90 ratio 12 bolt R&P in the test car's rear & the car was some kind of factory "Ringer", OR whether the magazine writer was wrong & assumed the tested 70 T/A had a 3.90 ratio rear, is all up in the air.

@ OPH, thank you very much for speaking up with such a detailed response.

What do you mean by "STT" - I am guessing this is meant to indicate the (standard) Muncie three speed?

I actually created this thread here because it has appeared as though exponentially more GTO's and Tempest/Lemans were built with the Muncie three speed (offered through to 1974 in the A-body) than the Firebirds built with the three speed (only offered 1970 & 1971).

First I didn't know that 3.90's were actually available in 1971, but only five(!!) cars being recorded as having the option, makes it seem incredibly rare!!
I did not expect that.

yes, my understanding is that this ratio was never offered outside of the "BOP" 10 bolt rear, never offered for either 1970 or 1971 on the Firebird;
The closest was 3.73 offered both years, on both the 12 bolt (1970) and 10 bolt (1971) "corporate" rear end.
I believe that after 1971, the best ratio you could ever get in a Firebird from the factory was 3.42:1.

Interesting on both parts, thanks for telling me this.
Maybe I'm wrong, but it has seemed to me that 3.73:1 wasn't an incredibly uncommon option for 1971 LS5 Formula's or Trans Am's!?

This is not a surprise to me;
Actually the surprise is that even 3.55 was offered - does this mean that 1972 Pontiac A-bodies used a 'corporate' 12 bolt, or a 'BOP' 10 bolt rear?

I had always assumed the writer made a mistake, and assumed that the 1970 Firebird RAIV standard gear ratio was the same as 1969 - but have understood that the different design rear dictated the ratio change.
I have understood that 3.90:1 was never offered for the 12 bolt rear, and that is only a more recent aftermarket offering.
I will be quick to admit, I am not too up to speed on 1970-1972 GTO/Lemans ect equipment & options.

Again, I only chose to point out this ratio because it was what was used for 1968 RA Firebirds, and was still shown as available for 1970 Pontiac A-bodies with the Muncie three speed (see attached picture in post #1).

STT - Saf-T-Track (or Posi as some same)


:)

/\ thanks - that makes sense!!

I was thinking;

STT = Standard Three ??

Re Jon: can't handle all the parsed links/quotes. Very hard to read & follow.

1) yes, '71 Pontiac A-body's with 3.90 HD STT were seldom ordered, dealers & salesmen seemed to know the wide ratio Muncie & 3.55's provided the best performance with the stock 71 400 4bbl engine.

2) No such thing as a "BOP" 10 bolt, have gone into depth on this many many times. The style of rear you are referencing is known as the PONTIAC late style 8.2 rear, it was introduced in later production '69 Firebirds, & continued on under '70-72 Pontiac A-body's & GP's. Olds & Buick did not use it.

3) Was referencing Pontiac gear ratio availability in '71 & 72 A-body's.

4) '72 Pontiac A-body's continued to use the PONTIAC 8.2 late style 10 bolt style rear, no early 8.5 A-body rears were used in Pontiacs. The Late Pontiac 8.2 is noted by 7/16" diam LH thread ring bolts on the ring gear, & tapered bearing axles. The 12 bolts used in '72 A & G body's when ordered with 455 engines continued to be McKinnon plant 12 bolts, McKinnon plant specific cast center housing, 3R pinion flange, specific c-clip axles, smooth style backing plates like used on Pontiac 8.2 rears, not the spotwelded flange Chevy style backing plates. This version of 12 bolt rear was not same as avail under a Chevelle, where the 3.73 axle ratio was optionally avail.

5) would have to dig out that particular roadtest, try & see if can note if the car was preproduction model. Pontiac Engr could have easily specced 3.90 gears, there is a factory Chevy part number for 3.90 12 bolt gear set. Have noted before there were at least two '70 RA4 T/A's invoiced out to Pont Fact Engr, eventually being shipped south & sold as used cars in late Feb '71, one could have been the magazine test car.

6) the 3.90 ratio was first optionally avail in a GM A-body in an early PONTIAC 8.2 rear in a '64 GTO. Was not avail in an early Buick 8.2 rear which came in a late season '64 442. Have ran across a few early Pontiac 8.2 STT rears with optional 3.90's. More common to run across 3.90's w a 3spd in an earlier production GTO's, def a price leader type build.

thanks for the information again;
I'm sorry you found my post hard to read, I intentionally typed it like that to make it easier to read and follow.