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I have a 72 LeMans that I put back on the road a few years ago. It's got a Pontiac 400 with mild cam, Edelbrock Performer intake, Holley street avenger 670 carb, aluminum radiator with electric fans, TH400 auto with 2.78 gears in a GM 8.5" rear axle. I also put a Hotchkis spring and swaybar kit into it, which tightened up the suspension a lot.

There are three major mechanical things I want to do the car still, all will cost in the same ballpark $ wise: 1) getting functioning AC 2) installing the TH200-4R that's in my garage 3) Ditching the carb for EFI.

I have some of the AC parts, and intend to use the factory setup inside the car, while converting to a modern style compressor and R134a, I estimate I need about another $1000 worth of parts to get it working.

I have a TH200-4R (BQ code) that I'm going to put in place of the TH400, but I will need to at minimum change the rear axle ratio from 2.78, probably to 3.55. While I'm at it I'll also put in an Eaton Truetrac, and potentially new axles and aluminum driveshaft, estimate $1500 total.

Also thinking of going the EFI route. The carb has a couple spots where it goes lean, and chasing it is driving me nuts. (I have a wideband O2 sensor installed to help in carb tuning). Looking at a Fitech setup, and will need to upgrade the fuel system. Estimate $1500 total.

Looking for thoughts on which should be the next priority?
 

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My thinking is that the A/C could be put off awhile since winter is upon us in many places and you have time before you need it. Likewise if the Holley is doing OK, the EFI could be pended.

I believe in doing the TH200-R4 and the ring and pinion/Eaton next. I'm sure others will advise differently but based on my experience I think this would be the best route.

(If you want to read some real life Pontiac experiences with FITech, you could check out this PY forum thread........ New self learning EFI at half the price.... - PY Online Forums

Best of luck with your Pontiac...and welcome to the forum.
 

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"...2.78 gears in a GM 8.5" rear axle...change the rear axle ratio from 2.78, probably to 3.55. While I'm at it I'll also put in an Eaton Truetrac, and potentially new axles and aluminum driveshaft, estimate $1500 total..."


Before you spend any $$$$ on it, make sure you have an 8.5. I say this because I think the '72 came with an 8.2. But, if you already know for sure you have an 8.5, please just ignore this.

Also, good luck on doing all that for only $1500.

"...The carb has a couple spots where it goes lean, and chasing it is driving me nuts.Looking at a Fitech setup, and will need to upgrade the fuel system. Estimate $1500 total..."

SMI can build you a good Q-jet for 1/3 that cost.

https://www.smicarburetor.com/products/sfID1/28/sfID2/9/sfID3/100

There's even a good Q-jet guy right there in your home state.

http://www.everyday-performance.com/
 

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Just wondering exactly why you are considering going with the OD trans. Is it for lower rpm cruising ? Is it for more acceleration, from the combination of the 1st gear ratio plus the numerically higher gear ratio ?

Just curious. Some make the change, for different reasons.

I'd probably stay with a 3-speed trans, a good, efficient, stall converter, and no more than 3.08 gears. You can even have a 2.75 ratio 1st gear built into the 3-speed trans, if you want more low gear. Lots of class racers are running TH350's with a 2.75 ratio 1st gear. These are available for the TH350 & TH400.

This also prevents having to deal with the TV cable of the OD trans.

Hey, these are just other options. As has been said many times on many car forums, "It's your car & your money, so build it like you want it.".
 

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Discussion Starter #5
Thanks all for the feedback.

BigD, I will check the rear axle before I buy anything to make sure I get the correct parts. As
far as why I want the overdrive trans, it's a combination of the two reasons you stated. The cruise RPM isnt terrible with 2.78 gears, but acceleration is. So I'm looking to improve on both with the OD, so that means picking rear gears just right. The math says 3.42 or 3.55 will accomplish that, and I break even at 3.73 on cruise RPM. So I think I will go with 3.55.

I already have the trans, it's been in my garage for about two years. So what I need to buy is rear axle upgrade stuff. Summit has the Eaton truetrac for ~$500, a couple hundred for ring & pinion, and another few hundred for axles plus some misc stuff puts it in the ballpark of $1500.

I have considered going to a Qjet, you make a sound argument about the $. I'm sure I could sell the Holley for a couple hundred and then only be into the Qjet for a couple hundred more. I don't mind tuning the carb to dial it in, but getting the transfer from idle circuit to main jets to be smooth has eluded me to date. Then I wouldn't have to do any fuel system mods, save for getting the gas gauge to work properly (when full it reads 3/8 of a tank, goes down proportionally from there, been like that since I first bought the car in 2001, and yes I have replaced the sending unit).
 
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