Greetings all,

Now that i've put some time behind the wheel and got some road time on the truck, I wanted to see if y'all could give some advice and/or educate me on options for the drive train. So here's what I've got:

a 302 out of an 87 Mustang with:
- block has a stock crank and bored .030
- e303 cam
- AFR 165 cc heads
- Edelbrock Pro Flow 3 Multiport EFI

C6 Tranny
12" TCI torque converter with 2000 stall
9" rear with 3.00 gears
rear tire is 295/40/18 = 27.25"

I just had the truck tuned on the dyno and the shop was able to tweak the air fuel ratios to give me 293 h/p and 254 ft/lb torque. The truck cruises on the highway at 75 mph while turning 3000 - 3100 rpm's. From 0 to 30 mph, the truck is a little sluggish, it won't even break the tires if I foot brake it and stomp it. I suspect that may be from the low stall on my torque converter and the tall gear I'm running. However, from 30 mph and up, the truck runs like a scolded dog. It absolutely gets from 30 to 85 - 100 mph in hurry. I'm averaging 9 - 10 miles a gallon, I know it's a hot rod and fuel efficiency really isn't in the cards for me, but I was expecting somewhere in the neighborhood of 12 - 14 mpg's. Also, we purposely chose the 3.00 gear for the cruising factor, but I figured it'd be good for a little roasting of the tires from a stand still.

After reading all the threads on C6 v AOD and rear gear ratios, it seems like y'all are getting better results (both fuel efficiency and low end torque) then me with the same type of numbers. So my question is, where, what, and how am I doing wrong? I would like to be in the 2100 to 2400 rpm range when cruising at 75 mph and still have the low end ability to squeal the tires from a stop. It'll probably way down the line for me, but do I need to drop my rear gears down into the 2.70's or go to an AOD or possibly the Gear Vendor route or revisit my torque converter stall? Any input would be appreciated, thanks in advance.

 

You could change the rear to a 3.5 , take off would be better but top end speed would suffer slightly .

 

I agree, that is the wrong cylinder head and cam to go with that rear axle gear. Those heads and cam are fine for a 302 because small cubic inch motors don't make much power at low RPM. Not only a gear ratio change so the motor will be more crisp at bottom end, but if you want to cruise down the freeway you'll need some type of overdrive. Going down to a 2.7" rear axle gear is not the best option.

For now, If it were mine (and it's not) I would install either a 3.50 or 3.70 rear axle gear. Then later look into some type of overdrive, either an AOD, 4R70W which work better than an AOD, or leave the C6 and install a Gear Venders overdrive unit on the back of it. But, if you want to drive 75 mph now, you will need to address both the rear axle gear change and overdrive at the same time.

Plus, don't forget, the engine RPM should be above the torque converter rated stall speed at your most common cruise speed. If not, there is risk of overheating the transmission.

 

My 2 cents . First of all you have 2 problems easy to fix one or the other tougher to fix both . The fuel injection should adapt to the best fuel-air so not an issue , 2000 stall is a little low for your gears -tires but not a deal breaker , 3.25 gears may make a huge difference , too much cam for your setup is probably your biggest issue . My coupe runs at 2900 @70mph with a carbed 350hp ish sbc and 3.00 gears and makes an easy 17 usg/mile . 270 gears will probably get you a little better millage but worsen your low end . 325 gears may or may not affect your millage but will help your low end . The obvious fix is a aod , lower first gear and overdrive

 

I agree with EBEAR. A rear end ratio of 3.25 to 3.50 with an AOD will solve your problems.

 

The C6 transmission is an extreme power hog and you'll lose 60 hp right there. There's no reason to ever use one behind a 302, they just don't make enough power and torque to require it, or overcome the power loss. There are a lot better choices. Switching to an overdrive type along with lower gears, 3.50-3.73 or so, would make a huge difference.

There was some information about stall converters in this article I found interesting, even if not directly relevant. https://www.fordmuscleforums.com/thr...03-cam.477537/

 

A quick way to test a lower rearend prior to changing gears is trying smaller diameter tires; maybe try 26”, or even 25.5”. Means you’ll probably have to go with a smaller diameter wheel.
I’m not an expert, but from my ancient experience, if you want to see better fuel mileage, you need to get the cruising RPM under 2500.

Good luck.

 

awesome! thanks for all the input guys, as ALWAYS, your input and advice is much appreciated. i was tracking the same direction/options/suggestions y'all provided, but just needed confirmation from y'all's knowledge and experience. now it's just a matter of figuring best bang for my buck and what kinda budget i'm looking at... C6 w/gear vendor and swap out rear gears vs tranny w/OD and rear gear swap out

 

There you go. Either of those paths should get you the performance and still be able to cruise down the freeway.