fuelonempty

Hey guys I have a built C4 auto tranny in my 67 Mustang, also with 373 gears and a ford 9" rearend.

What could be my next upgrade to get some more power on the freeway, with out having the motor rev so high??

thanks

jcp123

Are you asking for more torque, or are you saying you don't like the motor to rev so high on the freeway?

If torque, post your motor build and maybe we can comment.

If you don't like how high your motor revs...well, that's purely a function of your short gearing and lack of overdrive. If you really want to bring your revs down, I'd suggest switching gears to a 3.5, 3.25, or 3:1 ratio (cheapest), or swapping in a Ford AOD or t-5 transmission.

fuelonempty

revving too high is the issue.. I have a FR 302 crate engine that is Paxton Supercharged..

I suggested changing the gears when I asked a performance shop, but they told me it would be a minimal difference. So I think the AOD is my best bet.. I think the ones in the Fox bodies should do well? is it basically a direct replacement? Or is there alot more to it than that?

Thanks

cmanf

Check out Gear Vendors Overdrive not cheap but u could go to a 411 gear then split the shifts wind up a 6 speed auto.
I think they run about $3500 not bad if you look @ having to buy a built AOD to handle that kind of power will cost about that anyway.

Norm Peterson

I'll assume that the AOD can handle the power that you're making or has been beefed up internally so that it can. I'm not particularly familiar with how strong automatic trannies are, so I'll let somebody else tackle that part of the topic.

Probably the biggest potential pitfall in backfitting an AOD into the early cars involves the TV cable (throttle valve cable) that replaces the kickdown rodfor the C4. Since the TV cable also controls the hydraulic pressures inside the AOD, it needs to be adjusted for proper tranny operation. Get it wrong and you'll fry the tranny inside of a hundred miles (with any engine in front of it). Don't get me wrong - I'm not trying to scare you away from this (the adjustment process isn't all that difficult and there is a little leeway in the setting - BTDT). Just that you can't overlook this step or con yourself out of having to do it.

One other TV cable issue involves interference with at least one header design (probably a long tube design - this happened on another guy's car, but unfortunately I don't remember the header brand/model).

Unfortunately, I don't remember whether there's any driveshaft work involved. I don't recall having to do that with the '66, but it's been a few years.

The AOD has about an 0.70 overdrive ratio, which would give you the same overall gearing with the 3.73's as you'd get with your C4 and 2.61 gears (if such a ratio was even available).

I think it comes down to one or two questions. Do you want to go taller in all three gears or keep the first three about where they are and have a tall overall ratio for part throttle cruising? Do you already have significant traction problems in 2nd? If you can roast the tires in 2nd already there's little point in keeping the 3.73's as far as street driving is concerned.


Norm

my77stang

^ what he said.

and whoever told you changing ratioswould have a minimal effect is crazy. going to a 3.55 wouldnt do too much, but anything higher (numerically lower) would be a pretty good increase (at the cost of bottom end grunt)

fuelonempty

Thanks for the replies, I'm getting some good schooling on this matter.

Well I guess the AOD idea is out.. Where are the links on the transmission upgrade you were talking about cmanf?? 6 speeed? I didnt really understand how thats even possible without major work. Forgive me, I'm a nube to auto's. Furthest my knowledge goes to is tourque converters,FTVB's for the modular motors and shift kits.

well it sounds like I'll just stick to the gear ratio swap and see if that helps... I'd like to get a longer gear in all three shift because the car is a bit wild to start off with, but then its just too loud and dissapointing once you get to 60 in third...

So with 373's now; what gear ratio would you guys suggest?

LCC

Why not the AOD??? It's a simple swap. You have to change the cross member and shorten the drive shaft, but you will have to the same thing using the gearvender unit. I run an AOD with 4.11 on a built-up 351w and drove on the high way all the time. Stock AOD can hold 325-350 HP and just a couple of upgrades you can handle over 450 HP.
For more info I use these guys http://www.lentechautomotive.com/

The AOD transmission and torque converter are a matched pair. The AOD uses
a hollow two piece input shaft (one shaft inside the other) for lock-up
purposes and requires a specific torque converter. This arrangement is used to
bypass the converter torque multiplication in higher gears (60% in third and 100%
in overdrive) for better fuel economy. This is an attractive feature when
using a high stall speed converter, since locking up the converter eliminates the
excessive slippage (and the attendant heat generation, RPM rise, and
increased fuel consumption) associated with such converters. On the down-side, the
input shaft is weaker than a similarly sized solid one piece design and you
lose the torque multiplication effect.