Gear ratio advice

USU_Stang · Dec 15, 2004

I'm looking to swap out my rear end gears. I have a 289 and a C4 with about 500 miles since it was rebuilt, and 2.79 gears. The car will be a street cruiser but I definitely want it to have some kick (as in I'm putting in a 4v edelbrock, performer 289 intake, aluminum heads (perhaps GT-40X if I can afford them), and a more aggressive cam). I'm not concerned about gas mileage since I have a very economical car for regular driving. My questions: 1) What gear ratio should I go with? I was thinking about 3.83 or thereabouts, but would like advice. 2) Is my current 8" housing going to work fine for this proposed engine (housing is in good shape)? 3) Is that C4 going to be enough to handle the power? I can't really imagine this setup getting more than 325hp at the flywheel...can anyone else?

--Jason

allcarfan · Dec 15, 2004

I hope RATIO411(dave) chimes in here.

I would suggest a 350 gear though. A small stall converter also. As for that C4 holding up...that will depend on how you drive it!

The Dan · Dec 15, 2004

I think the C-4 would be fine. 325hp shouldn't kill it too quick anyways. Your 8" will probably give before the tranny, but that is highly debateable! Like allcar said, put a mild stall in it, maybe 22-2400. With a C-4 and 3.83 gears you'll be sreaming anything above 60mph, might consider the 3:55 as allcar said. It will still give you the acceleration you are looking for, but more forgiving at higher speeds. The one other thing you might consider is using a 67 or later center section when you swap gears as it has extra webbing for more rigidity and support.

Edbert · Dec 15, 2004

3.25-3.50 is about right for a C4 car that will see any significant amount of time on the highway. 3.70-3.89 is pretty steep if you ask me. Take a look at this chart:

http://www.edbert.net/rpm_chart.htm

The 3rd gear part is what you look at with a 1:1 final gear. It shows you at over 3,000RPM at 60MPH with just about any tire that will fit your car. If you wanna go 70MPH+ it'll only get worse.

91conv · Dec 15, 2004

I have a 3.25 Trac-loc in my 65, 289, c4, and it was a bump up from 2.79. I have and earge to try 3.55's though.

ForceFed70 · Dec 15, 2004

I have 3.73's with a FMX (same gearing as the C4).

The 3.73's are a little steep. Great for driving around town, but kinda suck on the highway. At 60mph I run almost exactly 3000rpm.

For me they are fine as the car rarely sees the highway and when it does it's only for 30minutes at a time. If you plan on taking your stang on any long trips, I'd suggest the 3.55's

jerry S · Dec 15, 2004

For those of you who know, how would you feel about a higher gear (3.73-3.89) mated to an AOD?

ForceFed70 · Dec 15, 2004

jerry S said:
For those of you who know, how would you feel about a higher gear (3.73-3.89) mated to an AOD?

Since it's an overdrive tranny, you can get away with alot steeper gears. Most of the 5.0 guys reccomend 4.11's I think you'd be very happy with gears in the 3.73-3.89 range.

USU_Stang · Dec 15, 2004

I did forget to mention that I was considering an AOD as the final peice of the project, but that might put the whole thing out of my price range. Sounds like I might opt for the 3.50s. If I have enough money for AOD then I have enough money to change gears again . This may be stupid question: how do I tell what stall converter I have now? I'm pretty sure it is stock...but any way to confirm easily?

Thanks
--Jason

jesserose17 · Dec 15, 2004

Just press on gas and hold brakes while you have the auto trans in drive - make a note of rpm where the rear wheels start spinning, if it spins below 2,000 rpm, then it's likely stock converter.

restomod22 · Dec 15, 2004

Before my T5 swap, I had a C4 and 3.55 gears and I thought highway driving sucked! Anything over 60 mph and she was a hummin'. Didn't have a tach at the time, though. With the T5, she's not screamin so much and the rpm's are nice and low.

USU_Stang · Dec 16, 2004

jesserose17 said:
Just press on gas and hold brakes while you have the auto trans in drive - make a note of rpm where the rear wheels start spinning, if it spins below 2,000 rpm, then it's likely stock converter.

This sounds like it's bad for the brakes or tranny...or both...

restomod - sounds like your stereo isn't turned up enough. I'm pretty sure stereo volume has a direct impact upon engine RPM.

jerry S · Dec 16, 2004

USU_Stang said:
This sounds like it's bad for the brakes or tranny...or both...

Nope. Neither.

Darkhorse845 · Dec 16, 2004

3.73's

Edbert · Dec 16, 2004

jerry S said:
Nope. Neither.

Doing it a few times wont hurt a thing, but it does create a lot of heat in the tranny and fluid. I would be doing it all the time.

My opinion is that an engine should not be asked to cruise (steady speeds for extended periods of time) at or above 3,000 RPM. It just causes too much wear-and-tear, just my opinion of course. But have you looked at how modern cars have low RPMs when on the highway? I also say that is why our Stangs came with 2.7:1 gears, just trying to keep the highway RPMS down.

You can go too low of course, but something that puts you at 1,800-2,200 while in top gear at the speed limit is ideal, as long as your engine makes enough power down there. If you need more RPMs for an acceleration move of some kind you can alsways downshift to your 1:1 ratio

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