what gear shld i have in rear end for a 4.6 dohc donor engine

[austingoblue]

I have a 273 gear in my fox rear end...shld that be changed and to what?? Using a dohc 4.6 donor from a 2000 mustang tt...thanks!!!

[Jeff Kleiner]

What are your first and fifth gear ratios?

Jeff

[Bob Cowan]

You're going to get about 40 answers to this question. The truth is, there is no "perfect" gear. Unless your car is going to be used for one thing only - like drag racing, or road racing at one track only. Everything else is a compromise.

Take a look at where you'll be doing most of your driving, and where your engine will make it's power. Plan to put your engine at the beginning of your power band where you'll do your most cruising. Then let the rest of the gears take care of themselves.

[FFinisher]

If using the stock trans I would use 355. I built built several with SOHC ans DOHC's, 355 are the best all around. This is the standard ratio in MACH1's with DOHC"s.

[mydream]

I have 327's and wanted to change them out to get a better launch. I had my diff open to replace an axle last winter and had second thoughts on changing them...
I have a SOHC and engine runs at 1900 RPM at 70MPH. I hate stop and go driving so I'm happy I stayed with them since the engine hum's at 70MPH, so the drive is nice, and exhaust is not loud.
As mentioned by others, it depends what you want. Mind you, If I ever NEED to change the diff, I will go with 355.
HTH

[austingoblue]

Oops I meant sohc not that it matters I appreciate the responses I think I am going with 355 gears....and yes using stock tremec transmission.

[edwardb]

Oops I meant sohc not that it matters I appreciate the responses I think I am going with 355 gears....and yes using stock tremec transmission.

Going through the same thought process with my Mk4 build. As stated previously, don't just look at the diff gears by themselves. You need to take into account your trans gears (especially 1st and 5th) along with your rear wheels. There are many, but I found this calculator pretty useful: http://www.tremec.com/performance/gear-calculators.html

The T5z along with 3.55's in my Mk3, with a pretty strong 306, is about perfect. Cruising RPM is just right. My only complaint is that it does run out of first a little quickly. Probably not enough to warrant different diff gears though.

[FFinisher]

If using the stock trans I would use 355. I built built several with SOHC ans DOHC's, 355 are the best all around. This is the standard ratio in MACH1's with DOHC"s.

My answer remains the same, I had a car with under car exhaust, for my driving 3:27 was not desireable, I changed to 3:73's and didn't care for that either as it was too high, and first gear was pretty useless. I never changed to 3:55's in that car, but have used 3:55's in the other 4.6 cars. These were a mix of SOHC and DOHC.

This is just my opinion, it all depends on your driving and your preferences.

[David]

If you have to purchase gears, I would say that 3:55 would be a good compromise.

[tcarlson]

I had an '85 Mustang GT with the 3.55s, and it was great. 3.73 or higher would mean you'd be quickly shifting to 2nd in street use. Hope that helps.