I've always been a little weary about making decisions about the rear end. My old car, a 93 mazda rx7, had factory 4.10 gears and torsen limited slip.

The tranny had a 3.483 first gear, and a .719 5th gear, and could pull above 160 MPH in no time at all.

I know how you set up your tranny and rear end ratios depends on both the engines power curve and the kind of driving you want to do, but I don't know enough to figure this out.

I'm building a motor that will have a pretty flat power curve from 2500-6000 rpm with a peak torque of 500 at 4000 rpm and peak hp of 480 and 5500 rpm (according to plan anyway.) I'm trying to kind of copy the rx7's "curve" (it really just peaked at 1900 rpm and held peak till 8000, but close enough).

If i have a similar power curve, and want the car to drive like that rx7, can i use the same gear ratio's? or is it a bit more complicated than that?

Thanks,
Oliver

got my specs from here http://www.rx7.net.nz/usspec.htm

 

If you can get the trans to attach and survive, fine. As you've decided on a realistic powerband, next you need to go 6000/8000x4.10=3.08:1.
Then you'll have a feel you already liked.
If this isn't the type of answer you were after, please restate the question for me.

 

I wouldnt be using the rx7 transmission, but a 5 or 6 speed with very similar ratios. Maybe a T-56 if the ratios can be had. I do think you answered my question correctly though.

So you are saying that, with an engine with a similar power curve and peak power at 6000 instead of 8000, and similar tranny ratio's, that a 3.08:1 rear end ratio will give me comparable drivability? If so, yes that's what I was asking, and thank you very much for your response lol.

Also, now that a ratio is decided upon, what sort of diff would be best? I liked the Torsen torque sensing limited slip, and dont want a locker or anything. I'd like something that is really made for taking turns and gripping. NOT a drag-race diff. You recommend anything?

Thanks again,
Oliver

 

The T-2 Torsen is available for the Camaro and Firebird 10 bolt rear end too. It was installed in many of the 4th gen Camaros and Firebirds. http://www.torsen.com/ These all had 28 spline axles, so if you have 26 splines you will need to upgrade your axles too.

 

a torsen or regular clutch pack style limited slip will work. youll probably wanna just stay away from the gov lock diffs.

 

Thanks alot guys

-Oliver

Oh, one last thing, can a T-56 Tranny be had with similar gear ratios? Copied these from the spec page I posted in the first post. I know there's no sixth here, but if there was i'd guess it would be something like a 2.7:1 or 2.8:1 2nd gear, then the rest would shift down.

1st 3.483:1
2nd 2.015:1
3rd 1.391:1
4th 1.000:1
5th 0.719:1

Thanks alot for your help,
Oliver

 

If you can find a T-56 from a 93-02 Camaro or Firebird you'll be really close to the ratios you want. Here they are:

1st 3.36:1
2nd 2.07:
3rd 1.35:1
4th 1:1
5th .8:1
6th .62:1

Also, a Detroit TruTrac functions the same as a Torsen LSD if you have troulbe getting one.

 

Awsome, thanks! What about the stock rear housing and all that. should i junk it if im planinng on putting 500+ horses to it? to a 12 bolt or a ford 9 inch? For me it mostly depends on how big of a s pain in the *** the swap would be.

Thanks,
Oliver

 

The Moser 12 bolt would be a very good swap and it is a bolt in.

 

If you contact Tremec directly, it's probably possible to get these ratios into one T56:
3.36
2.07
1.43
1.00
0.74
0.56
Or if you don't need a six speed, how about this:
3.38
2.00
1.32
1.00
0.74
This can be had new for $700, but would require an adapter plate. Still, it is strong enough to hold 460 rwtq on slicks.
----------
Oops, fifth on that second one comes as 0.67:1, but the 0.74 is available.

 

Great, thank you Attila and big gear head. I would actually go for the 5 speed then, since I've never owned a 6 speed and never really wished my 5 speeds had a 6th for any reason. That, and a 700 dollar price tag pretty much make up my mind.

Is the requried adapter plate just for the belhousing bolt arrangment? would I need a longer input shaft to compensate for the thickness of the adapter plate? Also, would I need a different starter or would the one now bolt up?

Thanks,
Oliver

 

I contacted Moser and they quoted me about $3,000 for the compelte 12 bolt rear, with a detroit truetrac diff(which really is exactly like a torsen, but they claim to have a patent on the torsen parallel axis helical design?), all mounts for torque arms, axles, 3.08 ring and pinion gears, cover, hardware, bearings, disc brakes, calipers, wheel studs, the whole deal fully assembled ready to drop in. That's not bad at all. 33 spline axles.

As for the tranny I havn't contacted TCI yet about their Tremecs, but I will probably go for a T-5 with the ratios Atilla suggested. I looked on Summit Racing site, since it's 10 miles from me, but all tremecs were manufactered by a company like Classic Motorsports or something.

Thank you all,
Oliver

 

What was that 2nd transmission? a tko?

 

I was gonna ask the same, for $700 bucks? Where? the T-5's I looked up were like $1,300