Final drive ratio's

[FTA1995]

I'm trying to decide upon a good final drive that I can maintain good driveability with. these are the following factors I have taken to mind; I currently have a T56 with the standard ratio's and the stock 3.42 7.5" 10 bolt. I also have 275/35 R18's in the rear, slightly taller than stock. I did build up the rear suspension pretty heavy; tubular everything up to the trans. I believe after I get a rollcage (8-point most likely) the chassis will be sufficiently stiffened to handle moderate abuse (mostly on the street). I just want to know peoples opinions/experiences are with the 4th gens as far as driveabilty problems or any irritating quirks when the stock ratio's are used with the six speed.
So far, the most appealing would be the motive 3.90 for a good rwtq increase.
The 3.73 is probably the most popular street gear upgrade I can think of. Any input or suggestions or preferences would help.

[Injuneer]

It all comes down to how much traction you can generate with the suspension and tires. 3.73's give you 9% more torque off the line, 3.90's give you 14%, and 4.10's give you 20% more. Any of those will work well with the T56's tall 6th gear. I ran 3.73's when my car still had the T56, and they were "comfortable". But with sticky tires, either of the others will be fine.

Couple minor points:

Your 275/35-18's (25.58") are not taller than stock. The 4th Gen V8's left the factory with either:

235/55-16 = 26.18"
245/50-16 = 25.65"
275/40-17 = 25.66"

Manufacturers round off to the nearest 1/10th of on inch, and quote actual dimensions, not theoretical, as above.

An "8-point" is a roll bar, not a roll cage, at least according to NHRA regulations.

[FTA1995]

Yea, now that I think about it, the 3.73 will save a bit more gas than a 3.90 or 4.10. I don't plan on launching the thing around town, just maybe at the track when everything else is finished.

I did not know that about tire sizes; I was going by how they appeared side by side with the stock 245's when they came off.

The next question in order would be if it would be a more worthy investment to change to a larger carrier and axel. I'm about to start a new project engine probably start out with a golen long block 396 and throw some nice afr heads on it with a pretty aggresive cam, at this point it won't be a DD of course. I'm going to get a stronger trans, but my preference is with the 6 spd, bt then I have the concern with breaking that secondary overdrive shaft and loosing 5th,6th and probably the whole trans. There's a nice shop down the road here were the guy build some really nice custom trans parts, i saw a t5 he set up for someone around here I might just go to him for a good trans instead of paying the same for a tko500 or 600.

[FTA1995]

this might be helpful to someone who wants to know more
http://www.wallaceracing.com/reargear.htm

[Injuneer]

If you plan to run the T56, a beefy clutch and sticky tires on a prepped track, you will need a 12-bolt or S60 rear axle package.

The trans itself isn't as big a problem. A buddy of mine ran his stock 97 T56 up to about 750HP in a 3,950# convertible and had no problems. Rich Krause at CamaroZ28.com ran his T56 to 900HP with no problems. There are various upgrades, available from places like D&D that will help keep it whole.

I ran my stock T56 up to 625HP with no problems. And that was launching on ET Streets, McLeod Street Twin, with 5,000rpm clutch dumps. Synchros and blocker rings, forks will take a major beating if you shift it hard, and those are the pieces that need to be upgraded. Worry about the input and output shafts with a major power added, not an NA application.

[FTA1995]

No kidding... that's a lot of muscle for a stock trans!

I was looking into getting this from Spohn, looks like a great package that will meet the requirements and it's pretty much ready to run when it gets here.

I think I need to replace my clutch again, I'm using a stage 3+ spec single for the second time, I think it's the throwout bearing they come with. I have heard a lot o nice things about dual friction clutches but have never had the chance to experience an application myself. Would yo recommend the McLeod again? Seems like a good clutch that can take an abusive dump at 5 grand like that seems pretty durable. I did find a few other great reviews on ls1tech etc but the only thing that might turn me off to it is the lighter than stock feel, but it looks like the pro's outweigh that.

[Injuneer]

The Strange Dana 60 is a good rear axle. Its very strong, but also very heavy. If you are planning on running 700-800HP or more, its probably a good idea. But at anything under that level, the Strange 12-bolt weighs less, and uses all the stock-style components including the drvieshaft length. Note also, if you didn't pick up on it, that the $2,035 price is the starting point, and includes a "spool". You don't want to drive a spool on the street. You have to opt for the Tru-Trac or the Locker for a street driven car. Appears they don't offer a conventionalo clutch-pack limited slip option. The 12-bolt comes with an optional Eaton super-duty (15-disc clutch pack) posi unit, that appears to be close to indestructable.

My McLeod was the "Street Twin". It's a twin-disc clutch, that comes with its own flywheel, either steel or aluminum. I got mine used from my buddy with the 750HP convertible. It took an unbelievable beating. Then when I had the TH400 installed I resold the Street Twin as part of an "M6 conversion package" of all my old parts. If you don't mind the price on the Street Twin (~$1,110) its the way to go.

[FTA1995]

It really sounds like you get your money's worth with both, sound like a good idea. That dana does look like a good build, and to get it going heavy duty street like you said isn't gonna be too nice to the bank. The tru trac seems like a good option, although the locker is very tempting. I'd probably be pairing a nice chromemoly driveshaft with it on the installation too. hopefully everythingwill match up and perform nicely together when it's all said and done.