Tranny, center diff strength

Ok, so as many of you have already seen, I may be acquiring a direct port nitrous setup in the next few days. Also, apparently the smallest I can run is a 75 shot.

Now I got to doing some math today on this project. For one, its going to take a lot of money :uhoh: but I am ok with that, I dont really do anything besides cars plus I have a fat chunk of change sitting in my spare parts so if I can sell those off its sort like "free money" for the car. Next math I got on to was the power.

Fingers crossed, by the middle of the summer I will have aquired DSMlink, a 2600, bigger injectors, the full nitrous kit, and the supra SMIC. Its going to be a push, but I am shopping around now so I can snag some deals. I think now that nitrous is in the picture, I am going to with 850's as they will fully support the Evo III 16g on E85 at I think lke 86% IDC. Then rather than make more power with the bigger turbo, I will make more power by upping the jetting, I think I can add as much as 150 hp on that direct port kit (though this would obviously not happen for a LONG time if at all ;)).

Well, I am thinking I will start it off by getting a decent tune at like 18psi and no juice. Once I am comfortable, I will throw on the nitrous. I'll then step it up to 22psi and do the same, no nitrous. Once that is a good tune, I will again, addin the nitrous. Then will come the 25-26psi tune and when its a fucking good, the spray will follow. I started to get my bench race on to guestimate what kind of power I may be running and what times I can shoot for.

Well, I dont see myself going past like 22psi with nitrous this summer anyway. My best guess would put that at around or a little better than 300 on the turbo, then another 75 with nitrous. Even so, this should be between like 350-380 hp, do you guys think? Not that this is overly important, but what is important is not over stepping my setups boundries.

I do have a spare 3 bolt so if I destroy that one, I will just throw in the other and take it easy until I can track down a 4 bolt. What I am worried about though is the tranny, more specifically the center diff. Will this kind of power wreak havoc on my tranny? About when does the center diff start to shit the bed? The summer after this following is when the built tranny would be going in, as well as the head rebuild, and the 25-26 psi tune so if I can last that long on the stock center diff I am going to. So what should I do about the center diff? Welding would be a cheap solution and I could do it when I put in the clutch. Or should I just run and hope it doesnt, then shell out for the built tranny when it does? I could also go with the poor man's 4 spider, but thats $400 I dont want to spend right now. What do you guys think?

So yeah, bottom line is would a stock tranny and center differential stand up to 22psi on a Big 16g, 272 cams, and a 75 shot of nitrous?

Mine first croaked when I was running mid 14s, LMAO. They care more abut shock loading (to the spider gears, which requires differential wheel speeds front/rear if I'm thinking correctly) than power, so if you don't laucnh overly hard or use a clutch setup that really bangs on the shifts, it should last. If it does go though, it most often takes out other parts in the tranny and you're in for replacement gears/shafts and a full rebuild. Which obviously makes a 4 spider more attractive. I think my Speed Design center diff was around 450. And when I cut that one in half at high 11s or low 12s, they stood behind it. Worth every penny, if they're still making them. I believe Shep offers one of his own as well, not sure on the price though. That would be an equally good option naturally.

Mmmmm, I see. I am kinda thinking that I am going to just use it and not launch hard very much. I sorta suspect its a rebuilt tranny anyway. I havent missed a gear yet with it and I did have had a couple ~6.5k shifts (when I raced that Camaro :)), plus it does not grind. In a couple summers my built tranny will come, then I can give 'er hell.

We busted the center dif doing a launch on bricks (there's a brick crosswalk downtown), and that busted it :(
However, my car was running 26 psi for a few days, and I had done a few launches at that psi, and have had no issues. I think I made all my passes at the track at 19psi with no issues, even running the 3 bolt still.

Yeah, silly 3 bolt. I am going to have to start looking for one soon, but I think I am just going to bring my spare 3 bolt to the track when I go along with a jack, jackstands, and my tool set. I've also been mulling the tranny situation over, I think I am just going to score a 4 spider and put it in like next year. I think I will wait on the rest of the built tranny until later. I kinda think I will be safe on the stock tranny/3 bolt this summer as I cant see myself running a big shit ton of boost or nitrous right off the bat. I'd like to get good at tuning on low boost and easy nitrous and enjoy the car in levels, I dont want to immediately jump to 25 psi and a 100 shot of nitrous and miss the fun I would have at 15 psi and no nitrous ;).

Second thought, shits getting welded when I do the clutch in the spring. I thought about it and did reading and I found I had a crucial error in my understanding of welding the center diff. I thought it locked each wheel at the same speed RPM which would make any turning a kinda messy bitch. I did some reading though, and it doesnt do that.... just locks power distribution to 50/50. Since the front is still open and the rear is still LSD the tires will still be able to spin at different speeds, just the front and the rear shafts will be spinning at the same rate. The reason the rear will skip now is because the rear wheels will be getting more power (I think I read that stock power bias is like 35-40% in the rear) and being that there is an LSD back there, the lesser weight in the rear doesnt provide enough traction for the LSD to get to the slipping point at slower speeds and on most stock tires.

Being that the tranny is coming out already for the clutch job, I am just going to rip open the tranny, weld 'er up quick, throw in a viscous coupling eliminator (not needed after welding), and maybe either a close ratio 5th gear or a 10% taller one for some better highway gas milage and call 'er good. Not having to worry after a hard launch is entirely worth the squeeking when pulling into a parking space to me, not to mention that TRE claims a spool (same thing as a welded center diff) is worth up to .2 seconds off your 60' time! 1.5's here I come. :p

I also found out that you can put in just the differential and axles of the 4 bolt rear instead of having to do the whole rear end suspension and shit swap. That is going to make things a LOT nicer for me as just the differential and axle swap is going to be about 12x easier and about 7x cheaper than the full rear end swap. I just hope I can afford one before I blow the 3 bolt!

Daily driving with a locked center diff will drive you out of your mind, as well as wear CV joints excessively. The drivetrain is constantly bound up. I've done it, but I don't recomend it, except on race only cars, or street/strip cars that get driven to the track only.

Bah, fuck. I've heard from a few people that its no big deal until you are doing sharp, slow corners, but you say otherwise. I think the best thing for me to do is to just drive one myself and see whats up before I make a decision either way.

You may only get tires locking up and dragging in slow tight turns, but imagine the pressures on the CV joints on the long slow sweeping turns, or highway ramps. In fact I found that the speed I took highway ramps at had to be reduced since the asss end always wanted to come out. The tires may not be hopping, but they still want to turn at different speeds, and have to slip to dissipate that force.

Feel free to try it! Just be prepared to have to deal with some side effects if they pop up.

Yeah, I never thought about those CV joints... man what a decision eh? Either A) worry about blowing a diff and possibly eating your tranny or B) worry about replacing your CV joints a lot and wearing out your tires faster. Man, I just need to win the lottery so I can just get a Shep Stage 4 and be done with it. :p

I do want to set the car up for a little oversteer as I sorta like that feeling and handling characteristics, but I dont want to be unintentionally power sliding on ramps all the time either. I honestly think I would enjoy it for the first couple days, but I also think you're right in that I would be driven crazy after a while.

I'll think more about it, I think my DSM may end up my DD (gulp) as I could use the cash from my current DD for school so I might want to keep it on the tamer side. I think I may just try it, I think theres a guy down here with a 90 tranny that he had in a FS ad advertised that if you came and got it, you could have it. Obviously wouldnt be something you would want in your car, but the center diff should be a useable core to weld. Maybe I'll do that and keep my currect center diff if the welded one gets to be too much.

Looks like you have a 90, so that should be a solid plan if that diff checks out good. For the archives, the 90 center diffs are completely different from the others. I'm pretty sure 91-99 are all the same. I have a bunch in the garage, but I have no idea what they are or what is wrong with them. I have an equally large pile of diff carcasses that I destroyed over the years, but that's another story. You know, I think I have a 90 diff that's locked up. LMAO. If I can find it your welcome to try it for a 6 pack and shipping.

Looks like you have a 90, so that should be a solid plan if that diff checks out good. For the archives, the 90 center diffs are completely different from the others. I'm pretty sure 91-99 are all the same. I have a bunch in the garage, but I have no idea what they are or what is wrong with them. I have an equally large pile of diff carcasses that I destroyed over the years, but that's another story. You know, I think I have a 90 diff that's locked up. LMAO. If I can find it your welcome to try it for a 6 pack and shipping.
Done! I hope Natty Light or Milwaukee's Best is ok, gotta remember I am a college kid on a budget. :lol: ;)

Ha ha ha, just playin. But yeah, if you do have one I'll gladly take it off your hands!