Issues w/ T-56 Magnum behind LS3?

[Nova_Cobra64]

Hey all, not quite sure yet if I've hit a snag here or what. I am quite certain I want to put a t-56 Magnum (with hydraulic clutch) behind my GMPP LS3. At least after comparing opinions and whatnot of the aftermarket offerings I feel this is the best route. I've sent out quite a few quote requests in the last while, the only one to respond at all was Hurst Drivelines. Scott sent me an e-mail last night suggesting I call their tech line first as there are some issues with the setup that are best discussed over the phone. I tried calling them this morning and it looks like they are only open monday to friday. I'll call again first thing monday and hopefully get the ball rolling.

I figure in the meantime it would be nice to get a sense of what I might be up against as at this time I am not aware of any "serious" (given the circumstances of the build) complications with this setup. I fully expect to do some transmission hump modifications and realize the driveshaft is going to need some work (maybe go to a 1 piece with the t-56 being so long???). Does anybody else know of any other issues with this setup?

[burlapen]

Well this is behind an LS2, but he goes into detail about the shifter location. Keisler makes a kit to move to the forward shifter location. http://67-72chevytrucks.com/vboard/s...d.php?t=413880

[Nova_Cobra64]

I suppose that may have been one of Scott's concerns. However, I am installing procar lowback buckets so I don't know if shifter location will be too critical. From what I've found the magnum's shifter location can be mounted about 5" futher forward (when in the forward factory position) than the original t56. The magnum's shift locations seem to be quite comparable to that of the TKO.

I found a good side by side picture of the t56 and t56 magnum that shows the difference in the shifter location. http://www.camaroperformers.com/cama.../photo_08.html

I've got my fingers crossed that Scott is just covering his basis before going any further.....I suppose a lot of people probably get pretty pissy if they buy something and it doesn't fit with their bench seat or whatnot. But so far I haven't found any huge snags. I'll be sure to update once I get this sorted out, the more information on here the better.

[Nova_Cobra64]

Well I talked to Jim at Hurst today for about 45 minutes and have a better understanding of what I'm up against. I never did much research with regards to RPM at cruising speeds in relation to tire size, which was largely what they were concerned about with my setup (shifter location and trans hump were discussed as well). I had intended on going with the T56 Magnum with the .5 overdrive. Cruising at 70mph with 28" tires (currently) would put the RPMs below 1800, which Jim felt was a tad lower than desireable. After some research around here I've concluded that odds are good I will end up with rear tires upwards of 29", which is what most guys are running with 18 or 20" rims. So now I've ruled out the .5 od T56.

Jim also put my mind at ease with regards to the shifting "issue" with the TKO transmissions. He raised the point that aside from some early recalls that were dealt with a few years back, there have not been all that many complaints about them, and those that are having issues above are pushing upwards of 6000rpm. He didn't openly say it but putting 2 and 2 together there were very few people saying anything negative about the TKO until Keisler started hyping their transmissions and playing up the 2-3 shift issue. Essentially he said that based on the transmission design expecting smooth shifting at unusually high rpm without significant upgrades is a bit much. It was also mentioned that the 2-3 shift pattern is also a tad different from a typical 4 speed and takes a bit of getting used to.

I don't really plan on spinning my motor past 6000rpm as GMPP's advertised max rpm is 6600. So the TKO is now back in play and the T56 Magnum with the 2.66 first and .63 overdrive is also a possibility. Both transmissions are very similar in terms of what I would get out of them as the final gear is only .01 difference. The T56 wouldn't jump out of the hole as quick being 2.66 as opposed to the 2.87, but I'm thinking a 480hp engine would just spin the tires that much more with the 2.87's anyway. The T56 is clearly the better transmission and has the benefit of 2 overdrive gears, but will require some transmission hump modifications and will have to be a hydraulic setup (mechanical can be done but actually costs more in the long run for those who didn't know). The TKO is going to fit better and can be significantly cheaper with the mechanical setup.

I have a bit of thinking to do over the next few days. If I really want to go with a hydraulic setup I think it would make more sense going with the T56 as at that point the cost difference is less significant (about $500). If I were to go with a mechanical setup the difference is closer to $1000. Maybe I'll get lucky and the answer will come to me in a dream.............

[TR65]

Hey Nova,

I am running 29" tires with 3.73 gears T56 0.63 sixth gear, 1800 rpm at 70 mph in sixth. I find that perfect for highway cruising. The LS2 / LS3's have so much low end torque sixth gear is really useful. Low rpm's = good mileage as well.

The hydraulic clutch conversion is not very difficult and really works well. See my thread on that if you are interested.

http://67-72chevytrucks.com/vboard/s...d.php?t=300087

I really like the LS2 / T56 swap, the truck is a pleasure to drive.

Good Luck,

TR

[Nova_Cobra64]

Thanks for the input TR65, any opinions at this point are appreciated. I can usually research enough to come to a decision on what I want but I am very much on the fence this time around.

The cheap side of me says just do the TKO with manual clutch and enjoy it....the extra $1000 could almost pay for an AC setup. I don't imagine I'd have issues adapting to the shift pattern of the TKO or notice the difference between hydraulic vs manual. After a quick period of getting familiar with any particular vehicle I've never had a problem.

My dad says go with the TKO and hydraulic, and out the extra $500 towards something else.

The other side of me says that the T56 is hands down the better transmission, and the $1000 really isn't a big deal at the end of the day. Despite requiring a touch more work, I think there no regrets this way. While I like the gear spacing on the 2.97/.5 trans, the overdrive just isn't workable as there is no way my tires end up under 29". I can play with tire size a bit on the 2.66/.63 setup a bit to bring the rpm down a bit if I want.