If I recall, the THM400 is a clutch-on-clutch shift where the second gear clutch engages 2nd and first is just overrun. The result is no loss of power thru the trans during a shift, AND no timing of band-release/clutch-apply or vice versa. Interestingly the new GM 6-sp automatic due out for 2005 or so is a clutch-on-clutch. What goes around... Then there's the new "preselect" VW 6-sp auto which reportedly shifts in .04 seconds stock! That 40 milliseconds.

I believe the engine braking in a 400 is done by a band which is applied sometime after a gear is engaged. Usually for full-manual drag-only the bands are removed. This is going back to '66 or so when a friend of mine was building some of the first 400 drag transmissions, so I'm a little(?) fuzzy. I don't see why those bands couldn't be left in. Maybe I don't remember correctly. Memory is the second thing to go.

 

That sounds like what Carl tried to explain to me. It's still sort of a "back box" Maybe I need to get some drawings and spend some time trying to figure them out. Or better yet, find someone who's rebuilding one and poke around the innards for a bit?

Rich Krause

 

holy crap you guys are getting way over my head (c: but at least its a good learning experince. thes reason i am thinking about this now is because i always like to get all my facts and option laid out on the table a little while before i make a major purchase. i dont want to go buy a tranny i wont be happy with to mate up with the ls1 if i am just going to switch it out in a few months after. it looks likes, thanks to all the comments, i will go the t56 route until get a higher power level (such as dp n20) after i drop the new engine in. at that point i will maybe get a th400 built well, but also for street action. currently i have like a hard shifting trans go (not level 1) with the EPC valve kicked up a notch also. so i am used to my tranny shifting hard, and this is a daily driver. thanks for all the info, even the stuff i dont understand. whenever i actually get a little closer and more informed on my plans, i will ask more specific questions. but by all means, keep the debate goin....

Paul

 

Rich,

I'll see if I can find a Gray's Anatomy of the THM 400, complete with color-coded 'arterial' and 'veinous' hydraulic schematics in my old shop manual collection.

It's only a little less complex than our insides. Lots of similarities, IMO. Engineers tend to copy Nature. My favorite engineering axiom is "You can't rape Mother Nature". Many have tried, none succeed.

 

I'll stick with my glide. I have a really small converter, 2800 rated. But with boost it's more like a 4500-4800 stall depending on where the controller is set at. It is as streetable as any other no OD transmission out there.

If I can carry the wheels for 5-6 feet with a 1.76 first gear ratio what good would it do for me to have an even deeper gear? The glide is considerably lighter, alot smaller and has alot less moving parts to break.

 

Rich,

Another way to save that tranny is to loose some of the weight out of your car. It's not like you have a lightwieght car. I would consider just looking at some little things for weight savings to add to the durability of the driveline. Your gonna put a hurting on it with 900-1000rwhp anyways.

BTW what heads are you running? You gotta be getting to the point where intake velocity is going to limit your max HP.

Bret

 

Bret: Since I'm only competing against myself, and I am the one making the "rules", I've decided to make hp the "easy" way, with boost and juice! Last years combo used a completely unported set of AFR 195cc castings with a stock TB. This year, I am having a little cleanup done on the intake side of the heads and major work on the exhaust side, as this is where I think there is more potential on my "boost + juice" combo. I am also going to pick up a 58mm TB if I can remember to order one.

I have immense respect for people who know how to make big hp NA, but if you don't have too, why do it the "hard" way? Before I discovered that centrifugal blowers and EFI were a match made in heaven, I too believed in "the Force". Now, I have been won over to the dark side and when I want more hp I "just" install some bigger jets or a different pulley . Well, we know it's not that simple, but you get my drift?

As far as weight goes, that's a point well taken. But I have my own set of "rules" which include A/C, power windows, heavy convertible top, etc. So it's a pig, but it's my pig!

Rich Krause

 

I like the boost too Rich.

For me, a strong n/a motor is as much as I need for the street. If I feel a need to go boost, then I'd most likely limit that to the track and my choice would be more akin to Mooneyham or PSI.

On the tranny thing, I just want to throw a few more suggestions in the pot. I like autos as much as the next guy at the track but I prefer manuals for the street. Just a preference in rolling my own gears.
I don't know about the T56, don't know how much it can withstand but I do know that there are a couple of manual trannies that'll take anything you can throw at em. One being the older Doug Nash 5 speeds. Same tranny used in alot of road race setups and the same tranny used in the old twin turbo Callaway corvettes. They're tough and relatively inexpensive to rebuild.
The other choice is the Jerico 4 or 5 speeds, clutchless or clutched. They'll take anything you can throw at em and they're light. They don't eat alot of power either. Not the cheapest thing on the planet but for what some are spending on suped up TH400's etc., the 4 speed models are in the ballpark.

-Mindgame

 

Mindgame: when you really look into these "exotic" trannys, it's not as rosy as it seems. They are a minimum of $4,000 for the tranny. But then you have to fab up some kind of a bell housing and figure out a clutch setup. They do not have provisions for a speedo sensor. They are pretty nasty to drive - they shift fine when rammed from gear to gear, but anything short of that is quite a herky-jerky proposition. Top gear is limited to 1:1, so you lose some of the advantage of a manny tranny. You can go <1:1 with an intermediate gear, but this does give a pretty awkward shift pattern: 1-2-3-5-4 for example.

I considered a G-Force GF-5R pretty strongly. But considering the $5,000 price tag plus the fab work, speed sensor issues, etc. and how nasty they are to drive at less than 10/10ths the high-end TH400 seemed like a better choice. I will let you all know if I like it or not. Also, I and most other people probably could get away with a mid-range TH400, which is a lot cheaper than an "exotic" manual even with a good converter.

Rich Krause

 

Rich,
You assume that I haven't owned one of these trannies?

I have... the Doug Nash 5-speed is a good tranny and it's not hard to live with on the street. I ran one for a little better than 3 years of daily driver, stop and go action. Same with the Jerico 4 speed, had one in a 71' Demon behind a 451 big block. Not as smooth as a T56 but it's not as "herky jerky" a transmission as you seem to make out. Granted, the shift is not silky smooth but it's not that bad either.
That same Jerico 4, then went to a Mopar small block street car and was driven another 2 years before selling the car to a guy who didn't want the motor or tranny. It's now sitting in a crate waiting for a new home and considering the going rate of a new one, I'd say they are plenty competetive with a full tilt auto tranny. Can't say I wouldn't mind putting it in another street car either.

How many of the above trannies have you dealt with in a daily driver situation? Jerico has an internal rail tranny in the works too. Won't be cheap though but I'd rather live with a manual than a high stall auto on the street. That's just me though.

-Mindgame

 

Actually, if an auto is wanted for a little more hp, Art Carr has a 200-4R on sale right now for $1799 with a converter, and it's supposed to handle 750hp. Sounds like a good deal to me, but I'm in the same boat with the new motor I'm building. I don't know whether to go auto or manual. I know my T56 is about stressed enough. So to upgrade to a viper mainshaft, or try a 200-4R, or build a T400 with maybe a Precision Industries lockup conversion? I have even found that a C4 corvette uses a ZF S6-40 with a 32-spline output shaft, which may also hold up better. Any more ideas/opinions on my selections. Or hopefully did I hit on something that may work with roughly 8-900hp?

Thanks.

 

Well, skip the ZF. It's got even heavier internal parts then the t56, which makes it more truck like without a HEAVY flywheel... That and it won't hold up to abuse like a t56 and parts are way more expensive. For the money that you're going to spend keeping the ZF happy I'd just go with a gforce 5 speed.

I don't know of anyone that's happy with a th200-4r conversion. Occasionally you'll see one turn up in a fast race car (usually a turbo buick), but I've seen a few similarly built 200's repeatedly die unhappy deaths in much lower powered cars. I'd stay away from yank (one of the big conversion sellers) altogether. A few locals have gotten trannys from then that were messed up out of the box and to say that their customer service is lacking is being kind.

Like I mentioned earlier, I'm still looking for an overdrive that will hold similar power to what you're talking about and good efficientcy and I'm not finding it. I'd prefer a manual but I just don't see spending $4000+ on it right now. If I was going to do it this instant it would be a toss up between a 400+GV or a 4l80, with a 350+gv (and an extra 350 sitting in the basement ready to go as the first blows up) as a distant 3rd place.

If you don't need to hold the power in OD (street car that sees drag use), I'd consider looking at a Lentech AOD, you'd be looking at something about similar or maybe a little lighter then a 700/4L60, better gear ratios and will hold the power as long as you don't push it in OD.

 

Rich,

I don't mean it in a bad way. But as you know mass is part of the force formula and the extra mass is not going to help driveline life.

I just price out a 800+hp blower build up, it might be a easy way to get 800hp for a street car, but it's not cheap. You know that. My way inclueded a set of AFR's a fully forged bottom end and a intercooled supercharger. On top of that you need the $ for the rear and tranny to hold it. I would be more than happy to build $13,000+ 383 blower engines (including the blower) for people, but I agree with Mindgame that kind of power is hard to use on the street. A healthy 396 LT1 can make 600+hp and that's not real easy to use.

Bret

 

If you go with a 400 which is what i will be doing also, just go pull it out of 1990+ chevy pick/van 3500 model and you can retain your stock speedo. I neever had any problems with my th350 in 1970 camper special long bed pickup 440rwhp 6000pounds. Th350 is ten times the tranny a 4l60e is.

 

thanks for all the debate guys...keep up the great work


Paul