??modify TH350 or new 700r-4??

[jon79flavette]

I have the stock TH350 in my 79. The new 383 stroker is complete and has been (fly wheel) dynoed at 468 h.p and 477 ft. lbs. I don't think the stock 25 year old tranny is gong to be the best chioce. any thoghts.

A: modify, rebuild the existing 350

or B: go with a high performance new 700 r-4 with a shift kit etc. Also any suggestions on best shift kits.

C: or possibly a hypo TH400??

Thanks

 

[Piet]

I was looking at the same thing for my '73 camaro... I talked to my tranny guy.
He told me to stick with my th350 (maybe rebuild it) but that it was a stronger tranny than the 7004r.

any tranny guys out there?

 

[MaineShark]

I've been looking into this quite a bit, and the 4L80E is looking very nice. The strength of the TH400, with a .75 overdrive added.

Joe

 

[Crickett]

I say go with the overdrive tranny!

 

[Michel73]

Is there any way to add an overdrive gear to a TH400? My TH400 seems just fine but sure would like to have another gear for the highway.

Save the Wave

 

[Scooter76]

Gear Vendors makes an add on overdrive for the th400. Its expensive & may not be compatible with the vette, as it adds about 10-12" to the legnth of the trans. We already have pretty short driveshafts. The 4L80E would be good, but it too is expensive & requires a $300 computer to operate it. The 700r4s can be built pretty strong, but I dont know if they can handle 477ft/lb. Check out Bowtie overdrives.com (I believe that is the correct address) they build hi-perf 700r4s. Maybe they have what you are looking for.

 

[MaineShark]

As scooter mentioned, the GearVendors overdrive unit is available (and it does fit), but it is rather expensive ($2200, I think).

The 4L80E is a TH400 with an overdrive unit integrated into the case.

You can get a full-manual valve body and skip the computer...

Joe

 

[Piet]

The question I got asked is.... do you do LOTS of highway driving? If it is just the occational trip.... pay the cost in gas and save in the cost of transmission swaps... just a thought.

Now from what I read, on http://www.bowtieoverdrives.com/ what you are looking for is either:

1) BowtieOverdrives Level 3 7004r transmission built to handle up to 600 horsepower.

2) They have JUST started to offer the 4l80e which sounds pretty agressive (and pricey)

Let us know what you find out !

 

[jon79flavette]

I am getting a cost on the 700 r-4 a high performance with a level 3 shift kit hardened "stuff" intalled, "all tricked out" in his words" with the yoke changes, shorter drive shaft, detent cable, new fly wheel (he says my flex-plate won't bolt up to a 700 r-4 stall converter) and 2800 to 3000 new hi-tourque (says up to 675 h.p and 580 ft. lbs.) stall converter, cost is 1500.00 total complete drive in / drive out, does that sound about right????

 

[MaineShark]

Is that converter stall correct for your engine? Converter stall must be matched to the engine's power and torque curves to achieve optimal performance. Since you have engine dyno charts, you are in a much better position than most people to talk to a tranny expert and get the absolute best possible converter recommendation.

Those numbers do seem high for a street-driven car. Remember, the stall speed is similar to the speed at which a manual driver "drops the clutch." Those numbers mean you'll have to rev the engine to 2800-3000 before the converter really grabs (it will still roll before that, like feathering a clutch). High stall speed also means that the car will want to roll against the brakes at stoplights and such (you'll need more pedal pressure to keep the car in place), and the converter will generate more heat, possibly overheating the fluid.

If that is the correct stall speed for your engine, then use it. But you should probably install an external tranny cooler to combat the heating of the fluid.

If that stall speed is not matched to your engine, then you could very well end up with less "real world" performance than your car had when it rolled off the assembly line, wasting the work that you put into the new engine.

You also need to decide if you want a lockup or non-lockup converter.

The technique used to shorten the driveshaft is also important. Ask if he will be cutting it himself, or sending it to a driveshaft shop. If he plans to do it himself, make sure that he has the equipment and knowledge to choose the right spot to cut, and to re-balance it. Most driveshafts (and I believe that ours are no exception) are not straight tubes - they have steps or taper to them, and cutting in the wrong place can mess this up.

And, you should ask this guy to refer you to some of his prior customers who are running setups which are similar to yours (both in the build of the transmission and the power and torque levels of the engine), so you can be re-assured that the transmission will really survive. A good builder should have a list of satisfied customers, and should not hesitate to give you some referrences. Remember that he's trying to sell something to you, so it is up to him to convince you that his product is of a high quality level.

Lastly, you need to check on things like the shifter and TV cable. Will he include a modified shifter (4-speed instead of 3-speed) and a quality TV cable setup? If not, these are added expenses, which you will have to purchase on your own. The TV cable, in particular, is a critical item. If the pressures are not set properly, the transmission will not survive long at all.

Joe

P.S., you might want to ask him about the 200-4R, if he does any work with them. It can be built just as strong as the 700-R4, but has closer ratios and will not require the driveshaft to be shortened.

 

[GerryLP]

FLAVette,

I do agree with Joe on the 200r4. It is supposed to be a very strong tranny (i.e. it was stock in the Buick Grand National), and most of the dimensions do coincide with the TH350. This means easier retrofitting of the tranny.

I am not certain about the 200r4's converter lock-up features though. It would be easy to control the lock-up through "Painless Harness" set-ups, but this will also allow you to install whatever stall torque converter you desire, and still be able to save a little gas when just cruising.

 

[jon79flavette]

Man, I just keep hearing contrasting views from these "expert" tranny shops. I spoke at length with this local guy that build high performance trans. and told me will will give many recent referrals, he does alot of work with the guys at the local morosso track. He says the 700 r-4 was built for gas, with the 4th gear OD, which I already knew that, but he feels you can't beat the durability of the TH350 (and 400) it is not a dayly driver, I may take the occasional 2-4 road trip accross the state or so. He has been doing this 35 years, a one man operation, and has done "hundreds" of vettes, in his words. I don't think he is after my money, unlike others. The motor is out, he says bring him the trans, he will do a total rebuild, seals, kevlar bands, install a transgo 2 stage shift kit. intall hardened race componants, and insists on me replacing the stock U joints with hardened splicer ones. qoueted 400- 450 bucks, and says it will outlast a 700 4 times over. I can manually shift or not, and he claims with the motor I have, the trans will be more than adequte, and he'll put it in writing. I drop it off, I pick it up, and less than 500 bucks. This guy seems to love the TH 350/400 trans, Idon't know!!! :confused :confused

 

[Glensgages]

jon79flavette, the question to ask yourself is: "What are my goals for this car?" If your primary objective is to just 'cruise for ice creams', and never 'USE' that 460+ HP, go with the 700R4. If you're gonna go to the strip, go with a 'built' THM400.
I have BOTH: a THM400 in my 12-second '79 Z28, and the stock 700R4 in my '82 Corvette. For my 'personal' tastes, I'd NEVER put a 700R4 in another car (my '82 Vette has only 19,000 miles, and is 'too-nice' to cut-up; the 700R4 stays-put) for a few reasons:
#1: Gear ratios... the gear ratios of a 700R4 are 'too-wide' apart; 3.06, 1.63, 1:1, and .7:1, where-as the THM400 ratios are 2.48, 1.48, & 1:1. Consider this; if your shift-point is 6000 RPM, here are the gear-drops of the 700R4, then the THM400 in (#):
1st/2nd shift- 3196 RPM (3580); 2nd/3rd shift- 3680 RPM (4054); 3rd/OD shift- 4200 RPM (no OD in THM400). The RPM-drop in the THM400 favors it over the 700R4 by virtue of keeping the motor in it's 'power-band'.
#2: computer/random shifting... you'll need to add a computer to 'run' the 700R4, for the lock-up converter feature (I think, unless BTO by-passes the computer/lock-up). With my '82 Vette, at low-speeds (30-45 MPH), the tranny doesn't know which gear to be in, or to lock/unlock the converter. At 40-45 MPH, the tach reads 1100 RPM, and the motor 'lugs'. About the time that I decide to 'kick-it-down' a gear, the computer un-locks the converter! It goes from OD/lock-up to 3rd/un-lock! You lightly squeeze outta the throttle, BOOM, it locks-up, then, up-shifts again! I've had mine looked at by a certified GM technician (who has hot-rodded Vettes 'on-the-side' for 20+ years!), and he says the 700R4 is working fine!
#3: durability/reliability with no dis-respect to BTO and other 700R4 manufacturers, if the 700R4 is so 'durable', wouldn't weekly bracket racers use it? You have an extra gear, a super-low 1st gear, they're becoming more plentiful as the years go by, and yet NOBODY uses them in 'serious' race cars (I repeat my first line of questioning: "What are my goals for this car?" )
Here's a thought; if you DO decide on the THM400, choose your rear-gearing based on the 1:1 high-gear ratio of the Turbo, but purchase an 'extra-low' gear-set for the THM400. I have TCI gear-sets in BOTH of my THM400s (an identical 'spare', just-in-case); the ratios are 2.75:1, 1.57:1, and 1:1 in high. This way, you'll have durability, AND a lower 1st gear ratio (3.73s 'feel' like 4.11s; 4.11s 'feel' like 4.56s; etc.); your 383" has a 'broad' torque curve, and will LOVE IT!!!!!:J
just my $.02 worth (what a ramble; I shoulda been charged a full dollar!)

 

[MaineShark]

he feels you can't beat the durability of the TH350 (and 400)

He's right. The TH350 and TH400 trannies are darn near bulletproof. You can build a 700-R4 or 200-4R to survive behind that engine, but it will cost a lot more than a similarly-reliable TH350/400.

The overdrive will be easier on your gas mileage and your engine's lifespan, if you drive for extended periods at highway speeds.

It's up to you.

Originally posted by Glensgages
the gear ratios of a 700R4 are 'too-wide' apart

The 200-4R does eliminate this, with much better ratios. Actually, I think that those "extra low" gears you have in yours are the same ratios as the 200-4R.

Originally posted by Glensgages
you'll need to add a computer to 'run' the 700R4, for the lock-up converter feature (I think, unless BTO by-passes the computer/lock-up)

They do. No computer is needed.

Originally posted by Glensgages
About the time that I decide to 'kick-it-down' a gear, the computer un-locks the converter! It goes from OD/lock-up to 3rd/un-lock! You lightly squeeze outta the throttle, BOOM, it locks-up, then, up-shifts again! I've had mine looked at by a certified GM technician (who has hot-rodded Vettes 'on-the-side' for 20+ years!), and he says the 700R4 is working fine!

Lock-up should disengage if you downshift. If not, it would be like shifting a manual without pressing the clutch. It certainly shouldn't be locking-up, then upshifting, though. It should upshift, then lock. There's no computer, in any case. Your 700-R4 is a mechanical transmission. It wasn't until later that computers were added.

Originally posted by Glensgages
with no dis-respect to BTO and other 700R4 manufacturers, if the 700R4 is so 'durable', wouldn't weekly bracket racers use it?

Expense. A properly-built 700-R4, to handle large power/torque numbers, is very expensive.

Like I said earlier, though, I'm leaning toward the 4L80E. If I'm going to spend big bucks for an overdrive tranny, I want one with the durability of the TH400, which the 4L80E has. It can be re-geared with that same "extra low" gearset that you're using, for added fun

Joe