TH400 vs. 700R4

[PJ Reynolds]

I'm doing some planning for a drive line swap out on my 91 RS 305TBI/700R4
will be coming out 383 Stroker w/770 Holly Avenger, (450HP)going in.
(I asked you all what you recommended on soupping up the RS vs. getting an 02, and the feedback made sense. I'm souping up what I already own outright, and not signing up for 5 more years of bank payments.)I'm getting a few recommendations, especially from my son in law, to go with a TH400 w/3,500 stall converter. Can anyone suggest why the TH400 might be preffered over the 700R4 with this turnkey crate motor(383)? I am on the Florida turnpike alot going back & forth to work, and the O-drive on the 700R4 cruises nicely. I would lose that with the TH400, wouldn't I? What are the pro's N Con's on the TH400 vs. 700R4?

[N20LT4Bird]

The TH400 is just beefier, hands down. The 700R4 could be built to withstand the abuse of 450 HP, but the TH400 in stock form would do it. So, the main advantage to the TH400 is the fact that it can be built to be pretty much bulletproof. You can only go so far with the 700R4.

The obvious disadvantage is the fact that the TH400 lacks the overdrive. When you couple this with a steep rearend gear, it make the car hard to live with on the street. The 700R4 has a nice overdrive and a steeper 1st gear ratio. THis makes for a nice street tranny.

So, the compromises would be to build a beefier 700R4 or get an overdrive unit for the TH400 from gear vendors. Gear vendors makes a split gear ratio unit that bolts on the back of the TH400. Both of these solutions would work, but the gear vendors unit would be a little more trick

[Injuneer]

You should be able to take the 700R4 to about 750HP with a good build... beyond that, its a crap shoot. A friend on my toasted 2 Art Carr "1000HP" 700R4's in minutes in a 900HP LT1 application. The TH400 as noted above is stronger to begin with, and appears to be capable of supporting huge HP with a good build... the car I mentioned above is now pushing over 1,300HP through a TH400 that started out as an Art Carr build, eventually "wore out" after 4 years of racing and has been rebuilt by a shop in PA.

I have the TH400 with the Gear Vendor unit, and it makes things a bit better as far as RPM on cruise, but the GV only comes in a 0.78 O/D, so it doesn't help a whole lot if you are running something like 4.11's and street tires. I was cruising at almost 4,000rpm at 70mph with that configuration, and the GV dropped it closer to 3,000rpm. But the GV is expensive (I bought mine used for 1/2-price) and adds 50-60# to the car.

[N20LT4Bird]

I have the TH400 with the Gear Vendor unit, and it makes things a bit better as far as RPM on cruise, but the GV only comes in a 0.78 O/D, so it doesn't help a whole lot if you are running something like 4.11's and street tires

I thought you had one, and was gonan mentionit, but wasnt sure. So, you dont think its worth it?

[PJ Reynolds]

Sounds like I need to find a good Tranni guy here in south Florida to do a rebuild on my 700R4. That or just swap it out with a hi performance one already built up by my crate motor guy "Jon Barrett". They are owned by "Ariel Performance" who specializes in gear mnfct. Great feedback I love this website!

[Injuneer]

I thought you had one, and was gonan mentionit, but wasnt sure. So, you dont think its worth it?

Don't get me wrong... its a great piece of equipment, and ESSENTIAL for running a performance TH400 on the street. I still remember the day I pulled it out of the shop... I told them not to wire up the switch. All I had was a single bare wire sticking out of the console. Before I left the shop, I pulled the connector off the back of the cigarette lighter.

I was following a buddy of mine in his pickup on I-78 at 70mph, and the tach was over 3,900rpm, and the entire inside of the car is rattling like crazy from the exhuast (which consisted of 2 shorty muffler on the header collectors, nothing else), and I am slowly going deaf. I reached down and managed to stick the GV wire into the cigarette light connector, and it was like I shut the engine off.... it got so quiet. But it was still cranking close to 3,100rpm.

For a track car, its a toss-up. Right now, I figure if I ever spray the 300-shot, the trap speeds should be approaching 140mph. The engine hits the cutoff for the nitrous (7,000rpm) at about 135mph in 3rd gear, so I will need the GV to shift at the 1000-ft mark or so. But the intelligent way to go would have been to just go from my 4.11's to 3.90's. And put a spool in it.... but I guess somewhere in the back of my mind, I see the car getting driven on the street again.

[N20LT4Bird]

but I guess somewhere in the back of my mind, I see the car getting driven on the street again.

I would have a hard time giving up street duty for my car. Thats what I love about it.....its street manners.