Auto tranny for the RX... which one?

[Thor06]

Hey again guys. As some of you may remember, my buddy and I are putting a small block in his RX7. A couple things changed though, its going in his 83 base model rather than his 85 GSL SE, hes going to use a Ford 8.8 rear, and hes going with a GM auto tranny since the T5 was shot down and the T-56 is a bit on the spendy side, plus theres none around.

So the mount kit we are going to buy is from Granny's Speed Shop and the options they have for the tranny mounts are a power glide, turbo 400, turbo 350, 700R4, 200-4R, T-5 and T-56. Well, the T-5 and T-56 are both out, and we really dont want a powerglide as I dont think the two speeds would have too great of street manners, but also all the dirt track racers have them picked over pretty good. That leaves the TH-350, TH-400, 700-R4, and 200-4R.

Turns out the supposed 383 with Edelbrock heads is a 350 with some stock 400 heads (333882 cast #'s). Knowing that now, we're going to leave it 350 with the flat tops it has, get some Vortec heads, a new intake mani, the 600 cfm Edelbrock it has (will that suffice?), a new cam if we deem the one in there not lumpy enough, and hope for 350-400 hp. When we get bored of that power I think we'll toss on a 100-150 shot for fun so thats the kind of power we're looking for. The car is also going to be mainly used for drag, but it will be a weekend cruiser too. Knowing that, which tranny would you guys recommend? I think we're leaning towards the 700-R4, is that a good plan? Thanks guys.

EDIT: I'd say its going to be like a 70% weekend car 30% track bitch. That said, is a transbrake a good idea?

[wrightz28]

700R4 is a overdrive trans, and you need to weary ofthe build dates, ones before 88 (mid 87) had issues that required a "upgrade" (really just a removal of a check ball, and I think there was something with the valve body that was upgraded? first cup of coffee).

I would think the 400 would be a better route.

I also wouldn't plan a carb out yet until you have your cam and intake requirements laid out.

[Genopsyde]

I'm with wright on the TH400. It's a pretty heavy duty trans and will hold up to your application much better than the rest. and since you plan on mainly draging and weekend cruising then it should work out fine there as well. If you decide to drive it on the street more than the track, then I would pick the 700.

[hotrod_chevyz]

A well built 700r4 transmission is not a bad selection if the car will ever see past 85 mph. You can gear the axle for a better launch and still end up with some sort of top end.

[Thor06]

^Thats what I was thinking too, I figured that extra gear would allow it to be good off the line but still pulling hard at the end of the strip.

I talked with Mike about this last night, there isnt a track in town and the closest is Brainerd International which is about 2 hours away. Theres also a shitty one 2 hours in a different direction and Rock Falls a good 5 hours away. I dont think we'll do bracket racing more than 3 times the whole summer, and I cant really forsee going to the track more than once every two weeks or so, so it will be seeing a lot of street time. I kinda get the feeling most of its miles are going to be out cruising with the other car guys on Friday and Saturday nights. The TH400 might not be a bad idea as Mike's sister's finance's brother has one sitting at his place we can probably damn near have. Will a stock one take it or will we need to go through it? Thanks for the help guys.

[hotrod_chevyz]

400 transmissions are good with the right stall and a transgo shift reprogram kit, but stock they are just boring.

[Thor06]

But will it hold up stock or will it need to be rebuilt? Remember, I think the most we'd see is ike 450-500 with nitrous. I think if a stocker 400 will work we'll just get that and snag the shift kit. If not, then I think we'll just get a built 700R4. I think the OD and extra gear would be nice on the 700R4, but I also think that if the stock 400 will work it would be really nice to get a tranny for $100 and two cases of beer rather than shelling out for a newly rebuid 700R4.

[hotrod_chevyz]

Its hard to say really. With extreme use it might last, it might not. Just depends on the transmission, the quality of the rebuild it may or may not have seen through the years ect. Ive seen SO MANY professionally built transmissions go up in smoke on track your pretty much guessing how many beans are in the jar..

As much power as your expecting i would buy a rebuild kit and replace all the seals, steels, and clutches if its been ran before and has sat since. They have a lot of pieces, but rebuilding one is pretty straight forward with a book that explains it if you havent torn one all the way down before. Dont use (or pay to have installed) the clutches that come in a standard rebuild kit. Better clutches can be had as an upgrade, as well as other parts that are known to fail. They cost extra but are worth the peace of mind IMO. I would also replace the pump, the governor and torque converter AND put in a full transgo shift reprogram kit so you can tune each shift independant and get it EXACTLY how you want it.

[89IROC&RS]

gear ratios are very critical here, as everyone else has covered alot of the issues of building either tranny to handle the power, ill talk about the gear ratios, and personal experience, as ive got a built 700 in my IROC, and a th400 in the truck.

The 700 has got (IMHO) a bad rap. I had mine properly built by a chevy trans tech, with a full B&M shift kit and high performance clutch pack, corvette 1st - 2nd servo, and a 2600 rpm stall lockup converter with a kevlar clutch, and i absolutely love it, and according to my trans guy, it should take a 500hp beating with no problem, but he'd be worried about it taking 600hp. I love the lockup and overdrive for the highway, but for drag racing there is a hiccup with using the good ol 700.

As much as i love that tranny i have to point out that its very deep first gear, being 3.06:1, causes an rpm drop on the 1st to 2nd shift. Off the line it will probly snap your head back, and then when it shifts into second you kinda snap forward again until the rpms build back up to haulin the car down the track. the rest of the ride is pure joy, but if your competing at the track, that rpm drop and subsequent lag will not be your friend.

The TH400 has a much higher first gear, 2.48:1, so off the line it wont haul as hard, but the rest of the shifts are much better spaced out. and you have a more constant acceleration with no rpm drop. course, you loose the lockup converter, and the highway cruising as a result.

Just one other thing to factor into the situation. Personally, if i was building this thing to go as fast as possible, and compete, id use the TH400, and go find a cheap trailer and old military CUCV, got mine for $1500 bucks, and tow that thing to and from the track. My truck gets 22mpg on the highway, not bad for a big ass truck. Even with a trailer it would probly cost less in travel fuel than driving a drag racer with a TH400.

just my