WAGE_SLAVE

what's it like with a th400 and no overdrive on the highway. i hear it screams in rpm's, and you cant go above 55-60. is this true.

john kilgore

depends on rear end ratios. 3.73s the motor will scream. 3.08 ok

MeanWS6

I am doing a TH400 right now, and I have 3.73's. Get a different rear end gear? What will I lose or gain other than lower RPM's at higher speeds? Will it still launch hard

It will have a:
TCT 4000 stall
200 shot

Hotrodhawk

iTrader: (1)

If you have a 4l60e in your car just drive around in third gear, its the same final drive ratio as a 400.

rpm will be 300 rpm higher than what you find it too be without a lock-up converter.

stangeater01

iTrader: (125)

this is true you will get the same effect i have a th400 with 373 and at about 3k its at 65mph you can go 70-80 if you want my car is loud and i dont like speeding tickets so i keep it around 65mph 1/4 is for fast acceleration

john kilgore

l favor over gearing the trans and under gearing the rear end. but you guys are doing ok

Hotrodhawk

iTrader: (1)

I turn 3000 rpm in third gear [4l60e] at 70 mph without locking the converter.
...yes its frick'n loud
You should have been around when we didn't have OD transmissions, 2800~3000 rpm at highway speed was a norm

jxaxsxoxn

iTrader: (2)

If you do the math...gear ratio times OD ratio times 336 (lock up) or 355 (no lockup) times mph divided by tire diameter, you get close to a 800 rpm difference. It varies with speed, etc.
I see almost a 1000 rpm gain when I go from OD locked up to drive not locked up.
So you could be looking at around a 700 to 1000 rpm difference.

I used to cruise my nova down the highway at 4000 rpm and 90 mph with open headers, this was on the way to the track. Only did it twice so far, I could drive across the country like that

MakoLS1

Its not to bad! I dont miss an overdrive one bit.

99ssleeper

iTrader: (98)

It's too bad there is no good way to test the difference....something like putting the trans you have in 3rd and going for a drive....

aram

iTrader: (7)

I drove 500 miles in one day with my th400 and 3.73s.. it was loud as hell and annoying. 3500-4000 rpm the whole way! With the th400 i am putting in my new car I am going with a 3.23 gear so highway cruising won't be that bad.

john kilgore

if you under-gear the trans by 21% your 3.23s will be 3.91 in first only and 3.42 in second. food for thought

BoonesZ

as said above depends on gearing

RevGTO

iTrader: (12)

Let me put it this way: in my 69 GTO w/3.23s, I drive at about 65mph @ 3000 rpms onthe KS turnpike. In my 00 Formula w/3.42s + OD, I drive at 80mph @ 2500 rpms.

V6 Bird

iTrader: (15)

Put some taller tires on the rear and drive it!

T400 and 3.70's here. I drive on 275-60-15 BFG DR's everyday. I cruise at about 70-75 at 3200-3400 rpms. Id never go back to an OD trans.

98sspullin'em

iTrader: (-1)

ive been thinking the same thing and im prob going to go with a 430 gears in my 12 bolt and just keep my 10 bolt with 3.23's and in racing season leave the 12 bolt in and non racing season, put the 10 bolt in there.... i thought that would be good for me

Dave00C5

iTrader: (4)

Hell with 4.56's 4k was normal back then!

BLK02WS6

iTrader: (2)

Yes sir - these youngin's don't know what they missed back in the day when there were no ODs! 4.56's will make her sing a nice tune at 55