Th350 vs. Th400
Thread Starter
Pro
Joined: Jul 2000
Posts: 590
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Th350 vs. Th400
Which is better and why? I currently have a Th400 in my 75. I don't like the fact that it's only got three speeds. Dose that have any advantages? I have a 3.08 rear end. On the hiway it seems to rev high which uses alot of gas. What do you guys think?
Safety Car
Joined: Aug 2000
Posts: 3,909
Likes: 26
From: Clymer PA
Re: Th350 vs. Th400 (Racer-X)
The TH400 is basically a bullet-proof TH350. The TH400 is used in high horsepower applications and came stock on many of the big blocks. If I remember correctly, don't you lose more power through the TH400 than the TH350? Anyway, if highway driving is a concern overdrive is your answer. I would look into a 700R4 or what not.
Le Mans Master
Joined: Dec 2000
Posts: 9,752
Likes: 0
From: Chattanooga TN
St. Jude Donor '08-'09
Re: Th350 vs. Th400 (Racer-X)
The TH-400 is just about bullet-proof, especially if you get it rebuilt by someone who knows what they're doing. The final gearing in the 400 and 350 is 1:1. If you want lower RPM's at highway speed go with a 700R4 (or a 4L80E, if you have deep pockets). It's not a direct bolt-in, but check out www.700r4.com. They make a kit for the Vette.
BTW... If you want to get rid of the TH-400, let me know. I may be interested.
BTW... If you want to get rid of the TH-400, let me know. I may be interested.
Race Director
Joined: Mar 2001
Posts: 11,601
Likes: 0
From: San Francisco CA
St. Jude Donor '07
Re: Th350 vs. Th400 (Racer-X)
From what I know, 350 has slightly better first gear, 400 is stronger, nearly bulletproof. 400 takes a little more power to operate than 350, if i remember right. I noticed high rpms on the highway too, so i was thinking about a TH700r4, which is 4speed w/overdrive. should be nearly bolt on installation. :chevy
Intermediate
Joined: Feb 2002
Posts: 46
Likes: 0
From: Pittsburgh PA
Re: Th350 vs. Th400 (e3pres)
The TH-400 is just about bullet-proof, especially if you get it rebuilt by someone who knows what they're doing. The final gearing in the 400 and 350 is 1:1. If you want lower RPM's at highway speed go with a 700R4 (or a 4L80E, if you have deep pockets).
-Sleek
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Re: Th350 vs. Th400 (SleekLines)
TH400's use more hp than th350. Gas mileage is how well your motor runs. I got 20+ with a hot 355 ci and 3.55 gears and 27 inch tires TH350 on a 2800 mile trip. I would shift kit the tranny and work on the max tune up
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Drifting
Joined: Nov 2000
Posts: 1,428
Likes: 0
Re: Th350 vs. Th400 (gkull)
Wouldn't think that Hiway RPM's would be much of a concern with your 3.08 rear end.......I'm turnin abt 3K RPM at 70MPH with my 3.55's. You should only be turnin 2500 RPM or so at 70......whats the problem? :seeya
Le Mans Master
Joined: Jul 2001
Posts: 9,622
Likes: 16
From: absecon nj
Re: Th350 vs. Th400 (tnt76vette)
i have the 400 in my vette now and had a 350 before andi can feel the difference of how much power i lost over it...yeah it is much stronger and final is 1:1 ill switch to a 700 next.
Burning Brakes
Joined: Dec 2000
Posts: 962
Likes: 0
From: Carlisle PA
Re: Th350 vs. Th400 (Racer-X)
Granted, stock a Turbo 400 is stronger then a Turbo 350, but the 350 can be made just as strong.. Talking to Coan Engineering, B&M, TCI - the intermediate sprag is the week link in the Turbo 350... The following parts are recommended.
HD Intermediate Sprag ($300), HD Sprag Race (Coan's is billet and runs $113), TCI offers HD Sprag for $50. Coan also recommended somekind of element that costs $20. So including a deep aluminum pan ($100), master overhaul kit ($120 - $200 depending on the type of clutches), and Transgo Kit ($50 - $70), you can build a Turbo 350 that can pretty much withstand alot of horsepower.
If you already have the 400, I would just use it... I ran across a B&M Street/Strip Turbo 350 for $50 and for the additional money I'll have something that will be stronger then a stock Turbo 400 and whole lot less weight.
HD Intermediate Sprag ($300), HD Sprag Race (Coan's is billet and runs $113), TCI offers HD Sprag for $50. Coan also recommended somekind of element that costs $20. So including a deep aluminum pan ($100), master overhaul kit ($120 - $200 depending on the type of clutches), and Transgo Kit ($50 - $70), you can build a Turbo 350 that can pretty much withstand alot of horsepower.
If you already have the 400, I would just use it... I ran across a B&M Street/Strip Turbo 350 for $50 and for the additional money I'll have something that will be stronger then a stock Turbo 400 and whole lot less weight.
Melting Slicks
Joined: Dec 1999
Posts: 2,116
Likes: 156
From: Mid West
Cruise-In III Veteran
Re: Th350 vs. Th400 (Racer-X)
I agree with the others that a TH400 is stronger in stock form, but a TH350 can be made strong enough for most people. I have a modified TH350 behind a 455ci Olds Big Block that runs 12.0 1/4miles at 115mph. Been in the car for over 5 yrs now with no problems.
If you are concerned about the "high" rpm's, first calculate if you are getting a lot of slippage through the stall convertor. Just take the difference between your actual rpm in 3rd gear and the rpm you would have if you didn't have a stall convertor. I'm not sure what is considered to be a bad amount of slippage in the convertor, but a good trans company could tell you if your getting a lot of slippage compared to the newer design convertors from B&M, TCI, Coan, etc. I have seen several of my friends have a lot of slippage in their cheap aftermarket convertors which really increased their RPM's in 3rd gear and lowered their gas milage.
Changing the stall convertor would be a lot cheaper than a whole tranny. Just an idea you might want to check on.
If you are concerned about the "high" rpm's, first calculate if you are getting a lot of slippage through the stall convertor. Just take the difference between your actual rpm in 3rd gear and the rpm you would have if you didn't have a stall convertor. I'm not sure what is considered to be a bad amount of slippage in the convertor, but a good trans company could tell you if your getting a lot of slippage compared to the newer design convertors from B&M, TCI, Coan, etc. I have seen several of my friends have a lot of slippage in their cheap aftermarket convertors which really increased their RPM's in 3rd gear and lowered their gas milage.
Changing the stall convertor would be a lot cheaper than a whole tranny. Just an idea you might want to check on.
Burning Brakes
Joined: Dec 2000
Posts: 795
Likes: 0
From: Madison MS
Re: Th350 vs. Th400 (Jason Staley)
I have a TH400 with 3.08 rearend and I am turning almost exactly 2500 at 70mph. If you RPMs are significantly higher than that, you either have go-cart tires on it or you have some slippage somewhere.
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