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Discussion Starter #1
Hey Everyone,
I'm new hear to this site but it certainly looks like the right place to get great information. I just bought a 1970 El Camino that I will be restoring and I had a question. I'm looking for the "perfect" engine and transmission combination. The truck currently has a 350/TH350 combo. Should I stick with this because I would like to put in a 396. Does anyone have any helpful suggestions about which combination of motor and tranny I should use. Any help is greatly appreciated and I'm looking forward to checking out the entire site, it's looks great!
Thanks Again.
 

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GM put a 400 behind their Big blocks as far as I know. My 72 came with a 402 (396 punched +030) factory and a 400 THD tranny. It is about the amount of torque the engine produces not HP.

So my "suggestion" is if you are putting in a big block go with the 400 not the 350. 350 is rated at something like 350 Lb./Ft. of torque and the 400THD is rated at 450 Lb./ft of torque. Hands down the 400 is a stronger transmission.

I am not saying that you can not build a 350 that is acceptable but for the same money you can build a far stronger 400. Anyway the 400 really doesn't need to be stronger unless your going to be putting more than a "constant" 550 to 650 lb./ft. on it all the time and I don't know anyone that has a daily beater or a weekend warrior that is actually doing that other than ProStock or ProModified.

Just my $0.02 worth.

BTW

Welcome to ECC and NECOA! Good to have you aboard! :D
 

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Discussion Starter #4
Thanks for the tips. I'd like to have a 396 with a TH400 or a 700R4 tranny. Which combo do you think would be better? As always, your advise is appreciated.
Thanks :)
 

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The difference between a TH400 and a TH700 are major. The 400 is far more simpler and would bolt right up to your 396 and in my opinion a much more logical choice. I think you'll have to do some crossmember modifications if a 700 is to be installed but I'm not sure. If you go with a 400 tranny you'll need the kickdown switch if it doesn't come with the tranny, the 400's kickdown is controlled electrically as opposed to the cable on the 350. These switches are available from Summit. The 700 uses a Throttle Valve cable (called TV cable) to control the kickdown and if there isn't a conversion kit available, you might be looking at some heavy rigging to make it work, connected to a carburetor. Also get a new vacuum modulator and a new vacuum hose, these can cause a lot of problems (too many to list now) when they go wrong.

In terms of strength, I'm not familiar enough with the 700 trannys but if they work on 454s then they must work on 396s and the overdrive feature is nice, when it comes to gears, I think more is better.
 

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The 700R4 is, simply put, a 350 with a fourth gear. It mounts 5" furtherer back and it requires a shorter drive shaft. I has roughly the same specs as the THD 350. It is a good transmission. Another transmission that is good is the THD 200R4 although, it is a little bit weaker in its stock version. Both can be built to handle more torque at a cost much like the 350.

I put a 700R4 on a 5th gen behind a 383 but I got it from a good transmission shop and it has been built up. I had to get a different cross member, drive shaft and another consideration is that most bowtie overdrives require a lock up type converter which means you'll have to add some electronics to lock it up in fourth.

350 has a final drive ratio of 1:1 and the 700R4s have a final drive ratio of .70 (roughly) so it effectively lowers the rear end ratio in order to lower the RPM at highway speeds. The 200R4s lower the final drive ratio to a .68 further lowering the rear end ratio in fourth and in turn lowering the RPM even more than the 350.

The 4L80 and 4L80e is another overdrive. The 4L80s are the THD 400 with an overdrive and that final fourth gear is the same as the 700R4 (.70) however, it can withstand up to 450 Lb. Ft of torque like the THD 400.
I've only read about the 4L80 but the 4L80e is a computer controlled and GM uses that in a lot of trucks with Big Blocks. Most restorers don't use them primarily because of the cost. The transmission its self is going to be $2000.00 if not more and another 2000 or so for the computer and wiring. I can't comment much on the 4L80, I never met or talked to anyone with that version. The "e" series means electronically controlled. I "ASSUME" the 4L80 is pretty much like the 700R4s. Meaning that it doesn't require the computer just the lockup wiring. I can't say for sure. What I can say is for a Big Block it is (Specifications wise) a best choice.

There are manufacturers that make an overdrive unit that mounts being the THD 400 that give the same strength as the regular THD 400, it requires some minor mods to the tunnel because of its size.

Another catch... The 350 comes in two or so configurations. One is the regular old THD 350 and one is a THD 350C. The "C" version is a lockup type. Meaning the torque converter is, in a manner of speaking, freewheeling at times and locked up in hard acceleration. Later models, say 5th gen Elkys had the 350C not the straight 350. It is a gas mileage thing.

Check this site out;

http://www.700r4.com/FAQ/faq.htm

I am no expert. I've just, more or less, regurgitated the things I've found out from discussions and reading articles. This is the understanding I have it could possibly be disputed. But it is what I have found out and the way I understand it.
 

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My info is pretty much obtained the same way ElkyPete's is, through reading books, articles and magazines. The only thing I can add is that the TH700 transmission also has a terrible tendency to develop cracks in its case, in the input shaft area and I think that building a strong TH400 is the best way to go behind a big block.
The transmission mount is further back on the TH400 than the TH350 (assuming you have one in there now) and the distance from the engine to the mount on the TH350 is 22 1/4" and on the TH400 it's 27 15/16" so there is some crossmember modification/replacement necessary. Driveshaft modification is also needed if you are taking out a TH350 since the TH400 is longer than the TH350 and it has at least three different length tailhousings, ranging from 4", 9" and 13".
Hope this will help some.
 

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Discussion Starter #8
Thanks again for all the great info. ElkyPete, that 700R4 website link you gave offered a lot of great information. Convient too since there about 100 miles from where I live. It's given me a lot to think about.
Once agian thanks,
Grant :)
 

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yeah pretty much what they said...but if your going to put a built 396 in it, thats pushing some pretty high numbers, i'd strongly reccomend the TH400, the 700r4's are awesome tranny's, especially for cruising, but for dragging most people i know go with the TH400, it can be built stronger, and you'd be best off doin it right the first time instead of waiting til the 2nd or third time ;)
 

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big block swap

Hello
looked at all the inputs you got.

The first and foremost
on the tranny the 700R4 isan outstanding tranny if built right. the 396 will eventually tear it up unless you have it built. stay away from th 200r it will leave you stranded and broke. the lockup feature of the 700 wil alow you to run a high stall converter on the street with out killing the tranny. there are company's out there that make the converters with a high stall and lockup function. the newer 460le and 480le trans are outstanding but you will pay for them. the earlier units are not controlled by the computer adn you can buy a complete tranny instal for around 3k. now this is steep but you get a industructable tranny with lockup overdrive and with the electronic versions you have a hand held that lets you controll all the tranny functions like shift points up and down and firmness.
As for the power train i just installed a 93 LT1 with a 6 speed i get 33 MPG hwy and 27 city the car is a blast to drive and tital cost was around 5k including engine and tranny.
 
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