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700r4 Swap to a Turbo 350

13K views 23 replies 12 participants last post by  87442lover 
#1 ·
OK i have a 1984 chevy camera with a 700r4 transmission in it but I want to put a turbo 350 transmission in it I got all the parts to do the swap but I was looking at the turbo 350 transmission and it has a vacuum line on it and the 700r4 does not so how do I make a vacuum line for the turbo 350 or can I just cap it off?
 
#2 ·
Ummm.. I have to ask.... Why?

I could understand if the 700 was dead, or dying, but you do realize that with the THM350 you will not only cut your take off speed down, but you will also kill your top end speed and gas mileage.

Seriously I would like to know why.
 
#4 ·
this is the same thing im doin in my s-10 but the reason im doing it is because i keep blowing 700s up and they never seem to work properly so now i got a rebuilt th350 that i knwo will work good -sure ill lose some milage but i highly doubt my out of the whole performance will change because this one has a stall and the other one had nothing but a stock 1600 rpm stall -but as for the vacum line just goto the local parts store buy some small diamater steel tubing(looks like brake line) bend it to fit down into your trans then attach one end to a manifold vacum source(should be at least 12 inches at idle) and the other into the transmission use small pieces of vacum rubber line to attach the steel line
 
#9 ·
The tranny also wont shift back down until you come to a complete stop. At least this was the case of mine. The 700 is a far superiour tranny in my opinion granted its hooker up right (Tv CABLE). Try and talk your friend out of it. Like was said . . . get a modulator and hook it up to a vaccum port and you'll be set.
 
#10 ·
I am putting a 700 in my 48 Chevy P/U after ruling out the th350. I don't have words of wisdom here but I do have a question along the same lines....sort of. The rearend I have to put in the truck is out of a 79 Nova and has 2.73 gears. Wanting to spend more of my money right just getting the truck on the road I am hoping these gears aren't to high. The lower first gear in the 700 should help with take off, but is the final going to be too high?
 
#11 ·
If your asking if the 2.73 rear end is too high for the 700, than the answer is no. The theoretical top speed would be over 200MPH. If you meant 3.73's than still no, your top speed would be like around 160 (which would be interesting to see a truck get that high :p )

If you mean a 2.73 rear end on a TH350 then your top speed would be around 150MPH, 3.73 would'nt be very usable with a 350 because it would limit you to a top speed of around 120 and thats pushing near 6000RPMs on 26" tires.

All calculated numbers though, up to you.
 
#12 ·
Thanks for the reply.... I guess I was a little nervous about the 700R4/2.73 combo and how streetable it would be. I would have loved to find a posi unit to put in it but this rearend was inexpensive (cheap) and available. I have looked at ordering new gears for the rearend, what do you all think would be a good number. 355ci, 4bbl, headers, 700r4. Thanks again.
 
#13 ·
My 84 blazer has 2.73's in it and before I hotrodded the engine it would never stay in od. After cam and heads it would stay in and now it gets around 17 mpg. When you get the 700 in make sure you have the lockup working and set the tv cable up right or you will cook the trans.

John
 
#15 ·
blazinwest said:
th350 is a lot better than a 700r4
parts are cheaper and stronger and there is more stuff you can do to them.
700r4s are weak and unreliable. but they work good for awhile as long as you dont have a lot of power.
Weak and unreliable?? I couldn't disagree more. 700 can be build every bit as strong as a 350 how ever its true that a 700r4 will cost more to build.
 
#16 ·
Go to your friendly local U-pull-it & get the tube from a car with a T350. See if the carb has a fitting (or a hole for one) at the rear of the base, or if there's a place for one on the intake just behind the carb. You might be able to use the fitting from the junkyard car also. If you use rubber hose, be sure it's strong enough to resist collapsing when vacuum is applied.
 
#17 ·
700R4 vs. TH350

Robinson Robin said:
Weak and unreliable?? I couldn't disagree more. 700 can be build every bit as strong as a 350 how ever its true that a 700r4 will cost more to build.
OK. The 700R4 can be built just as strong, and actually stronger than a TH350, since it is roughly based on the TH400. The real problems with the 700R4 is the huge gap in gear ratio going from 1st gear into 2nd, and the fact that it sucks up a lot of HP, much more than a TH350. Without exception, every vehicle I've seen running a 700 at the drag strip falls flat on its face at the 1-2 shift. Granted, they're in the lead prior to the shift thanks to the huge 1st in the 700.

So, if you want to have good times at the strip, stay away from the 700. If you want to have good mileage and a tranny that shifts like a truck, then be my guest. But don't be surprised when I blow by you when you hit 2nd gear running with my TH350.

Just my $0.02....
 
#18 ·
Re: 700R4 vs. TH350

425hpOlds said:
OK. The 700R4 can be built just as strong, and actually stronger than a TH350, since it is roughly based on the TH400. The real problems with the 700R4 is the huge gap in gear ratio going from 1st gear into 2nd, and the fact that it sucks up a lot of HP, much more than a TH350. Without exception, every vehicle I've seen running a 700 at the drag strip falls flat on its face at the 1-2 shift. Granted, they're in the lead prior to the shift thanks to the huge 1st in the 700.

So, if you want to have good times at the strip, stay away from the 700. If you want to have good mileage and a tranny that shifts like a truck, then be my guest. But don't be surprised when I blow by you when you hit 2nd gear running with my TH350.

Just my $0.02....
===== the 700r4 tranny is not remotely based off of the T-400.
 
#20 ·
Re: Re: Re: 700R4 vs. TH350

425hpOlds said:
My mistake. Major league brain fart.

4L80E is the one based on the TH-400.

My humblest apologies....

happens everyday, if I had a nickle for each fart I've had.....

I always remind people ( I think I remind them) I learn something new every day... the problem is I forget 3 things.
 
#21 ·
The 700R4 should not consume more HP than a TH350. It is a much later design than the 350 and I'm sure is in many ways more efficient than the old and tired 3 speed THM350. Worst case scenario I'm sure the HP loss is about the same, but I'd put my money into building up a 700r4 anyday over a TH350. 4 speeds are yesturdays technology, but 3 speed power hungry trannys are archaic.

Got no hard facts to show off, so I'm just saying I'm pretty sure the 700 is a much more efficient design. Plus should'nt we be back on the original topic of this thread?
 
#23 ·
I have a 355 with a 700r4 running 3:89 gears and 30" tires.
It tachs 2300 @ 75mph. I ran 3:23 gears before and tached 1900 or so. The 700R4 is a great trans as long as it is set up correctly.
I have a friend who just bought a BlackMax from Street-n-Strip (FL) which they say can handle 750HP. Hope this info helps.
 
#24 ·
Re: haha

blazinwest said:
yeah they are more efficient, but so are hondas.
they are weak, and expensive to modify and only little girls have them.
are you sure honda doesnt manufacture them in japan?
Yeah...... okay. :rolleyes:

I say we need to get back on topic, if the question has been answered enough, then let the thread die, you can ***** about TH-700r4's in your own thread you post. But all it'll be is another person not willing to admit defeat. :p
 
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