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Why is the turbo th-350 so popular?


Ansel Marrow

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Ive got one that came in my v8 z swap i purchased (305 sbc), and it seems to be very common. I have a 4 barrel 650 holley carb, and this is not a good combo for gas mileage. on the freeway i get like 3200-3500rpms. So what im asking is this:

 

is it popular becuase its a quick transmission?

 

what can i do besides adding larger wheels to improve gas mileage?

 

what manual transmission would be a better replacement within budget?

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The TH350 is popular because it's cheap and can be built pretty strong for fairly low bucks and it's a bolt-on to the Gen1 SBC.

 

With a 305 I'd get a 200-4R (OD) with a mild/moderate build... depending on the torque of the motor and what the future might bring (motor rebuild/swap). Some folks like the 4L60E for the low first gear but I don't. With either tansmission, you'll likely need specific upgrades. Just be sure to research what mods are needed for your particular performance goals... for now and the near future.

 

Then "maybe" I'd consider larger diameter tires... depending on style and performance goals.

 

EDIT: These OD trannies will bring your 3500 highway RPMS down to around 2245-2450... depending on which one you choose.

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For the hassle of swaping a tranny, I'd just wait for the deal/money/ect for a 5 gear. Not much more work, and a better combo for what you seam to want to do with the car.. I'm assuming mainly average daily driving? A T5 would get your freeway rpm down quite a bit, and probly be a little quicker on acceleration... Also, you may be able to 'play' with the rear gearing a bit to drop the revs.. If you're runing a 3:90 say, droping to a 3:56 will lower the cruising rpm even if you stick with the current 350th. And seeing as it's a V8 in a Z, the low end accel. wont get hurt too much. Torque is a wonderfull thing!

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The TH350 is popular because it's cheap and can be built pretty strong for fairly low bucks and it's a bolt-on to the Gen1 SBC.

---not to mention...Lightweight...at least for an automatic---

also.....it is still fairly common in boneyards...GM used them in production cars right up to the late 80's maybe even into the 90's on some stuff

200-4r is a good choice, used both bolt patterns (chevy and BOP), had a .75:1 overdrive, can be easily modded to lock up without a computer (all you need is a pressure switch in the 3-4high pressure port, wire that to 12v and the other end to the lockup solenoid), and can be built to handle a chev V-8 (they can handle the torque of a built, boosted turbo buick...so I'm sure they won't have a problem with even a fairly wild 350..as long as it's beefed up)

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Mike,

I'll have to check availability and pricing.

 

Ansel,

With a mild 305 you could use either the 700-R4 or 200-4R. I personally would do the 200-4R in the Z car due to size, driveshaft length, and gear ratios.

 

Price varies according to who you get it from.

I build these units but I try to only do turn-key installs, that way there isn't any issue with installation and setup error.

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Anyone know a place to get a 200-R4 in southern California?

 

I really like that overdrive ratio. I don't want to be one of the old school hod rod drivers on the freeway puting along at 65 mph on a long trip with all the house wives passing you in modern cars.

There has to be a nice tranny shop in Los Angeles somewhere...

-Les

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