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Old 08-28-2007, 10:25 PM
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TH350 or 200R-4 Trans?

Turns out that I could have chosed a little higher rearend gear ratio for the glass '32 I'm building. I got a great deal on a third member with 3.50 gears. So, a friend suggested possibly using a 200R-4 Trans rather than a TH350. He said the shifting range of the 200R-4 would be more compatible with those 3.50 gears than the TH350 trans. What do you all think? Is this true, and if so, can someone please explain it in terms a guy without a heck of a lot of experience in this area might understand? Thanks all

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Old 08-28-2007, 10:54 PM
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A Turbo 350 has no overdrive so the transmission turns 1 RPM for every one RPM the engines turns ( when in Drive ) ... The 200-4R has a 30% overdrive . This means that the Engine RPMS are reduced by 30%.

3.50 X 30% = 1.05 gear reduction

... 3.50 rear gear
- ..1.05 the 30% reduction
_________

.. 2.45 final drive ratio in Overdrive.

When you are in high gear ( 4th ... which is overdrive ) is would be like you have a 2.45 rear gear ratio ... instead of the 3.50 gear you actually have.

First gear is also lower ( 2.78 ) versus the Turbo 350's 2.52 ( which means you would have a lower overall first gear with the 200-4R.

2.78 X 3.50 = 9.73
2.52 X 3.50 = 8.82

The 200-4R should accelerate quicker also.
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Old 08-29-2007, 06:37 AM
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the first gear of the 2004r is about .50 ratio deeper than the first gear of the th350 so yes better acceleration off the line

plus overdrive of the 2004r is great

th350 is 2.52 ratio first

about 3.06 in the 2004r

th350 is direct 1 to 1 ratio in third

200r4 is less than that

about .70 to 1 ratio

but it is 4rth gear


th350 has no overdrive

hence no 4th gear

all the gm trannies other than powerglide are three speed

except 2004r and 700r4

200r4 are 3" shorter than 700r4
and 10 bolt hole bellhousing and IL or TX shaped pan
no vacuum modulator

700r4 are only 6 bolt
and deep square rectangle pan
with vacuum modulator

we have a 200r4 in the 85 elky ss

it is original

runs awesome

we dont have the TCC plugged in on it


caddy and pontiac and oldsmopbile big block racers put 200r4 trans behind their very heavily modified engines all the time and they hold up with a few modifications

tough little suckers it seems

and will pop right in place of the car length th350 trans(28 and 11/16" - 6" tailshaft housing) and also behind the TH250 and the TH200C
are all the same length trannies
about '79 and up these were made, X body, G body, B body, and F body


or 69-72 TH350 and SM326(fully snychronized., 292 L-6 and the V-8 engines) equipped trucks, both very common
trucks before 73 used the 6" tail th350
73 and up were 9" tail 700r4 length

some wagons in the 70s had a 12" tail th350 i have only seen one in person so far they are very uncommon
and odd looking

Last edited by fast68; 08-29-2007 at 06:43 AM.
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Old 08-29-2007, 07:46 AM
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kripes;


200-4r first gear is 2.74 : 1.


2nd gear is 1.57


over drive is .67

Length wise the 200-4r length is near close to that of a t-350 trans that has a 6 inch tail housing.... 200-4r

same yoke spline for the output shaft on a t-350 & a 200-4r trans

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Old 08-29-2007, 10:05 AM
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Crosley has the ratios right.

http://www.vibratesoftware.com/html_...nsmissions.htm
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Old 08-29-2007, 12:59 PM
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re: TH350 or 200R-4 Trans?

fast 68, I hate to appear ignorant, but I am! Heck, the last car I built was in 1984, and that was small block Ford. So I have a lot to learn here. You mentioned that the 200R4 uses a 10-bolt bellhousing. Will this bolt right up to any small block Chevy engine. If it will, this sure sounds like the right trans for me. My chassis/crossmember is set up to accept either the TH350, or 700R, and since I obvioulsy don't have the torque converter, flex plate, or a driveshaft yet, it's ll looking positive. Thanks again guys. I really appreciate your help, and your patience
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Old 08-29-2007, 02:36 PM
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There are two different GM bellhousing patterns and they basically fall into the chevy category and the everything else category. The everything else is usually referred to as BOP for buick olds pontiac. Some call it BOPC since cadillac also falls into that category.

Most 200-4r trannys (in fact one can safely say all you would encounter) are dual-fit, meaning they have the holes for both BOP and chevy patterns.

When it comes to determining ratios, its just a matter of simple math. The rear axle ratio has a lot to do with it, but as you'll see it can mean very little. The ratio is always expressed as the first number being the input and the second being the output. If you have a 2:1 gear in the tranny, that means the engine turns twice for every one turn of the tranny output. That is also why ratios of less than 1 (like 0.7:1) are called overdrives because the output is over the input.

So, you just multiply as you go back the drivetrain to get the final drive ratio. Lets take the th350 for example with your 3.50 rear ratio. The ratios of the th350 are 2.52, 1.52, and 1:1 so your final drive ratios look like this

2.52 first gear X 3.50 rear axle = 8.82
1.52 2nd gear X 3.50 rear axle = 5.32
1.00 thrid gear X 3.50 rear axle = 3.50

Those final drive numbers mean that in first gear, for every 8.82 turns of the crankshaft, there is one turn of the axles, and in that way you can see that the lower the final drive ratio, the lower the RPMs on the highway. Switching to a 200-4r keeps very similar ratios for the first three gears 2.74, 1.57, and 1.00, but it adds a 0.67:1 overdrive. The final drives would look like this:

2.74 x 3.50 = 9.59
1.57 x 3.50 = 5.50
1.00 x 3.50 = 3.50
0.67 x 3.50 = 2.35

Notice that the 3.50 gears would ACT like 2.35 gears and a non-overdrive tranny on the highway, and the slightly lower first gear would give you a little more jump off the line. You probably won't notice a difference in the first three gears, but that OD will really drop the highway RPMs.

To show you how the rear axle ratio sometimes means very little, here are the calculations I just did for my swap. I'm going from a 4L60E automatic OD to a T56 six speed manual. People look at me like I'm nuts for trading out my 3.08 gears for 4.56 gears on a highway vehicle, but if you look at the numbers, you'll see I'm keeping a very similar overall gear spread and highway RPMs.

4L60E and stock 3.08 rear:
3.06 x 3.08 = 9.42
1.63 x 3.08 = 5.02
1.00 x 3.08 = 3.08
0.70 x 3.08 = 2.16
* a little sidenote on the 700r4/4L60E... notice the wide spread between first and second gear. Many folks (myself included) don't like that huge jump because it causes such a big drop in RPMs. Unless your engine is built with a very flat torque curve (or a light car) it may cause acceleration to suffer. GM did that as an attempt to take advantage of higher gears for highway mpg while making a really low first so that drivers didn't complain about sluggish off the line performance.

T56 and 4.56 rear:
2.66 x 4.56 = 12.13
1.78 x 4.56 = 8.12
1.30 x 4.56 = 5.93
1.00 x 4.56 = 4.56
0.74 x 4.56 = 3.37
0.50 x 4.56 = 2.28

You can see that I'm basically adding one gear lower, but ending up at almost the same highway ratio. So you can see that rear axle ratio isn't always the only factor in things. Its the tranny and rear together that determine's things. My manual tranny with 4.56 gears will still have lower RPMs on the highway than your OD automatic with 3.50 gears. Many builders fail to take that into consideration and just recommend "yeah, 3.73s are a good street performance gear." If I took that recommendation with my T56, my final drive ratio in sixth would be 1.87, and 6th would be useless below about 75 mph because it would be lugging the engine. Inversely, if I had a th350 and took that same advice my final drive would be 3.73 and I'd be DOUBLING my highway RPMs.

I suggest that you use that link above to find your ratios, then visit www.f-body.org/gears to input some of the numbers and find out what your highway RPMs will be. Find out where you want to be on the highway in terms of RPMs, then play with tire size, transmissions, and rear gears. There are a few non-OD trannys with 1:1 top gears, then the 700r4 with a .70:1, the 200-4r with .67:1 (and a more favorable 1-2 ratio spread), and the overkill 4L80E with a .75:1 OD. You should be able to find an easy to assemble combo that will get you whatever RPMs on the highway you want with that 3.50 rear. Your target highway RPMs vary depending on the vehicle, engine size, cam, etc, but for most street/performance vehicles I like to see them between 1700 and 2200 on the highway. More cam, smaller cubes, and heavier cars would like to see higher RPMs. Lighter cars, less cam, and more cubes like to be on the slower side of that range. I will be turning at about 2000 with 26" tires in a heavy car with a mildly cammed 350... just for the sake of reference.

... of course, it also depends on your idea of "highway speed." When I'm driving, that means 70. When my wife drives that means 85-90.

Last edited by curtis73; 08-29-2007 at 02:55 PM.
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Old 08-29-2007, 05:55 PM
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Quote:
Originally Posted by curtis73
Most 200-4r trannys (in fact one can safely say all you would encounter) are dual-fit, meaning they have the holes for both BOP and chevy patterns.
Not true. There are BOP only 200-4R's floating around. Most of the early cores were BOP only. 81-82 models. So you cannot "safely say" that a person would only encounter Uni-case 200-4Rs.
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Old 08-29-2007, 06:06 PM
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Correction

The 700r4 uses a cable connected to the throttle linkage to control shifts. There's no vacuum modulator. I replaced a 350 with a 700r4 from a 1988 Trans Am and it was almost a direct swap. I had to modify the rear cross member a bit on my 67 Camaro and that was it as I recall.
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Old 08-29-2007, 08:31 PM
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BOP 2004r trans;

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Old 08-30-2007, 12:48 AM
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Quote:
Originally Posted by jakeshoe
Not true. There are BOP only 200-4R's floating around. Most of the early cores were BOP only. 81-82 models. So you cannot "safely say" that a person would only encounter Uni-case 200-4Rs.
I should rephrase. In the 40-50 that I've encountered, only one was a BOP, the rest were all dual-fit. I think the actual number of BOP-only 4-rs is pretty small, especially given how widely used they were from 83-88 in the dual-fit configuration.

But you're right, they do exist, just not commonly.
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Old 08-30-2007, 12:57 AM
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I buy them for hard parts from wrecking yards. They were used until 1990.

There are still quite a few floating around out there they just aren't as desirable.
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Old 08-30-2007, 01:47 AM
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Find the right core

Early GM overdrives had a lot of reliability issues,both the 2004R's and the 700R4's.The best cores to build are from 1987-90 as the problems were pretty much engineered out by then.Drop by www.transmissioncenter.net these guys know overdrives and can hook you up with the goods to make the swap easier.Good LucK!
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