I WANTED TO GET SOME FEEDBACK ON WHICH TRANS WOULD BE MY BEST CHOICE FOR THE FOLLOWING SETUP 1985 EL CAMINO USING A GM CRATE MOTOR350/330HP /308 REAR IT WILL BE A DAILY DRIVER SO THE MPG NEED TO BE A FACTOR IN MY DECISION .THE MOTOR WILL BE TBI WITHOUT THE SMOG PUMP AND CONVERTER /HEADERS WITH 2 1/2 DUALS THRU FLOMASTER DELTA 50'S. THANKS FOR ANY FEEDBACK

i would go with a 700r4 just because they're a little stronger.

A 200r4 is easier to swap in & can be made stonger than a 700. That's what I have heard cause I am still with a th350.

I have a 1989 305/TBI with a 200 4R out of a Caprice in my 82 SS. It's a great combo with the 2.44 posi. I average 27 mpg on long trips, 18 around town with good throttle response. I still have all the smog appliances hooked up! I also reused my original driveshaft.

a 2004r and a 700r4 as built by us can reliably handle in excess of 600 horsepower.with that being stated selection will be more closely related to hosepower,torque,maximum engine speed,power curve ,vehicle weight ,induction systems and final drive ratio.a heavy car with an engine that will see a maximum of roughly 5200 rpms such as in this case the 700r4 will provide increased vehicle acceleration through the extra torque multiplication generated by the 700r4s compound planetary gear sets when operating in reduction,verses the 2004r.if the engine makes power to 6500 rpms ,the 2004r will provide increased performance by reducing starting line ratio which limits traction and reducing the engine rpm drop on a 1/2 ratio chance.this improves performance by keeping the engine on the fat part of its torque curve allowing a greater amount of flywheel torque to accellerate the weight of the vehicle at the right time.a 700r4 brought to 6500 rpms will drop a greater amount of rpm on a 1/2 ratio change putting the engine below the torque curve and introducing a flat spot in accelleration by putting the engine in a state of operation where it will need time to gain rpm to a level where maximum performance can be obtained.this also causes a severe vaccum drop accross the engines induction system further reducing the engines ability to ingest air and gain rpm.a forced induction system such as a turbocharger or nitrous will be less sensitive to this phenomenon as well as camshaft with wide lca angles such as 114 to 118 degrees common with the small block chevy v8 and also good dual plane intake manifolds such as the performer rpm or dart dual plane.

Excellent information!
Thanks, Chris, and other members.
-dan

Here is one of the 200 tranny builders the Grand National guys use. http://www.2004rperformancecenter.com/

Like you I am deciding between a 200R and 700R. The advantages/disadvantages kinda cancel each other out so I have decided to go with the trans most available at the best price.

I recommend a HT400 but my next would be the 700r4. A tranny builder/friend says that he gets more 200's than 700's. Now if you completely rebuild a 200 with after market parts you can get'em strong but strait up the 700's are stronger. And isn't that what really matters?

Chris718 has made note of one of the biggest issues with the 700r4. The RPM drop from the 1/2 shift is dramatic. Many engines will not have a broad enough torque band to stay in it's power range once in second gear. When I had a mild small block in my 72 it would fall down when it went into decond and took it a bit to get back in it's power range. When I went to a 454 that problem was solved with raw torque, but then it was a question of durability. The other problem of a 700R4 is the stock drum and shell assemblies are not going to stand much more than 400 hp if you drive it hard very much. I think the final drive ratio on the 700 may be a little lower(better for fuel economy) but the 700's lower first gear will launch even a heavy 3rd gen with ease. I went with a Bowtie Overdrives Stage 3 unit http://www.bowtieoverdrives.com/catalog/catalog_inc/viewitem.php?ITEMID=9 and it has handled the 454 for about 5000 miles now of all kinds of driving.

If I did it all again I think I would go with a built 200R4. But great performance and economy can be had from either.

There's still plenty of both in the boneyards so it's a low buck alternative to get one, rebuild it, and hit the road.

Many of the problems that people have from fist to second is because they use a small set of gears like a 3.08:1 or even 2.73:1. My belief is that for any overdrive a minimum set of rear gears would be 3.4X:1 and I personally start at a 3.73 which will give less takeoff and 2/3 step then a 3.73:1 and THM 350 because of the 700R4's gear ratio. If I was looking to race a lot I'd change to a 4.10:1 which give a better take off than the THM 350 and the 1-2 step is not a shock. Also with a 3.08 or smaller you can be adding too much work for the transmission (overdrive) its highway RPM and RPM at even 45 to 55 would be so low that the torque converter would have issues. It could shift from 4 to 3 a lot more and the converter might not lockup correctly.

Therefore, you have to balance it out. Build the power plant to the characteristics you like and plan the drive train around those characteristics (Chris pointed this out) or you end up fighting with problems or always disappointed.

If you look at the factory gear ratios of all the GM Automatics, the fastest and most wasteful (fuel economy wise) of the more modern ones is the THM 350. The next in line of fastness, if that is a word, is the THM 400 and then the THM200R4 and finally the 700R4. My belief is the THM 350 is also the weakest of all of them and the THM 400 is one of the strongest along with the 4L80e. The overdrives were made for fuel economy so you wouldn’t expect they’d have high ratios (Numerically High) like the THM 350 does.

Take a 350 and a comparison of the THM 700R4 @ 5000 RPM

-------------350----------700R4
1st. gear----41 Mph------33 Mph
2nd gear----65 Mph------62 Mph
3rd gear----103 Mph----103 Mph

This assumes that the vehicles are identical with a rear end ratio of 3.73:1 and its just an example of the differences.

Another good point Pete!

A lower gear will reduce the impact of the 1-2 shift issue, but then you're putting the effective first gear of the 700 down near granny gear territory and that makes launching from a standing stop an exercise in feathering the pedal to keep the tires from going up in smoke. As you say though a 3.73 gear or maybe even a 3.55 would be a good choice.

I'm running a 2.73 and when I had the small block I'm sure that was a factor in the problem. With the big block the tires will go up in smoke anyway but with drag radials, KYBs, airbags, and such I can get enough grip to make a pretty good launch. The second gear transition is no problem, the 454s torque pushes right on. I'll be changing to a 3.31 gear after I get back from the ACES SE Regional in Georgia the first of the month. I think that will work out ok but I'll know for sure in a few weeks.

I'm running a 2.73 and when I had the small block I'm sure that was a factor in the problem. With the big block the tires will go up in smoke anyway but with drag radials, KYBs, airbags, and such I can get enough grip to make a pretty good launch. The second gear transition is no problem, the 454s torque pushes right on. I'll be changing to a 3.31 gear after I get back from the ACES SE Regional in Georgia the first of the month. I think that will work out ok but I'll know for sure in a few weeks.

Adding the 3.31 or a 3.42:1 will feel like you are in a different truck. That rat has different characteristics than the SBCs do. Your power is being produced at low RPM and the upper RPM limit is lower, generally, than the upper limit of the SBC. So all your power is being produced between say 800 RPM and 4500 maybe 5000 RPM. This is one reason you are having what is considered decent performance out of an old lady rear.

Typical SBC limits with a good cam and intake, heads, etc... will be between say 1200 RPM to a bottom limit of 2000 RPM and up to around 5000 to 6500 RPM for its power curve, generally. Getting there is the battle with a 2.73:1 gear. You would be somewhere close to 55, or even 60 Mph before you got to that point with a 2.73:1 gear. With a stall converter, the problem is even worse. You then effectively hit the transmission with, mostly maximum, torque all at once and then shift to second and if you’re not able to salvage those RPMs in second gear you have to start over at the bottom that is not what most people want to happen. It’s hard on the transmission and the rear end and for most people it’s just not acceptable.

2.73:1 works with the Rat engines because of their power curve and the overall characteristics of the engine. It’s the difference between hunting dear with a 30-30 and with a Sherman Tank. :D