TH350 vs 200R4

[KEL]

On the highway, what is the MPG and RMP difference
for each tranny running behind a stock 350 ?
Thanks

[KEL]

that's "RPM", not "RMP" !

[cdowns]

the final drive ratio of a 2004R is 0.71// multiply your present RPM by 0.71 to get what the RPM will be. divide for mpg

[Longhorn Man]

there are too many variables to answer either question.
What gear ratio do you have in the diff, ans what size tires do you have. What is your cruise speed?
Adding an overdrive can actually HURT the MPG on the freeway if you have tall gears out back.

[raycow]

The rpm drop will be a little better than the O/D ratio because the 200-4R has a converter lockup. Even a "tight" converter still slips at highway speed.

Ray

[ubtripn]

I am interested in this as well since I have a powerglide and want to switch. So which one is overall better? Stronger? More efficient? (sorry, not trying to hijack your thread)

[gonzo6869]

I currently have the th350 and I am looking at going with the 200-4r. With my set-up now; 3.73 gears and a 26" tire(275 60 15) at 60 I am pushing about 2800-2900RPM, with the swap to the 200-4r evryting else the same, my RPM will drop to 2395 (thats at 70MPH). Thats a good drop in RPM and I believe it will increase my MPG on the highway to about 12 or so.

[cparman]

Find an RPM calculator on the web. The inputs to this formula will be : tire size, gear ratio, and MPH. I am a big fan of the 200r4, because of the spread in the gear ratio's of the transmission. 700r4 has a very low 1st gear.

I will tell you that to get a 200 to shift firm in all gears can be some work. UNLESS you get the BRF calibration. I have done several of these, and it usually takes dropping the pan a time or two to get what I like in firm, but not too harsh shifts.

The final drive ratio in a 200 is .67

[cdowns]

Originally Posted by cparman

Find an RPM calculator on the web. The inputs to this formula will be : tire size, gear ratio, and MPH. I am a big fan of the 200r4, because of the spread in the gear ratio's of the transmission. 700r4 has a very low 1st gear.

I will tell you that to get a 200 to shift firm in all gears can be some work. UNLESS you get the BRF calibration. I have done several of these, and it usually takes dropping the pan a time or two to get what I like in firm, but not too harsh shifts.

The final drive ratio in a 200 is .67

for some reason most seem to believe the final drive is ,71

http://fbperformance.com/viewtrans.a...nsmissionID=27

[gonzo6869]

Gear ratios of the 200-4R are: 2.74 first, 1.57 second, 1.00 third,
.67 fourth.
You will find different answers depending on the website you’re looking at

[capev86]

my dad's suburbans with stock size tires:

'72 2wd w/ th350, 305 swap, q-jet and 3.73 gears: 15mpg highway (60mph)

'84 2wd w/ 700-r4, 350 q-jet and 3.73 gears: 18mph highway

'87 2wd w/ 700-r4, 350 tbi and 3.73 gears: 18mpg highway

you guys need to remember that trucks have poor aerodynamics and weigh more yet everyone is driving faster and faster each day. mpg's drop off drastically over 60mph as drag increases exponentially. even with optimal highway gearing, most vehicles get best fuel mileage around 50mph. keep it to 60-65 so you aren't contributing unduly to all the anti-truck/tree hugging/poor mpg hype!

[gonzo6869]

I really don't care about milage, right now I get about 8.5-9MPG and that dose not bother me. All I really want is to be able to drive on the freeway (60 or so) and not be pushing 2900RPM. The mileage increase would be nice, but if I don't see an increase I would not care.

[capev86]

you are nuts....

i think less than 10mpg sucks....even back 12 years ago when gas was still a buck a gallon. my 72 burb gets 10-11 with a 307, 3 on the tree (more efficient than an auto) and 4.57 rear gears. i'm swapping a 4.10 third member into the ho52 rear and hoping to get my mileage up to 14 or so. 50 bucks for gas every 200 miles makes it really tough to enjoy driving my truck. guess i'll have to save up a bit for the big camping trip coming in a couple months. i'll be back down to 8-10 pulling the family camper!