CK5
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- Thread starter 79jenny
- Start date
Quite a bit. But honestly lets talk about what you're looking for and expecting to gain. A turbo 350 isnt a bad platform at all.
What is it used for, power expected, and details of the vehicle its in.
What is it used for, power expected, and details of the vehicle its in.
Towing? Changing auto to stick? Crawling? Need OD? More gears?
Lots of questions.
Lots of questions.
It's on a 79 Jimmy 4x4.. and mostly only weekend drives.. around town but would want a bigger tranny so it can do better on the freeways and for longer trips as well with light to moderate off roading..
Bigger is kind of a misnomer when we are talking transmissions. A th350 and th400 are only marginally different in size, but both have 3 speeds with no overdrive. The 400 is stronger, but don't have OD to make the highway drive better.
A 700r4 would be giving you the OD for better highway manners.
How big are your tires and what is your current gearing at in the axles?
Yeah was thinking 700... the tires are 33" BFG All Terrain and as far as the gearing I honestly don't know I only know a little bout cars..
Assuming you have 3.73 gears in the axles which could have been stock that would put your rpm at 65 mph would be 2,470. With a 700r4 in OD with the same tires and gearing it would drop to 1,729 rpm at 65mph. That's a pretty big drop for cruising speed.
If the rpm at 65mph is close to 2400-2500 rpm right now my guess of 3.73 gears is probably close. If it is higher or lower by a lot then it's probably not 3.73's.
So for good highway cruising speed is it better to have higher RPMS or lower RPMS.. that u mentioned? And as far as the gearing ratio what is a good ratio for it ?
For the 700r4 it likes higher rpm in overdrive to be happy. More line pressure, less slip, not hunting for gear on hills. You could say around 2200 or at your desired cruising speed.
That would necessitate an axle gear change which isnt exactly cheap.
That would necessitate an axle gear change which isnt exactly cheap.
Cruise rpm is really depends on where your engine makes power. So that will possibly make it different.
Which that ties in with what obijaun is saying. Too little rpm in OD and the engine may not be making enough power to keep in OD effectively. Hills or headwinds would have it dropping to 3rd to maintain speed and possibly shifting in and out of 4th excessively to the point of overheating the trans.
Having a little more axle gear (higher numerically) would keep the cruise rpm up in 4th, with the engine more in it's torque curve allowing it to maintain in that gear better with hills or headwinds.
Still, knowing what you have for axle gearing would give a baseline of what you have and how a 700 would work with your combination.
I had 4.10's 33" tires and 700r4 my cruise speeds where under 2k rpm, engine was barely working. If I wanted to accelerate to pass on level or slight up grade truck was a dog. I regeared to 4.88 which put cruising speeds above 2k 70 is @ 2500. I am thinking 35" tire will be nice with set up, haven't tried yet.
So by regearing I am close to stock configuration with th350 and stock size tires. The best thing about a 700r4 is 1st gear is lower than the th350, so much easier to get these fat square bodies rolling.
So by regearing I am close to stock configuration with th350 and stock size tires. The best thing about a 700r4 is 1st gear is lower than the th350, so much easier to get these fat square bodies rolling.
