[P8riot]

I discovered recently that my Elky has a 250 tranny. Because I am building a 350 to replace the 305, I want to make sure I have a tranny that will handle the increased horsepower without coming apart.

I am looking to generate only about 300 HP, which is about twice what the Elky had new. I want to have decent highway performance, too. Would a 200-4R be a better choice than a 700-R4? I definitely want the overdrive gear and will be converting from column to floor shift as well.

So I guess my questions are these:

1. Which is the least expensive option?
2. What do I need to look for when I am picking a rebuildable core (bell housing/sunshell, particular ID number, etc)?
3. Which will require the least amount of modification to my existing drivetrain components (driveshaft, rear end, etc.)?
4. Which will give the best performance/mileage combination for daily driver and grocery getter?

I will be using the rebuild parts list, so thoughtfully provided by Tranny Mike (I think?), so that when I do rebuild it, it will last for a while.

I know that I will have to drill/cut into the tunnel and have no qualms about doing so, since I will be replacing the carpet and POR-15'ing the floorpans anyway.

Thanks!

 

[michaelj]

I cannot say which unit is less expensive than the other. That all depends on the deal you find. I found a great 200-4R core for $150 with converter. It also depends on the level you build it to (kolene steel plates comes to mind.) Your mileage may vary.

Your TH250 has an overall length of 27.625", and the 200-4R and 700-R4 are 27.75" long. You should not have to change your driveshaft. You will have to change your cross-member either way you go, though, so your choice is a wash.

The 200-4R and the 700-R4 can both be built to handle high horse power, and 300HP isn't really considered high output. Both trannies in a stage 1 or 2 form can easily handle that. And you don't really have to go with the super high quality kolene steel plates to do this, unless you have the cash to spend. Again, your choice is a wash here.

The 700-R4 has higher ratios for 1st (3.06 vs 2.74) and 2nd (1.62 vs 1.57), so it will be quicker off the line than a 200-4R, but it also means that around town fuel economy will suffer. The 700-R4 also has a higher ratio for OD (.70 vs .67) so your OD fuel economy will also suffer. So if you're looking for economy, the 200-4R wins this round.

As for picking a core, the number one test, if it's out of the car, is to smell/look at the tranny fluid. Is the fluid still red or is it dark and nasty and smell like burnt feet? If you can, look in the pan for sediment and large chunks of metal/debris (which would be bad of course.) A little is natural, but only a little. This will help you decide if you'll need a new torque converter or not. But if you're looking to do a full rebuild and completely replace all clutch plates, seals, etc... I can't see that these test matter very much, other than determining the reuse of the torque converter. Burnt fluid and debris in the pan means that the converter has seen some heat and may be filled with crap that you don't want in a fresh build.

Try to get the TV cable's carb bracket if you can, both trannies need it.

I'd say your decision is leaning to the 200-4R based on fuel economy alone. The two ways to easily spot a 200-4R are by the mounting bolts pattern (aka Chevy/BOP) and the oil pan:

Bolt Holes

Oil Pan

GOOD LUCK!

 

[P8riot]

Awesome information! Thank you very much for taking the time to help me decide which way to go. I am hitting some boneyards this weekend and will keep my eye open for what I need.

Thanks again!