My engine is a .030 over 440 low compression short block with a .528 solid cam. The heads are 906's bowl blended and port matched to an M1 single plane with a holley 750.
The car is a 70 Dart Swinger, stock body.
The tranny is a pretty fresh 727 and stock converter, and the rear gear is 3.23.
I'm looking to upgrade the converter and rear gear to do some bracket racing this summer. What do you think would be good for my combo?

I would buy a really good, not a economy or cheap one 8 inch race converter and probally 4.10 or 4.30 gears for your altitude and probally small rear tire hieght Don't be suprised with the results

A 4.10 gear ought to be about right. Converters are one of those parts where you definitely get what you pay for. I'd give Ultimate Converter Concepts a call.

What size is your rear tire Spurman? Driving to the track or trailering?

Rear tires are 26" dia x 8" slicks. The car will be trailered to the strip as it's a good haul from where I live.

With that small of a back tire and a fairly stock motor I think I'd run a 3.73 gear, maybe a 3.91.

And traction could be an issue with an 8" converter but it'd sure be fun!

What length track and what is the elevation of the track? BTW, I've had and raced several different Darts with 440 in them I took a 1972 Dart in trade that I ended up using a set of V.W. 6 inch wide on 15 inch rims drag slicks that worked real well on that car with stock leaf springs I ended up massaging the front edge of the rear wheel well opening at the rocker panels to get a set of 10x28x15 slicks on 8 inch wheels on that car later, that didn't make much difference That car had 3.91 gears and a decent 8 inch race converter

The track is 1/4mi and altitude there is around 5200.

What rear suspension are you running.. your chassis
set up will make a lot of difference... do you have
5" of travel in the front

Any street use?
For a track car, ET is in launch and first few hundred feet, so gear/converter is important but you need traction (tires and suspension) or you will just smoke the tires. A 8" converter and 4.56:1 gear is great if you can get it to hook, and you only do limited street driving.

9.5 are great converters... With that much motor/torque, it is going to stall the converter higher that say a std 440 therefore the tightest converter is probably going to stall at least 3500 ...there are only so many combinations of pumps and stators

I have the stock 6cyl leaf spring suspension and 6cyl front torsion bars. I'm not sure how much travel it has. I'll have to measure. I have a CalTrac bar set up on the way for the rear. I will eventually use the caltrac mono leafs and move them into the frame.

I will drive it on the street, but very little.

The 4.10 should be okay at that elevation and on the 1/4 mile track, the 4.30 might be a tiny bit quicker in the 1/8 mile but they may limit you at a lower elevatiion 1/4 mile track. It use to be consider normal to have the motor run out of steam, reach peak HP RPM, between 1100 and 1200 ft at a 1/4 mile track on a all out drag race combination I've done that, it gets old real quick when the car quits pulling the last 200 to 300 ft at the track
I made my old NHRA A/SA M.W. stocker quicker in the 60 ft, 330, 660 and 1/4 mile by adding a low gear set (2.77 verus the stock 2.45 1st gear ratio) and changing the rear gear ratio from a set of 4.89 to a set of 4.56 Some other racers with the same combination tried that and spun the tires, I guess my car worked better than thiers did on the starting line

I don't have much experience with racing at 5200 feet but I'm thinking a 26" tire with a 4.10 is gonna put him through the traps at around 6400 RPM, I was basing that on 118MPH as I really don't know what his combo will run for MPH. Seems like that RPM is slightly high for that combo but I might be wrong if the altitude brings the RPM down some.

Well, it looks like an 8" converter is the consensus. I will probably go with the 4.10 gear. Eventually, I will step up to a bigger slick, when I move the springs inboard.

Based on my suspension(6cyl torsion bars, CalTracs/leafs), what shock do you think I should run? Thank you all for your help, by the way, this forum has been a great help.

I did not see tire size listed, but short 26-27" tires, you would want a bit less gear than the 4.56:1 I mentioned.
With the high altitude and low compression you want to keep the engine in the high RPM range to avoid the loss of low end torque.

Have a weight on the car? I'm thinking that combination at that altitude may only be around 110 MPH through the traps?

It's a completely stock body, no fiberglass. I haven't weighed it, but I'm thinking 3200-3300 lbs.

Thanks for the great info. Just ordered some 4.11's and I'm working on finding a converter now.