Looking for feedback to validate a claim. A friend of mine told me that whatever 1/8th mile time my car ran with a TH400, it would run quicker with a powerglide? What are you guy's experience? Also, how streetable is the powerglide vs the 400? Thanks
I've found that with the heavier cars, 3000 plus, the th400 works best. Lightweight and tube cars like the glide with the 1.94 1st gear. Others may have different opinions and experiences.
Here are some facts for you: 1. The TH-400 takes a bit more HP to turn 2. The 1st gear ratio of the 400 is far better for heavy vehicles especially if the engine is under about 550 hp. 3. Over 550 hp especially in a light vehicle the powerglide is a good option because less gearing is needed to get the car off the line. 4. Either trans is streetable, but the powerglide would require more throttle to get the car off the line. They would both rev the same on the highway.
Since I'm under 600 hp and tipping the sale at 3550 I better stay with the 400. Thanks for the input.
You also better have a good rear gear in there which puts you at peak power or higher in the traps(1/8). 4.56's or 4.88's for a heavy car unless you are making big power and mph. 3 series gears with a 'glide only work with the big power/light weight. The more power you make the less gear you need. Plus most guys running a 'glide are running converters with serious stall speed so you have to figure on converter slip, 8-10% maybe more? I run 4.10's and hit around 96+ mph in the 1/8th and I'm shifting to 3rd(6000) and the engine is just starting to get excited again and the 1/8th goes by. If I was running the 1/8th normally I'd put less gear in it and blast through at 6000 in 2nd. That may be worth a smidge in the 1/8th because it removes a shift and I'm pulling through at max power. Not to mention easier off the line and only one shift on a run it should be more consistent. Assuming a few hundred rpm for converter slip a 3.31 0r 3.42 gear would work pretty good. Again I'm only thinking about a real street car or no roll bar racer. If you're faster than that you'd probably want to go the serious route.
Powerglides can be streetable,if you have highway gears,so NO,that is not what you want. IF you were to do a trans swap,you could go to TH350,with its steeper 1st gear,and it takes less power to turn,but since you already have a TH400,I would leave it alone. Either one of those 3-speeds can be built to handle a ton of power.
OR if you want to switch transmissions a 700R4 or a 200R4 overdrive trans would be great on the street! But since you have a TH400 in it now, the drive shaft length would need to be altered for either of the above transmissions to install one. Had a powerglide in my '65 Impala and swapped in a 700R 4 and picked up almost a full second in the QM and IIRC around 5 mph and .25 faster 60 ft times. Unless you're salt flat racing to get max mph, the better gearing trumps parasitic loss almost every time. IMO
