Looking for some advice here. I'm considering converting to a five speed transmission, but I'm concerned with the overall performance of the car. I'll be running a slightly modified 400 engine with 255/65/R15 tires.
The TKO500 has a 3.27 first gear and 0.68 fifth gear. At 70 mph with 3.55 gears, the engine is turning 2101 rpm's. However, the first gear final drive ratio is 11.609, which seems high to me.
The TK0600 has a 2.87 first gear and either a 0.64 or 0.82 fifth gear. At 70 mph with 3.55 gears, the engine is at 1978 or 2534 revs. The first gear final drive ratio looks a little better at 10.189.
The original Muncie M20 has a 2.52 first gear and a 1.00 fourth gear. At 70 mph with 3.55 gears, the engine is turning around 3090 rpm. The first gear final drive ratio is 8.946. I've heard this is a excellent performing combo, I just prefer to have an OD trans because I like to go on longer road trips.
What I'd like in the end is to have a good mix of off-the-line acceleration with fairly low rpm's at highway cruising speeds. Can I have my cake and eat it too? Lol. Maybe someone can shed some light onto what a good choice would be for my situation. I'm not set on the 3.55 rear gear either. The TKO500 looks like a good choice with a 3.36 or 3.55 rear gear, but I'm concerned with the relatively high final ratio. I think the engine will have plenty of low-end torque, but I don't want to end up with a car that's a pig to drive around town. Thanks in advance.
Too much gear in first will result in wasted time and rubber, as you suspect. 10:1 is usually about as much as the tires can handle with a reasonable 400.
A final drive ratio at or slightly below the mid 2s should work just fine depending on your engine specs. I'd suggest the TKO600 with the .64 fifth and keeping your 3.55 gears. A mostly stock 400 should have no trouble rolling along at 2000 rpm, just make sure you have your mechanical and vacuum advance settings right and watch the temp gauge on your first few runs.
Sorry, I forgot this part. I have a tko600/.64 and a 373 rear, I'll be changing the rear to something not so steep, maybe around 336-342 I had a hard enough time getting traction with the Muncie. I'd like to put some wider tires on the back put there's not much room back there.
Bluebird, it appears I was incorrect. I've actually got 215/65R15's on. No rubbing issues anywhere on the car, but I think that's the standard 15" tire.
Thanks for the input folks. The 10:1 final drive ratio is what I read about for Chevy's, just wanted to make sure it applied to Pontiac's also. I figured it was a pretty universal thing, but I'm learning as I go along.
