I am considering bolting a 200R4 tranny to a '70 455 engine in my '68 GS400 conv. What gears would work best for this type application? I am attempting to find an entire posi rear to switch with my open 2.96.
I will be doing a 2004r conversion. I plan to use 355 gears. There are many ratio/RPM calculators on the internet. With 355 gears and a 2004r it is estimated to run a about 2500 rpm. This is with a 350 motor however. Hope this helps. :beer
I LIKE 3.73 GEAR IN MY 69 CONV. BUT IT HAS A T350 TRANS. 4TH GEAR WOULD BE THE BEST WAY TO GO :3gears: GREAT LOW END AND LOW RPM ON THE FREEWAY MIKE
I am currently doing this swap. I have 3.73's in my car with a 28" tall rear tire. My rpm's on the highway at 70 mph will go from @3300 rpm with my TH400 down to @2250 rpm with the 200R4, according to several gear ratio calculators online. And with the slightly better gearing, I'm hoping for a little more, I mean less, at the dragstrip come Norwalk. There is an article in an older GSXtra and they took a 1970 Stage 1 that had run a best of 12.68 and swapped in a 200R4. They made no other modifications, and the car ran a 12.41. Sounds like a win-win situation to me!!
Use careful consideration here. A lot depends on whether you use a lockup or non-lockup converter. CPT (The REAL Art Carr) does not recommend lockup, most other builders do. If non-lockup and a 2500 stall converter (which is what I have) and 3.55 gear you cruise 80mph at less than 2500rpm with 28" tire (275/60). SO the converter is not totally coupled and could cause heat. I have this combo with 27" tire and have no heat problem with a 15 row, high dollar cooler. I like it ok but am seriously considering the move from 3.55 to 3.90. Final drive goes from 2.38 w/3.55 - 2.61 w/3.90 - negligible IMO, plus the added bonus of a 4.30 effective 1st gear (compared to 3.90 w/TH400 - see below). The 3.90 will bring the cruise rpm up to help couple the converter. Of course this is all moot if you run a lockup converter. Also, my rpm through the traps at 108mph is about 4600rpm w/28" tire. This should move to about 5000 with the 3.90 gear. I'd considered 4.10 also, for a trap rpm of 5500 or so, but want to keep the top end, should I choose to go there, around 160mph. That's 5000rpm with the 3.90 and 28" tire. I'm thinking also that the shift to 2nd and 3rd sooner I might gain rpm, trap speed, and ET so expect 111mph (and high 11s ET) to rpm about 5200 with the 3.90 and 28". 4.10 might be even quicker if able to hook and if my theory isn't full of holes but again I want the top end. 5000 w/28" and 3.90 in OD = 159mph. These numbers are off the top of my bald head. You can verify and fine-tune using this calculator. http://www.1bad69.com/calc.htm Rule of thumb: add 0.4 to your gear ratio to get equivalent 1st gear from TH400 to 200-4R. 4.10 = 4.56, 3.55 = 3.90, 3.90 = 4.30. Add 0.2 for 2nd gear. TH400 1st 2.48 x 4.30 = 10.664 2nd 1.48 x 4.10 = 6.068 200-4R 2.74 x 3.90 = 10.686 1.57 x 3.90 = 6.123
