Having my 350 engine freshened/upgraded and swapping the T350 over to a 200-4r with one of Jim's converters. I'm currently running a '72 8.5 10 bolt with 3.23 rear gear and will be changing that out as well. Is there a big difference between a 3.73 and 3.90 gear? Wondering which one to run and where to get the new gears. Looking for your experiences and suggestions. Thanks!
Gears are multipliers of torque. Being you have a 2004R, the .67 OD gear brings the 3.73's down to 2.50 final drive. For 3.90's, it's 2.61. Unless you are going down the track, you really don't need 3.90's, 3.73 or even 3.42 is plenty. The higher numerical gears will put you closer to your HP peak RPM in the 1/4 mile.
If I was to go 200R4 (I'll be building a 350/auto car & am definitely leaning towards it), I'm inclined to go 4.10's. First, 350's love gears & the OD will drop it 2.74 which is still a perfect highway gear so there's no real downside and 1st-3rd it'll be a screamer. Heck, depending on what I do with the engine I may even consider 4.33's.
To me there was a big difference. I suppose it depends on your comfort levels with rpms. 3.73 was the gear that felt the best driving, to me.
On my old '70 350 4-sp. I went from stock 3.23 to 3.42 to 3.73 & w/every change the car went a few 10ths quicker. When I put the 3.73's in I'd already bought a 4.10 ring & pinion and was getting the car ready to drive 700 mi. ea. way to the '87 Nationals and at the 11th hour chickened out - The Chevy dealer (no time to order) had a 3.73 gearset in stock. Was glad I did as it still turned 3500-4k all the way to BG (would've been a long ride w/4.10's) but if I hadn't sold the car I was going to go for it.
Agree on the 3.73 and I used mine as a daily driver w/them but w/a 200R4 like the OP is going w/ there's not even the comfort level with cruising rpm's to worry about.
I’ll definitely be running the 1/4 mile many times and also plan on driving the 900+ miles to Bowling Green for the GS Nationals as well. I’m leaning towards the 3.90s, I suppose I better decide on new tire size as well. Then a new set of drag radials for the track!
Hi, I've been going through a similar debate with a 65 Oldsmobile Cutlass, my engine builder and trans guy suggested 3.73, and currently running 225 70 r15 rims. Been doing some serious thinking of going to 15 inch rims so 3.90's will most likely get. Not sure may go 255's maybe 275's depending on how they fit. I have a set of 4.56's which with a 200r4 would be 3.06, car originally has 3.08 and was fine doing 80-90 down the freeway. Regards,
For me, 410's with 255's work well. From the light, 2004r trans shifts out of 1st to 2nd in what seems like 10-20 feet under normal driving. Had 390's before the 410's and not a large differance. Under throttle, you can manually string 1st out to your max rpm though. Most street guys have 342's or 373's, good to have the advantage..... Andy Angelucci, Storm 1's builder, once told me if you want to race & win light to light, run 513's
I'll have to check that with phone gps app. My speedo gear is still the orig brf GN I think 3.42 ratio, so it's abt 10 mph off. Haven't worried abt it. Rough guess abt 2,500. Locking the convertor drops it 300 rpm. I'll check it when I can, as I'm curious too.
