I have a 68 GS400 with the original 400 now, 435 at 400hp. I currently have a 3:08 posi with the 200-4R. I get 17 mpg city and 20mpg highway. I have had a toggle switch for the lock-up until today. Now that we fixed the lock-up with the lock-up kit, it is obvious that the 308s have to go. So, I want to keep the gas mileage fairly high... I am not looking to have a real hot racing machine... I am trying to figure out if 3:42 will be too low and lug / lag on the engine and tranny or will work ok? I know that I can run 3:73, but I am not sure how that will affect the gas mileage. Also, the tranny will shift into OD and lock-up at 35mph. Then, depending on how you accelerate, the lock-up will kick in and out until you get to about 50mph. Will this happen with the 3:42 or 3:73? Any ideas and/or suggestions would be greatly appreciated... Thanks!
Don't fear the gear. I'd go with a 3.73. With an overdrive tranny, that'll put you exactly where you want to be. It might even increase your city mpg due to the face that the engine doesn't have to work as hard to get it going from a stop. If you wanted a more race oriented setup, I'd recommend 4.10's.
i would go with the 3.42 I run 3.31 and i love it Buick motor make more torque and that is the perfect gear as far as i am concerened I use 3.42 in my 64 post car ( 450 HP ) and it would be perfect with a 2004R Ken
The 200R4 has a .67 overdrive. It's easy to figure out your final drive ratio, and RPM. With your current 308's, your final drive is 3.08 X .67 =2.06 RPM = 336/tire height X rear gear X MPH. Assuming a tire of 26.6" RPM 336/26.6 X 2.06 X 60 = 1561 RPM at 60 MPH For a 3.42, final drive will be .67 X 3.42 = 2.29 At 60 MPH, 336/26.6 X 2.29 X 60 = 1735 RPM For 3.73's, Final drive is .67 X 3.73 = 2.50 336/26.6 X 2.50 X 60 = 1895 RPM This is with the lock up engaged. I think the 3.73's are what you want.
I have run both ratios with my 200r4 setup. I prefer the feel of the 3.73 ratio, all around. Especially in the Overdrive, locked up. However 3.42 is still a very nice gear ratio, and if gas mileage was a concern I think they would still be acceptable. Its just my opinion that the 3.42s in overdrive, locked up with 255s, ran the motor a little lower in the RPM range than I liked. My 350s prefer to run in the 2200-2500 rpm range, and the 3.73s are perfect for that, with the 200r4.
I'd go with the 3.73 over the 3.42. I've got a 4.10 in mine and even that calculates down to a 2.75 in OD.
Larry, He has nearly the same motor you had for years.. STG 1 iron head, 118 cam ect... I know you switched up to 3.73's recently.. any regrets with your VP/GV setup? The converter we just put in yesterday, reminds me very much of one of my 12" VP's, in high stall, in normal light throttle around town driving. JW
Thanks Ken, was looking for just that input.. from somebody who has had both. BB may be a bit different, but rpm "feel" as speed is important too. JW
No regrets at all Jim. The GV has a .78 OD, so the 3.73's became 2.91's. I am now running a 28" tire, so the 3.73's are more like 3.55's, and the GV brings that down around 2.76, about 2200 RPM at 60 MPH. Very responsive on the highway, no complaints at all.
I should also mention that I started out with an OG coded trans out of an 86 cutlass with a 307. When I first installed it, shift points were waaaay too soon under all conditions. I installed a CK Performance shift kit/recalibration in it, but the shift points were the same. I took a look at my governor and it was the "heavy" style I ended up cutting material off it to duplicate/approximate the lighter one from a BRF or CZ coded trans. I have ended up with 5000RPM WOT shift point, and vastly improved performance all around. It just plain drives right, if you know what I mean. Shifts are now comfortably/normally delayed at low and part throttle. And they are very responsive to throttle cable input now. Winds out only when I ask it to. I have been meaning to update my 200r4 swap summary thread with a scan of the final dimensions. I have a sketch right now. I will try to post it tonight. dont know if this helps any, but I guess my point is you dont have to have a BRF to get a good 200r4.
I would not chnage the rear gears at all you will LOOSE mileage for sure in the city and hwy esp. my sklark has the original 350 with 180000 miles with a 200 and a 308 gear i used a b&m lock up kit i can adjust what speed the converter comes in at. if you like how soon the converter comes in at when cruising and just dont like when you want to pick up speed because the converter stayed locked up ...... hook up a throttle switch so it will unlock for you at the throttle opening you desire ....... just my thoughts i love the 308 my roadmaster has 2.56 gears with the lt1 and it gets 27 mpg on average with a best of 33 i will start driving my old skylark from boston to northern maine when the weather is nice i will post fuel economy once i start . if you look at all the new gm trucks they are using 308 gears again with the 6 speed auto trans the auto vette has 2.56 gears i know the 6 speed used a real low first and second gear but the 5.3 and 6 liter dont really start to pull untill 3000 rpm most 455 are real strong at 2000 if you have your car on a dyno ... the best fuel economy i would run my rear gearing at 75 mph at peak torque or a few hundred rpm under that peak number like i said just my thoughts ou: would love to hear what everyone has to say about my thoughts
