I currently am running a SBC with a TH 350 and a 9" Ford 3.89. At 3000 RPM the truck is going 60 mph. If I were to change the ratio by 17% to 3.25 would it also lower the RPM by 17% to 2500. Tire is 29.5. Just would like to get the RPM more reasonable at 60-65 mph. I know a 700r4 is the answer but that is hindsight for me now.
yes it would in 3rd gear as that is a 1:1 ratio on a th350 , also figure in your cam and torque converter stall speed , if the stall speed is lower than the cruise rpm it will not be locked up ( if its stock its good as low as 1700-2200 depending on what application it came from ) and make the trans run hot . also find out where your cam like to run also , as if the rpm is lower it might be out of the band and run like a slug , and also if yor running a open intake compaired to a split intake it will be a little sluggish and boggish too .
Thanks for the reply. Its a 383 SBC , it really likes to run that RPM at cruise but I just want to tone it down a bit, actually at lower RPM it is a bit of a dog. Good point about the converter I have to check my info but i think it is a TCI breakaway 2000-2200 but I'm not sure. Carbs are 3 deuces, i know not the greatest performance choice but that is what i wanted to run. I will check and post the accurate info.
Let's not forget about an approx. 10% loss on output RPM because of converter slippage. So engine RPM's will be higher.
im running a 3:25 gear,30"rear tire,turbo 350,383 with decent cam and a 3000 flash stall conv.its not bad at 60 but I should have gone with a 3:55 rear.
I would compare the cost of changing ring and pinion + setup cost against installing a good used 700r4 before spending any $.
plus the advantage of locking up the converter for more fuel milage , and you can always drive in 3rd if you want the need for speed ! ( and I have seen some where they get rid of the throttle pressure modulator cable to make it more reliable too . )
Dane and Stimpy, I agree but changing tranny now is kinda out of the question. I would need new shifter, etc. My brother has set up many ring and pinions and we can make this change for 200 bucks
if the stall is 2400 try to stay in that area for the lowest cruise speed so the convertor will be fluidically locked and will run cool . I see what your saying about the r&P gears , atleast you have someone to install them , I have to pay out the (pardon pun) rear to have mine done and last time it was close to $600 just for labor . but the guy was good and could take the howl out of richmond gears .
..And take advantage of a lower first gear ratio for better out of the hole performance too! I would look at a 200R4 before the 700R4 just because of length issues on an "A" frame. I know you are thinking "cheap and easy" as far as the ring and pinion swap, but the first time you stab it at a stop light with your new gears and it falls on it's face, or when you are on the freeway and listen to that converter flashing in and out, it'll make ya a bit crazy! right now you have a car that runs stop light to stop light very well, but sucks on a freeway. With the gear change your contemplating, you'll end up with a car that does neither very well. How do I know? I did exactly what you are contemplating with my avatar Plymouth a decade ago, and I can't describe how badly it sucked!!! I went with the complete nuclear option and yanked that auto trans and threw it as far away as I could, and replaced it with a Tremec five gear... best money I have EVER spent on a car. An overdrive auto would be the best you'd ever spend on yours, too.
online search: project33.com - click on calculator to help figure things out. need louvers? is right with 200R4 trans suggestion.
Can't argue with that. I had 3.23 in my dodge and a 727 Torque Flight. With 27" tires running 65 was too much RPM for comfort on the freeway. You will be OK with 29" tires, but just something to ponder...
Im not totally sure about this ,but I believe that a 200r is also the same size as a turbo 350 which may come into play with the trans tunnel on some appliciations and mount locations.i heard they are good for 400 horse but I think they used them in grand nationials and they seamed to due fine.
A Stock 200 will not hold 400 hp. After just about $2000.00 worth of work they will be capable of that and more. OEM GN made 245hp @ 4400 rpm
I do not own a 200r,my cars have turbo350s.i was given that info by guys that run their gn at atco with way more than 245 hp and have been doing it for years(stock trans).maybe they are just lucky ,I really don't know.
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