I havd a 28 sedan on a Brookville frame, mildly rebuilt 350 sbc, a rebuilt Ford 9" rear that is 3.08 geared. the rear tires meassure 30" tall. I want to be able to drive it on the expressway at 70 mph just to try to keep up with traffic. Am I better off with a T350 or a 700r4? Would a 700r4 even work with the 3.08 rear?
How fast is traffic where you live?A3.08 gear is already a highway gear. The OD transmission will work if you want really crappy mileage. Stay with a 1:1 final drive if you want to stay with the 3.08 gear.
or not...I get pretty good mileage in my old Suburban with a 3.08 gear and overdrive. Although the tires aren't quite that tall, and the od isn't quite as steep (.78 vs .70 for the 700). I used to have a later model car with OD and 3.08 gears and it got 25 or so mph on the road. Full size car. of course, having a stock cam in them helps! if you have a lumpy cam then you want to either get more gear, or not bother with overdrive.
It helps if you are going to run an airplane gear with an OD that you have either a Low RPM motor or engine management other then a distributer and a gas peddle. Mildly built small block is a pretty nominal term too I guess. A 375-400 horse 350 is mildly built to one guy, where as a 325-350 horse motor may be mildly built in someone else. Just for grins a 28" tire with a 1:1 top gear and a 3.08 rear end gear you are turning about 2600-2700 RPM with a common OD (.7) you are turning about 1800-1900.
I know you didn't ask about this one, but all things considered, the T-200-4R would be the better of the two you mention. Smaller, lighter, can handle the same engine power output as the T-350 and T-700-R4. It's also got a MUCH better gear ratio package, which is the best reason to get this one over the others. Well, the T-350 has decent ratios, it obviously doesn't have the overdrive or the lockup converter..! Mike
I have an O/T 86 El Camino that came stock with a 2.41 ratio rear end, 2004R and a 305. The tach shows about 1700 RPM in O/D at 70 MPH. Granted, it isn't a racer rear end (7.5 inch ring gear) but it does get damn fine mileage. Does "mildly rebuilt" mean you just did a valve job and regasketed the top end, or does it mean it actually has a performance cam, higher compression, different intake, carb, etc.? Tell us more about the motor, and it'll be easier to tell you what ratio would work.
Having owned both, I'd go with the 2004r instead of the 700R4. Gear ratios, size, a little lighter. Use the lockup, pick the right cam/tire/gear combo, really a sweet deal.
3.08 to me doesn't need an overdrive and I don't trust 700's nearly as much as TH350' s. Just my opinion.
back in the early 70 and late 60s when the 350 was in everything chevy built and 70mph was the norm,just don't expect mpg in the 20s tom
Thank you to everyone for the feedback. I dont have many details on the motor. I know its one bore over stock with an "rv cam" and emission era heads......88 something. I inherited the motor from my Dad who rebuilt it several years ago and never used it and now details are sketchy. I also have a 350 tranny that I got for free and a local shop will freshen it up for around 350 bucks.
"RV" cams are typically ground for low RPM torque, and emission era heads are likely small valve that don't lend themselves to high RPM. I'd not hesitate one bit to use an overdrive trans. If you want it to act like a TH350, just leave it in 3rd gear.
The Jalopy Journal
