That should give you a ton of torque, which is the real fun-factor in these little cars!
Project Blue Bird
- Thread starter TrueBlue
- Start date
That should give you a ton of torque, which is the real fun-factor in these little cars!
I read that..its a super cool motor imo, were picking the block back up Tuesday from the machine shop. Also, made a little progress this weekend as well. Went and got my rear end from a buddies junkyard, a Ford 8" from and old Grenada, and a th400 tranny. Busted the rear end apart to take and get one side shortened 3 in. or so to straighten up the stump. My OCD will be on full tilt with a misaligned transverse spring and center stump. Pretty sure the driveshaft will be long enough to help the off centered pinion. Parts are ordered for the rear suspension, and should get to mocking something up in the next week or 2.
Do you know what rear gear you have in that 8" punkin?
choppedtop
Well-Known Member
Probably, maybe, perhaps a 2.73. That is what I have in one of my hot rods. Probably depends on what area the car was originally sold in.
its a 2.79 gear. Trying to figure out the best ratio for my motor/tranny combo. Any thoughts or recommendations??
I'd say with all that torque on tap, a tall gear like 2.79 might be OK, provided you don't go too tall on the wheel/tire combo. You'll still be able to jump away from a stop light, and have a nice low cruise RPM. I have a 3.08 in mine, but my rears are only 26.5" diameter (2,350 RPM at 60mph with the 1:1 3rd gear in my TH 350).
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Indycars
Well-Known Member
What do you want the car to be good at ....... gas mileage or acceleration ??? What about using
a 4 speed automatic like a 700-R4 or a 200-4R, both made by GM.
Or you can calculate your own specific RPM using the Excel spreadsheet below. Only change
the numbers in the first 3 columns, the rest are calculated.
.
a 4 speed automatic like a 700-R4 or a 200-4R, both made by GM.
Or you can calculate your own specific RPM using the Excel spreadsheet below. Only change
the numbers in the first 3 columns, the rest are calculated.
.
I'm running towel city cheater slicks, I think they are 28.5
awesome info,,I'm still trying to learn this part of the build. I got the 400 cheap, and its been rebuilt already. And to answer your question, I couldn't give a shit less about gas milage tbh lol
By my calculations, with those tires you'll be turning 1,975 RPM at 60 mph. How fast you get there is strictly up to you!
Indycars
Well-Known Member
Well then, you will want to change that rear gear for better Gitty-Up-And-Go !!! LOL !!!
Indycars
Well-Known Member
I built a 200-4R with a 0.67 final drive ratio since it had the same drive shaft length as my TH350. With 31 inch rear tires and a 3.7 rear gear I only turn about 1900 RPM at 70 MPH. The later 4 speed trans have a lock-up torque convertor, that drops the rpm another 300 rpm since there is NO slip.
Your actual RPM will be higher than calculated for an automatic without a lock-up TC. All the calcs assume zero slip or a manual trans.
The 472 is a high torque low rpm motor,,would that make much difference?
fletcherson
Well-Known Member
I would suggest obtaining an honest power/rpm rating for your engine, figure out where it’s sweet spot is, power band, and calculate to arrive at that number. Should be fairly straight forward to do, if you decide what your cruise speed will be and plug in your numbers to the equation. I used to have a desk top Dyna software that had several calculators that were helpful for such decisions. I’m sure there are some available on line via cam manufacturers, etc.
Island Girl
Well-Known Member
Not in most everyday circumstances, . . . .
It'll pull the numerically low 2.79 gearing easily, even with the tall tires, but won't have near the "slam you into the back of the seat" feel that you's get with lower, (numerically higher) gearing.
The Caddy mill will give you good 70 mph cruising without pushing the rpm range, and noticeably more "slam you into the back of the seat" feel with something around 3.40 to 3.70 gearing. . . . which is after all the main reason we put big motors in these tiny light weight cars.
Higher than something in the 3.70's and you'll end up hating driving on the interstate.
My bigger worry would be using the 8" rear from an intermediate sized vehicle behind the 472
Indycars
Well-Known Member
The car should run just fine with the 2.79 rear gear. But is it what you want or what
you can afford?
You could put off making these changes until later after the car is running and you
can better afford to get exactly what you want.
With a 350 trans and 31" tires I am running 3.70 gears in one car, 3.89's in the other two, and with a 700R4 I am running 4.29 gears. All work just fine on the freeway. Gas mileage? Seriously? I also have a good friend who has 29" tires with a 'glide and 4.11 gears and drives freeway speeds all the time so don't think it can't be done.
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