Best gearing with a 28" tire

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dadnova · #1 Post by **dadnova** » Sat Jun 23, 2007 12:53 am

I have a TH400 with a 2.45 first gear, and a 28" tire. Max RPM is 6700.
Trans brake at 4500 RPM
What would be the best ring and pinion?
4.10
4.33
4.56

Goat Hearder · #2 Post by **Goat Hearder** » Sat Jun 23, 2007 1:10 am

Not totally sure how sound this is, but had picked up a book called Racers Math at Barnes & Noble that has some formulas in it which may help you out with that! It has a variey of math formulas which may help out some other questions you may have at a future date. Not pefect I'm sure but as a predictor it would be very close. Hell of a lot easier to plug numbers into a calculator and get a fairly accurate resut (cheaper to) than spending for gears, bearings etc.! Any other opinions on that?

sc racing · #3 Post by **sc racing** » Sat Jun 23, 2007 9:38 am

I ran a 28" tire with a 4.56 in the firebird 4000 stall no brake th350 shift point 6200 came though around 6600-6700 at 123 mph.

rustbucket · #4 Post by **rustbucket** » Sat Jun 23, 2007 9:51 am

1/8th mile or 1/4?
small block or big?

I run 28 tires and 4.56 gear with a small block and with a t350 i was coming through the traps at 6500. now, with a glide, my shift light is on at 1100 ft.
my light is set at 7000 rpm's. I could not run the quarter with 4.56 or a t350 without turning my motor to hard. If you run n20 you can expect to run out of gear alot sooner. My buddy with a big block vega and 5.38 gears can run farther than my 4.56.

55delray · #5 Post by **55delray** » Sun Jun 24, 2007 8:59 pm

i run a 3.90 with a 275/60 /15 drag radial with a glide. 7200 thru the traps on the spray.

ytnova · #6 Post by **ytnova** » Mon Jun 25, 2007 9:13 am

I am using 3.73 with a 275/60/15 radial and it goes 7200+ on the spray, depending on the tune-up.

427belair · #7 Post by **427belair** » Mon Jun 25, 2007 7:36 pm

Im running a glide with 28x10 tires and a 4.30 gear and go 129 thru the traps at 7000

dadnova · #8 Post by **dadnova** » Tue Jun 26, 2007 10:34 pm

Right now I am on all engine. Nos or blower will require different gears.
I am thinking of 28" tire with a 2.45 first gear with 4.33 or 4.56
Which won would be better as RPM is below 7000 for now?

55delray · #9 Post by **55delray** » Tue Jun 26, 2007 11:37 pm

dadnova wrote:Right now I am on all engine. Nos or blower will require different gears.
I am thinking of 28" tire with a 2.45 first gear with 4.33 or 4.56
Which won would be better as RPM is below 7000 for now?

also depends on how tight/loose your converter is,.

race9899 · #10 Post by **race9899** » Wed Jun 27, 2007 2:04 am

6700 / 4.10 =1634 axle RPM

1634 x 88" (rollout for 28" tire) = 149072 inches per minute

149702 / 12 = 12423 feet per minute

12423 x 60 = 745380 feet per hour

745380 / 5280 = 141 MPH with no converter slippage no tire growth

141 x .9 (10% slippage) = 127 no tire growth

127 x 1.03 (about 1 inch growth)= 130 MPH

1320 / 130 MPH = 10.15 ET

4.30 gear would be 118 MPH capable of 11.18

4.56 gear would be 111 MPH capable of 11.89

Both of these were using the same 10% converter slippage when in reality the same converter with more gear will slip less

If you have enough HP to carry the weight of the car to 130 MPH then the 4.10 would be the gear you wanted

project71nova · #11 Post by **project71nova** » Wed Jun 27, 2007 7:23 pm

race9899 wrote:6700 / 4.10 =1634 axle RPM

1634 x 88" (rollout for 28" tire) = 149072 inches per minute

149702 / 12 = 12423 feet per minute

12423 x 60 = 745380 feet per hour

745380 / 5280 = 141 MPH with no converter slippage no tire growth

141 x .9 (10% slippage) = 127 no tire growth

127 x 1.03 (about 1 inch growth)= 130 MPH

1320 / 130 MPH = 10.15 ET

4.30 gear would be 118 MPH capable of 11.18

4.56 gear would be 111 MPH capable of 11.89

Both of these were using the same 10% converter slippage when in reality the same converter with more gear will slip less

If you have enough HP to carry the weight of the car to 130 MPH then the 4.10 would be the gear you wanted

how much hp we talking ? saying a nova was about 3300 or so....?

race9899 · #12 Post by **race9899** » Wed Jun 27, 2007 8:33 pm

625 hp or so to run 130
500 hp or so to run 118
425 hp or so to run 111

There are a ton of Horse Power calculators online, but many will give you a wide range of actual HP numbers. the HP levels above would be approximate flywheel HP

clutchdude · #13 Post by **clutchdude** » Fri Jun 29, 2007 4:09 pm

I would say the best option is run the car first so we can kinda figure out the power your making, and then it would be easy to figure out the gear ratio you need with your current setup.

More power generally means less gear and less power generally means more gear if your car has the rpm potential to use it.
Jim

P.S. im only running a 4.30 gear with a 28" tall tire and im running 135mph @7000prm...why, no converter slippage.

race9899 · #14 Post by **race9899** » Fri Jun 29, 2007 5:08 pm

Could just be a very efficient converter,

I started looking into slippage when swapping from a standard shift to an automatic in my bracket car, went from running 142@7000 to running 135@7500, tires had 103" rollout when but were 110" at speed,

Converter company wanted to use the 103 to figure slippage, they thought they were doing just fine, It was a piece of crap!!!

after a few converters I finally got one that using the static rollout actually made MPH!!

Knowing what the tire rollout at speed is will help tremendously getting your gear and converter properly set up. Find someone who has a Datalogger that is running your tire and that will get you real close.

On Todd Kitchens car the 33x10.5 W grows 7" at 200 MPH

race9899 · #15 Post by **race9899** » Fri Jun 29, 2007 5:11 pm

I just notice you run a stick

What tire do you run, because we can figure at speed rollout real easy

Clutches are cool

Best gearing with a 28" tire

Best gearing with a 28" tire

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