Torque within a usable range of Speeds
 

Well we could never get my Excel Spreadsheets to post on this forum, always said the PDF files were too big. Yesterday I posted them to another Forum (GMC owners) So if you need to see this information go here see post 6 and 7 the spread sheets go from 24 to 32" tire diameters and most common engines, transmissions, and rear axle ratios. If you need a custom chart PM me here and I will email you one like we did before. Kieth

ps guidelines are minimum 460 ft/lbs of torque shoot for 65mph @ 2000 rpm this will keep you from building a truck that cannot get out of its own way.

:gmc2:

http://6066gmcclub.com/forum/showthread.php?t=48090

Re: Torque within a usable range of Speeds
 

I went to that site and it wouldn't let me open it due to not being a member.

We spoke of this previously in the past but I couldn't understand what everything meant ... numbers aren't really my forte' ... LoL

Can you help me understand it?

I plan on running a 28" tire (275/60/15) with an aftermarket T56, my tranny gear ratios are

(1st) 2.97
(2nd) 2.07
(3rd) 1.43
(4th) 1.00
(5th) 0.80
(6th) 0.62

I can't decide on using a 3.73, 4.11, or 4.56 rear gear. The cam I have (hyd roller) is a 230*/236* duration @ .050" lift. & has a usable range of 2000-6000 rpm. I was advised to have my highway rpm about 2100-2300 rpm. I will be running multi port fuel injection (TPI based setup). "Estimated" power will be in the 450-500 range on both horsepower and torque.

Most of my driving (to work ... ) is at 55-60 mph right now but if I move (very likely) my drive will be interstate driving at 70-75 mph.

Here's what I've come up with on my own but I'm not sure what to run rpm wise for the best mpg's.

3.73 x .62 = 2.31 final gear ratio
55 = 1525
60 = 1663
65 = 1802
70 = 1940

4.11 x .62 = 2.55 final gear ratio
55 = 1683
60 = 1836
65 = 1989
70 = 2142

4.56 x .62 = 2.83 final gear ratio
55 = 1868
60 = 2038
65 = 2207
70 = 2377

3.73's seem too low based on my rpm recommendations, 4.11's may even be a bit too low, the 4.56's seem about right ... based on mph's and rpm's ... ???

Re: Torque within a usable range of Speeds
 

"450-500 range on both horsepower and torque."

You will have no problems, i have a pontiac with those numbers verified and 3.45s where 70-75 is about 2k rpm. Plenty of response and not lugging at all. I wish i had 3.91s for more stoplight fun, and becaues at 2k rpm the exhaust drones, i wish it was more like 2400-2500 just so i wasn't in that "sweet" vibration spot for the exhaust.

I had a 428 (current is 455) with less power but more streetable cam with lower rpms (like 1k to 5k) and i still had 2.56s in it with i think .69 OD in it. It was ridiculous, 1700rpm was like 80. BUT i got good mileage, and it didn't chug at all, because the cam was suited for running down low and i had tons of torque.

Some will talk about custom ignition curves and making sure timing is all in by cruise speed for efficiency and all that, i can't speak to that.

Re: Torque within a usable range of Speeds
 

Keith there was a site that had torgue/HP/gears/rpms some where on the net and it was free, but have not been able to find it, it was linked to one of the hardcore racing cites, I will keeep looking for it, it was a really neat program.

Re: Torque within a usable range of Speeds
 

Here's my motor with specs, posted in the "Lets see your motors, Stock to wild" thread.

http://67-72chevytrucks.com/vboard/s...5&postcount=31

cortcomp - You saying I'd be better off (mpg wise) with the 3.73's or 4.11's? As far as the stoplight fun, with a 2.97 1st gear and 3.73's giving a 11.07 1st gear ratio and 4.11's giving a 12.20 ratio and 450 lb/ft of torque ... 1st gear might be re-labeled "tire melt" ... LoL

For comparision sake, a Muncie 4 speed and maybe a TH 350 has a 1st gear ratio of 2.52 and even with a 4.10 rear gear, that equals a 10.33 final ratio.

Re: Torque within a usable range of Speeds
 

I had the original 283 / 3 speed with 3.73s and 28" tires(275/60/15) and could let both tires go in first or second. Then dropped in the t5 with .67 od and still had plenty of go with 20+ MPG cruise at 55. Now with 406 cui and 425+ of torque and 28.5"(295/45/18) it's in the sweet spot 75 and 2000rpm in 5th. Close to 3000 in 1:1 So anything over stock is gravy.

Re: Torque within a usable range of Speeds
 

I considered using a 1988 WC Camaro T5 with my 250 L6 but decided against it. Fifth gear is 0.63 and calculations suggested my engine would lug unless I was doing 70MPH. RPMs would be 1906 at 70 MPH and 29" tire + 3.73 rear. So basically I'd have to downshift to 4th gear below 65 MPH. I decided to use a T5 with a 0.73 5th gear.

What kills me is that GM put that same T5 with a 0.63 OD in a 1988 Camaro with a 26" tire and 3.08 rear. Yes! A 3.08 rear!!!!
That Camaro had a 305ci V8 and RPMs would be 1755 at 70 MPH with a 26" tire and 3.08 rear. The V8 had enough torque to make it work but 1755 RPMs is kinda low. It seems to me that the Camaro would have had the same problem and couldn't use that 0.63 gear below 65 MPH. That's a guess of course since I have never driven a 3rd generation Camaro with a T5 and 0.63 OD.

If my truck had a V8 then I would have used the T5 with the 0.63 OD.

Re: Torque within a usable range of Speeds
 

My T56 is basically a replacement 6 speed for the T5 transmission. A 93 transmission adapted to replace the weaker T5 since a lot of guys were running 350's and 383's in the 3rd gen F-bodies.

I was big into g-bodies for a while and I had an 86 Cutlass. A stock option for them was a 200-R4 with a 2.56 rear gear ratio and either 195 or 205 14 tires.

Re: Torque within a usable range of Speeds
 

Your 383 will not bog no matter what rear you choose. I'd worry more about 1st gear being too low.

Re: Torque within a usable range of Speeds
 

:devil: Yeah I know what you mean, gives a whole new meaning to "granny low" doesn't it ... :lol:

Re: Torque within a usable range of Speeds
 

I`m still considering the Jeep AX-15 trans, its a 5 speed , .79 overdrive, the first gear ratio is 3.88, the jeeps used a 307 rear gear ratio for the 2 wheel drive models, so eventually will change the rear gears to a 3.31 or 3.42, the current 3.73 is just to short for the trans....!

Re: Torque within a usable range of Speeds
 

will run a spreadsheet just for your set up, send me a pm here and I will email you the information. You have plenty of torque so getting the speed right will be the deal.......Kieth

ran the information, you are correct plenty of torque no matter what speeds are:
3:73------72mph @2000rpm

3:90------68mph @2000rpm

4:10------65.5mph @2000rpm all have plenty of torque, if there are no 3:90s' for your rear end then the 3:73 are the correct choice.....Kieth

Re: Torque within a usable range of Speeds
 

Kieth,
You already sent me a spreadsheet and we talked on the phone too. Good advice and info. My 2.95 1st gear and 0.73 OD will be perfect with 28" tires and a 3.73 rear.
Thanks again.

Re: Torque within a usable range of Speeds
 

give me the tire diameter of your truck, and the tire diameter of the jeep, we can then compare them.....Kieth

Re: Torque within a usable range of Speeds
 

Here we go, due to a lot of hard work "ACK" a member of this board worked diligently to get this information in a format that this forum can download. So here it is, I really think it should become a sticky with a lot of the credit going to ACK "Sean" Hope this helps someone ??

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