Technical Very Hokey Rear gear v. Torque/power band

Okay,

So I’m driving along on the highway doing 75 MPH, when some wannabe pulls up beside me in his 2008 V6 charger. I’m thinking sweet this should be easy I’ll dust this guy with my hot 350sbc.

So we both floor it and he pulls ahead of me no problem while I’m lugging up to 4000 rpm. Once at speed i easily pass him ( I’ve got tons of rpm to spare ).
Months later I’m on the Hamb having Vietnam flashbacks to that humiliating moment of realization that maybe my hot 350 isn’t so hot?
4200lb Pontiac, 2.56 final drive 3rd gear @1 ( TH350 ), 750 Holley 4160, 1 3/8 headers dual exhaust straight out behind rear tires.
Current solution: better cam (2800-6800rpm), 2600 rpm torque converter, and 3.08 gears.
Actual discussion point: final drive vs torque curve?
Hypothetically your torque curve is 3300-4000 hitting 419 max and dropping off to 380 after 4000rpm. 3.08 gears put you at 75 mph doing 3300.
3.73-4.11 gears are bigger and faster? Faster as in you run out of rpm or faster as in acceleration?

 

Horsepower curve vs torque curve... sweet spot is a much argued point and could be different on different combos. Lower gearing will help you in most instances, up to a point. A 2:56 final gearing will probably never give you a good 50 mph trope off. But you don’t want 4:11 for a crusier with out an overdrive transmission. The best combo would be the 4:11 and an overdrive auto.




Bones

 

You need a bigger stick, like something based off a 455 starting point. Your axle gears will be fine then.
-Dave

 

Did the passing gear not work? 4200 lbs and a 2.56 gear aint going to be no rocket, but you should have plenty of top end on the highway. To answer your question, the larger the rear gear number, the faster the car takes off, but it also runs out of breath sooner. Good luck.

 

You've got some pretty small tires (23.5") to turn 3300 RPM at 75mph with 3.08 gears. What are you running?

 

Little engine info would help...but 2.56's are not gonna get out of the way of too many cars with a SBC...

 

Yea, either a LARGE inch engine, or properly matched gears in smaller inch engines.
Normally a 3.73 or 3.90 ratio is a great compromise for power at the ground and overall driveability, including the freeways. You shouldn't be afraid to let the engine breath a little on the freeways.
I've run both gears in cars over the years. I have a set of 3.73's in a car I'm building right now. Small inch engine, NEEDS gear to help it run well.

Mike

 

Was this at the salt flats??? 2.56 WTH,
3.73 gears and a straight three speed automatic transmission with a SBC would work great.
^2X what happened to your kick down?
3.90 gears and an overdrive would work great.

 

Looks like your trying to run a buck fifty. lol

 

I think you need a reality check! The V6 Charger probably has as much hp and torque as your old school sbc. If you started at 75 mph, the only reason you passed him "at speed" was because his computer limited his speed to around 112 or 116 mph. If you would have started from a dead stop, you may never had seen his tail lights again because of your rear end gear. He started out with somewhere around a 3:55 rear gear, then the 6 speed auto has 2 sets of OD gears, knocking the final drive down to around your rear gear. At the point his computer limits his top speed, he is probably not near the motors red line. If he had bought a performance computer, it would not have limited his top speed, though his brain may have set his limit.

Old speed technology is good stuff when it doesn't have to be compromised to meet the standards we set (fuel economy, drive ability at anything other then wide open throttle). Old speed can get to a predetermined speed really really fast, or it can go really fast but it is a little slower getting to the real fast speed. A computer that controls the ignition system, the fuel system, has the ability to vary the cam timing, and can control the gear selection every 1/100th of a second is a pretty tough competitor. Gene

 

They are 26.1”

 

I want to be right in my torque curve like I said, so with a 3.08 rear gear and TH350 3rd I should sit at 75 MPH @3300rpm with 400 Tq (ish). Drop off for tq is 4000. Will I beat someone who has 3.73 or 3.90 at that speed? This is just random highways in Canada btw

 

700R4, 3.73:1 rear gears.

 

You need a real motor to pull that boat. Not a small block Chevy. I realize the Canadian Pontiacs didn't get the good stuff. I owned a 68 Grand Prix with a 428 Pontiac and I would run the speedo off the dash with no hesitation . It would run an honest buck and a half. It only had an Edelbrock intake and a ram air cam and 2 1/2 inch exhaust. It had a 2.41 gear.

 

True, very true. That’s a very cool car you owned, btw. I guess for now I will try this new cam, high stall and if necessary 3.36 gears and porting heads.

 

Here is your competitor.......

Canadian 3.5 liter SOHC V6 Charger 250 HP @ 6,400 RPMS
250 FT-LBS @ 3,800 RPMS
4 speed automatic transmission
2.82 rear
weight 3,800 LBS

 

Typo?

 

Let's hope so. On a stock 350 1-1/2" would be fine. With decent hop-up: 1-5/8".

I rarely see 1-3/4" on a good running street engine.

 

Loose a thousand pounds..

 

Your figures are off. With 26.1" rear tires & 3.08 rear gears you'll be spinning the engine 2974 rpm's at 75 MPH.

https://www.strangeengineering.net/gear-ratio-calculator/