[Mango Daytona]

In basic terms, torque is low end power, horespower is more for high end. At the track you can have a the same E/T with the same car with both combinations, but one will have a higher trap (MPH) in the 1/4. MPH in the 1/4 shows hp, my Father's TT Vette ran a 12.0 with a junk 60' sandbagging it the whole way at 140mph.

 

[CHRGRhemi]

Yes, prior discussion on torque and hp was assuming sufficient traction. You're right, as soon as you throw a traction limitation into the equation, it changes significantly. Your dad's TT Vette had way more torque than the tires could handle. If you had super sticky slicks, the time would be much lower, but the speed wouldn't change as much.

If you sat on the starting line roasting the tires for 5 seconds, it would affect your ET by 5 seconds, but you still have the same distance to hit the trap speed. That's why they say trap speed is a better indicator of power, because it's less dependent on traction.

 

[dejuan7]

Thanks guys for the replies. Im getting a better understanding :bigthumb:

 

[dejuan7]

I notice our torque on the 3.5s kick in the 3k 4k range. after that cant feel crap lol.

 

[KStryker]

Nice explination

x2

 

[TopBanana107]

That really makes alot of sense. I was wondering all this crap guys because i wanted to know since the supercharger for the v6 makes less torque than a hemi how would that pan out in a race? Would the higher hp make me catch up in the higher rpms. or would his torque still out run me?

What numbers are put out by the SC for a V6? Just wondering...

Anyhoo, personally, I would like to see close to an equal number for both hp and torque in smaller applications.

all things equal, lower torque car would lose the race
same torque, higher hp, depends on how fast you take the race

Lot of variables, including minor things like our hemi's hate hot weather.

One of the variables is traction...:bigthumb:

 

[daytona torRed]

In the charger you are going to want alot of torque to get you off the line.Torque is what sets you back in your seat off the line.Which is actaully HP in a low gear.HP is the power a giving engine produces(at the crank or wheel).Gearing is used to produce desired torque.A lower gear will get the RPM's up to max HP faster which produces the max torque quicker,as the car speeds up the engine rmp's increase in a somewhat equal amount which reduces the strain on the engine.
Also when you are driving down the road and you down shift and punch it,that force on your body is torque and as the force lessens you are switching from torque to HP.
I'm probably the only one who understands what I just wrote.

An example my charger has 350 HP at the crank and weighs 4000 plus.
My previous car was a 90 daytona torbo which had 249 HP(I never confirmed that)and weighed alot less.
With the chargers extra weight and more torque launches really push you in the seat where the light weight less torque daytona launched easy but got to the RPM HP pretty quick.
Ok I'm done babbling

 

[zoomzoom1]

OK, Hears my .02....On the dyno sheet I had done before heads and cam..this is stock w/just bolt-ons w/CMR tune..You will see lots of bottom end torque at say 2200rpm-all the way to say 4900-5100rpms...HP was way low until say 3500rpm until say 5800...This is good, you want lowend torque to get our sleds going, then the HP takes over and finishes the job at the higher rpms...BTW, the stock cam does a great job with lowend torque with a good CMR tune........OK, I'm done

 

[Ujokin2]

Okay you gear heads and engineer types... this is a great learning thread... now advance it up a notch..

Add what different gear ratio ( High/Low) coupled with tire size does for you torque\HP wise getting you down the track at a good click so even a DUMMY like me can understand.

 

[zoomzoom1]

Okay you gear heads and engineer types... this is a great learning thread... now advance it up a notch..

Add what different gear ratio ( High/Low) coupled with tire size does for you torque\HP wise getting you down the track at a good click so even a DUMMY like me can understand.

OK James, I will try, even though I might be wrong...Here goes...Lets start with your sled being stock, 3.06 gears...20" wheels with 245/45zr20's..You put down 370 HP peak at say 5800rpm and 375 torque at 5100...where as both cross at 5252rpm...You start dropping torque at 5200..but you are making more HP higher up to carry you through to shift point..say 6250 stock..boom..drop to 335 torque and 300HP into second..the torque is ramping hard, but the HP doesn't get there until 5000, the torque brings on the surge when hitting it on the upper 1/3 of its range...and goes on like 1st gear..OK?
Now...the rearend has to turn 3.06 times for every 1 turn of the drive axles(halfshafts) Makes for along time to spin up the engine...and 20" wheels also add to the equation by not helping with rpms of the wheel..anyway, you can't rev. the engine very quick to hit the peak torque and HP of the engine,,,Now put 3.55 gears and smaller tires on and all of a sudden, the engine can rap up quicker to peak tqe and HP..and shifting w/the stall tc will put you into the peak of both worlds, when you change gears..ie..1..2..3....It hits right under the peak of your power band..so you get the torque carring you up and HP to finish it max rpm...I hope this helps....I think..

Ralph

 

[Ujokin2]

OK James, I will try, even though I might be wrong...Here goes...Lets start with your sled being stock, 3.06 gears...20" wheels with 245/45zr20's..You put down 370 HP peak at say 5800rpm and 375 torque at 5100...where as both cross at 5252rpm...You start dropping torque at 5200..but you are making more HP higher up to carry you through to shift point..say 6250 stock..boom..drop to 335 torque and 300HP into second..the torque is ramping hard, but the HP doesn't get there until 5000, the torque brings on the surge when hitting it on the upper 1/3 of its range...and goes on like 1st gear..OK?
Now...the rearend has to turn 3.06 times for every 1 turn of the drive axles(halfshafts) Makes for along time to spin up the engine...and 20" wheels also add to the equation by not helping with rpms of the wheel..anyway, you can't rev. the engine very quick to hit the peak torque and HP of the engine,,,Now put 3.55 gears and smaller tires on and all of a sudden, the engine can rap up quicker to peak tqe and HP..and shifting w/the stall tc will put you into the peak of both worlds, when you change gears..ie..1..2..3....It hits right under the peak of your power band..so you get the torque carring you up and HP to finish it max rpm...I hope this helps....I think..

Ralph

As Always Ralph... you make it sound so easy.... BUT Wait! As I raise my hands to ansk another question ...

Now that I have say 3.23 gears using your analogy the rearend has to turn 3.23 times for every 1 turn of the drive axles(halfshafts) .. and being that normally I use 17 inch wheels with 28 inch tall tires Drag radials or slicks which is 1 inch lower than stock 20 inch wheels with NITTO 555Rs... what happens when I drop down to use a smaller tire such as the 25 inch tall HOOSIER 315's DR's that I am fond of ?

 

[CHRGRhemi]

The "shorter" the tire gets, the more it acts like increased gear ratio.

For the really anal explanation...(I warned you)
For example, if a tire is 24" tall, it's about 12" (or one foot) from the center of the wheel (where torque is applied) to the contact patch where it is converted to linear force to accelerate the vehicle (F=ma).

If the engine makes 350 lb-ft of torque average over some RPM range, you then x by 3.59 first gear ratio x 3.06 rear gear ratio x 75% efficiency (or so). This would be 2880 lb-ft of torque to the tire. If the tire has exactly 12" (or one foot) of radius, it comes out to 2880 lbs of force at the tire contact patch. A taller tire will reduce the force, but give a higher linear speed for a given RPM. Trading RPM for torque or vice versa... just like gear ratio!

Now, in this example, because a Charger weighs 4300 lbs with driver, it would be capable of accelerating at about 0.67 g's (2880 lbs of force / 4300 lbs of weight). That is, IF the tire can hold it. If so, you hook. If not, you spin. As an aside, if the tire has a coefficient of friction of 1.0, the Charger would have to have 67% of it's weight on the rear tires under acceleration to sustain 0.67 g's. Sticky tires can have more than 1.0 coefficient of friction, and obviously loose suspensions will allow more rearward weight transfer.

The trick is to match gear ratio to engine to tire holding power. Do it right and you'll have a perfect combination.

By the way, some of you guys are talking like torque is completely different than hp. Torque is a COMPONENT of hp, RPM being the other. They are different, but related.

-

 

[Part Deux]

ZZ, excellent description. For advanced studies, you can start playing with gearing to cross the 1/4 mile line 10 feet before the vehicle shifts into the next gear. Shifting drops you way down in the power band, and there's the loss in power during the shift.

 

[zoomzoom1]

Thanks PD..I try, rackin my old brain from college days, have to think about this...OK..James, so you want to go with a smaller rim, with smaller tire height, Now, you run into a problem that may hurt you, as you know, 3rd gear is the sweet spot for our cars,..I can't remember the gear ratio for third in the tranny, but anyway, I know you don't hit 4th now as your highest trap speed is 122....You haven't shifted into 4th yet, and I know your engine is high revin, but you might have to think about the possiblity of it hitting 4th during a run with the smaller dia. tires and rims, now your bac down in the power band, I don't know the ratio for 4th, but I think it's pretty long....It looks like you might try it and see what the engine feels like at that shift point.....I have a question.....You hit 4th in the TT chally, how did the 4th shift point feel???..something to think about......Hey PD, I just remembered what you said....same point....I just reread James post, and if you go to 3.23 gears instead of 3.55...uummmm...and keep the smaller tires and rims.....Might work...Hey
CHGR hemi...that sound about right???...where is the shift point for fourth in your car James??

 

[CHRGRhemi]

Just remember you want to accelerate as hard as you can as EARLY as you can in the race, even if you shift into 4th the last bit of the run. Very little is done at that point in the race.

If the tires can hold it, give them as much torque as they'll hold!

If two cars are identical but one has 3.23's and one has 3.06's, AS LONG AS THE TIRES CAN HOLD IT, the 3.23 car will get out of the hole faster and establish an early lead, which it should never lose, even if it shifts to 4th for the last second or so. The other car, even in 3rd at the end of the run, won't be able to make up the difference it lost at the start.

If you plot acceleration vs. speed and/or distance, you'll see what I mean.

-

 

[dejuan7]

The "shorter" the tire gets, the more it acts like increased gear ratio.

For the really anal explanation...(I warned you)
For example, if a tire is 24" tall, it's about 12" (or one foot) from the center of the wheel (where torque is applied) to the contact patch where it is converted to linear force to accelerate the vehicle (F=ma).

If the engine makes 350 lb-ft of torque average over some RPM range, you then x by 3.59 first gear ratio x 3.06 rear gear ratio x 75% efficiency (or so). This would be 2880 lb-ft of torque to the tire. If the tire has exactly 12" (or one foot) of radius, it comes out to 2880 lbs of force at the tire contact patch. A taller tire will reduce the force, but give a higher linear speed for a given RPM. Trading RPM for torque or vice versa... just like gear ratio!

Now, in this example, because a Charger weighs 4300 lbs with driver, it would be capable of accelerating at about 0.67 g's (2880 lbs of force / 4300 lbs of weight). That is, IF the tire can hold it. If so, you hook. If not, you spin. As an aside, if the tire has a coefficient of friction of 1.0, the Charger would have to have 67% of it's weight on the rear tires under acceleration to sustain 0.67 g's. Sticky tires can have more than 1.0 coefficient of friction, and obviously loose suspensions will allow more rearward weight transfer.

The trick is to match gear ratio to engine to tire holding power. Do it right and you'll have a perfect combination.

By the way, some of you guys are talking like torque is completely different than hp. Torque is a COMPONENT of hp, RPM being the other. They are different, but related.

-

I was just about to ask how do gears apply to torque. What's the stock gears for the 3.5? I thought is a higher gear or lower gear ratio generally better?

 

[daytona torRed]

I was just about to ask how do gears apply to torque. What's the stock gears for the 3.5? I thought is a higher gear or lower gear ratio generally better?

A lower gear (higher number) is better for the track but a higher gear is better for dailey driving.Better gas milage,engine turning less RPMs eqeuls the motor working less and the top speed will be more if you need 5-10 more MPH.

Here is a small example of tire size difference:
If you have two tires at different sizes and you mark them at the ground and rolled them one full rotation and mark the ground the smaller tire will have a shorter distance than the tall tire.
So in a set distance of say 100 feet the smaller tire will have to turn alot more times than the tall tire which means the engine will be turning more RMPs which means instant lower gear ratio.
But in the same turn the taller tire will have a higher gear ratio so a mile down the road you will see that car start to gain a higher speed.

 

[370 HEMI]

OK James, I will try, even though I might be wrong...Here goes...Lets start with your sled being stock, 3.06 gears...20" wheels with 245/45zr20's..You put down 370 HP peak at say 5800rpm and 375 torque at 5100...where as both cross at 5252rpm...You start dropping torque at 5200..but you are making more HP higher up to carry you through to shift point..say 6250 stock..boom..drop to 335 torque and 300HP into second..the torque is ramping hard, but the HP doesn't get there until 5000, the torque brings on the surge when hitting it on the upper 1/3 of its range...and goes on like 1st gear..OK?
Now...the rearend has to turn 3.06 times for every 1 turn of the drive axles(halfshafts) Makes for along time to spin up the engine...and 20" wheels also add to the equation by not helping with rpms of the wheel..anyway, you can't rev. the engine very quick to hit the peak torque and HP of the engine,,,Now put 3.55 gears and smaller tires on and all of a sudden, the engine can rap up quicker to peak tqe and HP..and shifting w/the stall tc will put you into the peak of both worlds, when you change gears..ie..1..2..3....It hits right under the peak of your power band..so you get the torque carring you up and HP to finish it max rpm...I hope this helps....I think..

Ralph

Ralph,

The gear ratios on our W5A580 is 3.59, 2.19, 1.41, 1.00 and .83. Reverse is 3.16.

The 42RLE 4 speed (for those 2.7L out there) is 2.84. 1.57. 1.00. 0.69.

Great discussion on HP and Torque. It is good to have when setting up a car for the quarter mile.:bigthumb:

Brian
440-821-9040

 

[CHRGRhemi]

For tire size, yes torRed you have the right idea. Tall tires act like tall gear ratio. Short tires act like short gear ratio.

For gear ratio specifically dejuan, the 3.5 uses a 3.64 rear gear ratio. This is how much it multiplies torque coming out of the transmission (which has already multiplied engine torque depending on what gear it's in). In other words, the 3.5 makes 250 lb-ft of torque. First gear is 2.84, rear gear ratio is 3.64. So to the tires you take 250 lb-ft x 2.84 x 3.64 x 75% (since the trans and rear gear are not 100% efficient) = 1938 lbs-ft to the tire. Because the tire radius is about 1 ft, it's 1938 lbs of force at the tire acting on the car to accelerate it.

If the tires can hold that force, you'll accelerate at about 0.47 g's (1938 lbs of force / 4100 lbs of weight for a 3.5 Charger with driver). If not, you would spin. Lowering the gear ratio (increasing the number) to, say, 4.10, will multiply torque that much more and accelerate that much harder, but it will shift into 2nd at a lower vehicle speed since you hit redline sooner. Again, with gear ratios you trade torque for RPM or vice versa.

So to answer your question, lower gear ratios (higher numbers) are BETTER for accleration if the tires can take it, but worse for RPM. It depends on what you want.
-

 

[Ujokin2]

Now we are talking!!!

That is why I would love to get my hands on a 3.91 gear set for our 2008 and older sleds. (only available on R/T with 20 inch wheels and SRT8 6 speed)

It will give me the ability to put as much TQ to the ground... you get the acceleration (it PINS you to the seat when you get that Great launch) and why you feel like you are going real fast).

Also being I am able to shift into 4th gear early.... I am now in the middle of 4th gear RPM.. crossing the line. Which means.. I am actually crossing at a HIGHER MPH then when I had 3.55 gears.

Actually got to test this out on a (test mule) 2008 Challenger SRT8 with a 426 .... for now it is a one of a kind...be it was a prototype. now...

That is why I was wondering about trying a set of 3.73 gear... and then putting shorter tires ( 25 inch) to try to get it to shift earlier.... and do the same thing as having 3.91 with 28 inch tall tires.