ls1tork

Examples;

1. Honda Civic- with 22+ psi boost on a built B18 4 cyl putting down 400+ whp at 9,000 rpm, 2,400 lb car, final diff gear ratio = 4.76 in 4th gear, power to weight 6.00:1, less aerodynamic drag and parasitic losses.

2. Pontiac GTO- with 10 psi boost on a built LS1 v8 putting down 600 rwhp at 6,500 rpm, 3,700 lb car, final diff gear ratio = 3.46 in 4th gear, power to weight 6.10:1, more aerodynamic drag and parasitic losses.

Question;

Based on the examples above with both cars having the same amount of wheel torque (torque multiplication on manual transmissions for both), which car would truely accelerate faster assuming all other factors are equal? Would applying the same wheel torque to 3.46 gears yield a faster accelerating car than the same wheel torque on 4.76 gears by virtue of mechanical advantage (further distance traveled with the 3.46's) or is it the other way around?

Alvin

iTrader: (2)

Funny thing about gearing is no matter what you do power at the tire is the same. Power is what your looking for to move the car down the track the fastest.

ls1tork

Most people would assume that because a GTO at 600 rwhp, and a honda civic at 400 whp, that the GTO would beat the honda badly by virtue of GTO having much more hp and torque. But as i cited in the examples above, these two have the same power to weight ratio, and the transmission gearing works out for both to have the same wheel force in thousands of pounds at the tire tread. But the only difference is the final gearing at 1:1-

Which car would accelerate faster? the 3.46 or the 4.76?

i'm thinking that if you apply the same force on taller gearing (3.46's), that should accelerate faster. It's just like the drag cars using taller slicks vs smaller slicks- the tall one would pull ahead (??)

Alvin

iTrader: (2)

I don't think you understood me.

Torque isn't what moves a car the fastest. Its power.

If you know and understand that the next step is to realise that power is the same at the wheel regardless of gear ratio. (power = torque * angular speed) Torque changes by n/1 where gear ratio is n and angular speed changes by 1/n

What moves a car down the track absoulutely the fastest is which ever gear combination that keeps the engine at RPM which it makes the most power the most amount of time.

nitsudls1

iTrader: (1)

Ive wonderd the same thing. I drive a John Deere 8200 for work. The axles turn EXTREMLY slow. Even with a 180hp it pulls like a freight train, but at a slower rate. Even with an infinate amount of traction, I feel like the larger tires would pull more at the same speed.............
Another example would be a helicopter with a propeller turning really slow(compaired to an airplane propeller) The heli has more than enough thrust to lift its own weight. I only know of 1 or 2 prop planes that have more thrust than weight. (jets excluded)

ls1tork

So as far as the example i've given, then the honda civic would win according to what you said. The honda would be sweeping across it's power band faster than the LS1 because of the shorter gearing of the honda (higher mechanical advantage). am i thinking correct on this?

then if this is the case, then why does the dodge viper take the total opposite approach of putting down torque and power by using 3.07 gears? And why is this car so fast and dominating if mechanical advantage doesn't make a difference? Everybody else goes shorter ratio with gearing into the high 3's and 4's (all exotics and imports), including f bodies and fords.

ThirdGenLS1

iTrader: (11)

think you missed his point, he's saying the gearing is to put your car in its power range. You can have too much or not enough gear for a car, all depends on where that engine makes it power. having a gear ratio of 6.00 in a engine that makes all its power from 1200-2000 rpms isn't going to work out to well.

Dont think of it as moving through the rpms the fastest because thats not going to move the car the quickest. You want to to get into the engines powerband as fast as possible and stay there the longest you can.

ls1tork

ok, i get it now. So you just gear the car based on the engine's powerband. if it's wide like ours, then taller gears allow it to stay in the powerband longer. But if it's narrow and peaky like a honda civic, then shorter gears are best. And a viper's powerband is even wider than ours, so it uses way taller gears.

it's about how much power you have, how wide the power band is, and the lowest weight possible.

burbanman

iTrader: (12)

in a highway race, it might be close between the 2 you listed........

in reality, in a drag race, the one with the most traction will win.

Mid/low 12 sec cars take out more powerful 10 sec cars on the street due to traction.........

ls1tork

So i would do it like this for a street killer?: i make a choice of what i want my top "sprint gear" speed in mph to be at max rpms. The sprint gears would be 3rd and 4th on an LS1/t56 combo. Then i choose a differential gear that would give the most mechanical advantage for that chosen range supporting that chosen top speed (shortest gear within reason), based on the transmission ratios. Then i build up power of the LS1 to have maximum cylinder pressure or torque for that chosen range of gears/rpms. So i'm not necessarily looking for the ultimate rwhp numbers am I? This looks like I will have to go to either a big cube LSx or FI, because of the weight of my car- and i really don't want to deviate from LS1. A big cam is not going to be enough unless I gear the heck out of it and add supporting valvetrain and bottom end parts to make the LS1 spin over 7,000 rpm safely, and i don't want a screamer (or do I?). It's my DD and the priority is that it has to remain streetable and somewhat reliable.

What do you guys think i should do? FI is probably the best way to get what I want. procharger??

Sparetire

Dont forget too that in a street car app on street car tires, a Vipers TQ will pretty much require a mild gear to keep its drivers from killing themselfs. Imagine Vipers with 4.10 gears in the hands of average drivers with 0 expirience. They would be wraped arount trees left and right from when they got on the throttle too hard too soon in a turn in 2nd.

ls1tork

True that. Vipers are wild machines, even with 3.07 gears. If they could find a way for that thing to hook with 4.10s, it would probably nearly be un-beatable, especially fully modded. But GM cars are pretty threatening too as they are. Our cars take full advantage of gear leveraging.

Sparetire

Bingo. Thats why everyone, even domestic haters, respect the C6Z. It doesnt just make 460WHP. It makes it into the higher revs (unlike Vipers untill the new 600HP model) and then has gearing that can take advantage. I love seeing people amazed when a stock Z bets a 500WHP car. Power under the curve in places where street trim stock small blocks usually dont have it.

DanO

460whp is 460whp.. i dont care if its at 2000rpm or 10000000rpm

When your drag racing your concerned with ~4500-7000rpms.. and whoever has the most average power through that range will win.. (all other factors equal).

ls1tork

i'm still trying to figure out something. As stated in most of the previous posts here, if whoever has the highest rwhp wins regardless of gearing, can someone explain why a typical liter sport bike with 150rwhp can out accelerate a 500rwhp car? The bike obviously has way higher gearing, and i know it's mostly because of the big difference in weight, but does not the same principle apply to cars? A lightweight 400rwhp car geared to the high heavens (like a boosted civic) would slightly out accelerate a 400 or 500rwhp f-body that's almost twice as heavy?? And if gearing doesn't make any difference as stated in above posts, then why are some of us installing 4.10's and 4.56's?

Sorry about the redundant questions, i'm just trying to learn and put all this together where it makes some kind of sense. i'm not looking to mod my GTO to become the king of rwhp- i want to buy only the right mods that will give me as much advantage and reliability on the street as i can get (combating the weight problem) without going to a ridiculous level like 800 rwhp.

Can these questions even be answered without too much complication??? i realize that i probably answered most of my own questions.

frustrated like a newb

LrngCrv

Interesting to think about but you also have to remember that there are more differences than you are comparing.

Using the following gearing info:
'95 Civic Si - 3.250 - 1.900 - 1.250 - 0.909 - 0.750
final 4.250 - redline 8200

'98 F-body - 2.660 - 1.780 - 1.300 - 1.000 - 0.740 - 0.500
final 3.420 - redline 6000

A '95 Civic Si when it shifts at redline will have to go through about 3400 rpm (41% of rpm range) before the next shift from 2-3 and 2800 rpm (34%) from 3-4. A '98 F-body only has to go through about 2000 rpm (33%) from 2-3 and 1600 rpm (27%) from 2-4.

RPM band that is used between shifts (assuming they launch at 0 rpm):

Civic
1-2 8200 rpm (100%)
2-3 3400 rpm (41%)
3-4 2800 rpm (34%)

F-body
1-2 6000 rpm (100%)
2-3 2000 rpm (33%)
3-4 1600 rpm (27%)

Now imagine having a dyno sheet for both of those cars and comparing what the average power was between those rpm amounts. Most likely the F-body would have much better average power over the % of the power band but even if it was an amazingly built Civic that matched the F-body in average power the F-body would still have a gearing advantage in that it would have a much narrower slice to take the best of it's powerband from. So the Civic might have the weight advantage but the V8 has peak and average power advantages with better gearing to take advantage of it from most examples.

1994Z28Lt1

iTrader: (1)

i dont think you're quite getting it.... these liter bikes have higher gearing than cars to take advantage of their powerband the typical liter bikes redlines at over 13,000 RPM where a ls1 f-body bounces off the rev limiter around 6200 rpm

it comes down to the power to weight ratio and 300 whp hatch civic will obliterate a 300 whp f-body because of the shear weight difference it doesn't really matter at that point how either of them are geared

in a drag racing situation you mess with your gearing and tire size so that you can fully take advantage of the power you have and the range at which you have that power, Take for example any car lets say with the stock gearing you cross the traps at the track close to the redline in 4th gear. If you putting in higher gears you might have to shift into 5th gear or bounce off the limiter in 4th and run a slower time even though you have higher gears

you cant make assumptions about how fast a car is by the gears that it runs. a lot of turbo guys fun lower gears in the diff so they can load the turbos more on their cars to run better times

it all comes down to taking advantage of the power you make and gearing the car to best use that power, thats how you win races

ls1tork

This is great, thanks for the detailed info. i didn't take any of this into consideration. I will have to study this further.

ls1tork

i understand and appreciate this info.

the way i was looking at this is the actual weight of the car per unit of force generated at the wheel. i may be wrong, but for some reason, i'm just thinking that weight has the biggest influence on what a car really does acceleration wise. Of course horsepower does too. A liter bike at peak torque may only have to carry 0.50 lbs of weight for every 1 pound of force at the wheels generated, whereas, a boosted f-body (15psi, 700 rwhp) typically would carry around 1.8 lbs of weight in the sprinting gear for every 1 lb of force generated at the wheels. Now on the street there are alot of variables (driver skill, turbo spool, shift points, powerband, etc) determining the outcome of that race, but in general theory, all else being equal, the bike should still out accelerate the boosted f-body up to a certain point.

if you play with gearing on a heavier vehicle, the ratio i mentioned above changes, sometimes in a dramatic way. i have found by certain calculations that you can get a match in torque to weight ratio between cars that have big weight differences and at least in theory appear to have similar acceleration characteristics. A heads and 224 cam car with the right gearing could match force at the wheels in lbs (up to a certain point- in the range of street driving rpms) to a boosted car that has a very broad flat nice torque curve. There's alot of play that you will find if you dig deep enough. i just don't believe in slapping a mod on a car and hoping for the best. I want to know what combinations work and why. This is the path that I take to hopefully get a little further than normal with whatever mod i choose to setup for the street. It's all about the details that others ignore.

Shooter_Jay

you can't calculate the acceleration using the peak torque numbers unless your torque curve is actually a straight horizontal line, which it will never be.