Can anyone tell me why the 600RWHP cars making big low end torque, (i.e. 542 strokers, Roe superchargers and such) and the 700-800RWHP centrifigal supercharged cars making big high end HP seem to be running approximately the same quarter mile times AND trap speed in the mid 10s and 138-142 mph? Doesn't it seem that with 100 to 200 extra HP that there would be a significant differnce in quarter mile times or speed?

it's all about the area under the curve. How much peak power a car makes is pointless if it only makes it for a few hundred rpm's. Your question is a little hard to answer because there could be so many variables that affect the outcome of a 1/4 race. But in theory, a car with more horsepower will always pull ahead in a race, should they just keep going past the 1/4 mile.

Last time I commented on this I got called a "Torquegeek" /images/graemlins/laughing.gif

Torque is the twisting force

HP is work done in a given amount of time

Translated - a lot of torque is needed to move heavy things, but high HP will enable you to sprint with it :thumb: You can use gears to multiply torque, but you need the ENGINE to make HP.

High Hp cars typically rpm higher and therefore use steeper gears. I was watching two street rotary Mazdas pull mid 8 second runs on the weekend - and those things have USELESS torque figures relative to hp - but they rpm high and make a lot of power. 8 seconds is fast by anyones standards for a street car.

On the Viper you have both sets of engines using the same gears. Therefore - as the gears are the same for both - the high torque at lower rpms will make more power than the high hp cars during most of the rpm range used. It's still the HP that counts - but it's at lower rpms.

Therefore - the problem is simply that some high hp cars are just not able to use the extra power they have on the top end - plus they do not spend enough time in the rpm zone where they make that extra power while the high torque of the lower powered cars is being used more effectively.

People that swear by torque to go quick are still actually relying on HP but at low rpms - and therefore go very fast on stock gear ratios. Their peak hp numbers may not look impressive - but in the rpm zones they use at the track - they make plenty of power!!!

The higher top end powered cars would go quicker than the high torque but lowered powered cars if they had steeper gears and closer ratios - assuming chassis and tires were matched. But stock gear for stock gear - the high torque wins - because it makes more hp where it matters.

SUMMARY: Torque moves an object but HP determines how quickly! Both are inter connected over a constant of 5252.... which is the rpm where torque and hp equal.

Torquemonster gave a pretty damn good explanation. Bottom line is that the theory is all on the side of HP. That is, if you could do anything you wanted with all the other factors involved then the higher HP car would always win. The perfect drag car would have an F1-like engine spinning at 20,000 rpm and a CVT gearbox to ALWAYS keep it's motor at the HP peak.

What you want to do is compare two cars at the same speed and see which one applies the greatest motive force (torque) to the ground. If you make that comparison (integration) over the range of speed seen during the race then you will see which will be the winner. Since we're just talking about the difference between torque and HP then let's assume gearing is completely optimal for both cars.

Take two identical cars with CVT's and run one of them at the torque peak and the other at it's power peak. Conservatively, the power-peak rpm will be something like 30% higher than the torque-peak rpm. So at the same speed, the HP car is using 30% deeper gearing because of the engine's greater speed ... thus factor in a 30% increase in rear wheel torque due to the multiplication factor of the gears. Of course the engine torque of the HP car is less at it's power peak than that of the torque car but that's typically only about 10% and doesn't make up for the advantage gained by the lower gearing in the HP car. Torque at the rear wheels translates into force and force causes acceleration. Therefore the HP car wins because it's always putting down more torque at the rear wheels at the same speed as the torque car.

Sure now pick me apart with real world gearing and all but my point about HP vs TQ remains true. A good drag racer is going to optimize his gearing for his engine anyway.

Torquemonster gave a pretty damn good explanation. Bottom line is that the theory is all on the side of HP. That is, if you could do anything you wanted with all the other factors involved then the higher HP car would always win. The perfect drag car would have an F1-like engine spinning at 20,000 rpm and a CVT gearbox to ALWAYS keep it's motor at the HP peak.

What you want to do is compare two cars at the same speed and see which one applies the greatest motive force (torque) to the ground. If you make that comparison (integration) over the range of speed seen during the race then you will see which will be the winner. Since we're just talking about the difference between torque and HP then let's assume gearing is completely optimal for both cars.

Take two identical cars with CVT's and run one of them at the torque peak and the other at it's power peak. Conservatively, the power-peak rpm will be something like 30% higher than the torque-peak rpm. So at the same speed, the HP car is using 30% deeper gearing because of the engine's greater speed ... thus factor in a 30% increase in rear wheel torque due to the multiplication factor of the gears. Of course the engine torque of the HP car is less at it's power peak than that of the torque car but that's typically only about 10% and doesn't make up for the advantage gained by the lower gearing in the HP car. Torque at the rear wheels translates into force and force causes acceleration. Therefore the HP car wins because it's always putting down more torque at the rear wheels at the same speed as the torque car.

Sure now pick me apart with real world gearing and all but my point about HP vs TQ remains true. A good drag racer is going to optimize his gearing for his engine anyway.

Some people take the info. from one dyno pull and hope that this info. will all come true during a 10 sec. blast down the dragstrip. Trust me, it never does. The dyno only tells the story of what your car does sitting still with no air flow and no load for about 7 second in 4th gear.

The dyno is just another tool to give you an indication on the direction you are going with your motor and its state of tune. When we dyno I just as interested in the shape of the curve as I am in the peak power numbers. If you can generate a curve that has strong average rwhp numbers from 4000-6000 rpm then you will see those results at the track.

Different power adders have different pros/cons as they run down the track:

All motor is usually the most predictable and will be less prone to heat soak as opposed to a forced induction car.

Turbo cars with manual trans. usually make no boost off the starting line. And wont make their full power potential til they get a full load on the motor in 4th gear.

Blower cars generate the highest inlet air temps and will be the most prone to heat soak. They can also have belt slippage issues. They do make all their power right off the line.

NOS cars can have all kinds of dynamics of power as their bottles heat/cool and as they emtpy going down the track.

Start mixing and matching the above power adders and it gets real interesting. Throw in an auto trans. and it gets more interesting.

Ahhh - but it is torque at the WHEELS not the engine that matters most... :nod:

That's why a high rpm, high hp, low torque engine will invariably beat a low rpm high torque engine.... GEARING!

An 800hp 20,000rpm F1 engine will make around 210ft/lb of torque at peak hp.... that's pathetic!!! Say an 800hp blown V10 makes it by 5252rpm so torque is the same.

But to get the wheels turning the same speed as a high torque engine that peaks at 5252rpm - where the Viper engine uses a 3.07:1 rear end - the F1 engine needs an 11.69:1 gear to match that speed - and 11.69 x 210ft/lb = 2456ft/lb to road verses 800tq x 3.07 = 2456rwtq.....

wait a minute....

OH Goodness me - look at that! They're the same!!! /images/graemlins/supergrin.gif

So these two cars put down the same rwtq - even tho the F1 engine only makes a patheic 210 lb/ft at engine vs the collasal 800 of the V10. THEREFORE It really is engine AVERAGE HP that matters most - gearing will translate that into the rwtq that will motivate the car :thumb: :cheers:

By the way - what does the dyno measure then? I know Vipers dyno in fourth cause the ratio is 1:1 - does that cancel the torque multiplication factor? In what gear would the RWTQ be 2456?

In my mind, if the ratio is 1:1 and the rear is a 3.07 then the dyno is measuring power at the 3.07 ratio - why then is the RWTQ 1000 ft/lbs less when measured on a dyno?

By the way - what does the dyno measure then? I know Vipers dyno in fourth cause the ratio is 1:1 - does that cancel the torque multiplication factor? In what gear would the RWTQ be 2456?

In my mind, if the ratio is 1:1 and the rear is a 3.07 then the dyno is measuring power at the 3.07 ratio - why then is the RWTQ 1000 ft/lbs less when measured on a dyno?

Good question. The # that the dyno reports should actually be called flywheel torque as measured at the rear wheels. You are correct in that a stock viper making 500 lb.ft torque (at the flywheel) is actually putting down 1500 lb.ft. at the rear wheels in fourth gear (minus losses).

So how does the dyno *know* how to factor out such things as gearing (trans & diff) and wheel/tire size? It does that by a ratio of drum speed to known engine speed. They're measuring your rpm, right? And the dyno knows at any instant how fast the drum is turning and that allows them to factor out the mechanical advantage (torque multiplier) due to gearing etc.

Why can you dyno one car with low profile 19's on it and then change them out to say 16's of the same overall rolling circ. and have the hp and tq readings be different? :idea:

All else being equal and the runs back to back with only the rim/tire change. And then switch back to see the same results the other way.

And who can tell me which will give the better readings?

Why can you dyno one car with low profile 19's on it and then change them out to say 16's of the same overall rolling circ. and have the hp and tq readings be different? :idea:

All else being equal and the runs back to back with only the rim/tire change. And then switch back to see the same results the other way.

And who can tell me which will give the better readings?

The readings should be the same. Tire size should have no affect. On the other hand, chassis dynos do not give repeatable results. Figure an error of +- 7%. That's probably what you're seeing.

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