Torque & Power Differences Between Cars

[Craig.]

Firstly, let me say that I am not a mechanic.

Just someone who doesnt know everything and doesn't mind asking even if it may make me look a little silly.

I have been pondering this for a while now though.

Do power and torque have any relationship with each other and what sort of effects do each have on how fast a car is compared to another?

I see dyno sheets put up here on a regular basis in the 300 club or the 400club, etc, with RWKW and NM figures, but the two vary from car to car, even though mods might be the same or very similar.

By that what I mean is I have seen cars with 320RWKW and 920NM, another car with similar mods make 315RWKW ( ballpark with the first car) but only 680NM.

Jump up in power a bit and you see the same thing. Cars making 360RWKW seem to have torque readings anywhere from 700NM to over 1000NM of torque.

So what gives? Which one is faster? Would the 320RWKW car with 900NM of torque beat a 365RWKW/700NM car?

Should we really be comparing cars based on their torque figures rather than max KW? I mean a 320RWKW car with 900NM of torque on board has to feel a fair bit different to drive when compared to a 315RWKW 680NM car doesnt it?

Maybe we need to redefine our 300 and 400 clubs to 700NM, 850NM and 1000+NM clubs?

Why is there no apparent relationship between the power and torque increasing in a linear fashion?

Your thoughts?

[dule]

I think there is a direct relationship. Torque +/*-something +-*/ rpm = power.

[Craig.]

How does this explain why a car running 40RWKW more than another can be running 200NM less?

With my examples above there are discepancies between which makes the most power and torque! These are real examples, not just made up in my head.

Edited 21/05/08 11:09 PM by Dagabond

[senna_T]

Its pretty hard to get an accurate reading on torque with a dyno Craig. The reason they fluctuate so much is due to the multiplying effect a cars gearing has. Most dyno's are set-up to calculate a torque figure by using a particular ratio, if the car running on the dyno doesn't match this ratio, then the torque output will vary greatly

As a general rule, a torqueier car will be quicker on the street and a more powerful top end vehicle will be quicker in a race situation. There are many defining factors to this though...

[Craig.]

  senna_T said:

Its pretty hard to get an accurate reading on torque with a dyno Craig. The reason they fluctuate so much is due to the multiplying effect a cars gearing has.

I understand this. I know that I can change rear sprockets on my road bike to multiply the torque effect and then show a difference both by the seat of the pants and a dyno on torque readings only.

But looking at all of our cars as a population sample ( statistically) they are all very similar gearing wise, well the majority anyway. Not too many threads on modding diff gears or group buys for guys wanting 4.11 diff gears!

All of our tuners would use 4th gear too. So is there really that great a variance from one vehicle to another?

Each brand of dyno can read different too, I understand, and even the same brand and make of dyno can read high or low from one to another. I dont think that this explains why one 350RWKW car man make 300NM more or less than another 350RWKW car though.

Edited 21/05/08 01:42 PM by craiginmackay

[senna_T]

hmm, I understand this too craig, I spose it comes back to every dyno is different.

There are plenty of ways to tune the cars too, you can make a car more torquey by bringing the boost on earlier, or bring it on more gradually and get the peak top end power. This, the turbo mods would define this though.

I spose my car is an example with the stock actuator I run 15psi peak, then fall off to 13psi. This creates an awesome midrange punch, but doesn't pull as hard toward the top end of the rev range. So lets say I make 340rwkw at 5000rpm, and I make 700Nm at 3500rpm. If my boost stayed constant throughout the rev range, I may be able to make 340 - 360 at 5500rpm, but because the boost doesn't come on as strong down low, I may only make 600Nm at 3500rpm.

This is my loose understanding of how our turbos work, but maybe one of the sponsors can give us some definate answers...

[Craig.]

  senna_T said:

This is my loose understanding of how our turbos work, but maybe one of the sponsors can give us some definate answers...

that's what I am hoping for Pat!

My ute was dynoed at 320RWKW with over 900NM of torque. Standard turbo with mods to injectors, exhaust and an intercooler.

Yet I see guys well into the 350+RWKW region with 200NM less torque on board. I just want to understand why. Similar mods. Only difference I can come up with is a different tuner. But there must only be so much a tuner can do within the parameters of the parts fitted to the car, like the stock turbo that you mentioned.

Maybe I am overthinking it.

Maybe I just don't understand it enough to comprehend it.

Either way it has been bugging me!

Edited 21/05/08 02:07 PM by craiginmackay

[BWST_XR6T]

as far as I understand the relationship between power and torque (still got my years 12 physics from just a few years ago in my head), the power figure is proportional to torque and rpm.

Found this formula:

Power (kW) = torque (Nm) x 2 pi x rotational speed (rpm)

-------------------------------------------------

60000

60,000 comes from 60 seconds per minute times 1000 watts per kilowatt.

where I think some of these differences in torque figures come about is in the tune. I've seen a tune where full boost of say 20 psi was dialled in at about 2800rpm or where ever it was, but it was then gradually tapered off to 15 or 16psi limiter.

the 20 psi resulted in approx 1017Nm and 400KW at bout 2800rpm, but the 15 psi tapered to at cut off resulted in about 750nm and 423KW at cut off. Was an XR6T in Perth Street Car, can't remember which issue.

Theoretically, if you also had a car that made a flat 15 psi over the whole boost range and using similar mods and conditions, it would make similar peak power but only have a peak torque of about 750Nm, which would remain for the rest of the boost range.

Other contributors to this but on a smaller level are piping length and diameter. Generally, short length and big diameter piping allows for huge volumes of air to flow resulting in bigger torque numbers higher in the rpm, which equals greater peak power; and longer smaller diameter piping promotes higher air flow velocities which is great for bumping up midrange torque when the volume of air isn't as great, but can restrict the volume at high rpm, resulting in lower peak torque, lower peak power.

Its not everything but these are some of what I reckon are contributors to similar power figures and completely different torque figures.

Bloody hell, its only my first post. HEAVY!!

Anyway hope that helps and I don't get shot down with the very next post.

[JP300]

  senna_T said:

Its pretty hard to get an accurate reading on torque with a dyno Craig. The reason they fluctuate so much is due to the multiplying effect a cars gearing has. Most dyno's are set-up to calculate a torque figure by using a particular ratio, if the car running on the dyno doesn't match this ratio, then the torque output will vary greatly

As a general rule, a torqueier car will be quicker on the street and a more powerful top end vehicle will be quicker in a race situation. There are many defining factors to this though...

This should be an interesting thread ...

Cmon Pat, do you want to have a rethink on this post? Sorry mate, I have to raise a few questions on this one.

Guys, I am no expert in the matter and can someone please clear this one up....

Why can't a dyno read real torque? ... I guess it depends on the dyno. Hint: Maybe "tractive effort" vs "torque at right angles to an axle" might have something to do with this. (I'm not going any further with this one!!).

Torque readings "fluctuate so much due to the multiplying effect a cars gearing has" ... Yes, torque readings on a dyno will vary with gearing but I beleive that there are correction factors to nulify the gearing so as to show the torque at the flywheel. So this should even it out for different cars.

I think that "particular ratio" you are referring to is the actual gear ratio correction from the flywheel to the axles. This is a constant ratio for a specific type of car.

and for the "a torqueier car will be quicker on the street and a more powerful top end vehicle will be quicker in a race situation" statement... You've really let it all hang out there and hear what you are saying... I agree that there are many defining factors that determine how quick a car is on the street and on the track. I think that with the high powered cars the most important factor is how much power & torque you can actually get to the ground !!

As for BWST_XR6T's post ... It's too early for me to think that one through.

Edited 21/05/08 08:36 PM by JP300

[senna_T]

Hey John, its a forum mate, raise as many questions as you want!

The "Correction Factor" is what I was trying to get at in regards to "the particular ratio". Yes that factor can be changed, but what happens if the dyno operator doesn't change that correction factor? They may have run a vehicle previously with a 3.23 diff gear and had the correction right for that, then they have run up a T with a 3.73 diff gear and not corrected. Automatically there is a big change in diff ratio, not to mention the gear ratios as well. The graph is still going to show where the car makes its torque, but it may be 200Nm higher or lower than what it should be.

Thoughts....