And I didn't really see an obvious section for this one... so hopefully this one is ok.

 

Probably because of the gear ratio. after a 1:1 ratio the numbers change. Thats why people always dyno in 3rd or 4th depending on trans.

 

Interesting i always thought they put it in the highest gear possible and do it. But third or fourth make sense. I would like to know more about this, i have never dynoed a car let alone been around one being dynoed. So how it is done and how it makes sense would be good and new information to me.

I guess i could always google it too lol

 

Why does your engine make more power as the load increases?

Thanks in advance,
Will

Because engines are not perfect. They are optimized for a certain RPM. They make more torque and power at higher RPM's because they are more efficient at higher RPM's. There is however a point where an engine will make less torque and horsepower, this just goes back to the point that engines are optimized and designed for a certain RPM or RPM range.

The peak efficiency is at the point where the engine makes peak torque. If you look at a torque curve of an engine, that is what the efficiency curve would look like. Torque is a more direct measure of how much get up and go an engine has. Horsepower is calculated using torque and RPM so they are related, but not quite the same.

Load is very similar to torque. If you had a curve of maximum load through the whole RPM range then you would see that it would look just like the torque curve and efficiency curve. Load is the measure of how much air is going into the engine. The more air you have going into the engine, the greater the potential for more power. This is because if you have more air, then you need more fuel to match that amount of air and this gives you more power.


(I'll add more to this in awhile) Gotta go to work.

 

...They make more torque and power at higher RPM's because they are more efficient at higher RPM's. There is however a point where an engine will make less torque and horsepower, this just goes back to the point that engines are optimized and designed for a certain RPM or RPM range...

The above dyno graph is not a good example of relating torque to HP because it doesn't used RPM on the y-axis. Horsepower by definition is torque (in foot pounds) times RPMs divided by 5252.

HP = torque · RPMs / 5252

So an engine HAS to make more torque than HP below 5252, the same at 5252, and more HP than torque above 5252.

A quick check on dynos graphs is to see if torque equals HP at 5252. If not the numbers have been monkeyed with.

 

Transfer rate of the power front engine through the trans and to the wheels. Higher gears mearly have less loss of the made torque so the mapping of the ECU runs leaner or richer as it needs. Lower gears have too much fluctuation to have a solid reading so getting into a higher gear with as much of the momentum of the rotating assembly and rotational mass to be stable and consistant.

Next time you are cruising along try being in two different gears and see wether the amount you are adjusting the throtle with your foot is more or less consistant in both the gears.

It's just physics.

 

This should help a bit too.

Another name for a Transmission, is a Torque Multiplier.
1st gear multiplies the torque by a much larger amount than 3rd gear.
And, as we all know, HP is a calculation based on Torque&RPM.
This is also why a dyno shows higher torque, and lower HP when you pull in 2nd vs 4th.
Remember, the Dyno doesn't really know anything about your trans, other than perhaps your final drive ratio (dyno dependent).

I think this explains what you are seeing.
You assume that more load equates to more power.
When in fact what is happening is that the higher gear (4th or 5th) is being used to reduce the "torque multiplying" of your trans. As was stated, 4th or 5th are more likely to be closer to 1:1 gear ratios. So, the higher gear, the torque goes down, but the HP goes up.

 

Based on the graph, I'm seeing torque increase as well as power though.

I got that the dyno won't know your gear ratios, but I would also expect the power curves to be the same shape (maybe it's because 3rd and 4th are longer, only going from about 4k to 7k, so they're like a zoomed in version of 1st). Not to mention the boost is completely different per gear.

Can the leanness/richness result in that much difference?

 

Or maybe it has more time to spool in the higher gears?

 

are you sure the engine was at WOT in all gears for that graph?

 

Just read this on another site and it makes sense.

"More torque multiplication = more friction = less horsepower."

So that means for the lower gears (which have more torque multiplication) they will have horsepower loss due to friction.

 

^ :wtf:

as was said HP = torque · RPMs / 5252, or, more basically power=torque*speed. additionally, as skidd said a transmission is a torque multiplier, more specifically the conservation of energy says power in = power out (minus a few % of friction/viscous/heat/noise loss). your input speeds and torques from the engine are teh same over teh same rpm band, depending on throttle. load affects the resulting acceleration. what changes between gears is that the output speed increases. thus, given power out = power in, you have less effective torque for driving the wheels than you would in lower gears (why your car's acceleration is higher in lower gears ..combined with increased wind resistance).

thats all fact, but still doesnt explain whats going on in that chart. i suspect the rest of the answer lies in throttle position and just general how dynos work. my intuition is that dynos have to correct for this and likely have a gear ratio input or something comparable such that if in WOT in any gear the INPUT torque/power (which is what we want to measure, not taking into account gearing, which would skew all results between all cars) as measure at the output, should be the same. this seems to be validated by the fact that the last two gears are very close. but as i said i really dont know how dynos work. anyone who runs one cna answer your question.
edit: i would guess their back-calculation of engine power/torque is based on knowing the given ground speed... fuck, interesting question, but i really cant put more time into thinking abotu this :lol: back to work

 

Wow that graph is a terrible example of what you are asking. Look at the boost in different gears. It raises for every gear. So it makes more power which is pretty easy to understand.

Like already said you get a better actual number based on 1:1 of the dyno since that how it was calibrated.

 

so dyno charts always just use the gear closest to 1:1 and results are what they are? that seems comical given theyre rarely going to be exactly 1:1... 1.1:1 is gonna look better than 0.9:1 all day long.... (?)

 

So basically what you're saying is that the people making this graph were not going WOT in each gear, if they were we'd see probably more than 3x the torque/hp in 1st as in 4th (I think it's a 3.6:1 ratio or around there). Boost characteristics should be the same per gear, and I've pretty much just misused the term "engine load" to describe the resistance caused by the longer gears.

 

^ Most power-pull dyno runs are like that.
They move up through the gears until into high gear, let the RPMs fall to a starting value.. and then go WOT for the full run.

 

Gotcha. Haha now this thread seems pretty worthless.

Thanks for the info.

 

learn somethin new every day, thanks.

now seems even more comical for people to whip out dyno charts for e-penis battles on the internet.

 

Don't they normally do some sort of adjustment? What's that all about?

 

As you move timing you can see the power come up with every degree of timing. Once you reach a maximum you have generally several degrees of timing where you make no more power. Then the motor will start to knock with more timing after that point.

This is the usefulness of dynos. Trying to tune with egt or how it feels will not get you perfect data like a dyno. After you figure out the max useful timing I generally dial the timing back a few degrees for safety. Might make a little less power but the engine can run a little off and not push over to the knock side.