Dyno sheet questions

[20v_rollaboy]

Had my car on the dyno at Torque Performance today.



Engine is a standard silver top. Only mods are exhaust and filter.

Can anyone tell me what would cause the power to dip down between 6800 and 7200??

Heres a video of it aswell
http://www.youtube.com/v/yocaM1daZtE

[avinesh]

maybe its ur vvt, an it mite be comin on at the wrong time but i dont know a lot about levins....

[Akane]

You went rich at that point.

PS: Cute video.

[flygt4]

pretty respectable for a silvertop really.

[strx7]

i still dont know why they dont print the TRUE torque readings. to work out what that HP is you need the torque so why not print it????????????

[atmosports]

They don't give a TRUE torque reading as they can't becuase it would only be a calculation from what they are reading at the wheels plus any driveline losses(TCF Transmission Correction Factor) & divided by the gear ratio(Gear ratio & Final drive ratio dependent). If you want a true flywheel torque reading you need to couple directly to the flywheel.

In saying that if you have the correct TCF you should end up with a very similar plot to that off an engine dyno with regards to shape & figures, probably more so on a Dynapack where you remove the variable of tyres. Seen this proven time & time again with V8 tourers & mini's that've been dyno'd on Superflows, bolt them onto a Dynapack run the same ype or run over the same length of time & with the correct TCF the graphs basically match within 1hp the whole way & you can pretty much overlay them the Dynapack one & the Superlow one with no difference.

[Akane]

It's what's at the treads that counts anyway.

[RomanV]

The horsepower is calculated not by engine RPM, or wheel RPM, or anything to do with the car....

It's the RPM of the rollers, and the amount of torque applied to the rollers that they print out... It's the only real way to do it. For example, you could go for a sprint on the rollers, and see what sort of HP you put out... (less than one, unless you're really harcore though!)

[Adamal]

They don't put true torque readings for 20v's because if you found out what they were, you'd cry.

[strx7]

The horsepower is calculated not by engine RPM, or wheel RPM, or anything to do with the car....

It's the RPM of the rollers, and the amount of torque applied to the rollers that they print out... It's the only real way to do it. For example, you could go for a sprint on the rollers, and see what sort of HP you put out... (less than one, unless you're really harcore though!)

They know what RPM the engine is doing, that have a POWER figure be it KW or HP for that given engine RPM therefore a Torque curve can be printed.

afterall
HP = (rpm x torque (lbft)) / 5252

[fivebob]

They know what RPM the engine is doing, that have a POWER figure be it KW or HP for that given engine RPM therefore a Torque curve can be printed.

afterall
HP = (rpm x torque (lbft)) / 5252

All well and good if they know the engine rpm, but from RomanV's post, and looking at their graphs (which are wheel speed based), it appears they only know the roller rpm, and use that to calculate HP.

[strx7]

the readings along the top of the graph look like engine RPM to me........

[fivebob]

the readings along the top of the graph look like engine RPM to me........

Doh, should look next time All the other TP graphs I've seen are wheel speed.

In that case there is no reason why torque shouldn't be recorded as "Engine" torque, even though it measured at the wheels and would include any drivetrain losses.

Certainly would make it a lot easier to comparee to other dyno graphs.

[AceSniper]

drop in power isnt todo with VVT been still on is it? as silvertop ecu turns off vvt at redline, but most aftermarket tunes find a sweet spot to turn it off around 6-6500rpm?

[RomanV]

the readings along the top of the graph look like engine RPM to me........

They dont give engine rpm 'torque' figures, because they wouldnt be accurate. Why not? Because the engine RPM is a guesstimate.

They dont calculate wheel RPM, final drive ratio, gear ratio etc, they just base it on what your tacho says you are doing, at certain roller speeds.

The 'roller' torque figure is an indisputable measured figure, the 'engine' rpms torque would be a bit wishy washy, seeing as its based on the roller torque, and a guesstimate of sorts.
Unless they got info directly from your dizzy or coilpacks or something, they're not going to get an accurate engine RPM scale, which is why they're sometimes left off. (my dyno plot didnt have an RPM scale, as my tacho wasnt working)

[RomanV]

Also, BTW. I emailed Robin at TP a while back regarding this topic:

Hi Robin,
I have a few questions regarding your dyno setup.
I'm trying to make some sense of my dyno plot, but I'm not sure how to
work the numbers back into something that makes sense to me.
How do you actually work out the HP rating, when you dont know the
wheel speed, or engine RPM?
Seeing as how the HP formula is:
HP = torque x rpm / 5252,
I cant say I know how you work out how much HP a car is making,
without knowing the rotational speed of either the wheels or engine RPM.

I know how to work the road speed back to engine RPM, so it doesnt
matter too much, but your initial numbers dont seem to make sense to me.
If you were to use the rotational speed of the wheels, you'd have to
know the rolling circumference, if you were to use engine RPM, you'd
obviously need to know what RPM the engine is doing.

the only other way I can think of that you could do it, is that you
use the RPM of the rollers, which have a fixed circumference which you
know, and use it in the formula with the torque applied to the rollers too.
This makes sense, but I cant help but wonder how it would differ, if
compared to using the engine RPM, and dividing the wheel torque
figures by the reduction ratio of the wheel size and gearbox/final drive ratios?

Thanks for your time.
Regards,
David

Hi Dave
In simple terms ALL chassis dynos must use the rpm of the roller x Torque applied to the load cell ,plus rotational inertia to make HP.

The torque numbers will differ with different dia roller ,but conversly the rpm will drop as well equalling the same power.

On the dyno plot you have from us it will show "wheel torque and wheel power"
The torque could technically be called tractive effort.
The shape however is correct.
Hope this helps
Robin

[strx7]

so in other words the dyno graph is a load of crap too................

Due to how HP is calculated you either have to say A) the power curve and torque curve are accurate, or B) they are of no use what so ever

ya cant say that is the power, but we dont know the torque.

[RomanV]

They know the RPM of the rollers... They also know the torque applied to the rollers at the given RPM. So why cant they can know amount of torque and HP applied?
It's not a load of crap.

Unless I dont understand what you're trying to say, which is possible...

They substitute roller rpm for road speed as the scale down the bottom.

[postfach]

so in other words the dyno graph is a load of crap too................

Due to how HP is calculated you either have to say A) the power curve and torque curve are accurate, or B) they are of no use what so ever

ya cant say that is the power, but we dont know the torque.

I think what dave is saying is that the both the power AND torque are accurate at the wheels but the torque isn't "true" because its not calculated using engine rpm. The only way to get a "true" torque reading would be to take an rpm signal from the coil or use an engine dyno.

[strx7]

a torque curve is just as important as the HP curve, and its from gains in the torque curve that you gain HP, weather that be by shifting the RPM of the torque or by increasing the torque at that RPM.

Basically what I'm saying is, that kinda dyno sheet is only usefull if you want to compare 1 vehicle to another, or if you want to compare HP before and after. For anything else its not really much use.