off to the dyno today

Post by **Merlin** » Thu Dec 19, 2013 8:56 am

spudep91 wrote:Yea foot to the floor I think.

That is what I thought. It seems the quicker the dyno goes through the revs the lower figure the dyno records. It is the same reason why you would get a higher figure doing a run in 4th compared to 3rd.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Dec 19, 2013 10:36 am

Interesting...

If they don't accelerate it that way though, you don't get the true max horsepower and torque throughout the rev range though, surely?

Post by **Merlin** » Thu Dec 19, 2013 11:01 am

It's all in the way the dyno interprets the power.

It was explained to me like this. If you have a car idling out of gear and rev it to the red line as fast as you can it will take a second or so to get there. In that second all of the engines power is being used to spin up the internals. If you put the car into 4th and floor it it may take 10 seconds to get to the red line. During that time the available power will be used to spin the wheels and spin up the engine. If you do the same in 3rd gear you will hit the rev limiter faster that what you would in 4th, which means more of the engines power is being used to spin up the internals of the engine rather than making its way to the wheels.

For this reason a car with a longer final drive will always produce more power at the wheels than an identical car with a shorter final drive.

So on a dyno where its is being revved up fast, more power is being used to spin up the engine rather than the wheels and so the dyno reads less power at the wheels. This problem is exacerbated when VTEC kicks in as we all know that the engine produces more power and revs increase faster in VTEC. Hence why the dyno is not reading power correctly in the upper revs.

Dyno dynamics dyno (fast accelerating)
[youtube]gmjMZ1e82_c[/youtube]

Maha dyno (slow accelerating)
[youtube]BLtHsJoPzNM[/youtube]

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Dec 19, 2013 11:34 am

So is that more to do with the resistance that the rolling road gives (to prevent the car spinning up too quickly) rather than to do with the operator having his foot on the floor or not?
I understand what you say about why one method would read differently to another, I'm just a bit lost here what you're saying the cause of the difference is...

Post by **Merlin** » Thu Dec 19, 2013 11:57 am

No idea dude. It is either the dyno putting more up more resistance or the operator controlling the rate of acceleration. I dont know enough about the mechanical differences between the dyno's and how they calculate whp back to the flywheel.

But the theory is the same, slower rate of acceleration = a higher whp read by the dyno.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Dec 19, 2013 12:15 pm

Ok...
I've just looked at a couple of videos I have from the national dyno day.

I have one looking into the cabin during Mario's run, so you can see the dials and what the tester is up to. Mario also has lights in his footwells, which is very handy

I have another video of my porka, filmed from the front. The throttle butterfly on the porka is right on the top of the engine, so you can see exactly what it's doing.

On both of those, the tester runs the car up through the gears into fourth (not to high speed, but rather than just sticking it into fourth and going from standstill). He then applies the throttle progressively rather than stamping on it, but basically it is fully open for the whole run. It spins up more slowly and progressively than the dyno dynamics runs though, so I guess it must be higher resistance then? The dyno prints from that day all seem look as expected, so that method must be right. It was on a Maha.

I can't upload them atm because the files are way too big, but I could e-mail them to you if you want to watch them Merlin? pm me your e-mail address if you do.

Post by **Merlin** » Thu Dec 19, 2013 1:44 pm

It's cool. So it must just be the resistance the dyno puts up. A larger resistive force from the dyno means the wheels are resisting the engine more. Just like going to a higher gear. Makes sense.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Dec 19, 2013 1:51 pm

Glad we're getting there!

So in summary, it's as simple as dyno dynamics suck and maha rock!

Post by **Merlin** » Thu Dec 19, 2013 2:00 pm

wurlycorner wrote:dyno dynamics suck

We knew that anyway

Looking back at all the vids of my past dyno's the Dyno Dynamics does rev up the fastest. I have had my cars on a Maha, Dastek, and Dyno Dynamics dyno's. I think the Maha is the most accurate, my H22a8 5th gen got 196 bhp on the Maha I was on. The same car on the Dastek got 203 bhp.

89 UKDM BA4 4WS (resto job!) · Post by **wurlycorner** » Thu Dec 19, 2013 3:18 pm

Maha FTW!