Power Now???? dyno

[steve125]

Ok I'm not slaming this product as it may help the 4strokes and response in some 2strokes. The dyno usually shows the smallest changes we make. To be honest I couldn't tell a difference in performance even before I saw this chart. Run 4 power now in, run 6 is with it out. Pete runs the dyno and he thought the PN was holding the engine back on top end,  that shows but it's ever so slight. There appears to be a tiny gain between 3k and 7k i'm not impressed :silly:  The bike is an 03cr139 with a 370 main jet. Ok maybe i'm slaming it just a bit :debil:

 

[Rich Rohrich]

Originally posted by steve125
Ok maybe i'm slaming it just a bit

:laugh: :) :laugh:

 

[Rider 007]

Okay, I'm confused again, but that isn't unusual.
I thought the Power Now essentially made the carb function like a 2-barrel. It supposedly gives good response due to the reduction in turbulence and increase in velocity of the intake stream at partial throttle conditions, perhaps 1/2 open or less.
I also thought that dyno runs were done at WOT with the egine RPM varied by varying the load.
My question is this: if these are true, how would this show up on the dyno? I would think the only thing that would be apparent on the dyno might be a slight loss in peak HP due to the small obstruction the Power Now creates at WOT.
If these aren't true, that explains why I'm confused!
I could understand some partial throttle testing on the dyno to see if the device affects performance under that condition, but I'm lost as to the other.
Thanks in advance for the input!

 

[fishhead]

007,

you have raised some interesting questions. Some modifications such as light or heavy flywheels don't show much on the currently popular inertia dynos nor do dyno results guarantee salient results in the real world. The prevailing party line that if it doesn't show a number on the dyno it's worthless may be myopic. The dyno is one tool in the box but it does not take the place of field testing and tuning. 

The increase at 3k-7k is interesting. I wonder what a smaller carb would show.

 

[MikeS]

I think some good fuel produces just as much power and the seat of the pants feel some people talk about.

The PN may indeed help some configureations with flow especially porting specs that may produce weak signals at certain RPM ranges.

 

[turboandy]

I think if you want to put numbers on the power now type plate it should be done by measuring the signal strenth at the dump tube at diferent throttle positions. I have one in my 01 kx250 and my sons 02 rm125. I made them myself, they are .020" stainless and .060" from the slide. There was a difenence in responce and I did need to lean up the pilot. By the necessity of leaning the pilot that tells me I increased the signal strenth at the dump tube. I believe the dyno but as pointed out a lighter flywheel would not show much on the dyno but the throttle responce would be evident.

 

[steve125]

Everyone, a dyno will not show response thats true and on some bikes the PN may help and may not. I felt nothing in my track tests, but some 4stroke guys swear by them. Mainly a better low end roll on feel.  The dyno is a "roll" on of the throttle from around 3-4k to peak rpm is the only time it's WFO. A flywheel itself does not make power one way or another, it only effects it's deliverly, so that won't show on the charts. There's no way the PN turns your carb into a 2 barrel. Mainly because after the slide there has been no change in it's bore size. It's just supposed to straighten the air flow into the slide area of the carb bell.

 

[fishhead]

Steve

Agreed the dyno is a poor measure of response and some modifications such as light and heavy flywheels, for example, affect response and the results are not shown on a dyno but are quite apparent to the rider.

I presume the bike was jetted up good without the PN and I'm curious if you rejetted after the PN installation. Its interesting that a lot of anecdotal evidence tends to support the statement that the PN holds the engine back on top but its not apparent on the chart. Makes me wonder about jetting and carb size or if the PN doesn't restrct flow by a measureable amount.

 

 

[steve125]

Fishhead when I worked with the PN at the track I tried a few different jetting settings. But always went back to my previous settings and that worked fine with or without the PN. So when I dynoed it, the jetting stayed the same on both runs. To be really effective I feel this divider may work best on the carb bore side, but then i'm sure there will be some problems with fuel delivery.

 

[Rider 007]

Permit me to demonstrate some more ignorance. :)
Being a layman, it appears to me that the difference between the two curves could fall in the range of experimental error. Just how repeatable are the numbers if you were to take the engine and do 10 consecutive runs? Would they all be exactly the same, and if so, to how many decimal places would it be considered the same? If not, what is the normal or expected variation between them?
I ask because, obviously, I have never run a dyno and think this would be an answer born out of experience with one.
Not knowing how sensitive or accurate the dyno and its measuring equipment are, would it be more accurate to run, say 10 or more runs with each set up to achieve an average curve, the only variable being the PN, or is it not necessary?
This is interesting and informative, thanks guys.

 

[steve125]

 With the PN installed and removed the engine was run 4 times each and then best run for each was selected. Of course the engine is run even more times previous to the actual runs to ensure proper pipe and engine temps. Sometimes we may go 5 runs on a change, but only if the dyno curve is still changing from the previous one. From what ive experienced so far, the dyno is very sensitive to any changes we make if it affects performance. As it turns out in this case, the PN just doesn't make a noticeable difference. As long as it's on the same day the numbers are very repeatable.

 

[crmx91]

So basically you just saved me 100 bucks steve. i was thinking about buying a power now for my 03 cr125 but your dyno run changed my mind. what i wonder about is how magazines claim a 1.5 HP increase with the PN. BTW any tips for getting more umph out of my 03 cr125? all i have right now is a Pro circuit shorty.
thanks for the information on the power now

 

[steve125]

Well since you already have the PC shorty. Then your next step is the PC pipe. It adds a bit of top end power without hurting bottom. It makes the bike feel real crisp. Stay away from the V-force reed valve. It only makes the bike harder to ride and adds no power. The stock reed valve is real good for 03, unlike the 02 that needed the V-force. Also 1 tooth up on the rear sprocket may help some riders.  Get your forks revalved as the shock is ok, you won't believe how good the CR handles when the forks work right, stock their just toooooo harsh!.....  :cool:

 

[crmx91]

awesome that helps a ton .. so a pro circuit works pipe is next.. stay away from the vforce..

i have both my forks and shocks done by JM Racing suspension( i only weight 125lbs) so that was the first thing for my bike.

 

[crmx91]

Hey steve. do you have a AIM screen name or something. i have a ton of questions about my bike and you seem to be the guru on them.
nearly 38 horses in a 03 cr125 is awesome

do you think a pro circuit ignition would be worth it?

 

[steve125]

Thats a cr139 big bore not a 125. PM me if you wish.

 

[nephron]

I agree that the main effects of PN could not be seen on the dyno. The dyno misses a whole hell of a lot,...how fast a motor spools up under a lighter load, throttle response, etc.

Did you remember to change the needle position and main? :p

 

[steve125]

For the money, I think next time I'll go with a fancy sticker kit and seat cover. At least then, I'll get some kind of added response.  :silly:

 

[Pete Payne]

Steve, I'm with ya bud. Ilove what you do. BRRAAAAPPPP!!!!
Maybe next time we will have to do some all gear tests and some fast acceleration tests on the Dyno and help put some critics to rest.
But, first let me say this, Steve --- you are the human dyno test machine and the fastest pipe and jet changer in the USA. Rock on !!!!

 

[marcusgunby]

I would be fast at changing pipes if i had as many as steve;)

 

[SpectraSVT]

I thought the PN was only for low end response which in turn allowed you to run a higher gear than necessary. I don't recall it being a power adder, just a power aider. It helps the engine breathe better at low rpm's. That was my understanding of the power now.

 

[Rich Rohrich]

Originally posted by SpectraSVT
It helps the engine breathe better at low rpm's

If you think about it logically there is no way it could accomplish that.

All it can do is change the strength of the signal that the jet circuits will see. Venturi boosters (which is all this ultimately is) are nothing new. Ask anyone over 30 who has spent more than 15 minutes in drag racing and they can tell you all about them.

 

[motometal]

Didn't some of the old XRs have two smaller carbs in a progressive setup?  If this was so great of an idea, why aren't the new XRs like that?

 

[nephron]

Funny thing is, the first time I looked at a bike carb, I wondered why there was no venturi booster. Anyone ever tried to put a conventional venturi booster in a dirtbike carb, ie complete with fuel passages through the supports as in a standard Carb?

And yeah, they're pretty damn necessary for any kind of fuel atomization in a V8 with a big ass cam. ;) Maybe they'll experiment with them in the 4 strokes some day when valve timing design becomes more aggressive for upper rpm. Maybe they'll just throw in the towel in lieu of FI.

 

[Swiss]

Quote: "Funny thing is, the first time I looked at a bike carb, I wondered why there was no venturi booster. Anyone ever tried to put a conventional venturi booster in a dirtbike carb, ie complete with fuel passages through the supports as in a standard Carb?
And yeah, they're pretty damn necessary for any kind of fuel atomization in a V8 with a big ass cam. Maybe they'll experiment with them in the 4 strokes some day when valve timing design becomes more aggressive for upper rpm. Maybe they'll just throw in the towel in lieu of FI."

I THINK that I have seen a version of a Harley carb that used a booster. Actually, in a car carb this isn't much aditional weight and as you said, it is pretty much a necessary complexity for good performance. With MOST bikes they can get by with lighter and CHEAPER non-booster designs. With the FI units, they are learning that smoothness is imoproved with the newer design dual butterfly systems. This is where your throttle cable controls one butterfly and the computer controls the other. The second unit is dependent on speed, rpms and various other data inputs from sensors on the bike. Back in the early '60s Honda had a CV carb on one of its small roadbikes that used a vacuum/diaphram controlled slide with a finger lever on top that controlled how far it opened and gave a positive control over closing. It seamed to be a neat system, but was replaced by butterfly and all vacuum units. Sorry to get off the topic a bit.

Swiss