what is a powernow?

[yellow400ex05]

what is a powernow?

[ZSNOW]

its a "fin" in the carb that reduces turbulence ,inturn making alot more power for what it is.

Zack

[Toadz400]

Otherwise known as the choke plate like in 400EX carbs that people usually take out. Don't waste your money.

[ZSNOW]

its the oppisite of a chock plug...

[ZSNOW]

*choke

[bwamos]

Not really. It does exactly the same thing the choke plate does in it's open position.

It increases air flow speed at 1/4 - 1/2 idle giving you better bottom end response. The deluxe version even has the little "flap" that allows an air surge to come from the upper half, just like the stock choke plate does. ;)

It's not a gimick. But, not necessary for mose ATV carbs. It works well on carbs that don't have a choke to improve bottom end response. It will reduce top end slightly, as anythign that inhibits air flow will. But, it's got it's place. Just redundant on most ATV carbs.

Granted their claims are a bit gimmicky. ;)

[ZSNOW]

sorry i was thinkin about the choke plug sorry, yes a choke plate would do the same thing, but the thing about the power nows is you can put them on both ends of the carb instead of only on one (for450s)

[bwamos]

What good would one on the engine side do? I would think it would just be a condensation spot for fuel (hampering atomization).

[Eviltanker]

^^^ I believe your right^^^
I don't think the second one would do anything but suck money out of your wallet.
Boyesen sells something like the power now for the choke side, it's called a powerwing. Part # PW17

[ZSNOW]

i have no idea what they do on the engine side, all i know is they have it lol

[GPracer2500]

The idea behind the engine side version is the same as the filter side version: better controlled, higher velocity flow. It's the same principle that makes "velocity" intake porting work (see pics below); the same principle that behind stepped headers; the same principle behind smaller carb = more torque (in many cases). The velocity at which you move air into and out of the engine is really important. Sometimes smaller passages can move more air because of higher velocities.

That said, I'm I don't think I'd use the Powernow devices for my application. For the most part, they're only effective at partial throttle openings (according to the testing I've seen) and can actually harm WOT performance. I'd rather keep all my WOT performance and just twist the throttle a little more from 1/2 throttle. What I mean is: if the device(s) gain you 2hp at 1/2 thottle that's great, but I'd rather just dial in that extra 2 hp by opening the throttle a little more and retain my WOT performance. If 0 to ~1/2 throttle performance and response is your goal then the PowerNow devices are probably worth a look (kinda pricey though).

Here's what Yamaha did to the 06+ YFZ450 head.
http://i34.photobucket.com/albums/d133/gpracer2500/42.jpg

Honda did the same thing with the 05+ CRF250R head. It's all about velocity, which is what the PowerNow devices are about.
http://i34.photobucket.com/albums/d133/gpracer2500/0405CRF250R.jpg



BTW, the purpose of the spring loaded flapper on a choke plate is to allow pressure release in the event of a backfire when the choke is activated.

[speedjunkie13]

So is removing the choke plate on a 400ex a good or bad thing? would i leave it in if i want to keep a good crisp partial throttle response, and take it out if i want to maximize my high end(WOT) power?

[GPracer2500]

Originally posted by speedjunkie13
So is removing the choke plate on a 400ex a good or bad thing? would i leave it in if i want to keep a good crisp partial throttle response, and take it out if i want to maximize my high end(WOT) power?

I don't thing it's really fair to compare a 400EX carb's choke plate to the PowerNow. They are different shapes and not intended to do the same thing. There are some similarities--so I can see why your making the connection--but they are different enough that I wouldn't draw any conclusions about one from the other.

I removed the choke from my 400EX carb and was happy with the results. My testing was far from scientific so I can't offer anything substantial--but I would do it again. Just don't expect a night and day difference or anything.

[speedjunkie13]

Thanks GPracer2500 :)

[bwamos]

Originally posted by GPracer2500
[B]I don't thing it's really fair to compare a 400EX carb's choke plate to the PowerNow. They are different shapes and not intended to do the same thing. There are some similarities--so I can see why your making the connection--but they are different enough that I wouldn't draw any conclusions about one from the other.

I humbly disagree, I feel it is perfectly fair to compare. In the fully open position the choke plate sits in the same position as the "powernow" would.

The 300ex & 400ex choke plate does have a flap for backfire. But it is also punched w/ a hole in the area the powernow is, as well as being dual-hinged allowing vaccume pressure to open it up when needed. It opens foward and backward.

Now one benefit the Powernow would have is a sleeker profile that would not cause as much interuption at full throttle as the choke plate will with it's hinge bar, etc...

Money is better spent elsewhere IMHO.

The concept is sound. The gimmicky part are their power claims (aka. making it more than it is). I can see a small boost at the bottom w/ improved throttle response, but not a 59% increase in power that their "dynocharts" show on their website.

[GPracer2500]

Originally posted by bwamos
I humbly disagree.....
I respect your opinion. Sometimes I'll see threads on the index page and notice you've responded. In some of those cases I may not even open the thread because I'll feel confident someone in there (you) is getting it right and setting people straight. :)

Originally posted by bwamos
...I feel it is perfectly fair to compare. In the fully open position the choke plate sits in the same position as the "powernow" would....
We may just have to disagree here. I don't think there's a meaningful comparison to be made. A big part of the reason I feel this way is the shape of each leading AND trailing edge is significantly different. The choke plate is circular. The the PowerNow has a straight leading edge that fully bisects the carb's opening. The back edge of PowerNow fin is designed to fit closely to the slide so no air can travel above-to-below in that area. The round shape of the choke plate allows air to travel over the plate and over the back edge of it--especially near the venturi walls where there's lots of open space.

I think that difference alone is easily enough to disallow any correlation between what adding or removing one of them would mean about adding or removing the other one. The don't "handle" the airflow in the same way.

Originally posted by bwamos
....The 300ex & 400ex choke plate does have a flap for backfire. But it is also punched w/ a hole in the area the powernow is, as well as being dual-hinged allowing vaccume pressure to open it up when needed. It opens foward and backward.

Now one benefit the Powernow would have is a sleeker profile that would not cause as much interuption at full throttle as the choke plate will with it's hinge bar, etc...
I still maintain that all the features of the choke plate are concerned with the function of the choke only.

Originally posted by bwamos
...Money is better spent elsewhere IMHO.

The concept is sound. The gimmicky part are their power claims (aka. making it more than it is). I can see a small boost at the bottom w/ improved throttle response, but not a 59% increase in power that their "dynocharts" show on their website.
We're certainly on the same page about that part. :)

[chad502ex]

there was a dyno test where i witnessed a simple installation of the powernow, nothing else, and could differentiate a small increase in torque, but no more than 1ft# increase...

in other words, it did something but not much on that test for the money to buy it..

[Eviltanker]

Here is the PW17 By Boyesen

[Eviltanker]

2

[GPracer2500]

Thanks for those pictures.

It's probably worth noting that AFAIK there is no PowerNow application for the 400EX carb. Their device couldn't fit in the carb because of the choke.

I hadn't seen the Boyesen PowerWing for the EX until just now. It seems to me that device would have all the same inadequacies the choke plate has in doing the same thing as the PowerNow OR all the other PowerWings I've seen. Those devices go all the way back to the fit against the slide leaving no space near the slide to draw air from above the wing until the slide clears it.

PowerWing
http://www.mxdeals.com/images/85-0571_lg.jpg

PowerWing
http://www.crfsonly.com/catalog/images/powerwing.jpg

Hell, I don't know--maybe the choke plate does mimic the effect of the PowerNow to a certain degree. But I certainly wouldn't assume that it does--which is why I say I wouldn't draw any conclusions from one about the other. For all I know the air making it's way over the top of an EX choke plate and then downward over the trailing edge causes enough turbulence near the slide opening to negate a significant PowerNow-like benefit.

BTW, if I'm wrong about all this I'd love for someone to convince me otherwise. I believe in the quote in my sig. I like being right as much as the next guy--but I'm more concerned with getting it right than I am about being right.

[Eviltanker]

The Boyesen PW is made to work with or without the choke. It actually sits on the lip of the in side if the carb. The reason you have never seen the Power wing for the 400EX is because I have the first one. Chris at there R&D dept. used my 400EX to make the Proto then gave me the first production piece. Excuse my drawing but, it kind of sits like this. With it in I did have better responce on the bottom end. It did lack at the top though. It did not affect my overall top speed, it just took me a second longer to get there. I think if you are just trail riding and not racing this part will be ok.

[bwamos]

Originally posted by GPracer2500
We may just have to disagree here. I don't think there's a meaningful comparison to be made. A big part of the reason I feel this way is the shape of each leading AND trailing edge is significantly different. The choke plate is circular.............

Dont get me wrong. I do see the advantages and disadvantages of both. The fact that it won't sit right up against the slide dies have some effect. Probably not as much as one might think though.

Obviously neither one of us has done a flow test on the devices, so we're running with speculation.

The holes created by the round choke plate will allow some turbelence but the plate in general helps to prohibit it as opposed to not having one there at all.

The area in the corners may not suck through as much as one may think. With the higher velocities and the vertical face of the slide you're going to get an effect similar to sitting directly behind the cab of a truck (but in reverse since it is suction.) 90% of the air flows through the center 50% of the carb which is seated fairly closely to the slide. The shokes are notched at the bottom to have a small area seated right against the slide. This is where the highest velocities, volume, and the highest chance of turbelence are. If it were simply a choke, and a choke only, whay would they bother making the leading edge seat against the slide?

Now don't get me wrong the powernow is a"specialized" product, so of course it excels at what it does a bit more. The choke is a dual-purpose part, with 1/4 to 1/2 throttle flow being a secondary or teritary function.

The powernow and boysen products are sound engineering. And could potentially benifit a quad w/o a choke. But one with a choke, I wouldn't think it would be worthwhile to remove the choke and add this product. Now it they could make a product to fill in those 2 gaps up front, while keeping the choke mechanisim in tact, then you'd have a winner. ;)

I understand where you are coming from as well. I just don't think it's fair to discount the choke mechanism's completely. Mikuni and Keihin are smart enough companies to captilize on existing devices in order to serve a secondary function. And when they are in competition with each other for the best carbs, then you'd think they'd captialize on such an easy system especially when it adds virtually no extra cost.

Just some food for thought.

[fireburns99]

From what i'm reading i think the only way to end this argument would be to put the carb with/without the power ring, etc, into a windtunnel or flow bench, or a variation, and determine whether there is a significant increase in the air velocity, and or streamline with the use of the power now, or the use of the choke. From a test like this conclusions could be drawn. Note that i am only stating that conclusions could be drawn about the effect on air velocity, and that does not neccessarily equate to more power.