Reviewing the PowerNow design/concept/theory...

"How it works" from the inventor http://www.worldpowerracing.com

It does increase velocity, but only because it increases forward momentum of air. Truth is it increases constructive(forward, non-turbulent) air because it decreases destructive air. Air doesn't flow to clever around a flat object, which in this case is the slide. If the slide is half way down, the only way for air to get around it is to turn downwards and hit the flowing stream at 90 degrees. This causes the turbulence, tumble, or whatever you want to call it. In any case, it's spending the few seconds it has to fill the cylinder spinning around instead of moving forward into the cylinder. At half throttle, the air passage is wide open with the power now plate in place. Without it, you have a flat object retarding the forward air flow. This retards the possible cylinder filling and power output. At every throttle opening below 1/2 trottle, the patent pending power now, increases the foward air momemtum and power output.

Addendum - my thinking anyway...

What they failed to describe is the plate cuts the chamber in half increasing the air velocity helping to atomize the fuel mixture quicker - this also makes the engine do less work since it doesn't have to suck as hard - i.e. even though the negative pressure is the same from the engine, the air is induced through the smaller opening (kind of like a turbo boost).

Physics - If you ever stand between two rooms with different pressures (such as your house and the outside world), you will notice that if the pressure stayed relatively constant on both sides, you can change the size of the door opening (i.e. the size of the venturi) and the incoming or outgoing wind will increase through that opening (i.e. the smaller size of the venturi due to the plate will induce the air flow into the engine). Another example would be the water pressure in your garden hose is constant, yet you can control the water via a softer stream (by having NO nozzle) or a strong jet spray using a nozzle. Similar concept in a jet engine, using turbines to push air out the smaller rear opening with tremendous force.

Here is a nice quote from NH_Kevin:

The Power Now divides the air horn in half...or two chambers per-se, an upper and lower.

At low throttle openings, this divider plate allows (the same vacuum) that normally draws off the ENTIRE area of the air horn to now draw off HALF (the lower half) of that same air horn. This results in GREATER VELOCITIES drawn from the lower chamber ONLY of the airhorn into the carb throat.

Greater air speeds means better atomization of fuel AT LOW THROTTLE OPENINGS AND REDUCES the typical 4 stroke lag (offset by a PROPERLY operating accelerator pump jet) often associated w/ 4 stroke engines. When the throttle (and slide) are > 1/2 open, the carb is drawing off both the upper and lower chambers of the airhorn the Power Now creates.

You may have read where a smaller carb is installed to increase low end torque. A large carb increases top end HP. The KTM 125/YZ125 have a large carb for sheer top end HP, AT THE EXPENSE OF LOW END TORQUE.

This is due to the venturi size (inside diameter) of the carb.

Advantages using the PowerNow

1) Better snap from low to mid throttle, crisper throttle response
2) Resists stalling better at low RPM
3) Starts better (cold & hot), the hot start button may not be needed anymore
4) You can ride/pull a taller gear better in low RPM
5) Even after a spill (i.e. possible flood situation), the starting is easier

This is from my experience using the PowerNow. You may have to rejet based on your location, but most people like myself don't have to change their setups.

Introducing the avNow

My thinking is to increase the pull in the LOW and MID range of the throttle even MORE by putting in two plates! In theory, the smaller chambers will again induce air into the engine focussing on these ranges and helping the engine do less work sucking in the air hence creating more power to the ground. Here is a picture of the final product:

The avNow (PowerNow x 2)

The making of the avNow

1) Grooving the venturi (the carb side), the air box side.

The blue line is where the PowerNow plate would usually go. Measure 8mm from this center line to make the grooves for the 2 avNow plates. Notice on the air box side that the venturi is thinner at the top so be sure not to groove the venturi any more than 1.25mm or you will cut through the venturi!

Hint: These are more difficult grooves to make since you're sawing at an angle in order for the plates to fit horizontally. The trick is to start the groove by sawing straight, AS SOON AS the groove is slightly scored, you need to take your time and SLOWLY saw at an angle to make the proper groove (see picture). I used a 'D' shaped hacksaw to do this job - I opened the blade up, put the venturi through the blade, tighten down the blade and TOOK MY TIME making the grooves on a block of 2x4 wood. This was probably the hardest part of the whole production.

2) The top plate, the bottom plate and the big picture.

All measurements are in millimeters(mm). Notice that the safety tabs for the bottom plate is 48mm versus 46mm for the top plate, this is because the venturi is thinner near the top on the air box side. The tongue area extends 12mm into the carb (you want to be as close as possible to the carb's slider plate without touching it), it is also tapered to fit into the carb's throat better (the 250F carb has a 37mm diameter throat, 39mm for the 4xxF). The shoulders of the plates are also tapered so that they will not interfere with the fitting and sealing of the venturi piece to the carb.

The final avNow product

avNow, the carb side view
avNow, the air box side view
avNow, the top view

I bought "Loctite Quick Set Epoxy" - it's supposed to be waterproof, highest strength, solvent resistant bond (I read that as gas) and is made for wood, metal, ceramic, glass, plastic and tile. I couldn't find any epoxy type glue made specifically to withstand heat - this is probably the best glue to use for this application (I hope the glue won't melt from the backfire).

Hope this brings all "Nows" together and explain their designs, concepts and theories.

I'm doneNow... finishedNow

Great job! Can't wait to hear a ride report.

Your plates arent parallel. Thats gonna give you fits. Also, if you didnt get them square to the bore of the carb, your eddie/vortice factor is going to throw your jetting out the window, and probably cause the fuel to fall out of the air or improperly atomize in the dead spot in the flow. And if you got it just wrong enough, you could cause the main jet to think there is more vaccum on the intake track than there really is, and end up way fat in one or more parts of your fuel curve. But good luck....

or You can buy something very similar from Dennis Kirk, Page 276 of the 2002 catalog, made by Starting line Products, named the Power Pack, for $28.99.

What you're saying could also happen to the original PowerNow as well as the "Starting Line plates" (which looks very similar to this mod).

Starting Line plates

Nay sayers will keep saying "nay" until they try a PowerNow and are pleasantly surprised. I don't see that you have tried this mod on any of the bikes you've listed in you sig. Please, give it a try before offering unsupported opinions...

Av,

Great documentation, but I have to agree with Shawn that the plates don't look parallel. I can't give an opinion on the performance aspects though.

Personally, I would have thought it would make more sense to have the 2 plates actually lower. Maybe the top plate about 2 mm above the center line, and the bottom plate about 6-8 below. WOT seems just fine on these bikes. So having a split that high may not be beneficial.

Of course, I'm the guy who tried to make my JamesNow out of plastic, so what do I know...LOL

ben

The nay sayer has the Homemade power now installed. You are also correct about the power now statement. I think it's great people are taking the initiative to improve and share their ideas. I just wanted to show that this(Your) idea has merit! I didn't mean to get your panties all ruffled up.

Will this work on the '03? Someone said that the '03 doesn't have the plastic collar. Any one know for sure?

Junior_Vet - the 03s carbs don't have the extra venturi piece to use to make the home made PowerNow. I haven't seen any pictures of the 03 versions of the PowerNow - I think it will look like their 2 strokes PowerNow piece which looks harder to "home build"...

Your plates arent parallel. Thats gonna give you fits.

I thought about all that - i.e. we can't make the thing perfectly unless we have it stamped out at the factory. My thinking is that it doesn't really matter. The fact is, the carb's slide is what lets the air in and it is straight! The plates' function is to increase the air flow past the slider and according to the inventors keep the turbulence down. I bet all the home made PowerNow units aren't exactly parallel to the slider too don't you think? As the slider lifts, you'll eventually pass the unparallel plates but by that time, they have already done their jobs and you're on to the next chamber and so on...

Also, if you didnt get them square to the bore of the carb, your eddie/vortice factor is going to throw your jetting out the window

Again, I don't think the fitting has to be perfect as long as you don't have huge gaping holes where the major air flow is compromised - even my original PowerNow unit has holes on the side of the tongue (see "the big picture" link above, it's in the background), its side is NOT tapered, it is like a step hence a leakage of air can occur there. Air will choose the least resistance path to get into the carb's throat - this is the main channel and not the cracks around it. The side effects should be negligible.

...probably cause the fuel to fall out of the air or improperly atomize in the dead spot in the flow. And if you got it just wrong enough, you could cause the main jet to think there is more vaccum on the intake track than there really is, and end up way fat in one or more parts of your fuel curve.

The fact that Dennis Kirk's people have designed, tested and are selling a similar mod gives me great confident that this mod will work. Their plates seems a bit shorter than the designs from PowerNow. I would think the longer plates will do better in controlling the turbulence and increasing the air velocity...

Anyway, when I get around to installing this thing (i.e. whenever I get my e-cam - which should be this month) AND my local area thaws out a bit, I'll post the ride test results (unless someone beats me to it)...

Personally, I would have thought it would make more sense to have the 2 plates actually lower. Maybe the top plate about 2 mm above the center line, and the bottom plate about 6-8 below. WOT seems just fine on these bikes. So having a split that high may not be beneficial.

Ben - whatever floats your boat man!

I wanted to focus on the bottom and mid for my application (i.e. where I use the power mostly). I think you can put those plates anywhere you see fit and they will do their jobs - I think the Dennis Kirk's version has upto 3 plates from their picture. Lowering the top plate may be a good idea to increase the low to mid-mid range (did that make sense?), but I wanted it to be even to cover the whole mid throttle range...

Man, that e-start is costing more and more. Let's see:
1. YZ Exhaust Cam.
2. Possible Vortex CDI (50/50 chance so far)
3. Power now instead of home made version.
4. Exhaust Pipe

That electric start is very expensive!

4. Exhaust Pipe

Don't forget to open up your air box somehow (relocate the battery?) in order to obtain the full power of your new can...

Funny last year when I first ran the Power Now everybody said it doesnt work! Now you are all trying to rip off Dave's product. I was stating that Dave's explanation was incorrect a long time ago. It was of course decreased venturi size that increased velocity of the intake charge, thereby giving the carb a better signal. It doesnt matter that he doesnt explain it well, it does work! It is the same as any dual plane manifold from cars. Two plates might work or if you want more low end use a smaller carb. Pay the man and enjoy his products and ideas. Tight Asses

Two plates might work or if you want more low end use a smaller carb.

These plates by effect, make it a smaller carb...

Pay the man and enjoy his products and ideas.

I did paid him for my original PowerNow and I love the thing but the dual plates idea is MY idea not his! Now he can't ask for a patent on the dual plate - everyone can make it...

I just wanted to add something. You can probably get away with not using glue if you make the plates a little smaller as well as the grooves. However, consider that you now have 4 grooves instead of 2 as in the original PowerNow design and this may weaken the structure of the venturi piece. By using glue, you will bind the plates to the structure as well as filling in the gaps where the plastic is now missing - i.e. using glue should make the piece stronger (as one whole unit) while not using glue may make the structure weaker. That being said, the plastic used for the venturi piece is not your typical plastic, it is much stronger (you can tell when grooving it) and it's probably heat resistance too as I'm sure the boys in blue have thought of all this already...

Since you had the original power now with 1 plate, I am curious what you will find when you get to test out 2 plates. That's a neat project you have going.

The Dennis Kirk thing said the "Dividers slide into carburetor bore on the engine side". All these so far have been on the airbox side, not the engine side. That's directing the air after it's already gone past the slide and picked up the fuel from the main jet. That may help to produce a smoother air flow across the main jet, but it seems much better to be on the airbox side. Is that a typo, or do you think they really go on the engine side?

Well Av, after you try out your new creation, your next project could be to try some plates on the other side of the slide in addition to what you made. Smoothing the flow coming and going.

That may help to produce a smoother air flow across the main jet, but it seems much better to be on the airbox side.

I believe the main jet, along with other jets, needle etc. sit right in the middle of the carb's throat (you can see what looks like a needle right behind the plates going into the main jet, I think they have removed the slider for a better view of the plates) - so having the slides "on the engine side" won't do much good with helping the velocity, turbulence or the atomization process. BTW, the slider should be between those plates and the needle, jets, etc. The PowerNow design makes the most sense, I'm not sure what would be the benefit of having the plates on the engine side since you might mess up the atomization process of the fuel by interfering with its flow (i.e. bouncing off of the plates) before going into the intake valves and cylinder chamber.

Is that a typo, or do you think they really go on the engine side?

I'm no expert in that design, but I think that might be a typo - does anyone have this actual mod installed? If you do, what does having the plates after the jets (and atomization process) do for you (if it IS on the engine side)?

That "Starting Line" picture of the carb is so dark it's hard to tell which side is which or which bike that carb belongs to (i.e. Honda, Yamaha, etc.) It is a PWK 39mm D-slide carb so this would be for a 4xxF if anything not a 250F...

Just looking at the lip of the carb's throat, it certainly does look like it's the engine side since the air box side is flat if the venturi piece is removed...

I hope we can see the before and after dyno runs.
I am looking forward to seeing what the dyno says about this device.
Not a flame, but I have made some mods that made the bike feel faster when in reality they didn't lower lap times or improve the dyno #'s.
Thanks, Bill