Pulse Induction Explanation

Hey guys, I rarely post here but I'd like to post about the Ron McCord of Pulse Engineering's Pulse Induction intake system.

First off, I don't sell it, I explain it and advocate the use of it. I keep a blanket explanation handy as a cut and paste because so many guys ask me about it, It might be dated but should help.




Most guys are under the misconception that everything is inward like the red lines in this drawing show.




In reality the crankcase pressure closing the reeds makes a reversion wave that travels back towards the air filter picking up fuel for a second time as it passes the metering system and almost completely stalling the inward flow. Blue lines represent the reversion.




Now we understand that the actual inbound mixture has a triple metered wave and a single metered wave drawn into the engine. As the wave is drawing fuel on its reversion pass it is also back feeding the fuel circuit and forcing the fuel from the carburetor metering back to the bowl which causes the first 10-20% of the inward bound charge to draw a leaner mixture until the fuel returns.
The strength of the reversion wave is altered not by the crankcase compression of the motor, but by the crankcase volume. It's this reason that a 125cc motor takes a 192 main jet, a 250 is 180, and the 500's a 172 (average jet requirement). Lesser pulse wave strength on smaller motors means less multiplied fuel so an initial larger jet is needed. This lower strength wave makes a pulse unit less effective on small cc motors. It is not uncommon to see the surge of the stock reed boot on a CR500, the appearance of the boot absorbing this pressure does not have any measure able difference when compared to the wave in a rigid inlet like the Boyesen Rad Valve .





A Pulse Induction system replaces the stock boot that mates the reed to carb, its cone shaped chamber traps the majority of the reversion wave (blue) and channels it into the pulse tube where a specific length tube dictates the time for it to be re-introduced as an inbound charge. Metering of the fuel has now been almost perfectly restricted to a single pass of the metering system which no longer is having fuel forced out of it. The single metering pass has now given us an acurate and predictable means of metering the fuel. Commonly the jet sizes need to be increased since they are no longer working on multiplied passes. Throttle response is crisp since you are no longer stalling the inlet stream 1/2 the time
Here you can see the reversion waves time has it half ways back to the plenum while the reeds are still closed.




Timing of the pulse wave set by the length of the tube introduces the wave to the chamber as the reed opens, adding velocity to push the almost stalled inlet stream (red). With the inertia wave more air is introduced than the motor can otherwise draw on its own because it is starting at a velocity equal to what is created 1/3-1/2 of the time into the standard intakes draw, basically its "supercharged". The Pulse system works from idle to high rpm and close to wide open throttle positions since its re-introduction point is post throttle valve. Commonly the engines will not draw fuel consistantly through the rpm range because of the reversion strength, The pulse equipped motors will continue to draw consistantly and evenly to extended rpm ranges not accessable without pulse induction. Intake tempatures are reduced since additional single metered air is aquired and engine tempatures are reduced significantly to where it is reccomended to run a heat range hotter spark plug than normally used.




I've done my best to explain this, I expect questions and have no problem answering them.
Adam Millar



This is the most recent version which I just installed. The reed is custom cut VF pedals on stock housings. I don't agree with the length of the reed and would like to use a spacer on it in these engines but I didn't have the chassis room properly. This one is in a 2009 crf450 bike using a 1999 cr250 airboot on the airbox, if I were to use the 2002 cr250 boot it would allow the reed spacer to be used but at compressed travel the shock spring contacts the airboot. When we'd used the rad valve components I could cut the reed plenum off and recess it into the plenum housing.

Adam have you dyno'd the pulse before ? What do you think is a reasonable number to associate with the pulse ? What's the fastest you have spun a 500 motor ? What about torque ?

Adam, the images give a broad overview of this process. It would be nice to provide an animation of this process. You might consider this. Blender.org provides a free tool that would work for this.

http://www.blender.org/

Seems a little late on the technology curve, seems like 90% of bikes are now 4 strokes.

I find it a little odd (in my mind) that the said reverse pulse headed out the carb(or intake) with the slide wide open would make a 90 deg. turn and head up into a little rubber hose.

Anyway, thanks for your post.

Skeptics already lol.

Thats a neat idea.

there is energy there for sure. anyone whos seen an engine run under load with no airfilter has seen the fuel spray back thru. lots of times it can go a long way.

piston coming down, reeds snap shut towards the carb. creates a pulse for sure.

Woudn't think you'd need to loop it though though. from my (limited) knowledge on resonance, basically its the length or volume envolved and not where the openings are. ie center dump pipes, the tubes hanging off vehicle intakes to cancel intake noise ect.

spiffy

roostius, what would you choose for max hp and reliability pulse induction or smartcarb???

Back in the 2 smoke days we used to call them boost bottles.

This is far from new some OEMs had them as stock equipment.

If you want max HP your gonna need Roostys TWIRP porting. Has more torque than the turbos I see on here lol. Not HP but TQ. the pulse would be just icing on the cake. Wish they could pulse the Smarty !

Boost bottle was a little different.

What you have here is basically a poorly designed helmholts resonator. Been in use around the world in various engines and designes for many years. Akin to a boost bottle that many many snowmobillers are used to.

summitboy said:

If you want max HP your gonna need Roostys TWIRP porting. Has more torque than the turbos I see on here lol. Not HP but TQ. the pulse would be just icing on the cake. Wish they could pulse the Smarty !

Boost bottle was a little different.

Click to expand...

i plan to have roosty do some work for me this summer

sledr2 said:

Seems a little late on the technology curve, seems like 90% of bikes are now 4 strokes.

I find it a little odd (in my mind) that the said reverse pulse headed out the carb(or intake) with the slide wide open would make a 90 deg. turn and head up into a little rubber hose.

Anyway, thanks for your post.

Click to expand...

there are 4 strokes out there too keep the service department alive, literally.

There are cones trapping the reversion, its back pressure forces it into the tube.

You could use a boost bottle which traps this charge and stops it instead of allowing it to continue and add velocity to the intake charge.

Eric Gorr had designed his "kinetic energy injector" based on the same theory. His introduced the reversion charge before the slide which multiplied the fuel map and had a horrifically sharp reversion resonance. Google it for more info.

Ron has the patents for this and other models including 4 stroke versions.

I understand the Idea behind it however the little rubber hose will in no way have enough volumetric flow to effect anything in a meaningful way.

A proper set up boost bottle works on a resonance basis not nearly as different as you may think just not in a loop.

Lets not forget the read valve designers trying to reduce said phenomenon as well.

There is definitely some gain to be had but it would need a whole lot more engineering than a little hose.

Just my humble semi educated guess

Roosty knows his stuff, just check out bannedcr500riders.com and you'll see.the guy isn't about blowing smoke. Seriously knowledgeable engine build. My next summer bike will be pulse injected.

Not just a "hose"! Lots of throat Venturi mods to make it all work!

Ha ha. Can u please tell us how the little black hose doesnt work exactly ??

I thought i would post some initial impressions of my Pulse intake. Ron McCord is super nice and very passionate about his design. He loves to talk about carbs and has tried many if not all of them. He provides great customer service and calls u back asap if needed.

I noticed quite a few things off the bat with my Pulse.

First off it starts much better than my previous carb. I had Ron open up the choke circuit just a little bit more and its like night and day difference. I just recently left my bike on the mountain for a couple hours and the CR was a block of ice, she fired up after 3 kicks with choke only. Awesome !

The next thing i love is my bike idles all day long. I use a Slavens extended idle and airscrew. Easy to grab with the gloves and adjust.

Next up is vibration. I notice the pulse is much smoother from idle through acceleration to WOT. Ron explains this as being the constant flow induction. I guess the air moves across the nozzle 1 time compared to up to 3 times of a regular PWK. It really is noticeable.

The jetting comes up a lot in discussion. With the way the PWK is modified the carb needs a baseline setting. Ron calls this the 270 setting. The carb needs to be jetted so u are at 2 turns out from full rich at 70 degrees. With the snow bikes i call it the 220 setting lol since we deal in the cold. The airscrew now adjusts fuel across the entire range from idle to WOT. It affects the pilot, needle, and main. Temp and altitude do not affect the Pulse as much as a standard PWK. With temp and altitude change, a simple adjustment of the airscrew is all that is needed. It amazes me how a simple turn of the screw affects entire range.

We start by setting the pilot. Ron's pilots are not just plain Keihin pilots rather pilots with a lot bigger holes. The mains on the 500 also are a lot bigger than you would run on a stocker. For example a main on a stocker may be 165. With the Pulse we run say 188-200 main. I'm using a Honda needle which is richer for the colder temps we see.

With a Pulse setup you don't do a plug check, its misleading. You can pull the plug and think you are running perfect. You don't know until you try 2 main sizes and feel a increase in power. You can run a couple sizes on either side of your perfect main and it will run just fine. So pilot, then main, then needle. Once you have the baseline set (2 turns out and perfection throughout the range) all that is needed is a turn in or out for increase/decrease of temp throughout the day. Simple.

I have setup my carb so i can change pilot and main without removing or turning the carb which has been handy for the baseline.

I did not run a carb blanket as of yet. The carb seems to stay snow free so I'm not sure if i will run one unless the temps get super cold.

So far i sure love the way the bike runs. Smooth and fast. No burbles and excellent power ! I thought the bike would eat fuel but thus far seems very good for the amount of time i have ridden especially at WOT LOL.

Here is a few pics of my install and setup:

What heat collar are you running and where did you get the valves for the coolant. Thanks

SB and I made up 2 heat collars. We machined them on my lathe the I tigged the parts together a little more machining and voila. The valves SB used are a Doo part I believe, I used a different style I had lying around. The main advantages of our heater design is you get 360 degree heating and it is much more compact and adds only about 1/4 inch to your length. The other heaters on the market will not clear a CR500 steel frame so necessity became the mother of invention, I can't comment on an AF bike.

M5