I ran a PCIII on my 2002 Deuce and loved it. Very tunable. My next bike was a 2005 Ultra which I bumped to a 95" and put in the SERT..buying the line the dealership gave me they were surerior to a PC. I should have stuck with the PC. One of the faults of a SERT is that only the dealership that installed the SERT has the download information...even if they give you back the CD...they have the information. If you next take it to dealer B to retune after another upgrade, they have to start all over again. A SERT locks you in to that dealer. A PC can go anywhere and be tuned by any one. Last summer I installed a PCIII on my wives Road Glide, met Dr. Dyno at the New York HOG rally and he tuned it in to perfection. Dr. Dyno recommeds PCs and will not mess with a SERT...and he is one of the best. Good enough for me.
I would disagree that only the dealership can tune the SERT - I have a SERT and my independent shop can tune my SERT - in fact I have him check and dyno it - he does a great job.
__________________ FREEDOM is NEVER FREE - GOD BLESS THE U.S.A.
2007 Ultra Classic
Nothing sucks more than that moment during an argument when you realize you're wrong.
It was my opinion that the reversion wave was a high pressure wave that reverted up the pipe?
Could you explain that in 101 terms for a dummy.
I’ve heard this a hundred times that you need more back pressure.
How does back pressure fit in the tuning of pipes, and cam choises?
Hope I’m explain that right.
Quik filled in a lot of the blanks, but if you want a theory?
Here is how I think about, Pipes 101: Quik pretty much covered basics to air and fluid flow. That is just too complex and over my head about how slow the air is against the wall of the pipe as opposed to the flow in the center of the pipe and all that is heat and air speed differences.
HC, I am thinking like you and you are on to something there if we are both thinking the same thing I think I understand your confusion. I am more like using a base single, 101? Like the bike is turned off and the pressure in the pipe is now at, 14.7psi; like the pressure on my skin. But once you introduce a push or a pressure, that darn 14.7 pressure is going to win every time, (being pushed out the pipe). That signal is heading right back in and that is better known as your, 'back pressure." Like, "back in" the 1Atmo she goes!
So, it is a war against hot air speed out of the cylinder chamber and the 14.7 being pushed out of the pipe. Oh, that 14 and change wants back in and that is the war of the tuned exhaust. That means; time the reversion of both intake and exhaust open at the same time to flush out the spent and help flow the speed up of the intake moving out the un-spents in the exhaust is a poor next cylinder charge.
So the reverse timing is paramount keeping the un-spents in and pulling the spent fuel out. That is the pipe tuning war and every cylinder's heat (speed) is different like a snowflake in a V8.
Say a carb is in the center of the manifold of a V8. That farthest intake runner is puddled with fuel. That means a cylinder has not filled as well as the dryer intake runner that is closer and makes more HP being better fed.
Like Quik said, you have that hot, fast air speed about to cool off and that 14.7 is a hunting for some popping pipe. That pop is more or less a hot wave hitting a cold wave. You know, like thunder clouds hitting each other is one is cold, the other is hot = Thunder Pop/Whiz/Bang!
So, more or less, the gas is feeding a closed throttle at idle at say, 1000's of rpm's and that revolution is cooling off as in lean or no gas at high rpm. There is a better running cylinder flowing more or less heat and those heat differences are all popping out of time with any valve opening in sequence to the popping is what I think the theory pops like.
Same theory as in a N/A engine with a carb. You WOT the throttle and all that you feel in the change of an air cleaner or a pipe swap is unplugging the speed event of the same suck single in. The, 'normally aspirated' (N/A) is not turbo'd or supercharged. You did not add more air to fuel ratio. You made the event happen quicker. If there were more air, would not the sensors need a different fuel range? No, they have to, HAVE TO run under this vacuum called, 14.7psi. That is what I think is how the theories go. With a little bit there is 14.7 and some there is think it out using, 14.7psi as your guide for everything as in tuning for... Plug read my 14.7 N/A to tuning.
This is where I think your first baby steps should be to get your seat-dyno to, "Tuning 101 = Better known as the, 1Atmo Signal = 14.7 PSI."
We are going to state this very clearly...Backpressure does not increase horsepower. Period.
An often heard statement from the well-informed is "You need a bit of backpressure for an exhaust to work". Usually this comes from someone who is not a tuner or someone who is faced with a situation where he does not have the tools or means to adjust things. Anything you do in the exhaust will change the flows, the pressures, or velocities somewhat. The correct scenario is that the exhaust has to be properly designed and then you optimize the jetting, ecu data inputs, camshafts, port dimensions, valve sizes and the like. The exhaust has to be designed for the intended use.
Before I started studying this theory I used to think the same way that most people thought and that was back pressure was a good thing. Actually it is in a way, if the pipe that you are using will not work correctly with your engine set up. Here is an example of this: When I first started building HD motors, I found that I could build the engines the exact same way but, they wouldn't all perform the same on different bikes or using different exhaust. I built a guy's 95" and after it was completed, it just didn't the power that it should. The guy was using "Ground Pounder" style exhaust. Using an old school tuning trick, I welded a one inch washer to a bolt then installed the bolt inside each pipe where the baffle securing bolt was. You could turn the washer where it could block (restrict) the exhaust flow or turn it so that it could flow more.
All that this was doing was slowing down the speed of the waves traveling down the exhaust better know as "adding back pressure".
But if you block the exhaust, you restrict the flow. This contridicts the theory of the more flow of air through the engine, the more power it will make.
This guy didn't want to give up the look of the pipes, so all we did by adding a bolt and washer was to help improve the exhaust problem with a band aid.
I agree with the 14.7 ambient pressure theory but that's not all that is happening behind the pressure wave. It's hard to describe what happens.
When the exh. valve opens, the pressure wave travels down the exhaust. Most people picture this by imaging pressure in a pipe. When the wave travels down the pipe, the pressure is not equal in the pipe.
Imagine this: If you have a tube and a bowling ball. If the tube is standing upright and you drop the bowling ball down the tube. The bowling ball fits so snugly in the tube that if you cap the end of the tube where the ball enters, the ball will not travel to the bottom due to the suction between the ball and the cap of the tube. Here is where the negative pressure is that we talk about.
The bowling ball is the pressure wave. The tube is the exhaust pipe. The cap is the closed exhaust valve. If the cap is the exhaust valve, and you open the exhaust valve, that suction that is holding the ball from falling will travel into the combustion chamber. This is called "scavenging".
Now imagine that the ball is at the other end of the tube (just starting to exit the tube) and you cap the entrance end of the tube. Here again, there will be a suction between the ball and the cap, trying to keep the ball from exiting. But if the ball was in motion and had enough momentum, if may very well exit the tube anyway. If it it did, here is what happens: There was a suction (negative pressure) behind the ball. When the ball exits, the suction will be replace with the 14.7 air that was standing on the outside of the pipe. Now the pipe no longer has a suction but, has a positive pressure that will travel back up the pipe.
Here is the catch. When that positive pressure wave travels up the pipe and the engine cycles again, there will be another pressure wave traveling back down the pipe. This will happen every time that the engine fires and the exhaust valve opens. The problem is that you have a 14.7 wave traveling up the exhaust while pressure wave is traveling down the pipe. These waves will collide. This will be a restriction (a blockage).
In summary, this occurs whither we want it to or not. The timing of these waves will either help the performance or hinder the performance.
Tuning these waves is complicated and can be very expensive. Formula 1 cars are using this technology to get 4-5 HP per cubic inch of engine. Of course they spend millions to achieve this.
Harleys are very difficult to tune the exhaust due to the bends and lengths of the primary tubes to go around obstacles such as frames and floor boards. It's less costly to find the best performing header pipe that you can and have the secondary pipe tuned as best as possible.
This is why it is so important to choose the correct cam/exhaust combination.
The way to choose this combination is by looking at the flow of TQ & HP lines on dyno graphs from other people.
This is why I started the "Dyno Shop" thread under :Harley Tuner and High Performance. Unfortunately, no one else has submitted their dyno graphs.
VRYQUIK, I've had that site bookmarked for a while myself, it's a great reference. I have always asked those who state the "back-pressure" thing to clarify and never get a solid answer.
Location: Winston Salem, Greensboro area of North Carolina
Posts: 130
Re: Power Commander vs Race Tuner
Quote:
Originally Posted by Twinpeaks
VRYQUIK, I've had that site bookmarked for a while myself, it's a great reference. I have always asked those who state the "back-pressure" thing to clarify and never get a solid answer.
Actually, anyone with a dyno can tune your bike with the SERT!
Good article.
I especially agree with the part talking about the stock header pipe performance. One easy way to check the VE between cylinders is to look at the spread sheet map and compare the front and rear cylinder map numbers. The closer that the numbers are (comparing cylinders) the more even that the VE is between cylinders. The stock header pipes have a very even VE between cylinders. The disavantage is that itis not a 2 into 1. If you look at the bottom of the article, you will see that it has a copyright of 2002. The W/B E-Series and the Thunder Header were the better VE pipes of the day. Now the D&D Fat Cat seems to have a more even VE between cylinders acording to the comparing the Fuel maps. The Fat Cat may have a more even VE, (which basically means that both pipes flow more evenly) but, the challange is finding the cam that will match the best cam timing with that pipe to gets it's full potential. Thanks
want to thank you quik for lending your insight and numbers. was looking for info on the thundermax and found it here. was hoping for more-info but i'm sure i can research it out. i obviously have a great deal to learn, re o2 closed loop sensors etc. just picked up an 07 flhtp with the 103 in it and plan on "waking it up" but really don't & never did, look too fondly on the stealers expertice. so thanks again for sharing your wisdom and numbers. TOO bad no one else is chiming in with their graphs & #'s. probly testimony to the high level & quality of your post's!?...
I just called the Harley Dealership about installing a set of Rush slip on's and a high flow air cleaner along with remapping on my girlfriends 08 Fat Boy and was told I had to install a Race Tuner on anything from 07 up if doing pipes and air cleaner. $1100 Total. Is this right ????
LJ, that is completely false. Just with pipes and air cleaner you probably don't have to do anything as covered in AIM magazine. IF you want to add a fuel adjuster there are lots availabe besides the Race Tuner, PC, Thundermax, Daytona Twin Tec, etc that work on 07 and up.
Hard to top any comment from the boys at laughing gas (said respectfully), but I too prefer the SERT. I like to tinker, (not as good as a dyno), ya' know ride download check it out until I had it (to what I think) dialed in. Gotta know what to look for, exhaust residue, spark knock, plug color (don't pull em when they are hot), times and temps to name a few. 16K on FLHRSE4, have run with hopped up bikes (not on nos) and all have been very surprised, espescially when I can top fifth gear out. Mine has all the original pieces on it, though they don't look the same (gotta take stuff off to see the shiny) and if I stay between 2000-3000 r's 20-30% throttle 65-70 mph I have gotten 54mpg. My little bro (6'3" 2??) with a hopped up 103 stroker, flowed heads etc., we run side by side to almost the top of 4th gear then his 7K engine realy shines. Oil Royal Purple 20-50 Max Cycle (dropped temps 20-25 degree's), changed every 5K or less (it'll use a little,but it's ok), follow your service suggestions in the manual, HD Filter chrome. If you don't have an oil cooler aaahooh scary.
Is it a must to have the bike up on the DYNO with the PC III USB, my FXDC 07 has only been modified on the SLIP ONs (Python 3) all else Stock, I am trying to decide on Fuel Pack or PC III or PC V (if avail for my bike), thanks ahead. I live in Honduras and Dyno machines are not available.
Re: PC vs. SERT 
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