Except, every single professional tuner on this web site will tell you the opposite; that if you put higher flowing AC and exhaust on a stock motor, with no cam overlap, it will run like crap.

Since I'm neither a mechanical engineer nor a professional tuner, all I can do is

 

I'm not sure what you thought you read in my post.

But I said nothing about the A/C, particularly the backing plate on the A/C, which is the restriction on our Fuelie Motors.

Of course, if you mess with the Air Flow AND the exhaust, you need to make tuning changes.

If you change ONLY the exhaust, I defy anyone in here to properly explain why a tune is needed.

Now, I'm talking about a 'real' exhaust, not a couple of 1-1/4" pieces of tubing bolted onto the Heads.

The only way a tune would be necessary with the addition/changing of an exhaust system would be if you had at least 10+ degrees (I'm being conservative) of overlap in our camshafts.

We don't...... Or; I don't anyway. And I doubt many other stock Harleys do.

Overlap is what happens when the exhaust valve remains open as the intake valve is opening.

Right at the very end of the exhaust stroke and at the very beginning of the intake stroke. This is done to allow the scavenging effect of the exhaust to help siphon in the A/F mixture into the combustion chamber.

The only thing making the A/F mixture move is the vacuum effect in the combustion chamber and the slight overpressure in intake manifold.

Higher performance engines will have 40+ degrees of overlap in them. IOW, the Intake and exhaust valves are open at the same time -- As the exhaust is exiting, it helps pull in the new, fresh A/F mixture.

But the EPA stopped that in our engines. Or somebody did

So there is no effect of the exhaust helping bring in the new A/F mixture.

The only thing that could screw up the combustion chamber mixture is if the exhaust isn't working, if there's too much pressure (there's technically no such thing as backpressure relating to exhaust, but we'll use that term for ease of understanding) in the exhaust, the exhaust can back up and not allow the spent fuel and air inside the combustion to exit.

THAT could screw things up.

But not a freer flowing exhaust. No way. Unless it's some ignorant, scooter trash straight pipes that are useless as a screen door on a submarine (I've seen 'em.... Not the sub, the pipes)

There's also the possibility that the MoCo is just tired of the fighting over it.

Maybe they figure that if they allow reasonable exhaust systems, then some moron who hasn't taken a shower this year shows up with his home-made idiot tubes on his bike and wants to pitch a bitch about why they allow other pipes and not his.

But I don't think so. I don't think that's the problem. I think that a lot of these people just don't understand their engines. Including a lot of mechanics.

I respect mechanics, they work hard for a living and they're good at what they do.

But they too often don't understand new concepts......... Like synthetic oil, fuel injection and radial tires.

(Note lack of smile icon)

 

Well, while I'm not an ME or a tuner, neither am I a virgin when it comes to understanding internal combustion engines, EFI, and cam overlap, lift and duration.

Here's where I'm confused: This forum, as well as many others, is full of riders who report dramatic increase in decel popping after ONLY an exhaust change. Since that (usually) indicates an increase in leanness, how can that occur?

I fully agree that without overlap there is no "straight through" path to allow a freer flowing charge and exhaust cycle. However, even after the exhaust valve is closed, the head pipe is still full of hot, rapidly expanding exhaust gasses. With a freer flowing exhaust, these gasses will expand more quickly, leaving a lower pressure inside the head pipe and muffler the next time the exhaust valve opens. This this lowered back pressure will result in a more efficient evacuation of exhaust gasses from the combustion chamber, which will result in more charge air input during the next intake cycle. Unless you believe that a stock HD motor is already running at the maximum efficiency possible. And, the pulse width affecting fuel input will not have changed more than narrow band O2 sensors running in closed loop operation can affect.

What am I missing?

 

[QUOTE=Grendel4;13345385][QUOTE=BigDogIdaho;13345235]

Bottom line, If the bike is not exactly the way it was when it came off the assembly line you're giving them an opening to void the warranty...PERIOD.

 

I know a few Service Writers and I can't think of one time the Manufacturer denied a claim on work that the dealer approved.

What's happening is; Dealers are denying warranty claims out of hand, without even consulting the MoCo.


That's because they don't submit claims that they know will be denied!
Seriously though it might depend on the cost of said repairs. If it's relatively low they probably won't look twice at it.


They very well may be denying claims without consulting. You would have to look at each case. I've seen some ridiculous things people think should be covered under warranty (i.e. blown motor due to NO oil changes). There is some things there is no point to consult the manufacturer.

 

Here's where I'm confused: This forum, as well as many others, is full of riders who report dramatic increase in decel popping after ONLY an exhaust change. Since that (usually) indicates an increase in leanness, how can that occur?


because with the stock exhaust you didn't hear the popping.

 

Interesting.

 

stock exhaust is way way more baffled and generally has higher back pressure so the pop gets burnt up before its ever popped....as explained to me...

 

Also interesting.

However, "the pop gets burned up before it's ever popped" is a completely different explanation than "you don't hear the popping with the stock mufflers".

Since one explanation is that "there isn't any popping", and the other explanation is that "there is popping but you just can't hear it", I'm guessing both can't be simultaneously correct.

Because, internetz.

 

Go with "there isn't any popping"...

Maintaining a certain level of back pressure eliminates the pop. That same back-pressure does
have an effect on power and torque as well, but on an otherwise completely stock HD engine,
it's negligible. Sounds cool, but ya ain't going to win the Super Nationals just cuz you've installed
a louder pipe..