Performance & Mileage impacts of the screaming eagle exhausts - Harley Davidson Street Forum - Street 500 and 750
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post #1 of 13 Old 05-27-2014, 04:09 AM Thread Starter
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Question Performance & Mileage impacts of the screaming eagle exhausts

Hello Guys,

The street 750 is just perfect for city riding all that it lacks is a powerful roar which again can be fixed with the screaming eagle exhausts!!!

Yes! This baby vrod with screaming eagles produces an amazing exhaust note! I just loved it when i first heard it. The bass produced when the engine was revved and the roar that was generated was enough for me to fall in love with this bike. It is just perfect for me. I do wonder how this piece of equipment (the exhausts) is able to give the sound of the bike a complete make over.

And then the big question arises - how does the screaming eagle exhaust affect the

1. Performance of the bike.
(without the screaming eagles it produces about 60 bhp but what happens to the figure when screaming eagles enter the scene? )

2. The fuel efficiency of the bike.
(which now is about 20 kmpl. will the screaming eagles reduce the fuel efficiency of the bike?)


I request the experts in the forum and the street 750 owners to comment on this.
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post #2 of 13 Old 05-27-2014, 07:39 AM
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Again a valid point here. Been hearing about power gain with just Screamin Eagle Slip on Mufflers but about Street 750 nothing! Is it just Aural gain or some gain in performance?!

I think if it's about sound only then way too much paid but if it adds performance then definitely worth it.
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post #3 of 13 Old 05-27-2014, 09:10 AM
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According to articles I have read, Screaming Eagle would increase performance and fuel efficiency.

It allows engine to breather more smoothly. Just my thought and only people who have screaming eagle fitted can confirm

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post #4 of 13 Old 05-27-2014, 03:04 PM
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a slip on that improves performance? really?
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post #5 of 13 Old 05-27-2014, 03:12 PM
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Don't expect any big changes out of the SE pipe. It still has to be noise and smog legal. The early SE slip ons for V-Rods actually reduced power output slightly.

You can get more performance gain from remapping the ecm. Don't forget to remap the timing too. There is a look up table in the ecm for the ignition timing too.

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post #6 of 13 Old 05-27-2014, 03:53 PM
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Does anyone have a link to SE for the Streets? I was under the impression that Harley had not released or developed SE pipes for the Streets?

Desert, if you don't mind me asking what are the benefits of an ECM remap, what makes it worth it over a simple pipe swap?

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post #7 of 13 Old 05-27-2014, 07:06 PM
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As delivered, nearly all production motorcycles are tuned to run as lean as possible to meet emissions standards. They often run miserably until fully warmed up as a result, misfiring under any kind of load. To meet noise standards most manufactures will introduce a lean spot in the power curve at whatever rpm the noise test is accomplished at. By accessing the ecm through something like a Screaming Eagle Supertuner or TTS Mastertune you can change the look up tables that determine how much fuel is delivered at a given rpm and throttle opening, air temperature, coolant temperature and manifold absolute pressure. You can also usually go in and change the spark advance on it's own look up table. What usually happens with a stock bike is whoever is tuning the bike will richen the mixture closer to 13.0 to 1 for best power (at the expense of emissions, stock air-fuel ratios, AFRs, are usually around 14.2 to one except for full throttle and high rpm) and using a dyno you can see what the air fuel ratio (AFR) and power are doing at every rpm to tune out rich or lean spots that lead to dips in the horsepower and torque curves. The engine and exhaust have enough airlow in stock form to burn more fuel and make more power, but you have to program the ecm to deliver that fuel.

Since the SE pipe has to be street legal, it won't change stock airflow. To do so would put Harley Davidson in violation of a stack of laws in the US. If you install an exhaust that changes airflow, you really have to remap the ecm or the bike will run very poorly. This type of fuel injection does not measure airflow into the cylinder head directly. It reads rpm and throttle position to determine the basic length of time the injector remains open (called pulse width), and trims the pulse width longer or shorter depending on coolant temperature, intake air temperature and manifold absolute pressure. There will also be cold start maps to keep the bike rich for a short period of time after a cold start. If you change the airflow through the engine through a different exhaust, intake tuning or whatever, you have to remap the ecm to deliver the right amount of fuel for the new airflow. The ecm has no means to figure this out on it's own.

Don't kid yourself into thinking a different pipe on it's own will make a big difference in how much power the bike makes. Most stock exhausts are very good in terms of airflow, they just don't make a lot of noise.
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Last edited by Desert Tortoise; 05-28-2014 at 10:27 AM.
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post #8 of 13 Old 05-28-2014, 07:44 AM
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i never really look forward to power gains for slip ons

id be happy if they just make the engine sound a bit better
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post #9 of 13 Old 05-28-2014, 11:09 AM
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Thank you Desert! Doing some googling I've just found out about Dynojet Power Commanders. They can be bought with an Autotune function, this is essentially the same thing no?

With a PC is a possible for one to manually fiddle with AFR? I'm a curious cat who likes to play...
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post #10 of 13 Old 05-28-2014, 03:15 PM
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Desert might have a better answer for this one. But to my knowledge with the autotune you can set the desired afr in a map. Ride the bike for a bit and the autotune will make adjustments and determine trim values. Then take those values are how much you would add or remove to meet the requested afr from the beginning. mate it to your cpu or laptop adjust the fuel table in the map and reset the trims to zero. go for another ride then finally there would be your new map.

I think autotune would be ideal for those who change up parts that affect the afr a lot. so basically for those who can't sit still with one exhaust.

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