I respectfully disagree on that point. Since when does the right amount of backpressure reduce performance? I suppose if you measure performance at idle and WOT and forget everything in between.. but 99% of riders don't ride like that.

 

I let that slip out. When talking about exhaust I am usually careful not to mention anything about back-pressure.

I know it is not a subject to step into. But since I did in this thread, I might as well go all the way. lol


Back pressure is Not good in that it creates engine pumping loss. The engine wants to pump the air out the tail end of the exhaust, anything that slows this down, like back-pressure, is working against the engine, thus, engine pumping loss.


Back-pressure can be a band-aid for reducing reversion, and in reducing reversion (thus reducing engine pumping loss) it is a "good" thing. The old, lesser of two evils thing. ie. taking a medicine that makes you sick but keeps you from dying.


However, if you can reduce or eliminate reversion WITHOUT creating back-pressure, this is an unqualified good thing in all scenarios, especially daily riding.


If you have written me off as a nut for not bowing to one of the strongest myths out there..."a certain amount of back-pressure is good", or if the subject simply does not interest you, don't continue reading.

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A brief overview of how exhaust systems work & how to improve them.

Technically exhaust systems cannot increase or decrease an engines power. However, and this is a BIG however, exhausts systems can have a profound affect on increasing or decreasing engine pumping loss.

You can loosely compare engine pumping loss with adding an extra 200 lbs weight to the bike. The engine still has the same amount of power, but with the extra weight on the bike it will accelerate slower...it will feel like it has less power than it would if the extra 200 lbs was removed.

Every engine will suffer to some degree from engine pumping loss (all back-pressure contributes to engine pumping loss). The goal of many exhaust systems (including the Thunder Torque Inserts) is reduced engine pumping losses, resulting in more felt power at the rear wheel. If efficiency of the engine increases then fuel mileage may also increase because less throttle is needed to move the bike forward at the same speed.

There are Many design factors that can affect whether an exhaust system increases or decreases engine pumping losses, far more than could be put in this post.

Generally most of us that ride Harley's want the most felt (rear wheel) torque in the low to mid rpm range as possible. Inertial scavenging has a major effect on that felt power.

The nuts & bolts of increasing inertial scavenging are the following-

When the exhaust valve opens two thing happen. A pulse (wave) of energy enters the exhaust pipe, generally at 1300-1700 feet per second. This can be understood as a shock wave from an explosion.

At the same time the spent combustion gases enter the exhaust pipe at 150-300 feet per second. (Generally the faster the exhaust gases travel, the better the inertial scavenging and the less engine pumping loss)

The energy wave that is heading toward the end of the pipe will get to a low pressure area faster (low pressure being a bigger area of the pipe OR the end of the pipe) WHEN that happens some of the wave will reverse direction and collide with the slower moving exhaust gases that are still traveling toward the end of the pipe. This will slow down the speed of the exhaust gases. This will produce the result of less felt torque at the rear wheel.

Exhaust systems that are are successful in increasing exhaust gas velocity (resulting in an increase in inertial scavenging and a decrease in engine pumping loss) will make the bike have more felt torque across the RPM band, especially in the low & mid range.


The Thunder Torque Inserts have a proprietary shape that is much better at increasing exhaust gas velocity, thereby reducing reversion, which reduces engine pumping losses, and increasing inertial scavenging. Net result is a significant increase in power & torque in the low and mid range Without sacrificing any top end (read-without creating back-pressure).

 

Keep the pipes and get rid of the dealer.I'm guessing it's still a bit lean.Dont sweat it.I don't.

 

One thing to keep in mind, our motorcycles have been around for centuries, gotta ask urself... When harley first started making these bikes did they really worry about all these computer mambo jumbo popping backfire? ... I wouldn't doubt it.... lol but I'm sure it wasn't a big deal and they rode the sh^t out of these bikes wih no issues. Popping and back fire is normal IMO, but good luck tho

 

they also didnt have suspensions, didnt care if a miskick would damn near break your leg. didnt seem bothered by oil leaks.... and was basically a bicycle with an engine.

progress is a good thing sometimes.

 

Since the OP already has (as I understand) the SEPST, then learning a bit about it and trying to use it with the Smart Tune and other features should be a first step before wholesale abandoning it in favor of the PV.

As I mentioned, there is a SEPST dedicated sticky thread with lots of very good info and decel pop is a frequently discussed topic for every type of tuner.

 

Yes, but did she actually receive the software? ... I rather doubt it... seems odd to buy a tune and not get the software.. I may be mistaken.

 

I did get the SE Supertune software, the box. I didn't get the cables for it. I can order that. I understand that the software cant' be downloaded via an apple, but from a pc. I will sort it out, in time. I did get a stage 1 as well. I bought the motorcycle, never road it, new from the shop, with all accessories and work done on it. So, I never heard the motorcycle without these V&H pipes. I mean, it opens up fast and hard on the highway. It is a marvelous motorcycle. A few glitches, and it will be outstanding. Thanks for all of your help.

 

Get the cables, and cheap pc laptop... I'm sure your forum buddies here can walk you through modifying a couple of settings that will help with the decel popping cheers!

 

You can run the software on a Mac - you just need a copy of Parallels or VMWare to run a "virtual" Windows machine. You could also run it using Bootcamp if you like.

I use Parallels to run my PC Powervision software and it works like a charm.