FXR, they are tuning their exhaust to their fuel system, not the other way around. In my opinion.

 

I did not say that back pressure did nothing.

I did say that back pressure can reduce reversion (which is a huge factor in weak low and mid range torque).

I also said that back pressure works against the engine like dragging dead weight.

What is better is to reduce reversion & increase the exhaust gas velocity WITHOUT adding back pressure. That way you have the benefits without working against the engine.


Below is more information on how TTI's work and also why even a bolt or a washer can provide improvement.


Short Answer:

The Thunder Torque Inserts have a proprietary shape that is much better at increasing exhaustgasvelocity, 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.


Long Answer:


Here's a bit of info that is relevant to the Thunder Torques that might be interesting to some.
The type of material, shape, size, thickness, & surface coatings all make a difference in how well the Thunder Torque works at increasing exhaustgasvelocity.

The TTI's obviously have their genesis in the simple lollipop concept. But they are quite a bit more, especially the W series.
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. 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 a post here (by me anyway lol).

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 is 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 exhaustgasvelocity (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.

There is much more to how exhaust systems help or hurt the felt power. But the main goal that is achieved by the unique design and combination of materials in TTI's is to increase felt power in most any exhaust system for a low price.

 

Hey Kevin,
Do you make a "W" TT specifically for the propipe? I looked on your website and all I saw was pairs...I only need one

 

Just asking but what would torque cones do? thanks

 

Propipes can be tuned in with 25 cent hose clamps, just by blocking off one set of holes at a time to get the the perfect flow as described in this thread.

2-1's are designed to scavenge spent gases with the flow of the fired cylinder under accelleration, the fired cylinder/pipe exiting the muffler is pulling spent gases from the opposite pipe, 2-1's shouldn't leave staggnet gases in the system or have reversion issues unless deaccellerating and just down to a fine line of finding backpressure or lack of for torque and power.

 

We sell them in pairs.

There are quite a few guys on the forum that have used them in their 2-1 pipes with good results...you might find one of them to sell you there extra.

 

We have had torque cones on the dyno...not seen much benefit to them...ranging from 0% - 3% increase in torque.

"W" series TTI's give a 8% - 16% increase in torque on every pipe we've tested.

 

Ok, since this is a public forum and all topics are concidered debateable plus I can't take it no more. Why would a Propipe that has no reversion with a scavaging design need a air altering lollipop to help reduce reversion? This compares to a guy with a 12" johnson buying a ***** pump, I'll never know about a 12" johnson but know Propipes can only have pulse collision (reversion) when you have too much backpressure by either owner modification or by trying to blow a big cube engine down the baffles throat.

The issue with the OP's high output is the manhole cover opening size is leaning out the engine, three things can happen: (1) tune the engine to the pipe best as possible as members have suggested, (2) slowly add backpressure which also raises AFR's or richens combustion by a less scavenging effect, (3) install a big motor in front of it or I guess there is a 4th of installing a exhaust system that is more suitable out of the box for a 70 hp engine. I know what I would try to do If I enjoyed the looks and sound of the high ouput and already owned it.

 

Ok, Bagger, I'll bite as I respect your opinion. What would you do? Hell, I put the lollipop's in my dragpipe's in my old shovel, year's ago.

Ride Safe,
Harold

 

I took a look at Nightriders site, something I should have done previously and got a bit of a surprise.
http://www.nightrider.com/biketech/exhaust_test_01.htm

VH Straightshots hang with or outperform most of the 2-1 systems with really good numbers @ 2500 rpms.
Just a case of being the right pipe for a stage 2 set up?