True Duals
Cruiser
Joined: Jun 2010
Posts: 180
Likes: 1
From: Minneapolis
Jeff, The chart you posted appears to be the after. Do you have the before?
One line is hp, the other is ft/lbs of torque.
Torque (thick line) peaks at about 3500rpm on your bike now, hp (thin line) peaks around 5000 rpm.
Can't tell where either hp or torque peaked prior.
One line is hp, the other is ft/lbs of torque.
Torque (thick line) peaks at about 3500rpm on your bike now, hp (thin line) peaks around 5000 rpm.
Can't tell where either hp or torque peaked prior.
Extreme HDF Member
Joined: Sep 2010
Posts: 14,744
Likes: 402
From: Phoenix '53, '88, '09 Big Twins
With a crossover pipe connecting multiple cylinders, the pulse of exhaust exiting the pipe creates a low pressure zone behind it
- as the other cylinder's intake valve opens - and while the exhaust valve is still open ( this is the "overlap" which the cam determines) this low pressure will cause the intake charge to come into the cylinder faster than it would with just the suck caused by the descending piston.
This can give a more than 100% cylinder fill
free power
This effect is called "scavenging", smart people who are engineers have written all kinds of stuff about it.
this is why exhaust tract length, diameter, restriction and connection to other cylinders are so important--- ( and you'll see this if you crawl under your v6 or v8 car)
---as is intake runner configuration.
The most difficult aspect of designing a 4 stroke motor is that we expect great results at different rpm ranges. IF a motor can be used so that it only has to run at a determined rpm, it can be designed to be much more efficient ( such as the charging motor in the chevy volt)
the concern with a 900 pound bike is getting the darn thing to move from a stop, which takes torque.
having a power peak at 6000 rpm is pretty much useless if it takes away from power at 2500 rpm ( 6000 to 8000 rpm is where drag pipes produce their best power)
------ and this'll be all the fun of an "oil thread".
Regarding cams:
the cam timing, overlap, duration, ramp etc. controls EVERYTHING- and can in itself determine torque/HP range and peaks-
stroke, bore, intake, exhaust, ignition timing and fuel delivery must all be part of a system- determined by weight of vehicle, gearing, rider expectations etc.-
You CANNOT compare pipes configuration if the cams are not the same.
Comparisons can only be made when only 1 part of the system ( in this case exhaust) is changed.
mike
Last edited by mkguitar; Aug 4, 2011 at 02:37 PM.
Road Captain
Joined: May 2009
Posts: 505
Likes: 2
I know everyone says you lose bottom end with TD's and I understand the reasons why (scavenging etc). But this is in comparison to a 2-1, TD's against stock pipes will perform well.
See the attached pics of my 08 RKC. The first shows the lower curve for it standard except V&H Dresser Duals with Jackpots plus a/c and Woods TW6-6. This is using the canned PC-V map from Fuel Moto. The curve above it is the effect of a good dyno tune - my point is that the dip in the curve low down almost disappears. The difference that a good tune can make is blindingly clear and is absolutely backed up with the feel of the bike on the road. The second pic shows the effect of adding a Fuel Moto 107/10.25 kit to the mix. All runs done on the same dyno.
So my conclusion is that although TD's wont ever be as good as a decent 2-1 the dip everyone goes on about can be tuned out largely.
See the attached pics of my 08 RKC. The first shows the lower curve for it standard except V&H Dresser Duals with Jackpots plus a/c and Woods TW6-6. This is using the canned PC-V map from Fuel Moto. The curve above it is the effect of a good dyno tune - my point is that the dip in the curve low down almost disappears. The difference that a good tune can make is blindingly clear and is absolutely backed up with the feel of the bike on the road. The second pic shows the effect of adding a Fuel Moto 107/10.25 kit to the mix. All runs done on the same dyno.
So my conclusion is that although TD's wont ever be as good as a decent 2-1 the dip everyone goes on about can be tuned out largely.
Last edited by fxdxrider; Aug 4, 2011 at 02:07 PM.
Outstanding HDF Member
Joined: Apr 2009
Posts: 2,523
Likes: 3
From: Illinois
Jeff, The chart you posted appears to be the after. Do you have the before?
One line is hp, the other is ft/lbs of torque.
Torque (thick line) peaks at about 3500rpm on your bike now, hp (thin line) peaks around 5000 rpm.
Can't tell where either hp or torque peaked prior.
One line is hp, the other is ft/lbs of torque.
Torque (thick line) peaks at about 3500rpm on your bike now, hp (thin line) peaks around 5000 rpm.
Can't tell where either hp or torque peaked prior.
To the OP, I apologize as I didn't want to change your subject. But I do believe I'm still correct in saying that any strictly exhaust change you make will have no bearing on performance +/-.
Outstanding HDF Member
Joined: Apr 2009
Posts: 2,523
Likes: 3
From: Illinois
To mkguitar, I apologize, but honestly a lot of what you said went over my head! But in the dyno chart I have shown, the cams were the same. The dyno run had been done prior to the cam change.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Tourer
Joined: Nov 2009
Posts: 410
Likes: 3
From: Central North Carolina
True duals do sound better and they are definitely cooler that the stock exhaust (especially if it has cats). My gut feeling is that most folks won't notice the difference in torque between TD's and a 2-into-1. Our "butt dynos" often tell us stuff that we WANT to believe. If you "have" to have every last bit of HP and Torque...get a 2-into-1. Otherwise, get what you like and ride that sucker.
I have Reinhart TD's on mine and it runs great. If I'm losing anywhere, I don't notice it. And...it sure sounds good...especially sitting at a stoplight. Gas mileage is great and it will definitely go faster than I need to go.
I have Reinhart TD's on mine and it runs great. If I'm losing anywhere, I don't notice it. And...it sure sounds good...especially sitting at a stoplight. Gas mileage is great and it will definitely go faster than I need to go.
Road Warrior
Joined: Aug 2010
Posts: 1,788
Likes: 5
From: Tennessee
If your doing TDs purely for sound and not performance I recommend Rineharts. I say this due to experience with them. The butt dyno will not notice the little bit of bottom end torque your gonna loose. I have friends that have used all different types of duals but it seems the Rineharts perform better on a stock bike with stock A/C. I think its due to the stepped head pipe design which helps retain back pressure and helps prevent reversion.
On my bike stock headpipes with SE slip ons = 72.74hp and 84.95 Tq. stock headpipes with SE slip ons and big air kit = 80.22hp and 90.34Tq Add Rinehart TDs and it goes to 82hp and 94tq. All with 203 cams and SERT. If your worried about Killing your performance and hating your ride after installing TDs ...............DON't! You'll love them.
On my bike stock headpipes with SE slip ons = 72.74hp and 84.95 Tq. stock headpipes with SE slip ons and big air kit = 80.22hp and 90.34Tq Add Rinehart TDs and it goes to 82hp and 94tq. All with 203 cams and SERT. If your worried about Killing your performance and hating your ride after installing TDs ...............DON't! You'll love them.