I've pulled my stock exhaust off a while back and have been running Samson Rolled Thunder slip-ons. Overall I'm fairly happy with them, definitely a huge improvement over stock. Eventually, I'm going to switch over to a RoadHouse Dooley's setup, once I can set aside the cash to responsibly do so! What I'm wondering is how much of a difference should I expect? Obviously I know the sound will be different, but the Samson's I have are pretty open, and I'm just wondering how much of a difference the fully aftermarket system might make. Oh, I'm also running a hypercharger with the stinger trap door as well. Thanks all!

I don't know this for a fact, but I don't think the inside diameter or contour of the stock head pipes pose any restriction problem. Does anyone here know any different?

I went with a Stage 1 mod on the stock mufflers before I went to a whole new system, but I have no recollection of looking at the head pipe ends and thinking they were small or of any different diameter from the aftermarket pipes I put on.

My current belief is that all of the exhaust restriction is in the heavy stock mufflers.

What say you others?

The stock header pipes have a one and a quarter inch diameter and most aftermarket pipes are one and three quarters inch. When I changed to the HK 3" staggereds, I noticed a performance gain but still think the stage one modified stockers have a great sound. the HKs are a little easier to take with the crumb cups installed. Still a bit loud when climbing hills (here in New England we have hills) but they sure turn heads when cranking it up through the gears.

Well, there you have it... that would constitute a huge difference in exhaust flow.

When those gases emerge from the valve and port, they are very hot, moving very fast and expand rapidly to fill any available space granted to it.

When giving plenty, or in this case, that much more area in which to flow and expand into, the performance difference, and advantage, can be substantial.

I went Stage 1 first, and liked the sound very much also.

The Santees I now have sound just fine and never too loud... I climb the New England hills too, here in SE Mass.

Exhaust pipe design is quite complex ... being a function of not only the pipes themselves but what they are bolted to.

It's not just a simple matter of putting on larger diameter pipes. In most cases, the addition of larger diameter, especially free flowing pipes, results in a decrease in Torque, HP or both compared to an equivalent smaller diameter pipe.

The pipe is determined by the diameter which allows the greatest flow of gases without exerting excessive backpressure in combination with a length which times the negative pulse with the valve timing.

Doc

Between diameter, length and shape, pipes can be "tuned" to produce a scavenging effect at a pre-determined RPM.

Ever ride a 2-stroke that got "on the pipe"? Much of that effect was due to tuning the exhaust to create that power boost at that RPM.

While not near as dramatic, aftermarket performance exhausts for 4-stroke cars and bikes perform a similar function, and can also be tuned to maximize power in the range you want it. In conjunction with internal engine mods aimed at that same RPM range, whether low for more torque, or high for maximum horsepower, you can really change the nature of your beast.

Thanks for all the input. I've heard enough on here to know that exhaust design can have a significant affect on the performance if not designed correctly.

That's what always amazes me when I see the shows on TV where these guys just start bending tubes to get a "cool look". Maybe they have a "hidden understanding" about exhaust design and are choosing the tube diameter based on the approximate length they want to end up with... but often I think they just go based purely on looks and don't factor performance at all

They are looking for looks not performance.

Doc

Ok the Doolies are nice pipes and they sound awesome..and they look good if yer going for the bagger look.....

With the R* here is my question....

1 3/4 pipes with 2 1/2 OD shields Road Burners ...1 3/4 pipes with 3" shields HK's and 1 3/4 pipes with 2 3/8 shields

Megacone...

I have sat and looked at these pipes and wondered how they could possibly be routed behind the rear cycl either in a true doolie or reg doolie set up


Now what I have come up with is on the doolies the cans are 3 1/2 OD but the head pipes are 1 1/2 OD with 2 1/4 shields...

based on harley configs..

Am I correct..?? just satisfying my technical curiosity..

so the Doolies are for looks and sound...

I like what Harley have done for 2009... re-routed the exhaust under the frame


about time

The exhaust configuration ..sending it thru under the frame behind the rear of the gas tank was poor at best..