Yeah, it's slightly off the beaten path, but I think this is a worthwhile discussion. A friend of mine has a Roadstar Warrior (v-twin 102" Yamaha) and recently went from Yamaha's engineered 2-1 exhaust to an aftermarket pipe-per-cylinder setup, and the bike lost a great deal of driveability at low throttle position. He's really dissappointed in the loss of power, and is considering going back to the stock setup or possibly an aftermarket 2-1 setup.

In order to leave a stoplight he has to run it much harder than before or it stalls. The whole process has me thinking about why harley guys drive the hell out of their bikes and get nowhere. Could it be that a zoomie style header isn't the best design for a street bike It makes a lot of sense to me.

Now, the reason I'm posting is that he got the idea to do that from me, and I'd hate to have him waste any more money on my account. Basically we were brainstorming and I recalled the tuning vs backpressure thread. It just seemed to me that there may have been some low-rpm scavenging from the 2-1 design, but I'm a complete layman, dropped out of engineering after two years .

 

My Harley uses a custom fabricated 2 into 1 system. Even factory Harley exhaust is 2 into 1. There's a crossover pipe between the 2 factory pipes.

2 singles is only good for WOT operation. ie drag pipes.

It's also hard to compare a Harley engine to a Japanese engine. Although the *** V twins may look and sound similar, internally they just don't work the same.

The Harley is a pushrod engine, The cylinders are 45* apart and the ignition fires both plugs at the same time. Both con rods are on the same throw. All this is what gives a Harley a distinct sound and feel and why certain modifications work better than others.

 

Tell your friend that if want's his low end back, his best bet is an aftermarket 2-into-1.

However, if he wants to keep his drag pipes, he could use an old biker trick to boost the low end torque.

You drill a hole, top to bottom, near the end of the pipe, and run a 1/4" bolt through the holes at the end of the pipe.

I've never really understood what this does, but I'm told that there is a wave that travels back and forth in the pipe, and that it's disruptive. The bolt breaks up the wave without restricting flow.


BTW, this is a harley trick, and I don't know if it's dependant on the design of the motor or not.

 

I don't know why it would be hard to compare this engine to a Harley. It's not all that different from what I see:

More info:
http://www.yamaha-motor.com/products...y&cid=4&mid=60

 

The harley's two cranks share a common journal. I don't know how the japs do it.

 

So the cylinders are 45* appart, and the big end's of the conrods share the same journal? How the heck do you light up the park plug at the same time then?

I'm damn confused now. Is this a wasted-spark design that ignites 45* apart, then 675* apart? how do they share a conrod journal and then spark at the same time?

 

Here's a pic of a billet-steel Suzuki stroker crank: http://www.flattrack.com/falicon/sv750stroker.jpg

They also share a common journal which makes sense from a strength and packaging point of view... but I still don't get the "firing at the same time" part. doesn't seem possible without a wasted-spark design.

 

Going from 2 into 1 vs. 2 individual pipes changed the exhaust tuning A LOT.

IMO, going back to 2>1 is the best solution. You could play with tuning to help the driveablility, but the "system" of cam timing and intake and exhaust tuning has been disturbed.

If your friend is modifying his ride for more power, that would be a goodtime to get a 2 > 1 system compatible with the mods.

If he is willing to cut up the nice individual pipe system, put a cross over pipe at a point in the primary pipes at the same distance from the head as the original joint of the 2 pipes.

 

steve in seattle hit it right on the head, the harleys dont go 180* spark 180* spark, its kinda like our american v8s compared to hondas they have there rods 180* separated an my lt1 has em 90* seperated which gives it that american sound, any way back to bikes the japs do there bike the same way they do the cars, 180* out thats why they idle allot smoother and and truthfully run allot better. But they dont make you the instant badass that the harleys seem to turn everybody into, so thats why everyone wants one. As for me im a young punk *** 19 year old kid who rides a Crotch rocket and makes fun of you old guys on harleys that think there fast, cool yeah maybe but fast, come on guys you know better dont get pist when i blow by you doin a wheelie on the highway just cause you cant.

 

I was wondering about putting a crossover in there, and whether that would help. I linked him to this post, I'm sure the information posted so far will be of value.

 

If you ever take a harley v-twin apart you'll notice the diference in crank design. The harleys have a setup similar to the old radial engines (plane engines mostly). There is a master rod and then all additional cylinders connect to the master rod. Its the master rod that is connected to the crank. But most engine designs like this have an odd amout of cylinders, 3, 5, 7...to keep it balanced. This is what gives harley its sound and its idle characteristics. The *** bikes v-twins use a common through crank design like everyone is used to seeing. Which gives them a smoother engine.

 

Steve -

The bottom ends of the rods are forked, which is how they occupy the same journal. Well, one is forked, the other is the "male" rod.
It's also a roller bearing setup, which is how it works with that gravity feed oil system.
Old saying was that there was no point in putting an oil pressure gauge on a harley, cause it's just scare the bejeesus out of you.
In fact, on the last harley I built, the oil "indicator" I used was a section of clear tube ron the feed side. As long as that tube was black (full of oil), I knew I was good.

And yes, it's a lost spark setup. Both plugs fire at the same time. Or in the case of my last harley, all 4 plugs fired at the same time.

 

Interesting... got any pics you could point me to? I've seen some weird looking conrods before, but I'm having trouble picturing how the rod could possibly cause a piston to be at TDC when the crank is 45* BTD, and not shatter the head once the crank advaces past that point.

Quote:

It's also a roller bearing setup, which is how it works with that gravity feed oil system. Old saying was that there was no point in putting an oil pressure gauge on a harley, cause it's just scare the bejeesus out of you. In fact, on the last harley I built, the oil "indicator" I used was a section of clear tube ron the feed side. As long as that tube was black (full of oil), I knew I was good.

Guess that explains the other old saying abotu Harleys (proudly explained to me by a friend who rides his Fat Boy soft-tail to Sturgis 5 years running): Drive a harley 1000 miles and you'll be pushin' her 50.

Quote:

And yes, it's a lost spark setup. Both plugs fire at the same time. Or in the case of my last harley, all 4 plugs fired at the same time.

hmmm... still having problems picturing TDC vs. crank angle... maybe I'll google a bit an dig up a diagram or sumthin...

 

I dunno, I saw a Harley and a new Suzuki Kubasaw do 10's in the same night at Pacific Raceways. Honestly I imagine at that point it has more to do with weight reduction and traction than it does what the crank/firing order is.

Also saw an idiot kill himself by doing a wheelie into a parked car while showin' off for some chicks at the night drags... come to think of it, he was ~19 too. Sad story really.

 

Probably save some weight in the process.