Rode my 1st Harley Davidson - Page 6

Rider · 10-24-2008, 10:15 AM

Quote:

Originally Posted by Gas Man

you got to have forward controls... its the only way. The wife's sporty mid controls suck IMO, that's why I have a set of highway pegs I made for it.

You can convert a sporty to have forward controls. The 1200 custom has forward controls on it form the factory.

Gas Man · 10-25-2008, 11:42 AM

Yeah but the wife likes the mids and they are favorable to a noob.

Rsv1000R · 12-16-2008, 02:01 PM

So, a while back I did a bunch of engine simulations where I'd pick a head, and then vary the stroke, and a bunch where I'd keep the same displacement and vary the bore and stroke to see how the output changed.

What I found was that the amount of air you can get in and out of the head was the critical factor. Torque peak occurs when the port velocity is in the 700'/sec range. Since everyone usually changes exhaust and intake manifolds, that means you can focus on the head and valves to determine performance capability. What I found was the more valve area you have, the more power you can make, if you can fill the cylinder. 4 valves usually have more valve area than 2 valves. So for the same engine a 4 valve head will flow more air. But what I also saw was that you can change the stroke and as long as you can spin the engine high enough, you can consume the air the head can flow. So for a short stroke engine torque peak will be at a higher rpm, and the same engine with a long stroke will just pull the torque peak to a lower rpm.

If you have a long stroke, you don't need DOHC's, the torque peak will be low enough that you don't need high rpm valve stability. A pushrod system will work just fine. However if you shorten up the stroke, you might run into valve float before you finish getting to your torque peak.

Also I think, if you normalize torque output per rpm with gearing between the long and short stroke engine the output will be similar.

And lastly if you're racing in a displacment limited category, you are better off going for Big bore, short stroke, high rpm as that gives you the most valve/port area. And this is the exact kind of engines unlimited class racing has evolved.

Crazy2sin · 12-30-2008, 04:04 PM

Quote:

Originally Posted by Dave

got to test out my buddie's vrod last sunday and i have to echo a few of marko's points. very comfy bike. killer styling, didnt feel very confident with the far forward nature of the riding position but i think thats mostly my lack of experience with it. really starts moving above 6k. tiny tiny tach

Yea that was my Vrod dave rode. And I'll also have to agree with markos points its a fun bike. And like dave said it rips like no other once it hits 6k lol

Apoc · 01-01-2009, 01:29 PM

Quote:

Originally Posted by Shift

Few years when full electronic valve control comes it'll be an old pointless discussion anyways.

you got to admit though, there will probably be some interesting problems with the first model years

i think its a long ways off.

10-25-2008, 11:42 AM	#52
Gas Man Trip's Assistant Join Date: Feb 2008 Location: Imported from Detroit Moto: 2009 HD Street Classic Posts: 12,149	Yeah but the wife likes the mids and they are favorable to a noob. __________________ -Chris "Why pay somebody else to fuck up your bike?" Run Amsoil Product

12-16-2008, 02:01 PM	#53
Rsv1000R WERA White Plate Join Date: Nov 2008 Posts: 1,059	So, a while back I did a bunch of engine simulations where I'd pick a head, and then vary the stroke, and a bunch where I'd keep the same displacement and vary the bore and stroke to see how the output changed. What I found was that the amount of air you can get in and out of the head was the critical factor. Torque peak occurs when the port velocity is in the 700'/sec range. Since everyone usually changes exhaust and intake manifolds, that means you can focus on the head and valves to determine performance capability. What I found was the more valve area you have, the more power you can make, if you can fill the cylinder. 4 valves usually have more valve area than 2 valves. So for the same engine a 4 valve head will flow more air. But what I also saw was that you can change the stroke and as long as you can spin the engine high enough, you can consume the air the head can flow. So for a short stroke engine torque peak will be at a higher rpm, and the same engine with a long stroke will just pull the torque peak to a lower rpm. If you have a long stroke, you don't need DOHC's, the torque peak will be low enough that you don't need high rpm valve stability. A pushrod system will work just fine. However if you shorten up the stroke, you might run into valve float before you finish getting to your torque peak. Also I think, if you normalize torque output per rpm with gearing between the long and short stroke engine the output will be similar. And lastly if you're racing in a displacment limited category, you are better off going for Big bore, short stroke, high rpm as that gives you the most valve/port area. And this is the exact kind of engines unlimited class racing has evolved.