1.7 rocker effect

[harleytuner]

Not enough information..

It was a 117, Wood cam [don't remember which one], 2" intake on stock heads. That's about all I remember.

Same dyno? Similar run conditions?

[wfolarry]

Yes & Yes.

[harleytuner]

Yes & Yes.

interesting.  Just a valve job and new (different valves)?  Same HG?

[wfolarry]

Yes.

[1FSTRK]

For those looking at the Vizard pressure chart he makes the statement that the red line and the light-blue line represent the starting and finishing pressures of the 15:1 and 2:1 on the same scale. Given that the bottom axis is only labeled TDC on the left and BDC on the right, I draw the conclusion that 90 degrees BBDC is the center of the chart, We then can clearly see that by about 60 degrees BBDC the two lines touch and the pressure is equal for the 15:1 and 2:1 engines. Given that very few HD street cams have an exhaust valve opening of earlier than 60 degrees and many of the popular ones are in the 40 and 50 degree range they would all open at the same cylinder pressure in both compression examples Dave uses. Now to our previous examples from Larry's post quoted below, see if anything in Larry's example engines has us working in the ranges of Dave's chart where there are actually pressure differences. I do not see where Larry's changes put anything in the area of Dave's chart where the pressures are different so if it does not show difference on the 15:1 compared to 2:1 pressure chart what kind of cylinder pressure difference will be seen with motors ranging from 10:1 to 11:1. While technically correct just like in my Softail example, not applicable to a street HD with a rocker ratio change. It is just my take on this after seeing many dyno tests involving race engines where these principals did apply.

My point has been that many solid principals and theories for high rpm, high compression, narrow tq band race engines either have little effect or adverse effect on street Harleys.

1.7 rockers & even exhaust valve size are tuning aids in different applications.
Example 1: Low compression. These motors like a later opening exhaust valve because they are building pressure longer so you want to get the most out of it. Now lets bump the compression up with the same cam. Since we can't open it sooner [same cam] going with the 1.7's will open it faster. With a little luck [no way of knowing for sure without testing] we'll make more power. If we go with the 1.7's at the same compression we'll lose power because we lose pressure in the cylinder faster.
Example 2: High compression. Here we want to open the exhaust valve sooner because the pressure in the cylinder is decaying at a faster rate. So with the right cam everything is fine. Putting a 1.7 here will do nothing. Will a bigger exhaust valve help? Maybe. Sometimes bigger valves with the same size throat will flow better because of the chamber shape. So what works in one head doesn't necessarily mean it will work in another. I like to use the smallest chambers possible but that's just me. You'll get arguments that go both ways on that.
The reason why you hear that increasing the ratio on the intake always helps because many believe you can't open the intake fast enough.
On the intake side the pushrod has a straighter shot so you can get away with it. On the exhaust side I think you're pushing your luck.
As far as exhaust lift goes. You don't need as much lift on the exhaust side because by the main event is over sooner but using a lower lift also means you should be using a different spring. Opening it to the same lift means you're just opening into dead space which doesn't hurt anything but you're using the same springs on both sides now. Easier.
As always it's all about the combination of parts. Some make more power than others because everything is complimenting each other. Same as the members here. 
JMO. Maybe I'm wrong. Don't just tell me I'm wrong. Prove it. I like having discussions. 

[Admiral Akbar]

Not enough information..

It was a 117, Wood cam [don't remember which one], 2" intake on stock heads. That's about all I remember.

And the flow was the same between these 2 valves? 

[attach=0]

Average Flow?

[wfolarry]

The low lift #'s were better with the replacement valve.

[Admiral Akbar]

The low lift #'s were better with the replacement valve.

OK so the motor liked more flow at low lifts.. It would be interesting to look at all the details, pipe used, cam, head flow, TB and where the HP differed.  First item would be flow area under the curve between the 2 head versions...

[wfolarry]

Why is it that guys will spend hours tuning their bikes going over every cell, fuel, timing & anything else they can adjust on the bike but they don't want to tune the parts that go into the motor?

[Admiral Akbar]

You talkin' them $299 heads again? 

[Don D]

Before everyone ditches Kibblewhite valves it is important to state the geometry is very different in other ways with the AV&V not just the under head angle.
Seat width, margin, top cut. Plus in some ports the Kibblewhite may have worked better just not in Larrys case. One point I remember from conversations with Mike Roland was he emphasized the importance of low lift exhaust flow and also in the same context discounted the value of high lift exhaust flow for reasons I already stated.