Rich, KTM576sx question

[hammerhead251]

Eric's got my head in for porting and oversize kibblewhites.

I read what you said about the stroke/rod-length having a big effect on the cam in the YZF. I'm building my bike with the KTM stroker crank (78mm instead of 72mm). The rod length is effectively 3mm shorter than stock to retain the same deck height. I have 3 cams to choose from: the '5521' cam (stock in the 04 525), the '8/06' cam (stock in the 03 525, higher lift and longer duration both in/ex than 5521 cam), and HotCam (compared to 8/06, intake has more lift and duration, exhaust has same lift longer duration).

From your experience, which will be best suited with the stroker crank/rod?

Thanks. You and Eric come to NC, let's ride! :thumb:

 

[Rich Rohrich]

Eric's got my head in for porting and oversize kibblewhites.

I read what you said about the stroke/rod-length having a big effect on the cam in the YZF. I'm building my bike with the KTM stroker crank (78mm instead of 72mm). The rod length is effectively 3mm shorter than stock to retain the same deck height. I have 3 cams to choose from: the '5521' cam (stock in the 04 525), the '8/06' cam (stock in the 03 525, higher lift and longer duration both in/ex than 5521 cam), and HotCam (compared to 8/06, intake has more lift and duration, exhaust has same lift longer duration).

From your experience, which will be best suited with the stroker crank/rod?

Thanks. You and Eric come to NC, let's ride! :thumb:

Post the bore sizes (stock and current) and the rod center to center length and I'll do some math to get a better feel for the cam requirements.

One of these days I'm going to make it back down to Yadkinville so my buddy Scott and I can hit the Charlotte round of the Danny Walker SuperCamp (I'm sure I can convince Eric to join in the fun) , so we'll look you up when we are down that way. The best road rides I've ever been on have been down there. I even got to tour Pilot Mountain on a heavily tweaked RG500 square four two-stroke. :yeehaw:

 

[Tony Tice]

I havte talking over Rich

In talking with the guys at Corse Superbike, Travis Smith, and Doug Chandler they all said the Hot Cam is the ticket. Especially so with the 570 kit installed. It softens the bottom end enough to allow the bike to hook up before the ower hits and then pulls higher up into the rpm. All of last year AMA Supermoto Unlimted Factory KTMs had Hot Cams in them.

Tony

 

[Rich Rohrich]

In talking with the guys at Corse Superbike, Travis Smith, and Doug Chandler they all said the Hot Cam is the ticket. Especially so with the 570 kit installed. It softens the bottom end enough to allow the bike to hook up before the ower hits and then pulls higher up into the rpm. All of last year AMA Supermoto Unlimted Factory KTMs had Hot Cams in them.

Tony

Thanks Tony. How are the Hot Cams specs different from the stock KTM specs?

 

[hammerhead251]

Hey Rich, I finally got the rod length specs. Stock 525 72mm stroke, 129mm center to center rod length. 576 78mm stroke, 126mm rod length (same deck height). I'm actually building a 600cc engine with 99mm bore, carb bored to 43mm, 1mm oversize valves, not sure on exhaust (suggestions?).

Here's all the measurements I took of the 3 cams. My measurements are all LOBE lift, not valve lift. I think the rocker ratio is 1:1.15.

5521 Intake 8.56mm total lift 320 dur@.006 220 dur@.050 138 dur@.200
5521 Exhaust 8.41mm total lift 308 dur@.006 208 dur@.050 130 dur@.200

8/06 Intake 9.12mm total lift 338 dur@.006 234 dur@.050 150 dur@.200
8/06 Exhaust 8.89mm total lift 320 dur@.006 228 dur@.050 146 dur@.200

HotCams Intake 9.42mm total lift 324 dur@.006 244 dur@.050 156 dur@.200
HotCams Exhaust 8.84mm total lift 314 dur@.006 234 dur@.050 146 dur@.200

Compared to the 8/06 cam, the HotCam has a much more aggressive lift and duration on the intake side along with longer duration on the exhaust (although almost identical exhaust lift). Also, ramp/valve speed is even better (slower) than on the 8/06 cam. Exhaust duration at .200in is the same, it just begins opening sooner and closes later (just like my favorite bar!). On the intake side, the duration at .200 is 6 degrees longer along with .050 duration that is 10 degrees longer.

Tony, Corse's logic seems sound to me. I hope Rich can confirm.

 

[hammerhead251]

Tony,

Do you know which pipe works best with the 576/HotCams combo?

 

[Rich Rohrich]

Based on my way of building things the Hot Cams combination is the closest to correct (especially at .200") if it's run at about a 102 LCA and if we assume a HP peak rpm of about 7800 (4000fpm piston speed). I don't really think any of the cams have enough lift for this combination, but the HC is pretty close .

On the pipe I would look for something with a primary length of about 34"-37" and an inner diameter of about 1.75" as a starting point if you want to tune the pipe for the basic rpm range of the torque peak.

 

[hammerhead251]

Thanks Rich. You got any snow there on Venus. I always thought it was hotter than 40 hells there.

Can you give me an update on my cylinder and head?

 

[Rich Rohrich]

Can you give me an update on my cylinder and head?

The head is pretty much finished, and the cylinder should be ready early next week, so it should be heading south sometime next week. :thumb:

 

[hammerhead251]

Rich & Eric,

Just looking for another update in a non-intrusive way.

Kevin

 

[Rich Rohrich]

Kevin - It's finished and shipping out today. :yeehaw: