Don Terrill’s Speed-Talk

Check with Stan Weiss.
I recall he did some work for DV and produced a program that recommended valve springs based on various inputs. Diameter, installed height, seat and nose pressure ,etc. Used a data base of various manufactures products.

I have been researching a few Aussie headers but the stock manifold really doesn’t look that bad as far as flow . Of course it probably provides little scavenging. What do you think the air feed to one of intake valves is ? Emissions or Economy ? The gaping hole right below the short turn can’t be ...

Let's assume that we are defining the intake port coefficient of discharge as 146 cfm per square inch of flow area at the valve. For low lifts this area would be the curtain area created by the minimum distance between valve seat and the valve (which is hard to measure accurately). The 146 cfm per ...

Here is a cam spec sheet for an intake on a 110 lobe center and the exhaust on a 104. The reality is its a 107 LSA -3 degrees as ground. 2008 CRF450R Web Cam PN 65246 Data.JPG Is that typical for a 450R ? Makes me curious what a 250R and 250X would have. Thinking they are trying to kill a bit of bo...

I know it’s going to upset a few people here, but there is a bigger world out there than the EMC. +2, +4, -6, etc. it’s all arbitrary. The events are the events and in my mind, whatever the cam designer specs is my new “zero” point. If a cam designer tells me to take a cam ground at 104* LSA (104 I...

This particular engine is known to respond with 30HP by porting the heads to 301cfm@.450", and using the low lift stock camshaft. it gains 25CFM @ .300" in that porting job. So i figured that stock heads would gain by using a higher lift cam that lifts it to where it flows in the 260's ve...

I have made 1 cylinder race bike tests with tumble on a small 4 valve engine. I have pictures of the ports somewhere. I lost no flow but more tumble gained responsiveness and made faster lap times. Erland Erland, I am currently working on a 2008 crf450r. It is a dump port configuration. Other than ...

Double post.

I have made 1 cylinder race bike tests with tumble on a small 4 valve engine. I have pictures of the ports somewhere. I lost no flow but more tumble gained responsiveness and made faster lap times. Erland Erland, I am currently working on a 2008 crf450r. It is a dump port configuration. Other than ...

Here is an article on dynamic valve event optimization at Design Judges also worth reviewing and consideration.

https://www.designjudges.com/articles/d ... timization

You guys may find this Darin Morgan video interesting. You will have to register to view it. It is worth it.

https://www.pera.org/dynamic-overlap-flo/

The ads end about 8:45 into the video

Anytime I see cfm numbers drop with lift, my first thought is flow separation caused by the SSR and the resulting loss of part of the valve curtain area to air distribution.

Tire pressures? Sometimes just a couple-few psi can make a difference with starts. My reading of the tire rules is grooving, siping and grinding is prohibited. (Mechanical treatment). If not... cross sipe those rears. Assuming day racing, Do you sun soak your wheels with dark covers if possible base...

I have a 2008 Honda 450 on my bench to review and perhaps modify. This head has been touched by another. The carb to head transition has been extended and smoothed. The bowls appear to have the same treatment. All in all, it is likely some company's "Stage 1 or 2 porting" that you see adve...

BMEP is directly proportional to TQ per displacement so it is not more effective at all as evidenced by your equation to me BMEP at peak hp rpm is more useful as the engine may not actually operate down at peak torque much or at all Digger, Those equations allow that very understanding. I never sug...