Don Terrill’s Speed-Talk

mag2555 wrote:When I know I am port a Exh side that will need sharp bent tubes off the flange I first head for getting the most flow gain by means of port width increases at a certain point around the short turn, and this still all hinges on how much lift is being used.

I had to hunker down with my ears pinned back to get the jist of that.

mag2555 wrote:Here's a example of designing / reworking, or assessing what you have already off of Throat size.

Kind of like the Golden Spiral...or The Fibonacci spiral if you will.

On to finesse stage.

I was asked for a ssr pic. Looks better than the drawing. Thanks, Charlie

Almost finished, aggressive burr is tough to finesse. Still needs hand sanding of ssr. Thanks, Charlie

Exhaust roof did get a bit more raising. Hopefully new improved flows Sunday.

90% of the time with most Heads ( wedge type) I have found that in terms of the valve bowl back wall that grinding straight down towards the top of the guide from the bottom cut makes for better low lift flow and rounding the transition from the back wall above the guide to the roof after the guide makes for better high life flow.
If your not getting the high lift flow you would like you will never hurt things by going for max low lift flow.

In terms of high lift flow as I look at the shot of your short turn I think your form as you get near the crown needs to be more of a D shape.
I know the two dimensions that we can see in photo may not represent the tru 3 dimension form , but this is how it looks to me.

I like to shoot for a form like in my photo.
When I am reworking a Exh port that is hindered by not enough short turn height , and is a short run lenght wise to the flange then in regards to the short turn once I get to the crown then I make the roof the D shape and I don't even touch the floor other wise your only making the pressure difference between the roof and floor even bigger and shotting yourself in the foot!
Sorry for going on and on here!

Mag, what kind of flow do you get out of that port? How many cc? Mcsa? I will take ssr pics later. Thanks, Charlie

Any of you guys ever run an engine on the dyno without any exhaust and the lights turned off to see what the exhaust is trying to do? Pretty quick you find out why flow testing exhaust ports without a pipe is bad info. The header is an integral part of exhaust port.

Tough pic to capture. Still looks off. Exhaust hand polish ssr.

Did you flow with and without polish?
If, what was the difference?

Erland

Erland Cox wrote:Did you flow with and without polish?
If, what was the difference?

Erland

Earlier in the thread it was worth 6 cfm. Now better on some lifts less on others.

Notice how nice this graph is! Clear and pretty. Thanks to Stan and my 11 year old computer genius.
Test #1 65 289 1.85" / 1.6" with bach cut valves and radiused exhaust face.
Test #2 65 288 1.85" / 1.6" without back cut valves or exhaust radius face

Back cutting valves make a huge difference on low lift efficiency.

Port velocity graph