Don Terrill’s Speed-Talk

David Vizard wrote:

cspeier wrote:Pipemax recommendations can be spot on for headers. Lengths, and sizes....

Chad,
It is really rare that I disagree with you but for the engines we most commonly deal with all the commonly used programs are far from accurate.

DV

David, do you also use Engine Analyzer pro? We've had good predictive results on street/strip and race engines with four tubes into one collector.

My limited experience has shown very close correlation between the exhaust specs produced by PipeMax and by Dynomation; enough so that I now start DM sims using PM's specs, then fine-tune after the rest of the engine is optimized.

MadBill wrote:My limited experience has shown very close correlation between the exhaust specs produced by PipeMax and by Dynomation; enough so that I now start DM sims using PM's specs, then fine-tune after the rest of the engine is optimized.

i do the same thing with ENGMOD4T. pipemax and ENGMOD4T seem to also agree

David Vizard wrote:

Rick360 wrote:What variables go into calculating port energy? Velocity I assume ... but is it average port Velocity or at MCSA?? Flowbench velocity or running velocity? and area is probably included ... but again the question of which area ... avg or min? What about engine or cylinder cid or port length? What all is used to determine this Port Energy calculation?

Rick

Rick,
Port energy uses mean area, CFM, resultant velocity and mass of port air. The real comparative deal here, and it is not in this current program but will be, is the 'port energy density per foot length'. With this you can make caparisons across the board including 2 v vs 4 v heads.

If you need to know the mean velocity at any give point down the port you can enter that area instead of the mean area.

The Mach Index uses the mean area and the numbers generated are by my method not Charles Fayette Taylor's. My method returns numbers more akin to high rpm engines not blown 2800 rpm 2800 cube units Taylor experimented with. Beautiful though those big radials are I don't have a Bear Cat, Thunderbolt or a Corsair to put one in.
DV

Seems to be the flaw there is that flow benches use room temperature air heated to a value determined by the vacuum source motors while running engines use significantly hotter exhaust gasses. That undeniably changes the resultant velocity value. This is one reason why flow benches are less than adequate for thorough exhaust port analysis unless corrections are applied to compensate for such differences.

One can use CFM/Sq.In with measured pitot velocity and / or calculated mean velocity to derive data of equal relevance. It's all just numbers and they can be manipulated to show any value that may be helpful to paint a picture.

What precisely is "port energy density per foot length" and why would you measure in feet when no such port length would ever exist?

larrycavan wrote: One can use CFM/Sq.In with measured pitot velocity and / or calculated mean velocity to derive data of equal relevance. It's all just numbers and they can be manipulated to show any value that may be helpful to paint a picture.

Exactly.

Mean velocity and CSA has been used for years.

Randy

Randy 331 wrote;-


I'd say optimum ex pipe size has nothing to do to do with what the ex port flowz on a bench.

Those types of ideas are based on theory only.

Randy

From the summer of 1981 until about 1988 I was a consultant to Cyclone headers and mufflers. As such I could order up whatever I wanted to test or research on. During my ternure as such Cyclone patented at least half a dozen of my exhaust technology ideas including the Hot Rod Gale Banks conducted shoot out winning Sonic Turbo muffler. Along with this I developed a header that was cleaner than the factory Corvette manifolds as well as making about 30 lbs-ft and 30 HP more. It's strong point is that it could, in the cold start cycle, light off the cat in 7 seconds instead of the stock systems 15 seconds. At the time the cold start emissions were a big issue.

This testing happened at a very convenient time as for about 3 years I had the big push on cam testing for Harvey. What this meant was I had a prototype header maker at Cyclone to do what I wanted when I wanted. Net result was the testing of a grreat number of total exhaust sytems.

Then came the first of the cam design deals I did with Kent cams in the UK. After sorting through a number of very fuctional cams the boss at Kent asked us to develop headers that were appropriate for these engines in varius popular specs. A number of adjustable headers in differing patterns and tube sizes where made up plus we had a lot of pre-bent tubing and my parter, APT's wiz kid David Anton a fabricator and welder of the first order, could make up what ever we thought of pronto. All this lead to a huge number of highly analytical tests which showed easily identifiable trends.

It is this work involving hundreds of tests that I base my recomendations on - NOT OPINIONS. The selection of pipe diameter by means of the flow bench numbers works very well in practice so it is not an unproven theory.

Randy (and any others that it may apply to) if you choose to ignore the fact that the pipe size selection is based on literally hundreds of dyno tests you are in effect rejecting tens of thousands of dollars worth of rigorously conducted testing. That is entirely you perogative.

I don't give out tech stuff based on opinions like many folk do. I think that is a point that should be kept in mind by the many critics I have.

DV

David Vizard wrote: I don't give out tech stuff based on opinions like many folk do.

DV

No they appear to be based on 30 year old conclusions and assumptions.

Rick

Rick360 wrote:

David Vizard wrote: I don't give out tech stuff based on opinions like many folk do.

DV

No they appear to be based on 30 year old conclusions and assumptions.

Rick

As far as I am aware the laws of physics has not, to my knowledge, changed in the last 30 years. So what was good then still holds good!

If you have a proven technique for sizing an exhaust pipe lets all hear it please Rick. Doing so will be more use to ST posters needing to know than taking unproductive pot shots at me.

DV

Rick360 wrote:

David Vizard wrote: I don't give out tech stuff based on opinions like many folk do.

DV

No they appear to be based on 30 year old conclusions and assumptions.

Rick

Randy 331 wrote:-
Mean velocity and CSA has been used for years.

Just a querie here - was Randy's method also included in the '30 year old conclusions and assumptions' or did it only apply to me?

DV

It only applies to you, David. You know that. You could invent the first portal to another dimension and some of these guys would poo-poo how you did it. It doesn't scale!

Warp Speed wrote:

Stan Weiss wrote:
Unless things have changed very recently. The 2.9 - 3.0 HP per ci N/A NHRA (500 ci) and Australian Pro Stock (400 ci SB's) are running closer 60% Exhaust to Intake ratio.

Stan

Weird huh?!? Lol

Warp, this went by me at near light speed. Exactly what was weird??

DV

Since the heads of this threads topic are around 30 years old....... Seems like those 30 year old ex tests should fit right in.

PRH wrote:Since the heads of this threads topic are around 30 years old....... Seems like those 30 year old ex tests should fit right in.

50 year old heads!

RevTheory wrote:It only applies to you, David. You know that. You could invent the first portal to another dimension and some of these guys would poo-poo how you did it. It doesn't scale!

See, I'm stuck in a different position than you.

Since my own actual testing don't follow neatly along with charts and formulas, I have to decide if I'm gonna give up and follow neatly along, or continue to dyno test things myself and make decisions on those tests.

What would you do ?

Randy

I think a lot of people do their own testing and coming to their own conclusions.

I can give you names of guys that dyno for a living that would swear Pipemax is as accurate as the day is long.

Does that make them or the program wrong? Does that make someone whose data doesn't match right?

It means who gives a shit, do it any way you choose. Believe anything you want.. PROVE YOUR OWN THEORIES.

But I will say this. To survive in this business for decades you just can't make stuff up.

Most are honest in their conclusions is what I have found.