200 CFM Research

[jfholm]

John,
I did two different graphs. Each had one at peak HP and one at peak TQ. Is this what you are looking for?

jfholm

[emarsh]

Man, I've got to get some of that software for myself.

Am I misreading those graphs or are the ports going supersonic? I believe that the speed of sound is about 1128 fps at 70 degrees.

[jfholm]

[color=#000000]You are reading the exhaust port and that is a whole different ball game. Temps way up there etc. And you will notice that the peak exhaust port velocity is right after exhaust valve opening. That is one reason I feel that low lift exhaust port flow is so important.

I found a great online calculator for the speed of sound:


Speed of sound at 1200

[200cfm]

That speed chart helped my thinking a lot. What about the port velocity value? It is hitting 500 fps. Is that predicting the air speed in the running motor?

Now under boost the air temperature goes up a lot because of the turbo compressing the air. So that means the speed of sound for the port must also go up. And since the molecules of air are denser and closer together then a increase (though miscule) is added. So that would mean from a porting CSA vs choke rpm point of view, the choke point of the port has moved or increased up.

Is my thinking correct on this revelation? John, these heads are the fast port bench heads I reworked last fall. Average speeds down the center of the port was ruffly 315-325

I notice EAP predicted 306 fps at 6000 rpm (live engine) and 331 fps at 6500 so I am assuming the pitot bench readings I made are in the zone for this motor at 6k and hitting the choke rpm at 6500.

[200cfm]

Guys, I just notice something. I made a Pipemax review on this same motor and it predicted I had minimum cam lift (.524 after lash) and this would cause valve curtain area choke at 5409 rpm. I couldn't understand why the EAP graph showed a squaring of the intake fps at 550 fps on John's next to last above graph. It must be EAP is agreeing with Pipemax that the cam lift is choking at 5409 rpm because to the far right of the graph the rpm being graphed is noted by EAP and it reads 5500. Both programs are seeing the same choke rpm caused by the limited cam lift of .524"

If my thinking is corrrect on this, I have learned a lot tonight!

[jsa]

[jsa]

Here is an inlet plot from Lotus Engine Sim I did a long time back to help determine port size for a YB engine. 1 bar boost ( 2 bar absolute).

Pressures are absolute, blue verticals are inlet valve.

[jsa]

And the exhaust side, orange verticals are exhaust valve.

[jsa]

Predicted performance of a few different manifold configuartions.

[200cfm]

What part on the EAP graph is the port reversion? I see a negative intake port fps but it doesn't occur during the overlap of intake and exhaust timing.

Pipemax shows the cam lift of .525 (after lash) is barely adequate.

intake min @ .533" normal @ .577" max @ .634, max eff @ .655

Pipemax shows my exhaust lift as better.

exhaust min @ .486 normal @ .524 max @ .576, max effort @ .604

EAP is showing max hp at 5500 rpm and this appears to be caused by the choke limiting lift of the intake. Pipemax predicts a min lift of .524 before choke at 6000 for the exhaust. I think this explains the "engine layover" effect I was sensing on the track and that ET Anaylst For Drags was predicting beyond the 1100 ft mark.

As a reminder of the cam specs: 14/58/54/10 R112 lsa, 252/244 @ .050 , 24 overlap.

But that is not exactly how it measured on a cam degree test.
It showed a 8 degree retard grind for: 6/66/46/18 with ICL 120

To deal with the negative retard grind I installed it 6 degrees advance, so it runs down the track with a net -2 retard.

12/60/52/12 with ICL 112.

[jsa]

[jfholm]

I'll do that when I get home. I am at my brothers setting up his network right now.

I did advance the cam to where it was straight up instead of retarded and that is where it made the most HP and TQ so I will do that when I get home and post the results.
john

[200cfm]

Thanks jsa. I always thought reversion could only occur during the overlap. Must be some odd physics going on to delay it until nearly IC point as shown in the graph.

I think I am understanding the fps graph as it relates to crank degrees. Is it correct to view the square of the intake fps at 550 as occuring during the cam max lift degree time?

Can anyone explain the pressure graph. Why is the intake pressure sometimes like a sine wave and why such a high pressure value. Boost is only 6.5 value in the program. How could it be up around 30 psi? (tom c)

[jfholm]

Tom,
There is an explanation of all this in the appendices in the EAP manual starting on page 223. It is a detailed explanation.

John

[jfholm]

Actually start in appendice 3 page 214. There is where it starts the basic explanation of wave tuning.

John