Port CFM for Simulations

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Stan Weiss
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Re: Port CFM for Simulations

Post by Stan Weiss »

Here are the flow numbers I used to get those 2 cam.

Stan
skinny_z_cfm254.gif
skinny_z_cfm247.gif
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Re: Port CFM for Simulations

Post by skinny z »

skinny z wrote: Sun Jul 18, 2021 11:31 am I may have to approach the software developer for an outright answer.
And I did. One of them anyway.
DV replied.

Kevin,
The flow required refers to the cylinder head flow only. The program assumed the use of an entirely adequate induction and exhaust, You should find intake and carb specs on subsequent pages
.

Between Stan's input and that reply posted above, I've got a pretty good handle on how this should shake out.
So, the onus is on me to ensure that the manifold is properly fitted. Whether that's the two plane Air Gap or a Vic Jr the cam spec will fall where it may. Then it's also up to the engine designer to make sure it's the right manifold.
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Re: Port CFM for Simulations

Post by skinny z »

Stan Weiss wrote: Tue Jul 20, 2021 3:00 pm This is from a program which is still in alpha testing. Hopefully I got all of your information entered correctly. The only difference between the 2 runs is one used your flow numbers and for the other all flow numbers were adjusted and 254 became 247. Both are for peak HP at 5610 RPM.

Stan

Cam Master 254.gif

254 CFM/283/279/105

Cam Master 247.gif

247 CFM/284/280/105





Running a few simulations with this program and I get these results.
What's interesting (but perhaps shouldn't be surprising ) is that at 10:1 and 254 CFM port flow, peak HP RPM falls in exactly as your 254 model. 5610 RPM. If I change the flow to 247, with the same CR, peak HP RPM falls to 5370.

383 10 254 SP.jpg

254 CFM/284/284/106

383 10 247 SP.jpg

247 CFM/279/279/106

Unlike the Cam Master results, there's still a substantial spread in the duration and overlap.

Something I just noticed was the reversal of the typical intake/ exhaust split. I get 4 degrees more on the exhaust whereas Cam Master has the reverse. I suppose that's indicative of Cam Master using the full cylinder flow spec as opposed to only the peak intake flow. Which makes a lot of sense.
I'm curious as to what Cam Master would specify if choosing a single pattern.

This a dual pattern as opposed to the single pattern posted earlier.
383 10 254 DP.jpg

254 CFM/284/288/106


383 10 247 DP.jpg


247 CFM/279/283/106


Still the same 5 degree spread.
More than one way to spec a cam I guess (duh)
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Re: Port CFM for Simulations

Post by Stan Weiss »

Kevin,
The 2 programs work differently. The program you are using based on your entered flow calculates a peak HP RPM and specs a cam. In Cam Master I enter the full flow numbers which I posted above and what I want for peak HP RPM. I used 5600 for both sets of flow numbers to get the 2 cams I posted. You cannot do that with the program you are using. Cam Master lets you do more, but at the same time you can also more easily get your self into trouble.

Stan
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Re: Port CFM for Simulations

Post by skinny z »

That's how I see it Stan. Both on the methods used for each program and the getting into trouble part.

That said, I genuinely like the results of the TM program and Cam Master. If I compare the two, I see a reasonable spec emerging.
~282 to 284 for a single pattern on a 106 LCA. I'm fully acquainted with dealing with that amount of overlap in a 350 which not coincidentally is the same for both programs at 72 degrees. Tuning a 383 with the same should be a piece of cake.
The peak HP RPM is spot on too. All in before 6k.

Thanks for your input. Much appreciated as always.
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Re: Port CFM for Simulations

Post by RDY4WAR »

I have PT Engine Analyzer Pro. When looking for an ideal cam for a combo in that software, I will use this calculator...

http://www.magneticlynx.com/carfor/calccam.php

I then calculate the E/I flow ratio to get the duration split and go digging into Comp's lobe catalog. For this particular 350ci LT1 wanting to shift around 6800 rpm, the calculator above said it needs to have 248* @ .050". So I picked out some HR XFI lobes in Comp's catalog.

298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

Here's what it spit out....
ST Pic 1.jpg
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Re: Port CFM for Simulations

Post by Stan Weiss »

RDY4WAR wrote: Sat Jul 24, 2021 2:42 pm I have PT Engine Analyzer Pro. When looking for an ideal cam for a combo in that software, I will use this calculator...

http://www.magneticlynx.com/carfor/calccam.php

I then calculate the E/I flow ratio to get the duration split and go digging into Comp's lobe catalog. For this particular 350ci LT1 wanting to shift around 6800 rpm, the calculator above said it needs to have 248* @ .050". So I picked out some HR XFI lobes in Comp's catalog.

298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

Here's what it spit out....

ST Pic 1.jpg
While it still needs some work which I never seem to get to. Try this version.

http://www.magneticlynx.com/carfor/calccamb.php

Stan
Stan Weiss/World Wide Enterprises
Offering Performance Software Since 1987
http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
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Re: Port CFM for Simulations

Post by skinny z »

Stan Weiss wrote: Sat Jul 24, 2021 3:09 pm
RDY4WAR wrote: Sat Jul 24, 2021 2:42 pm I have PT Engine Analyzer Pro. When looking for an ideal cam for a combo in that software, I will use this calculator...

http://www.magneticlynx.com/carfor/calccam.php

I then calculate the E/I flow ratio to get the duration split and go digging into Comp's lobe catalog. For this particular 350ci LT1 wanting to shift around 6800 rpm, the calculator above said it needs to have 248* @ .050". So I picked out some HR XFI lobes in Comp's catalog.

298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

Here's what it spit out....

ST Pic 1.jpg
While it still needs some work which I never seem to get to. Try this version.

http://www.magneticlynx.com/carfor/calccamb.php

Stan
254@.050.jpg

How does 220 @ .050 translate to advertised values in a hydraulic roller? I'm seeing everywhere from 270 -280 in COMPs lobe index.
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Re: Port CFM for Simulations

Post by skinny z »

RDY4WAR wrote: Sat Jul 24, 2021 2:42 pm
298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

How did you arrive at 83 degrees of overlap? And that huge exhaust split?
Which heads as well? My 6500 RPM 355 was with 72 degrees with these same 254 CFM heads. .050" was 236 on the intake. But the heads are small. Same cam was in an AFR 195 Eliminator headed 355 that buzzed to 7k. 288/294/236/240/110/106 off the shelf grind.
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Re: Port CFM for Simulations

Post by RDY4WAR »

skinny z wrote: Sat Jul 24, 2021 3:29 pm
RDY4WAR wrote: Sat Jul 24, 2021 2:42 pm
298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

How did you arrive at 83 degrees of overlap? And that huge exhaust split?
Which heads as well? My 6500 RPM 355 was with 72 degrees with these same 254 CFM heads. .050" was 236 on the intake. But the heads are small. Same cam was in an AFR 195 Eliminator headed 355 that buzzed to 7k. 288/294/236/240/110/106 off the shelf grind.
Stock LT1 heads that flowed 205 / 140 @ .400".
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Re: Port CFM for Simulations

Post by skinny z »

RDY4WAR wrote: Sat Jul 24, 2021 4:56 pm
skinny z wrote: Sat Jul 24, 2021 3:29 pm
RDY4WAR wrote: Sat Jul 24, 2021 2:42 pm
298 / 312 @ .006"
248 / 260 @ .050"
.624" / .624" lift (1.7 rockers)
111 +3 LSA

How did you arrive at 83 degrees of overlap? And that huge exhaust split?
Which heads as well? My 6500 RPM 355 was with 72 degrees with these same 254 CFM heads. .050" was 236 on the intake. But the heads are small. Same cam was in an AFR 195 Eliminator headed 355 that buzzed to 7k. 288/294/236/240/110/106 off the shelf grind.
Stock LT1 heads that flowed 205 / 140 @ .400".
Interesting.
Using this TM program I had a question along those lines. With a flow limited port, keep the valve open as long as possible was the general consensus. That's where the seemingly excessive duration from I guessing.
That said, I thought the Vortec intake port was modelled after the LT1. That would be 220 @ .500".
Being an LT1, and I'm assuming a Gen 2 SBC, is that also a relatively high compression ratio?
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Re: Port CFM for Simulations

Post by RDY4WAR »

skinny z wrote: Sat Jul 24, 2021 6:09 pm
RDY4WAR wrote: Sat Jul 24, 2021 4:56 pm
skinny z wrote: Sat Jul 24, 2021 3:29 pm

How did you arrive at 83 degrees of overlap? And that huge exhaust split?
Which heads as well? My 6500 RPM 355 was with 72 degrees with these same 254 CFM heads. .050" was 236 on the intake. But the heads are small. Same cam was in an AFR 195 Eliminator headed 355 that buzzed to 7k. 288/294/236/240/110/106 off the shelf grind.
Stock LT1 heads that flowed 205 / 140 @ .400".
Interesting.
Using this TM program I had a question along those lines. With a flow limited port, keep the valve open as long as possible was the general consensus. That's where the seemingly excessive duration from I guessing.
That said, I thought the Vortec intake port was modelled after the LT1. That would be 220 @ .500".
Being an LT1, and I'm assuming a Gen 2 SBC, is that also a relatively high compression ratio?
Yes. 10.4 stock compression with reverse cooling. The LT1 heads aren't quite as good as the Vortec 062/906 heads. The smaller 54cc chamber could be why.

When flow is limited, you have to hold the valve open much longer to fill the cylinder at higher rpm. That's why stock eliminator cams can be in the 270-280 @ .050" range.
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Re: Port CFM for Simulations

Post by skinny z »

Stan Weiss wrote: Sat Jul 24, 2021 3:09 pm While it still needs some work which I never seem to get to. Try this version.

http://www.magneticlynx.com/carfor/calccamb.php

Stan
254@.050.jpg

How does 220 @ .050 translate to advertised values in a hydraulic roller? I'm seeing everywhere from 270 -280 in COMPs lobe index. I suppose that's a question of application vs intensity but for this TM program, all values are advertised.
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Re: Port CFM for Simulations

Post by Stan Weiss »

Kevin,
That is a very limited calculator and only has enough input for the output it shows.

Stan
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http://www.magneticlynx.com/carfor/carfor.htm
David Vizard & Stan Weiss' IOP / Flow / Induction Optimization Software
http://www.magneticlynx.com/DV
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Re: Port CFM for Simulations

Post by skinny z »

Stan Weiss wrote: Mon Jul 26, 2021 12:08 pm Kevin,
That is a very limited calculator and only has enough input for the output it shows.

Stan
Fair enough. It certainly isn't overly complicated although it does have some interesting features.
Now, as for the 220@.050" your calculator produced (in the post above your latest reply), how does that translate in seat to seat values? Or is that now more of a choice of the engine designer? As I'm thinking it's now a question of durability vs intensity.
Kevin
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