#21  
Old 09-04-2020, 12:00 AM
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Originally Posted by pastry_chef View Post
Here are some theoretical cam examples for two different target velocities.

463 Pontiac
5500 RPM
1.65 Rocker.
Hyd Roller specs.

300 FPS
-----------
295 @ .006
242.5 @ .050
167.5 @ .200
.659 valve lift.

310 FPS
-----------
291 @ .006
239 @ .050
164 @ .200
.651 valve lift.
If you take the bigger port (im assuming its a good port which means it flows better) stick a cam in it with less duration and a good amount of lift it'll like it. This is the race section so im taking in terms of a race engine with good heads.
Now if the heads are hacked up and are just big and the rest of the shapes are junk then it probably needs duration.

  #22  
Old 09-04-2020, 12:02 AM
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Just a fwiw, more cfm = more velocity. So bigger ports can have as much or more velocity than smaller ports

  #23  
Old 09-04-2020, 12:40 AM
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Originally Posted by slowbird View Post
more cfm = more velocity. So bigger ports can have as much or more velocity than smaller ports
For sure.
There are many ways to evaluate, one is CFM / Sq.inch.
The CSA must also be well matched to displacement and RPM range. Displ and RPM are major factors in pressure differential - how hard the engine will demand from the port.


Last edited by pastry_chef; 09-04-2020 at 12:49 AM.
  #24  
Old 09-04-2020, 01:30 AM
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You size the CSA area to the engine size, RPM, VE / HP. Velocity shoild pretty much stay the same.

From Larry Meaux's PipeMax

462.184 Cubic Inches @ 6500 RPM with 105.00 % Volumetric Efficiency PerCent

--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
151 FPS at Intake Valve Curtain Area= 4.741 sq.in. at .600 Lift
144 FPS at Intake Valve OD Area and at Convergence Lift = .629
178 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 4.024 sq.in.
--- 6500 RPM Intake Cross-sectional areas in Square Inches ---
350 FPS CSA= 2.044 Port has Sonic-Choke with HP Loss ( too fast FPS )
330 FPS CSA= 2.169 Port may have Sonic-Choke with HP Loss ( too fast FPS )
311 FPS CSA= 2.302 Highest useable Port velocity ( possible HP loss )
300 FPS CSA= 2.386 Smallest Port CSA ( Hi Velocity FPS • good TQ and HP )
285 FPS CSA= 2.512 Smallest Port CSA ( very good TQ and HP combination )
260 FPS CSA= 2.753 Recommended average Intake Port CSA (very good TQ and HP)
250 FPS CSA= 2.864 Largest recommended average Intake Port CSA ( good HP )
240 FPS CSA= 2.983 Largest recommended average Intake Port CSA (less Peak TQ)
235 FPS CSA= 3.046 Largest recommended Intake Port Gasket Entry area CSA
225 FPS CSA= 3.182 Largest Intake Port Gasket Entry CSA ( Slow FPS )
215 FPS CSA= 3.330 Possible Torque Loss with Reversion ( Slow FPS )
210 FPS CSA= 3.409 Torque Loss + Reversion possibility ( too slow FPS )
200 FPS CSA= 3.579 Torque Loss + Reversion possibility ( too slow FPS )
Note : these are calculated average Port cross-sectional areas and FPS

Stan

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  #25  
Old 09-04-2020, 06:15 AM
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Stan, are these fps numbers from Larry at standard temp and pressure I would assume, because standard temp is 60 F and that's by far not the norm in fully warmed up motor .

The greater temps will lower the air density a good amount and allow for faster / higher fps numbers before sonic port choke takes place, no?

Just to make it known here, factory big Intake valve iron heads hit 350 fps when the go into sonic choke.

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Old 09-04-2020, 09:33 AM
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Standard temperature and pressure are 77 F and 1 atm, sonic velocity (or velocity when choked flow occurs) is 1,125 ft/s or 767 mph.

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Old 09-04-2020, 09:55 AM
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Quote:
Originally Posted by steve25 View Post
Stan, are these fps numbers from Larry at standard temp and pressure I would assume, because standard temp is 60 F and that's by far not the norm in fully warmed up motor .

The greater temps will lower the air density a good amount and allow for faster / higher fps numbers before sonic port choke takes place, no?

Just to make it known here, factory big Intake valve iron heads hit 350 fps when the go into sonic choke.
Steve,
Those are probed velocity and I am not sure at what temp and BP.

Edit - Let me restate that. Those are calculated average velocity using ACSA. But if you have not probed the port in different places at the standard 9 point grid points, your average can be good but a local grid point (or more) can be very bad and you would not know it.

Stan

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Last edited by Stan Weiss; 09-04-2020 at 10:18 AM.
  #28  
Old 09-04-2020, 10:02 AM
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Quote:
Originally Posted by AG View Post
Standard temperature and pressure are 77 F and 1 atm, sonic velocity (or velocity when choked flow occurs) is 1,125 ft/s or 767 mph.
For most, standard temp 60. As far as sonic velocity (SOS) that is not a fixed number but varies with temp. In a 1100 deg exhaust port your 1125 ft/s would be way off.

Stan
Attached Files
File Type: pdf FORD_pages-62-63.pdf (78.4 KB, 102 views)

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  #29  
Old 09-04-2020, 10:58 AM
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Sonic velocity occurs when the upstream pressure is 0.528 of the downstream pressure in general regardless of temperature and can vary slightly. As temperature increases, the velocity to achieve Mach 1 velocity decreases so you are correct about the 1100 °F exhaust port velocity. The intake Mach 1 velocity will be close to 1,125 fps depending on gas temperature. The article you sent states, " the most commonly accepted standard (for the correction factor) is J1349" which is 77 °F and 29.31 in Hg. Either J607 or J1349 can be used for the correction factor, but they say the J607 correction factor is usually 4% high compared to J1349 correction factor.

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  #30  
Old 09-04-2020, 11:48 AM
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Quote:
Originally Posted by AG View Post
Sonic velocity occurs when the upstream pressure is 0.528 of the downstream pressure in general regardless of temperature and can vary slightly. As temperature increases, the velocity to achieve Mach 1 velocity decreases so you are correct about the 1100 °F exhaust port velocity. The intake Mach 1 velocity will be close to 1,125 fps depending on gas temperature. The article you sent states, " the most commonly accepted standard (for the correction factor) is J1349" which is 77 °F and 29.31 in Hg. Either J607 or J1349 can be used for the correction factor, but they say the J607 correction factor is usually 4% high compared to J1349 correction factor.
I am going to have to double check that. As I have it As temperature increases, SOS increases

Stan

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  #31  
Old 09-04-2020, 12:16 PM
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The Mach velocity changes as a function of temperature by: Mach number at some temp = Mach vel at stp/sqrt(CpRT), Cp is the heat capacity of the gas, R is the universal gas constant and T is the absolute temperature in Kelvin. "sqrt" is the square root.

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  #32  
Old 09-04-2020, 12:27 PM
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Quote:
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. As I have it As temperature increases, SOS increases

Stan
Yes.
I'm pretty sure in my Pipemax 4.5 on the header specs report it tells you the exhaust SOS factored for temp. It will be much higher than 1125 FPS.

Somewhere I think I have the same formula Larry uses for it also.
A few months back I was able to correlate required exhaust "area under the valve curve". Also needs to take VE in consideration, complicated.

  #33  
Old 09-04-2020, 12:52 PM
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Quote:
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Yes.
I'm pretty sure in my Pipemax 4.5 on the header specs report it tells you the exhaust SOS factored for temp. It will be much higher than 1125 FPS.

Somewhere I think I have the same formula Larry uses for it also.
A few months back I was able to correlate required exhaust "area under the valve curve". Also needs to take VE in consideration, complicated.
Mike,
I sent you an email a couple of days ago. Did you get it?

Thanks,
Stan

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  #34  
Old 09-04-2020, 02:19 PM
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Quote:
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Mike,
I sent you an email a couple of days ago. Did you get it?

Thanks,
Stan
Just took a quick look at my mail, yes I got it.
I'll check it out tonight.
Thanks Stan,

  #35  
Old 09-04-2020, 07:14 PM
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Over on speed-talk a member asked Larry,
How did you determine exhaust gas sonic velocity?

Larry reply ----
Sorry , the equations are "proprietary",
i can't Post a Source Code example ,
but they accurately predict Exhaust System specs .

--
This brings a smile to my face. I have huge respect for Larry.

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Old 09-04-2020, 10:44 PM
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If you are really interested I can supply the equation to calculate the change in velocity as a function of gas temperature (and consequently velocity when choked flow occurs as a function of temperature) in detail if anyone wants to send me their email, offline so it doesn't impact this thread. None of this information is confidential and is readily available in the literature.

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  #37  
Old 10-01-2021, 02:26 PM
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Wow, 600/600 with the Stump Puller. What compression and exhaust were you using?
I have a a 462, 10.5:1, Cliff Q-jet, Ram Air 2.5” exhaust manifolds, RPM intake, made 505hp / 570TQ with a HFT 236/244 @ .050 with 1.65 HS roller rockers. Would be will I get to update cam and exhaust If I could gain another 70 - 80 HP.
Thanks

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71 GTO, 463, SD 295 d-port heads, 10.75:1, RPM intake, 502hp/560tq @ the crank, 200r4, 10" Continental convertor, Bullet 234/244 cam, Cliff's Q-Jet, 3:42's w/Eaton True Trac, 5 Power Tours. New performance numbers coming
  #38  
Old 10-01-2021, 03:07 PM
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Wow, 600/600 with the Stump Puller. What compression and exhaust were you using?
I have a a 462, 10.5:1, Cliff Q-jet, Ram Air 2.5” exhaust manifolds, RPM intake, made 505hp / 570TQ with a HFT 236/244 @ .050 with 1.65 HS roller rockers. Would be will I get to update cam and exhaust If I could gain another 70 - 80 HP.
Thanks

My apologies. The cam we used was called Road Paver. 246/252. Dave had 3 cams. Old Faithful, Stump Puller, and Road Paver.



We did 2-468 early 4 bolt blocks. We used Crower Solid roller lifters on Hydraulic Cams. both used 950 quickfuel carbs with torker 2 intakes port matched to heads. 3" mandrel Exhaust right out tailpipes with X over. Headers on both were Doug's 1-3/4". I believe compression was 10.5-1. Also use 1.5 Roller rockers.

  #39  
Old 10-01-2021, 05:20 PM
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Originally Posted by chuckies76ta View Post
My apologies. The cam we used was called Road Paver. 246/252. Dave had 3 cams. Old Faithful, Stump Puller, and Road Paver.



We did 2-468 early 4 bolt blocks. We used Crower Solid roller lifters on Hydraulic Cams. both used 950 quickfuel carbs with torker 2 intakes port matched to heads. 3" mandrel Exhaust right out tailpipes with X over. Headers on both were Doug's 1-3/4". I believe compression was 10.5-1. Also use 1.5 Roller rockers.
Thanks for clarifying, one more question……..what was vacuum @ idle?

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  #40  
Old 10-01-2021, 05:50 PM
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Vacuum was in the 12 inches as I can remember. I run a Hydraboost on my setup and my wife used the 11” booster wth no issues with brakes.

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