How many seconds in a minute?

:) 60 but i think

at 6k RPM you will have 3k power cycles (inlet only open on power cycles) so that should read (6000/2)/60 or 6000/120

Gert

I don't think that power cycles matter in this case. We're only interested in one power cycle. If the engine turns over 6000 times in a minute, this is 100 cycles per second. So one rev (aka: 360 degrees) takes .01 seconds. Of this 360 degrees, 270 degrees (270/360 degrees) * .01 seconds would be the time during which the intake valve was open.

John,

I dug around and found this site. This formula supports your calculation above.

t = (60/n)x(z/360) or t = z/(nx6)

t = time in seconds
n = crankshaft speed in RPM
z = port open duration

This eq to 0.00761s of port open time @ 6K RPM and 274 cam duration.

Gert

Update on Flowbench
 

I have been working to get the flowbench finished and it is getting close, it took way longer than i thought, but should be able to finish this weekend and start with the calibration.

I also received the silicone and resin for making a mold of the port and CC. I will start getting ready to cast a copy of the head once i cleared up the mess in my garage.


Cheers

Gert

http://forums.pelicanparts.com/uploa...1236051303.jpg

http://forums.pelicanparts.com/uploa...1236051369.jpg

http://forums.pelicanparts.com/uploa...1236051419.jpg

http://forums.pelicanparts.com/uploa...1236051561.jpg

WOW - WOW
That flowbench is a work of art. Congratulations!

...lets hope that after he gets the fine art of flowing & tweaking heads understood that he will give ALL pelicans a great price to flow & tweak our cylinder heads as he ramps up his hobby business... ;-)
Best of luck here Gert!!
A stunning looking cabinet for sure!! How many hrs & how much did all the parts cost to make this flow cabinet??
Bob

Hi

No matter what that device is capable of doing it definetly does looks awesome.

A display of skill and devotion.
Really looking forward to the actual flow testing.

Jesper

Nicely done, Gert. My compliments to the "Chef".

Now,..........you're gonna learn some things,... :)

Thanks Steve et al,

I can not wait to start testing i have read so many articles, folmulas, threads and information in books that my head hurts and i have to start doing something with it :)

Bob,

I think about $800 in the flowbench including the digital manometer and pitout tubes, and if i have to add it up about 50 hrs labor and about 20 hrs of research.

what do you measure with that tool?

Then why the ridges in the exhaust port? Does the machinist also want turbulence in the exhaust path? If so, why?

To add to previous posts on turbulence, turbulence is desired only inside the combustion chamber, not in the port where high-velocity gas flow is desired. Correct me if I'm wrong here.

In addition, while cutting off the valve guide flush with the port wall increases flow, fine for a dedicated track engine, the abbreviated valve guide also reduces valve stem stability and thus increases valve guide wear. YMMV.

Sherwood

Hi Sherwood,

A few observations, if I might.

As you know, those are the artifacts of the CNC machining process however I've not seen any noticable effects on the flowbench nor on the engine dyno.

This gets complicated. In the case of the 911 engine's hemispherical chambers, these have little natural swirl of their own and are considered to be pretty lazy (not good). To help fill the chambers and get a proper homogenous fuel/air mix, one employs measures to achieve that in the port's shape, surface finish, and piston crown design. The CNC-machining ridges do assist carbureted engines more than MFI or EFI port-injected ones as they must pass the air/fuel mixture through the entire length of the port. Once again, they have not been a liability on the flowbench or on the dyno,... :)

This is a very complex subject with a lot of variables.

While that short guide path may suggest a shorter life, we've not seen that to be the case when good non-factory guides are installed and properly fitted to the valve. Like you say, YMMV based on who does what,... :) :)

Hi Steve,
thanks for your astute answers, as always.

I'll have to agree with you in regards to encouraging turbulence in the A/F mixture in the non-squish chamber. However, if the ridges from the cutter promote needed turbulence in the intake port, why then have them in the exhaust ports where turbulence isn't a requirement?

Sherwood

The way I understand it is the ridges in the intake port create a thin boundary layer of air rolling along the surface of the port called surface turbulance, while the air just above the surface of the port is shooting right on through never touching or dragging on the surface of the port.
It's almost as if the air tumbing along the metal surface is like a lubricant for the air moving along quickly just above it because it keeps that air from dragging on the surface of the port.
If the port was perfectly smooth that wouldn't happen and the airflow would drag along instead of tumble right at the surface. The tumbleing surface turbulance also keeps fuel atomized that may wet out on the surface of a smooth port. Especially on carburated and CIS cars.

Rough surfaced intake ports flow a little more air than polished smooth intake ports because of this.

The ridges in the exhaust port will probably fill up with carbon in short time and not have any effect.

Hey Sherwood,

The tooling marks are simply the result of the cutter working on the alloy and truly hard to eliminate in the exhaust port without almost doubling the costs. If the machine tool needs to make 4-5 more passes with smaller tooling, its simply adds to the cost and I've not seen a benefit to the additional expense to make it worthwhile doing.

I suppose if those tiny ridges really bothered someone, some time with a mild flapwheel would make them happy,... :) :) :)

Update
 

Flowbench is now fully done with digital manometer installed and all the velocity probes hooked up. I will wire the garage with the 220v feed and will hopefully be ready to start testing this weekend.

In the mean time i made a mold of the port and CC and will cast a copy of the head to start working with.

http://forums.pelicanparts.com/uploa...1236783014.jpg

http://forums.pelicanparts.com/uploa...1236783046.jpg


There has been some good information from the threads above and what i have taken from that is that the inlet surface finish and port shape is very important to promote good high speed flow, keep fuel in suspension and introduce swirl with the port shape to promote A/F mixture and combustion with the lazy ports. The exhaust port finish is not that important for flow (i.e. doesnot have to be a mirror polish) but could have some benefits if polished i.e. carbon is less likely to stick to port walls and also some heat reflection.

While creating the mold i measured the port volume and it came to 129cc on a centerline lenght of 3.6" This gives an average cross sectional area of 2.18"^.

Some information for interest :)

Below is the output of the PipeMax program based on my engine configuration and an estimated inlet flow of 236.25 CFM @ 28" as Kenikh had in the thread of the S registry in the beginning of the thread as a target.

These numbers are probably not accurate until it can be corrected to a known or measured engine output but still provides some indications.

From the average CSA above it seems like the port size (CSA) is still ok and should yield ~260Fps @28" (Maybe someone can comment on this)

The VE in this case was calculated based on the total induction flow of 236.25 CFM. (TBC when i have things hooked up to the flowbench)


82.651 Cubic Inches @ 7800 RPM with 126.8 % Volumetric Efficiency PerCent

Required Intake Flow between 234.9 CFM and 248.0 CFM at 28 Inches
Required Exhaust Flow between 184.7 CFM and 199.7 CFM at 28 Inches


------- Piston Motion Data -------
Average Piston Speed (FPM)= 3602.30 in Feet Per Minute
Maximum Piston Speed (FPM)= 5870.11 occurs at 75.584 Degrees ATDC
Piston Depth at 75.584 degree ATDC= 1.2228 inches Cylinder Volume= 220.1 CC
Maximum TDC Rod Tension GForce= 3053.55 G's
Maximum BDC Rod Compression GForce= 1734.86 G's


------- Current Camshaft Specs @ .050 -------

IntOpen= 28.00 IntClose= 60.00 ExhOpen= 49.50 ExhClose= 17.50
Intake Duration @ .050 = 268.00 Exhaust Duration @ .050 = 247.00
Intake CenterLine = 106.00 Exhaust CenterLine = 106.00
Compression Duration= 120.00 Power Duration = 130.50
OverLap Duration = 45.50 Lobe Center Angle (LCA)= 106.00
Camshaft installed Straight Up = 0.00 degrees

-Minimum Intake Valve Lift to prevent Choke = .521 Lift @ 7800 RPM
Minimum Exhaust Valve Lift to prevent Choke = .505 Lift @ 7800 RPM


- Induction System Tuned Lengths - ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 30.867 (usually this Length is never used)
2nd Harmonic= 17.519 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 12.231 (ProStock or Comp SheetMetal Intake)
4th Harmonic= 9.627 (Single-plane Intakes , less Torque)
5th Harmonic= 7.811 (Torque is reduced, even though Tuned Length)
6th Harmonic= 6.571 (Torque is reduced, even though Tuned Length)
7th Harmonic= 5.671 (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 4.988 (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood


------- Operating RPM Ranges of various Components -------

Camshaft Intake Lobe RPM = 7123 Exhaust Lobe RPM = 5889
Camshaft's Intake and Exhaust Lobes operating RPM range = 4815 to 6815
Note=> Lobe RPMs are only BallPark estimations

Minimum Intake Valve Lift to prevent Choke = .521 Lift @ 7800 RPM
Minimum Exhaust Valve Lift to prevent Choke = .505 Lift @ 7800 RPM

Current (Intake Valve Curtain Area -VS- Time) Choke RPM = 7521 RPM
Current (Exhaust Valve Curtain Area -VS- Time) Choke RPM = 7563 RPM

Intake Valve Area + Curtain Area operating RPM Range = 5448 to 7448 RPM

Intake Valve Diameter RPM Range = 5521 to 7521

Intake Flow CFM @28in RPM Range = 6183 to 8183
__________________________________________________ _________________________

Best estimate RPM operating range from all Components = 6051 to 8051

Note=>The BEST Engine Combo will have all Component's RPM Ranges coinciding
__________________________________________________ _________________________


--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
182 FPS at Intake Valve Curtain Area= 3.104 sq.in. at .502 Lift
185 FPS at Intake Valve OD Area and at Convergence Lift = .492
229 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 2.464 sq.in. at 7800 RPM
350 FPS Velocity CSA= 1.609 sq.in. at 7800 RPM Port Sonic-Choke with HP Loss
330 FPS Velocity CSA= 1.708 sq.in. at 7800 RPM Port Sonic-Choke with HP Loss
311 FPS Velocity CSA= 1.812 sq.in. at 7800 RPM Smallest Useable Port CSA
300 FPS Velocity CSA= 1.879 sq.in. at 7800 RPM Recommended Smallest Port CSA
285 FPS Velocity CSA= 1.978 sq.in. at 7800 RPM Recommended Smallest Port CSA
260 FPS Velocity CSA= 2.168 sq.in. at 7800 RPM Recommended Port CSA
250 FPS Velocity CSA= 2.255 sq.in. at 7800 RPM Recommended Port CSA
240 FPS Velocity CSA= 2.349 sq.in. at 7800 RPM Largest Intake Port Entry CSA
220 FPS Velocity CSA= 2.562 sq.in. at 7800 RPM Largest Intake Port Entry CSA
210 FPS Velocity CSA= 2.684 sq.in. at 7800 RPM Torque Loss + Reversion
200 FPS Velocity CSA= 2.818 sq.in. at 7800 RPM Torque Loss + Reversion

Cheers

Gert

Gert;
You're making great progress. It looks like you've got a lot of data and calculations there -- the trick will be to sort through it all and pick out what what's important and what doesn't really tell you anything new. A couple of specific questions and comments that came up as I read through your latest post.

While creating the mold i measured the port volume and it came to 129cc on a centerline lenght of 3.6" This gives an average cross sectional area of 2.18"^.

I'd beware of using "average cross sectional area" since it's not the average cross section that affects performance so much as the minimum. That being said, port volume is important to know, but I'd measure the volume all the way up the pipe to the butterfly, and then the trumpet tip. Once the air column is in the intake track, it doesn't care if it's in the head, in the throttle or carb body, or in the case of WOT in the trumpet. But I found it interesting comparing the cylinder volume to the intake volume. If you were to dump all of the mixture from the intake into the cylinder, what would happen to the pressure in the intake track?

------- Current Camshaft Specs @ .050 -------

What cam shaft design are you using?

Best estimate RPM operating range from all Components = 6051 to 8051

This sounds about right for a full-race engine.

--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
182 FPS at Intake Valve Curtain Area= 3.104 sq.in. at .502 Lift
185 FPS at Intake Valve OD Area and at Convergence Lift = .492
229 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 2.464 sq.in. at 7800 RPM
350 FPS Velocity CSA= 1.609 sq.in. at 7800 RPM Port Sonic-Choke with HP Loss
330 FPS Velocity CSA= 1.708 sq.in. at 7800 RPM Port Sonic-Choke with HP Loss
311 FPS Velocity CSA= 1.812 sq.in. at 7800 RPM Smallest Useable Port CSA
300 FPS Velocity CSA= 1.879 sq.in. at 7800 RPM Recommended Smallest Port CSA
285 FPS Velocity CSA= 1.978 sq.in. at 7800 RPM Recommended Smallest Port CSA
260 FPS Velocity CSA= 2.168 sq.in. at 7800 RPM Recommended Port CSA
250 FPS Velocity CSA= 2.255 sq.in. at 7800 RPM Recommended Port CSA
240 FPS Velocity CSA= 2.349 sq.in. at 7800 RPM Largest Intake Port Entry CSA
220 FPS Velocity CSA= 2.562 sq.in. at 7800 RPM Largest Intake Port Entry CSA
210 FPS Velocity CSA= 2.684 sq.in. at 7800 RPM Torque Loss + Reversion
200 FPS Velocity CSA= 2.818 sq.in. at 7800 RPM Torque Loss + Reversion

I don't understand what this set of data tells you. Especially given that everything is at 7800 RPM. BTW, I'd take a look at the model data at your expected torque peak. I believe that this will be key to making the engine strong. Above the engine's peak torque speed, it's just a case of declining returns, and trying to prop-up the curve as long as you can. Below the engine's peak torque engine speed will have a big impact on how driveable an engine is. If you design the engine around "peak HP", that means you're optimizing it's performance within about 500RPM-1000RPM of the engine's rev-limit. In your case this would be 7000-8000 RPM. This is a relatively uncommon situation and you'll risk having the engine be a dog at anything except that very narrow rev range. There are relatively few places on most race track where you'll be pulling those sorts of rev's for any amount of time (Road America and ovals excepted).

Hi John,

I will be using the DC62 Cams on 106 LCA. They are not full race cams but fairly "hot"

I used the average CSA to get a calculated average flow potential for the whole port and is based on some CFM number chosen, in this case Kenikh's head flow numbers as they are known and can be acheived. This will give a target for the runners and the carb and what i deducted from the program is that they calculate VE % for the whole tract and can use that as a comparitive target when i test it on the flowbench.

The rate of flow will vary at each CSA down the port for the same CFM ( in this case they calculated a value @ 28" simulating peak HP, not sure what they used or how they calculated that and mapped the velocities for a range of CSAs) and in my case the minimum will be (40mm) 1.94 sq in. What i read of the table at the end of the data stream is that at the minimum CSA point I will be @ 278 Fps, the ave CSA puts me @ 260 fps and i am still in the acceptable CSA range before i get into trouble with too big a port.

These are for me at the moment some data points that i can somehow relate to i.e. have known variables like pressure to test at and velocity numbers. I can perform order of magnitude comparisons to at least give me some ideas where i am at.

The formula that we used in the calc above yields a dynamic velocity number (in my case i think it was 285fps) but i don't know at which pressure to do a comparative test to measure that against on the flow bench, so its hard for me to use that as a target, maybe i am missing something and there is a way to do it .

Gert

Gert, great stuff!

To add to John's questions, how can the intake and exhaust lobe rpm be different given that our engines are SOHC, i.e. both lobes are on the same camshaft. Maybe that doesn't make a difference in the calculations.

John, I think the final table shows the port velocity at various port cross sectional areas and the impact on performance at a fixed RPM. Since you cant show a three-variable analysis without a graph, I think that is why RPM is held constant and the velocity varied with area.

Hi John. I agree on your interpretation of the last table. I'll reiterate that I think that this data is far more meaningful if you're looking at the peak torque RPM, or maybe across the rev range for a given CSA. As far as your cam question, keep in mind that both lobes don't share the same profile, even though they are mounted on the same shaft.

Another thought that might be interesting Gert, is to run a couple of known engine configurations through your model to validate it -- for example your stock engine configuration. You should be able to correlate the outputs from your model with your engine's factory HP and torque graphs. Chances are the numbers won't match exactly, but hopefully the peak torque and peak HP numbers should occur at roughly the same points on the rev range as your model predicts. Hopefully the rough order of magnitude numbers will be similar to the stock configuration, and trend in a similar fashion. If these don't happen, you'll know that you need to do some more work to understand the variations from the model's predictions.

John,

Thanks,

I am not sure what his data means I can only infer that it relates to the RPM @ at which efficiency peak for the exhaust and inlet lobes are achieved based on the rest of the engine components like valves, L/D ratio etc. I dont hink they mean they will be spinning at different RPMs as they are, as you mentioned on the same camshaft. I will email the owner of the program (Larry Meaux) for clarification.

Gert

John; in response to your question about why the intake and exhaust valves would have different ideal engine speeds. I remembered a couple of equations that I worked out when I was doing the "How to select a 911 Camshaft" thread. Specifically there were two formulae that I derived by doing a regression analysis against a number of the 911 engine configurations.

Peak torque engine speed = -3151+(Intake Duration degrees * 32.53)

Peak HP Engine Speed = (exhaust duration degrees * 66.62) - 9083

Looking at what Gert's model produced:

------- Operating RPM Ranges of various Components -------

Camshaft Intake Lobe RPM = 7123
Exhaust Lobe RPM = 5889

The thing that is strange at first blush is that it would appear Gert's program suggests that the intake cam lobe has a bigger affect on the HP peak (which you would expect to be up in the 7000 RPM+ range) and the exhaust lobe on the peak torque RPM (usually a couple of thousand RPM less then the peak HP engine speed). My analysis suggests that the relationship is vice-versa.

Curious...:confused:

You can have a head that flows real good high numbers that doesn't make the hp of one with proper designed ports that flow less. Flow isn't everything.

Long post
 

Response from the creator of the program:
What is camshaft intake and exhaust Lobe rpm? Is that the speed of the cam? And why a range?

Lobe RPM estimations are equivalent to how much
"Area Under the Curve" they represent from a
combination of Valve Lift and Duration @.050"

From these "Lobe RPMs" estimations the User can see
at what RPM Range those particular Cam Specs will give
you the greatest Power

or

Lobe RPMs are the "BallPark RPM estimation" at which each Cam Lobe
would naturally like to operate.

Lobe RPM = is a combination of Lift and Duration and Centers
...similar to Area Under the Curve, or Lobe Area

As suggested I ran the same program with the stock SC configuration and came up with this:

I used the cam timing and HP data from Bruce A’s book and tweaked the VE% until I achieved the quoted HP number. Tq also came close i.e quoted values to the program’s calculation. Peak Hp RPM was adjusted to be the same as the choke RPM of the exhaust valve andd was not the same as BA book, closer to the plot in Johns post on selecting Cams.

What is interesting and maybe the reason Porsche reduced the port sizes again:

Based on the highlighted areas below it is clear that in this configuration i.e. 39mm (1.85 sq-In) SC ports were way to big and could have been prone to reversion due to low port velocities


182.651 Cubic Inches @ 6250 RPM with 94.0 % Volumetric Efficiency PerCent

Required Intake Flow between 127.6 CFM and 133.9 CFM at 28 Inches
Required Exhaust Flow between 99.7 CFM and 108.0 CFM at 28 Inches

600 RPM/Sec Dyno Test Lowest Low Average Best
Peak HorsePower 171.7 178.8 182.3 185.9
Peak Torque Lbs-Ft 160.0 166.6 169.9 173.2

HorsePower per CID 0.940 0.979 0.998 1.018
Torque per Cubic Inch 0.876 0.912 0.930 0.948

BMEP in psi 132.1 137.5 140.2 143.0
Carb CFM at 1.5 in Hg. 310 345 363 380

Target EGT= 1486 degrees F at end of 4 second 600 RPM/Sec Dyno accel. test
Octane (R+M)/2 Method = 86.3 to 88.9 Octane required range
Air Standard Efficiency = 58.05734 % for 8.500:1 Compression Ratio

Peak HorsePower calculated from Cylinder Head Flow CFM only
600 RPM/Sec Dyno Test Lowest Average Best Potential
Head Flow Peak HP = 166.3 205.6 244.9

----- Engine Design Specifications -----
( English Units ) ( per each Valve Sq.Inch area )
Engine Size CID = 182.651 Intake Valve Net Area = 2.824
CID per Cylinder = 30.442 Intake Valve Dia. Area = 2.923
Rod/Stroke Ratio = 1.816 Intake Valve Stem Area = 0.098
Bore/Stroke Ratio = 1.350 Exhaust Valve Net Area = 1.996
Int Valve/Bore Ratio = 0.516 Exhaust Valve Dia. Area = 2.094
Exh Valve/Bore Ratio = 0.437 Exhaust Valve Stem Area = 0.098
Exh/Int Valve Ratio = 0.847 Exh/Int Valve Area Ratio = 0.717
Intake Valve L/D Ratio= .233 Exhaust Valve L/D Ratio= .242
CFM/Sq.Inch = 43.6 to 45.8 CFM/Sq.Inch =47.6 to 51.6
Curtain Area -to- Valve Area Convergence Intake Valve Lift inch= .482
Curtain Area -to- Valve Area Convergence Exhaust Valve Lift inch= .408


------- Piston Motion Data -------
Average Piston Speed (FPM)= 2886.46 in Feet Per Minute
Maximum Piston Speed (FPM)= 4703.61 occurs at 75.584 Degrees ATDC
Piston Depth at 75.584 degree ATDC= 1.2228 inches Cylinder Volume= 220.1 CC
Maximum TDC Rod Tension GForce= 1960.54 G's
Maximum BDC Rod Compression GForce= 1113.87 G's


------- Current Camshaft Specs @ .050 -------

IntOpen= 7.00 IntClose= 47.00 ExhOpen= 49.00 ExhClose= -3.00
Intake Duration @ .050 = 234.00 Exhaust Duration @ .050 = 226.00
Intake CenterLine = 110.00 Exhaust CenterLine = 116.00
Compression Duration= 133.00 Power Duration = 131.00
OverLap Duration = 4.00 Lobe Center Angle (LCA)= 113.00
Camshaft Advanced = 3.00 degrees

-Recommended Camshaft Valve Lift-
Minimum Normal Maximum
Intake = 0.395 0.426 0.468
Exhaust = 0.368 0.396 0.435
Max-effort Intake Lift = 0.491
Max-effort Exhaust Lift = 0.456
Minimum Intake Valve Lift to prevent Choke = .426 Lift @ 6250 RPM
Minimum Exhaust Valve Lift to prevent Choke = .396 Lift @ 6250 RPM


------- Operating RPM Ranges of various Components -------

Camshaft Intake Lobe RPM = 5819 Exhaust Lobe RPM = 5551
Camshaft's Intake and Exhaust Lobes operating RPM range = 3752 to 5752
Note=> Lobe RPMs are only BallPark estimations

Minimum Intake Valve Lift to prevent Choke = .426 Lift @ 6250 RPM
Minimum Exhaust Valve Lift to prevent Choke = .396 Lift @ 6250 RPM

Current (Intake Valve Curtain Area -VS- Time) Choke RPM = 6608 RPM
Current (Exhaust Valve Curtain Area -VS- Time) Choke RPM = 6236 RPM

Intake Valve Area + Curtain Area operating RPM Range = 4787 to 6787 RPM

Intake Valve Diameter RPM Range = 4608 to 6608

Intake Flow CFM @28in RPM Range = 3995 to 5995
__________________________________________________ _________________________

Best estimate RPM operating range from all Components = 4050 to 6050

Note=>The BEST Engine Combo will have all Component's RPM Ranges coinciding
__________________________________________________ _________________________


--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
112 FPS at Intake Valve Curtain Area= 2.727 sq.in. at .450 Lift
105 FPS at Intake Valve OD Area and at Convergence Lift = .482
129 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 2.367 sq.in. at 6250 RPM
350 FPS Velocity CSA= 0.874 sq.in. at 6250 RPM Port Sonic-Choke with HP Loss
330 FPS Velocity CSA= 0.928 sq.in. at 6250 RPM Port Sonic-Choke with HP Loss
311 FPS Velocity CSA= 0.984 sq.in. at 6250 RPM Smallest Useable Port CSA
300 FPS Velocity CSA= 1.020 sq.in. at 6250 RPM Recommended Smallest Port CSA
285 FPS Velocity CSA= 1.074 sq.in. at 6250 RPM Recommended Smallest Port CSA
260 FPS Velocity CSA= 1.177 sq.in. at 6250 RPM Recommended Port CSA
250 FPS Velocity CSA= 1.225 sq.in. at 6250 RPM Recommended Port CSA
240 FPS Velocity CSA= 1.276 sq.in. at 6250 RPM Largest Intake Port Entry CSA
220 FPS Velocity CSA= 1.392 sq.in. at 6250 RPM Largest Intake Port Entry CSA
210 FPS Velocity CSA= 1.458 sq.in. at 6250 RPM Torque Loss + Reversion
200 FPS Velocity CSA= 1.531 sq.in. at 6250 RPM Torque Loss + Reversion

--- Cross-Sectional Areas at various Exhaust Port Velocities (@ 28 in.) ---
123 FPS at Exhaust Valve Curtain Area= 2.026 sq.in. at .395 Lift
119 FPS at Exhaust Valve OD Area and at Convergence Lift = .408
147 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 1.696 sq.in. at 6250 RPM
435 FPS Velocity CSA= 0.573 sq.in. at 6250 RPM Sonic Choke at Throat Area
350 FPS Velocity CSA= 0.711 sq.in. at 6250 RPM Port Sonic-Choke with HP Loss
330 FPS Velocity CSA= 0.755 sq.in. at 6250 RPM Port Sonic-Choke with HP Loss
311 FPS Velocity CSA= 0.801 sq.in. at 6250 RPM Smallest Useable Port CSA
300 FPS Velocity CSA= 0.831 sq.in. at 6250 RPM Recommended Smallest Port CSA
285 FPS Velocity CSA= 0.874 sq.in. at 6250 RPM Recommended Smallest Port CSA
250 FPS Velocity CSA= 0.997 sq.in. at 6250 RPM Recommended Port CSA
240 FPS Velocity CSA= 1.038 sq.in. at 6250 RPM Recommended Port CSA
225 FPS Velocity CSA= 1.108 sq.in. at 6250 RPM Largest Exhaust Port Exit CSA
210 FPS Velocity CSA= 1.187 sq.in. at 6250 RPM Largest Exhaust Port Exit CSA
190 FPS Velocity CSA= 1.312 sq.in. at 6250 RPM Torque Loss + Reversion
180 FPS Velocity CSA= 1.385 sq.in. at 6250 RPM Torque Loss + Reversion

Next post i will use to model my planned engine to create some gasflow and velocity targets.

Subscribed!

Theoretical model to start head porting with from the PipeMax program:


CFM # is based on VE% required to fullfill cylinder demand of 222.6 CFM at peak RPM between 70 and 80 deg crank angle as per the screen shots below

Target inlet flow : 222 – 234 CFM (Carb, Manifold, head with valve at .502” lift & WOT)
Target inlet port velocity: 275 FPS down centre of port bare head
Target inlet port CSA 1.92 (sq-in) for above velocity
Target 0 turbulence at all lifts especially convergence lift for both intake and exhaust
Maximize swirl by port shape (better combustion, need to find a way to measure this)

Will start flow testing by next week.

Screen shots of program output.

http://forums.pelicanparts.com/uploa...1237860486.jpg

http://forums.pelicanparts.com/uploa...1237860899.jpg

http://forums.pelicanparts.com/uploa...1237860573.jpg

http://forums.pelicanparts.com/uploa...1237861302.jpg

http://forums.pelicanparts.com/uploa...1237861438.jpg

http://forums.pelicanparts.com/uploa...1237861524.jpg

http://forums.pelicanparts.com/uploa...1237861635.jpg

http://forums.pelicanparts.com/uploa...1237862217.jpg

http://forums.pelicanparts.com/uploa...1237861780.jpg

http://forums.pelicanparts.com/uploa...1237861866.jpg

Here are some interesting tidbits on Porsche head shape. These graphs show the 3.0 exhaust port's cross sectional area from the port (left) to the valve (right). The Y axis is the area in in^2. The first graph is of an unmodified 3.0L exhause port and the second is a port that has been smoothed by machining off the protruding valve guide etc... I do cnc porting and the coarsness of the ridges are determined by how much the tool steps over during machining. To make the ridges 1/2 as big it would double the time it takes to machine the port. These graphs are taken from the CAD files that drive the CNC machining process so they are extremely accurate.

http://www.youtube.com/watch?v=2lsS05SbYyI


http://forums.pelicanparts.com/uploa...1238016326.jpg

http://forums.pelicanparts.com/uploa...1238016343.jpg

The x axis is arc length along the "centerline" of the intake port tract?

I assume the big dip in the stock graph is the valve guide boss intruding into the port?

Here is the same port that has been further refined.


http://forums.pelicanparts.com/uploa...1238016799.jpg

Right, the X axis is a line down the center of the port pointing in the flow direction. The area accounts for the valve boss, guide, and valve stem and it is normal to the flow direction.

Interesting how the area just behind the valve opens up quicker in graph#2 and then smooths out again in graph#3. Is this a "5-angle valve grind" job?


Thanks for posting these. I find this information very interesting and useful in visual form.

No, the walls have just been stretched and massaged a bit. It is very difficult to get it just right and tiny differences really show up on the graphs. The difference between smooth and not smooth is very subtle.

Just a data interpretation point, note that the graphs do not have their origin at 0,0 which tends to accentuate the difference.

For example, it looks like a stock port loses about 9% of it's area at the valve boss, so the velocity through that venturi would increase by almost 10%. I don't remember off of the top of my head how much the pressure will drop as a result of this. The question is -- is this a good thing or not? Obviously obstructions are bad things. But 9% doesn't strike me as a huge issue, especially if an engine isn't port constricted except for potentially at peak revs. A couple of hypothetical mental examples...

1) It might be advantageous to increase the charge's velocity prior to it flowing into the combustion chamber since this will increase turbulence downstream of the venturi and the valve -- specifically in the combustion chamber. Thus it aids the mixture of fuel and air in combustion chamber which can improve combustion quality and performance.

Alternatively...

2) You might want a straight shot down the port to allow the smoothest possible flow past the valve, and depend on the combustion chamber shape to provide the turbulence needed to ensure a high quality combustion event. In this case, just grinding the whole boss away is easy enough. But then the question is what does this do to the flow past the valve stem? In many cases a smooth transition may be preferable to the reduction in cross-sectional area. I suspect that Bullet Bob is actually opening the port up around the boss and leaving the boss in place, thus leaving the boss to smooth the flow around the valve guide while still keeping the same cross-sectional area.

Either approach might be successful, but they both depend on making port design do what is best to support the most efficient and powerful combustion in the chamber. So the design of the piston crown and combustion chamber in the head also come into play. So my point is that I think that we need to be careful to assume that either "More is better" or "Straight is better."

Am I reading these wrong, or does the stock port (top graph) have more cross sectional area behind the valve?

Like graduate school work without the school, actually more exciting because it is automotive/motorsport.

Comphrehensive, and with good planning.

Good point. How did that happen? Are you adding material as well as cutting it away Bullet Bob, or maybe using a different head as the raw material for your porting excercise?

Another Update
 

My apologies for the slow updates, been busy at work with new projects.

I finally got time to calibrate the flowbench and get the first flow tests done. I used 3 sharp edge orifice plates that were sized for 100, 200 & 300 CFM @28" of H20. The flow numbers measured on the bench were 99 , 201 and 300 CFM for the respective plates and i was very happy with the numbers for a home built bench. :)

I fabricated the attachment in the pictures below to connect the cylinder and head to the flowbench and the mechanism to open the valve and proceeded to do my first flow tests.

I had done some light porting on one head previousy and did a comparative test to one of the stock heads. The ported head used a +1mm inlet valve.

http://forums.pelicanparts.com/uploa...1239241274.jpg

http://forums.pelicanparts.com/uploa...1239241454.jpg

The heads flowed a respectable amount of air/sq-in of valve area (82CFM stock and 87CFM modified) and compares favorably to other flow numbers posted on the forum. This doesnt really mean a lot as the flow alone is not the begin and end-all, but at least gives an idea. Low lift flow is still very close to stock and there was a slight lift in the flow numbers from .150" up to the end of the lift range for the modified head.

The logged velocity measurements were taken with a pitot tube 1.5" into the port in the center, I also measured the airspeed just off the SSR and measured 390FPS. From the research i have done, indications are this might be too high and it will be one of the areas to focus on in the next steps together with the low lift flow.

I have also done flow tests without a radius on the port and that yielded lower flow numbers (~-6CFM) but higher velocity numbers. I have not logged them but will in future. This might be useful in future to get the port velocity up for lower lift numbers.

I also flow tested the 50PMO carb on a manifold and then the PMO connected to the slightly ported head all at 28"

The carb and manifold flowed 305CFM and the carb and manifold connected to the head flowed 250CFM @ full lift (.502") and introduced 15CFM loss over the bare head. The loss could be due to the fact that the manifold was not mached to the head and the head port edge was in the airstream.

I will next map the port velocities and pressures at various positions in the port to get an idea of the flow patterns to plan the next modifications.

Head mounted on flowbench with digital flow readouts:

http://forums.pelicanparts.com/uploa...1239241595.jpg

http://forums.pelicanparts.com/uploa...1239241629.jpg

Excellent! http://forums.pelicanparts.com/support/smileys/wat6.gif

I'm not really sure how this happened. I ran these tests over a year ago and it was more out of curiosity than anything. The cnc porting I do is to convert 3.0 small port heads to big port heads and T heads to S heads. These are an exact match to the factory heads to comply with the 911 spec racing class.

Since I had accurate CAD files for these heads I played around with them to see what the characteristics were and the impact of minor modifications. In modifying the heads I removed a bit of material right around the valve boss on the outside of the port and I eliminated the valve guide protrusion in the same manner as the pictures of the machined heads shown earlier in this post. If I remember correctly I think I even tried valves with different size stems.

One thing that stood out was the factory 3.0 heads had a much smoother transition than the T and S heads leading me to believe that this was the direction Porsche took as they refined their port shapes.