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4-VALVE HEAD - OPTIMUM PORT VELOCITY??
4

4-VALVE HEAD - OPTIMUM PORT VELOCITY??

4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
I just recently found out about this forum and am very impressed so far with the topics and discussions.  I decided to post a question.

Quick background is that I am designing a head for a V twin from a clean sheet of paper.  It is a DOHC, 4 valve design.  I have a mechanical engineering background and I have experience with flow simulation software and would like to utilize it to design the proper port sizes and shapes for this engine. The engine has 4.25 bore and 4.00 stroke. The rev range should be 7000 to 8000.  I would like to see it make peak power well above 6500.
Most of what I find for literature exists for 2 valve designs.  

What equations /rules apply for max port velocity at 28 inches H2O ( intake and exhaust)for a 4 valve design (2 intake, 2 exhaust?

Any other suggestions on good port design practices would be appreciated.  

Thanks

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Max port velocity should not (cannot) exceed the speed of sound.------ Phil

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Phil is right, the thing to consider also is the total valve area of the design & this will govern what the port area etc will be. Everybody has there own idea's on things like this, but for me it is better to design the ports with the intention of porting to the correct size & shape to get the engine characteristics required. In other words start with the smallest ports in the design stage & test from there to get what you need, allow ample port wall thickness.

Don't forget the velocity around the valve head as well, there is a calculator at
http://www.rbracing-rsr.com/machcalc.html

There is also another calculator for runner area vs torque
http://www.rbracing-rsr.com/runnertorquecalc.html

Of coarse i wouldn't take these as being 100% correct but it might help get a better understanding of whats required as starting points only!

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

I have had good results with single and twin cylinder engines by keeping the average intake port velocities around 360 to 380 fps based on port cross section .do every thing you can to keep the port straight to reduce localized velocities .

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

A number of sources quote a figure of 50% or so of the speed of sound. This is based on average piston speed, the temperature of the inlet charge (which determines the speed of sound), and the flow area. The flow area might be the port area, the area under the seat, or through the seat depending on who is quoting the figures. There is at least one good SAE paper on the subject.

I think these rules of thumb are very usefull to get one started on a design. Simulations may have their place, but eventually you will have to slug it out with a good 2d or 3d cad program to figure out what will fit within the bore, how you will run the ports, how to get the spark plug in, and how to get enough cooling for the exhaust. This is what will make or break a design, and there will be lots of compromises.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

3.0L V6 4valve - max power at 6850:
Mean inlet port speed = 100m/s
Mean exhaust port speed = 120m/s
Based upon average port diameter (exc. throat area which was CNC machined)

Any higher and the powerband just went higher and torque dropped off, and vice versa.
This was also shown to be optimum based upon 1D engine simulation.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
Thanks for the info.  

For Andyv8:  

I assume that the velocities of 100 intake and 120 exhaust were measured/calulated based on flow bench work using 28 inches H2O?  Is that correct??  If so, these are well in line with what I have been using so far.  

One more question for all:  We have built a prototype of this head design and flow tested it.  The intake port is very "noisy".  Piecing whistling sound.  I am working with an experienced builder and he suspects turbulence.  The port flows 300 CFM at .200 lift, 360 CFM at .500 lift at 28 inches and the ports are not overly small.  Problem is this engine made best power at only 5200 rpm.  Could the noisy port be responsible??

Any thoughts??

Thanks, Jim

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Jim,

The 100/120 port velocities were calculated from mean piston speed.

port vel = (bore^2/port_dia^2)*mean_piston_speed
where port_dia is the equivalent dia of the combined 2 inlet ports. (all in mm)

I'll try to dig out some flow bench data from the same heads.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

My experience with four valve engines comes from experience developing maximum useable power in existing engines rather than design. I have found some basic differences between 2 valve and 4 valve designs though. One of the basic differences is the ability of the 4 valve design, because the lighter valve train weight, lower valve spring pressures, the lowered requirement for valve lift (more low/mid curtain area) and the resulting ability to open and close the valves faster, to require much less valve open duration for an equivilent rpm/cylinder size than the typical ohv 2 valve design. I have found that in long duration 2 valve applications you need a higher port velocity to get the flow moving at the low lifts when the piston is still moving slowly and you need high velocity when the valve is closing to prevent blow back. I believe that on well designed 4 valves the shorter duration and much faster opening and closing lessens the need for this high velocity. Furthermore this fast action (and the multi valves much higher low/mid lift flow) require a relatively larger volume behind the intake valves (less velocity). The same applies to the exhaust side, the blowdown occurs so much faster that larger ports (compared to a 2 valve and less velocity as derived from an engine size formula) are required. IMO velocity has a time element (duration) along with the engine size/port size normally associated with it. I have found 4 valve designs with smaller ports and more duration can develop more rpm but with less torque and do not perform as well. The larger port and shorter duration engines I have experience with are superior even at the lowest rpms. I have no knowledge on how this would affect any low emission requirements though.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
Thanks for the info.

Couple of more questions:

1.  We are using 246 duration and .460 lift for both the intake and exhaust.  Does that sound reasonable for peak power near 7000 rpm?

2.  "Furthermore this fast action (and the multi valves much higher low/mid lift flow) require a relatively larger volume behind the intake valves (less velocity)."

Do this mean that the intake runer length should be longer or bigger in cross section than on a comparable 2 valve??

3.  Basically, this engine has very good low end torque but will not make power past 5200 rpm.  We are tying to figure out why.  Both cylinders now are sharing a single 48mm carb and we suspect that we may need more.  The engine is 4.25 bore and 4.00 stroke.  

thanks




RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

These are only my opinions, and they are based on smaller cylinders than yours and much higher rpms. I would suggest listening to everyone and drawing your own conclusions. I would think that comparing equal engine sizes and rpm ranges a four valve would require at least 20 degrees less duration, .100 less lift and a small 10 to 20% increase in port cross section compared to an optimum 2 valve. I have only worked with a throttle body or carb for each cylinder so I have no knowledge of manifolding or carb size for multiple cylinders on 4 valve engines. We successfully use 41mm throttle bodys for each 300cc cylinder with port injection. Carburetors this size will result in a loss of low end torque and are limited to 38mm. I can't give an opinion on your specific numbers not knowing how the duration was measured or valve/port sizes etc. I have seen good power peaks at 10,500 with less than 220 degrees duration @.050 lift in admittedly smaller cylinders than you are working with. My experience favors equal or slightly less duration on the exhaust side. Camshaft phasing is very critical in these engines and can alter the rpm range considerably.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

I needed a 74mm throttle body on the V6 for best power - 65mm wasn't too bad, but still reduced power by ~6bhp @ 7000rpm.

Found the flow bench info (25" water):
Hope it's of some use.
Bore = 87mm
Stroke = 82.6mm


Bare Cyl. Head with plasticine bell mouth        
Cylinder 1 - Forward Flow            
Lift (")    Flow %    Range    CFM
0.050    13.10810811    4    38.8
0.100    27.90540541    4    82.6
0.150    40.97972973    4    121.3
0.200    52.63513514    4    155.8
0.250    61.68918919    4    182.6
0.300    68.31081081    4    202.2
0.350    71.99324324    4    213.1
0.400    74.69594595    4    221.1
0.450    75.70945946    4    224.1

Cylinder 1 - Reverse Flow            
Lift (")    Flow %    Range    CFM
0.050        4    41.9
0.100        4    81.4
0.150        4    120.5
0.200        4    147.7
0.250        4    166.8
0.300        4    177
0.350        4    183.5
0.400        4    188.9
0.450        4    191.9

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Years ago a Cosworth BDA four cylinder 1600 cc (about 100 cu. in.)had a 50 mm carb per cylinder (two each DCOE 50).

One 48 mm carb may be starving your twin.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

i like you're idea, one thing I have always thought about is trying to maintain a constant port cross-sectional area, the best port velocity is going to depend on your application and design, start modest and get bigger while testing power output. Use numbers as an initial test, when it comes to engines, even the best engineers int he world rely on research and development. I'm sure I didn't add much, but good luck.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Here is some additional input you may investigate. Although not relating to the cylinder head, the 4 cylinder oval migit engines have found for some time now, that the single most rpm extending area of attention is, the increased taper in the injector manifold to the butterfly. The port stays the same in the head, albeit the size of the butterfly has become remarkably larger in relation to what one would concider adaquate. It has nothing to do with airflow in, but affect the pressure wave in reverse. This wave is succesfully dampened enough to allow the flow to reverse forward into the port with decreased pumping loss, allowing these engines to hang on conciderably longer than without this taper. Although the power band your looking for may not apply, there is certainly a finger pointing in the manifolding direction IMO.

John Haskell
Aire Research Engr.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
In general, how does a 4 valve differ with respect to port velocity as compared to a 2 valve?  I am looking for some specific guidelines as far as proper port velocity (feet/sec) using a pressure differential of 28" H2O. This a 7-8000 rpm potential motor.  

My goal at this stage is to use a port flow simulation program (which I have access to) that I can set up to simulate flow performance on a flow bench.  Input to my program are pressure differential (28" in this case) and also port velocity.  

Thanks again   

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

V114,

No one is answering our question about flow bench velocity because thats not the way most of us approach the problem.  The demand placed on the head comes from piston motion (and exhaust scavenging).  You need to calculate the demand first, and then apply the demand across the cross-sectional area of the head, and this gives you the velocity in the head.  Most people look for intake manifold mean port velocities in the 300-360 ft/sec range.
The flow bench can be misleading because when you put a bigger head on it, the pressure drop goes down, and common practice is to crank the motor up to restore the 28 in pressure drop.  Does an engine do this? No.  The piston motion generates the available potential energy, in other words you only get so much to work with.
Shrieking ports on the flow bench are not good.  Because you have super high low lift flow, and not much gain as the flow increases (what size valves?, the short side turn may be too high, however this usually is not noisy.
360 cfm should be plenty to take a Harley to 8,000 rpm.  Are the exhaust pipes proven with regards to length and diameter?
 

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
AboveRedline:

"Shrieking ports on the flow bench are not good.  Because you have super high low lift flow, and not much gain as the flow increases (what size valves?, the short side turn may be too high, however this usually is not noisy."

Only the intake ports seem noisy.  There is a divider where the single runner divides into separate ports leading to the valves.  There may be something there that is causing the problem with noise.  I just don't know whether that noise has anything to do with the limited peak power rpm we see on the dyno.  Can the port be limiting rpm because of turbulence??

"The demand placed on the head comes from piston motion"

What is the correct calculation for the demand from piston action?

"Are the exhaust pipes proven with regards to length and diameter?"

Nothing on this engine is proven.  It is a completely new design. We are learning what it needs.  On the dyno, we tried two completely different exhausts and the peak power would still not go beyond 5200 rpm.


RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

v114,

RE: Carburetor

Your description of the carburetor as "48mm" is somewhat vague. The airflow limiting feature of a carburetor is usually the venturi. Assuming you have a 48mm butterfly, the venturi ID would be smaller in diameter. You may need a larger venturi ID. You probably need a much larger carburetor as well.

I used to build V-8 road race engines in the early seventies with 48mm Weber carbs. I used four 48mm Weber IDA's (butterfly diameter). The engines were about 300 cubic inches displacement. These carburetors had removable venturi's and various venturi ID's were offered. These were two throat carburetors, i.e. one throat per cylinder. We had excellent power to around 8500 RPM.

If your carburetor has a venturi that is too small, you could be going into choke flow easily. Hence, your 5200 RPM upper limit. We used to size the venturi's to match the track. Small relative diameter for tight "torque" tracks. Larger venturi's for a track like Riverside International Raceway (long track). Venturi size will move the torque curve like a dial on a radio.   

Flow test your carburetor and compare the test results with what the engine needs at say 90% to 110% VE or so.

I have a Porsche 996 GT-3 Cup head (four valve) in my shop that I would flow test if I had a bunch of extra time. Whatever the Porsche factory did to this head, they did right.

Will  




 

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
"Your description of the carburetor as "48mm" is somewhat vague."

The carb used is an HSR48mm Mikuni flat slide.  No buterfly.  It measures about 48mm at the bore.  

"Flow test your carburetor and compare the test results with what the engine needs at say 90% to 110% VE or so."

Mikuni states that the carb will flow 270CFM at 12".

I calculated the theoretical flow rate needed for 114 cu.in. at 8000 rpm to be 264 CFM (assuming 100% VE).  Given this, what is the recommended intake/carb flow for the application?  Is it safe to design to only 264 CFM? I assume there is a multiplication factor needed for a design flow rate based on theoretical flow required.

If the theoretical flow is 264 CFM
The intake flows - 360 CFM at 28"
The carb is capable of 270 CFM at 12"

Could the carb and intake port be a limiter????



 

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

If the carb is too small, you will see an increase in manifold vacuum at 5200. If the problem is in the manifold or ports you won't. What is the crankshaft degree at the intake lobe center? How does the area of the smallest point in the port or manifold compare to the valve curtain area?

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
"What is the crankshaft degree at the intake lobe center?"

I've used 106-108 degrees

"How does the area of the smallest point in the port or manifold compare to the valve curtain area?"

I don't have this info handy. What do you recommend?

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

V114,

I envy your project. OK if the carb flows 270 CFM at 12" it would flow 413 CFM at 28" in a perfect world. I would want to flow the head first with a radius inlet at max valve lift plus .1 inches (for good measure), then add the intake manifold with a radius inlet, it should be within -1% or better yet show a gain. Then add the carb to the whole thing with air cleaner (if you run one), it should again be within -1% to -2 %.

Port area, if it is a CNC port contact the porting people they will know the minimum cross sectional area, and possibly the average area. Not a CNC port, get some two part pour-able rubber low durrometer (12-15) from say Walco (www.walcomaterials.com) I use GE-25. Make a plug of the port, cut it into sections ink it with a stamp pad and stamp it on a .1" grid graph paper, count the squares (average the small parts around the edges) and divide by 100, poof port area. Do this several times down the lenegth of the port, look for the smallest cross sectional area (the choke point)around the valve guide boss or other obstruction.

As for the whistle port, yep it could be a problem. Try this little test, flow the head at 5" of water, do the flow correction for 28", does it flow the same as the perfect world correction? Try flowing the port at the highest depression your bench can provide, back the numbers down (with math) to 28" are they equal? The test is looking for high speed port problems the higher the test depression the higher the test velosity.

As for max port speed, average port speed etc. I have yet to see any concrete numbers, as for one of the posts " Ideal velocity is .0000001ft/sec less than the speed of sound, and you can get that from a .05cm/2 port, but it's the combination of volume and velocity that's going to equate power." I think you would be looking at F1 technology to prove a port at this speed. The best numbers I have found are around .55 MACH, say 614 FPS (max not average), this can make as much as 2.5 hp per cubic inch at near 10,000 RPM in a pure race engine.

Good luck,

PFM

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

First off your cam is to small the Rotax engines that i had worked on were only in the 670 cc range and required a cam with 270 degrees of duration @.050 judging from your flow figures your going to need a cam with 260 to 270 degress i also stated in here that average port velocitys should be in the 300 to 360 range higher of course for a wider curve .the 48 mm mikunis are probally a bit small for a cylinder this large i had built some special mikunis for a 80" dual carb project that had 48 mm venturis and tapered out to 52 mm. its going to be hard to over carb an engine with individual runners that is this large .my experience comes from building and porting single cylinder dirt track engines to working with the late Jim McClure on his fuel bike 4 valve heads .these numbers are just based on past experiences theres knowledege on this forum well beyond mine .

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
Any experience out there on what to use for crankshaft degree at the intake lobe center for an engine like this??  

Does 110 sound reasonable??

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

I'm sure opinions vary quite a bit on this. My experience shows that, combined with very fast valve opening and relatively short duration, figures in the 102 to 106 range give much broader torque and hp figures. I know it sounds low tech, but the most important aspect in a 4 valve is to make sure the intake valves open as quickly as possible (not earlier but faster), meet the piston, and follow it down the bore. If the ports are sized correctly to supply the very strong draw that this achieves, then the valves need to be closed much earlier because the cylinder fills fast and well and any long delay will cause back flow out of the cylinder into the port. The other way to try to accomplish all this is to have smaller intake ports, longer duration to try to fill the cylinder, and later closing of the valves to take advantage of the velocity in the smaller ports. This will work to some degree, but IMO you are giving up the basic advantage of the 4 valve head, it's ability to keep up with the demand in the cylinder as it occurs.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
Richdubbya,

On a 2 valve design, going from 106 say to 110 would imporve the top end HP and going from 106 to 102 would improve the low end torque.  Is this not the case on a 4 valve?

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Yes, the numbers work the same way. Advancing the intake cam will favor the low and mid range. The difference is that the 4 valve IMO, with correct porting, will fill the cylinder much quicker and the intake valves can be closed sooner without hurting the top end. When the valves follow the piston down as mentioned above, and the duration is shorter this moves the intake centerline forward resulting in a lower number. I didn't mean to imply that these numbers would work with your ports and cam, I was just trying to explain the difference between 4 and 2 valve porting/velocity/cam timing. I have seen 4 valve engines with intake timing at 101 make good power to 12,000. IMO the sooner you achieve your max volumetric efficency the better and closing the valves at that point makes the best power.







RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Hi Guyz,

  I'm new to this forum, and have been reading this with greate interest, and trying to use the formulars to find the best port size for my 3ltr v6 motor peak power at 6850-7000rpm, has 83mm stroke-87mm piston diamiter, 4 valve, very simular to andyv8's examples, but if best air speed is 100meters a second, thats going to need a big port, considering the piston is moving faster than that, so the port will need to be bigger than the diamitor of the piston, to slow it down to that speed

   What am I missing here, is it to do with avarage port speed, so do you calculate it at 3500 rpm?, how do I calculate best port size for peak power around 6800-7000 rpm, or for any rpm,

Thankyou,
Ryan

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Ryan, I think you have your piston speeds miscaculated.  They can't be more than 100m/s even at peak - more likely around 40m/s.  

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

V114:

I'd like to toss in a suggestion.

Why don't you get one of the available engine simulator software applications (available from www.performancetrends.com among others) and do a rough model of your engine. You can then play with a lot of variables and get a feel for how they interact.

No doubt you'll find - at the end of the process - that the dyno gives a slightly different optimum than the program, but right now you're facing an awful lot of interacting unknowns - and that's a great time to use computer simulation.

I've tried several of the inexpensive engine simulators and like the Performance Trends Engine Analyzer the best.  I'll confess I haven't yet validated the results, but the results vary in a way consistent with my experience modifying production engines for racing.

Good Luck!

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
ads22,

I went to the performance-trends site.  From your experience, what engine analyzer would be a good package for getting close - I was thinking the PLUS model and not the full blown PRO model.  I would be looking for general trends out of this simulation.

I like your idea - I didn't think the software was this affordable.

Good suggestion

Thanks

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Hi,

thanks Incandescent, hate that when you doing the math late at night, I looked at the piston speed, twice even, forgot to div by 60 for per second..

All looks good now on calculations.

Cheers
Ryan

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

The head design is one of those "The more you know the more complicated it gets." I thought I knew everything about head design untill I spent time at Branch Flowmetrics and Feuling R&D. My point is the velocities , delamination reversion waves, converging port walls,valve size and shape,rod ratio,lobe centers etc. The best chance of hiting your mark is use as many imperical formulas as possible with heads that are working in your rpm/bore requirements.
I use a ratio between exhaust & intake sizes of 1.2-1.3 after looking at everthing from Cosworth to Ducati. I use a 1.8:1 rod ratio gatering info from Jerry Branch Grumpy Jenkins and others. One last point that flow bench numbers can be deceptive as there is no piston in motion...

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Hi All,

 Now with theese caculations for peak power/rpm port sizes,  would the port size be the same for turbo charged engines?.


Thanks
Ryan


RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

I use the Performance trends soft ware and have had some good results on HD engines .theres a couple of examples in the pro version that are ether engines i built or worked on and they have produced very close results .i have also ran Hondas CRF 450 in the program and have shown very similar results in stock and modified engines these are a 4 valve engine. Ron Hamp, RHC

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

V114:

If you're mostly looking for trends, either the regular or the plus version should do fine.  The plus version is mostly convenience enhancements.

If you're going to actually model your engine in detail, you might want to consider the pro version as mentioned by Ron Hamp.  I think it's a rather different, heavier duty program that allows modeling of actual port profiles, etc.

But you'll certainly learn a LOT playing with the regular or plus version, and it should get you in the ballpark as to port sizes, valve sizes, required cfm flows, approx cam specs, etc.  Actually quite fascinating to play with, and really helps develop a feel for how all this stuff interacts.

Al Seim

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
richdubbya,

earlier you posted a rely stating "How does the area of the smallest point in the port or manifold compare to the valve curtain area?"

The valve curtain area here is approx 4.75 sq in for both intake valves together at max lift

The smallest x-section of the port is approx 2.7 sq in.

The existing intake x section is approx 3.00 sq in.

question is: what should the comparison look like?


thanks again for the help


RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Does that valve curtain area at max lift take into account valve to cylinder wall clearance? May need to approximate that part if you're trying to simulate it.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

You seem to be fairly close to what I use, port x section about 61% of curtain area. Your figures are a little lower. Making the transition from the single port to the 2 short ports is important. There has to be an increase in x section to accommodate the 2 valves and curtain area but try to make this gradual rather than abrupt to avoid a sudden loss in velocity. There is a trade off here, between velocity and the ability to keep up with the excellent mid lift flow of the 2 valves. Four valve engines need very fast opening intake lobes with less duration than you might think. It sounds simplistic, but IMO the intake valves must closely follow the piston down the cylinder. If the typical 2 valve cam lobe is used, then you need high velocity and long duration, and you end up with very little benefit (just combustion efficency) over a 2 valve engine.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
richdubbya,

I mentioned earlier in the thread about shrieking intake ports. As we test more on the bench, it seems that the noise does not interfere with the ability to flow.  The ports continue to increase flow as we increase lift.  We tested up to .500 lift.

In your opinion, is the noise something to be concerned with?  I am ready soon to put the motor back together and get in on the dyno again.  But if there is something to do about the port noise, I'd like to address it now.

Any thoughts?  Are 4 valves more likely to have ports more noisy than 2 valves?

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

A few years ago. when I first started working with 4 valves, I flow tested quite a bit. You can definitely hear the air but I wouldnt describe it as shrieking. Could it be a sudden velocity drop? With the intake valves in and the intake port flange up and level, add CCs of ATF and keep measuring the distance from the flange, you will be able to see if there is a sudden increase in area. Flow testing helped develop valve and seat/chamber shape but in my experience changes in ports and resulting flow measurements dont correlate to power output on 4 valves. You need a certain amount of flow but the head that flows the most could be way down on power compared to another. Dyno and track testing is the only way to know IMO.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Does the intake prot divider have a knife edge?
Might try putting a radius on it with clay while on the flow bench.

If the engine's on the dyno it might be worth retarding the cam a few degrees to simulate a little more cam.

What's the Brake Specific Fuel when the power is starting to drop?

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

(OP)
With all I have heard on this discussion, I am unsure about the trade-off between port and intake volume vs port flow rate and velocity.  Before I leave the flow bench, is it better to target the best flow numbers or let the flow numbers drop off (if that's what happens) as a result of making more volume behind the intake valves (larger area runners and intake ports.  
We have experimented with a few designs for the intake manifold configuration.  The one that had relatively large cross section runners and relatively large volume flowed much less than the more streamlined, smaller cross section design.  Not sure why? More importantly, not sure if one is more likely to work (make more power)than another.
The next round of dyno work will happen soon, but it would be nice to anticipate/predict Hp gains based on flow bench data.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

My experience is almost strictly with 2 valve heads,
but I generally try and get the choke point to flow
a ceratin % of the valve capability. That is what was
mentioned above, use 61% of cross sectional area at
the divider, and yours calculated to be 56% and I believe
that is where the problem is. I use sims too, and admittedly,
the Harley V Twin not being an example motor on it, I simmed
your exact combo (within reason) and it needed a much larger
cam than a 246* cam. Were you using the Harley standard .053"
lifter rise or the more common automotive .050"?
Makes little difference, the cam was much larger than
this would allow for, I was getting a cam in the 290 range
but using program supplied head models. I will adjust from
there and see what it suggests.

But back to the point I started on, I work it from
choke point and taper it both directions from there.
If Rich's suggestion that your choke is the divider section,
then I would enlarge it some, and IMO the noise might
subside too. That part bothers me, some reading I have
done that quotes (Ken?) Chapman indicates that a "perfect"
port will be just about ready to sound off (make noise)
and this indicates the flow/velocity is well balanced.
I know that is somewhat vague and applies to 2 valve   
stuff he works with, but the concept may follow thru to
the 4 valve arena.  

Flow on both sides of the choke is critical to get
just so, whether it is the valve, guide or some other
point of minimum flow/max velocity.  

Sounds like your 520M RPM HP peak is quite low, I'd really
inspect the choke point suggestions and the carb sizing.
The carb seems adequate if you used 2 of them, I know a
common plenum reduces overall carb needs but I do not know
the factor for a 2 cylinder. I'd exceed the the calculated
CFM needs of the engine by ~10% to start, after the choke
point is addressed. This assumes the common plenum arrangement.
Those appear to be the 2 problem areas from my viewpoint,
but I'm just a Jr. compared to these fellows around here!  

I love this board!    That's me, finally
a BBS where I can read more than post!  

PS: ran a quick sim with your flow figures and
a cam very similar to yours shows a 9k HP peak,
Either I am using too many wrong assumptions
(you list very sparse specs) or your setup is
quite overbuilt after you work out the RPM problems.

More specs please?  :D  

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

I have hear the strange shriek on ports that had a tight radius.  (old honda exhausts and mid 80's 1100 and 1150 Suzukis).  On the exhaust side - I was told it is the the air separating from the port floor as it exits.  Building up the floor and raising the port resulted in less noise and more power.

FWIW

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Choke point at 65% of inlet valve diameter seems to work the best for high performance motorcycles.  This is SMALLER than stock, yet seems to yield better results all the way trough the powerband.  Unbelievable?  Decide for yourself: www.mototuneusa.com/thanx.htm, check out high velocity porting.  The sites interesting, but lacks any kind of updates for a number of years.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

From my experience all this noise is turbulence.
i spent many time modifying cosworth and bmw M power heads, both of them they are "silent". You test them on the flow bench and you just hear the motor of the flowbench.
try to add material (clay) to see if the turbulence stops.

george

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Any updates V114???

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

NzRyan,

Probably way too late (been away from the forum for a while), but the answer your looking for is probably 27mm diameter ports for a 4v head on the v6.

Andy

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

Hi I was quickly scanning through your questions and answers and I have a suggestion. Look into the original work Jim Feuling did with his four vavle Harley Heads for Evo motors. They were often used for similar applications to yours (IE 3 and half to 4 inch bore v-twins), how many pushrod v-twins had torque peaks at that many rpms. Not many, his did without breaking valvetrain parts. the only complaint I every heard was cracking around exaust ports and that was not by the owners. I used to see a lot of those heads around before the whole aftermarket build a $30000 redneck rigid thing. Talking to him one time he mentioned the biggest thing he had to overcome was the abrupt angle required with 90° into the intake ports he did it with opposing dual  intake tracts merging into a common plenum. Visve two opposing firehoses (His explantion not mine). Now I don{t know what what bank angle you have or even if it is relevent to you head flow question. Of course elimination of obsolete valvetrain components for lighter more modern componants is desireable. Hell you could even eliminate those crappy poppet vavles with slide vavles mounted to a wheel/coonecting rod arrangement as I often dream about when I see an antique train.

For practical purposes Fueling{s work (Ok I dont have apostrophies) most reflects your own inquiry.

RE: 4-VALVE HEAD - OPTIMUM PORT VELOCITY??

what does you ignition timing curve look like

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