4-VALVE HEAD - OPTIMUM PORT VELOCITY?? 4

[v114]

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

 

[v114]

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?

 

[richdubbya]

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.

 

[Tmoose]

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?

 

[v114]

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.

 

[RGRv6guy]

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?

 

[Craighell]

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

 

[muuramenian]

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:

http://www.mototuneusa.com/thanx.htm,

check out high velocity porting. The sites interesting, but lacks any kind of updates for a number of years.

 

[flowmetrics]

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

 

[RGRv6guy]

Any updates V114???

 

[andyv8]

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

 

[jayskind]

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.

 

[djcramond]

what does you ignition timing curve look like