high velocity porting on a 2v per cyl pushrod motor

[knighty]

take a good look at this link below, you will need to register, but believe me, its worth it!......this guy is tuning on 4v per cylinder bike engines, he is reducing the intake port area by about 30% in height, by adding epoxy/devcon/liquid ali to the floor of the intake port floor.......I think you can call it high velocity porting or super sonic porting, take your pick

-=MototuneUSA Motorcycle Performance Roadracing Superbikes & Wild Girls

he is achieving fantastic results, and so are hundreds of other poople, the site is a bit tacky, but the technical theory is all backed up with dyno data and other peoples references with good feedback

the million dollar question is.......has this ever been done on a push-rod 2v per cylinder motor?......did it work?

[automotivebreath]

Sometimes class rules make you do things that are out of the ordinary. Such
is the case with NHRA Super Stock engines. Read more about some testing
done by Larry Meaux on 162-165 cc intake runner SBC heads.

Could it be in the case of the bike heads the original ports were too large?

Originally Posted by maxracesoftware

here's some Threads from a couple of Posts that might explain
CHOKE to you

here's a very good quote from STEVES
that explains the general idea and reason why Choke
or too fast FPS hurts HP+TQ
just read rest of Posts with that in mind .

As I understand it, ports don't actually go into sonic choke at .55 Mach - but
at this point (approx.) we reach the trade off where the energy required to
move the air through the port becomes higher than the power increase
(cylinder filling) that comes from higher velocity.
---SteveS

Posts=>


From a previous Thread

too fast Velocity FPS can be a total disaster

Note=>all 3 of these Heads were tried on
the same Short Block with all the same pieces
and Dyno Tuned for best possible HP/TQ Curve
with those pieces.


#041x SBC Heads = 165.0 CCs
1.940/1.500 valves
these are the very Hi-Velocity Heads
with too much velocity everywhere inside
the Intake Port, same FlowBench numbers

and the "BEST" Dyno test with them
600 RPM/SEC , i don't have the Sheets
that we started at 3000 RPMs and all the
rest of the Sheets , but only kept the
Copies that stood out, and these are every
200 Hundred RPM increments as its too much Info to type
every 100 RPMs, but it should give you enough Info ?

note=> at 600 RPM/SEC you get a little Needle/Seat
action showing up especially with small gas bowl
chamber in Q-Jet, so look at Fuel Lbs/Hour trend
as well as rate (Same Q-Jet Carb all Dyno Tests)

RPM---TQ----HP----Fuel Lbs
4500-419.3-359.3--178.4
4700-438.1-392.1--171.5
4900-449.1-419.0--177.2
5100-451.0-437.9--169.8
5300-445.8-449.9--174.1
5500-443.2-464.1--188.3
5700-441.0-478.6--209.8
5900-429.6-482.6--222.1
6100-424.3-492.8--227.4
6300-413.9-496.5--214.9
6500-412.7-510.8--200.8
6700-407.6-520.0--210.3
6900-388.8-510.8--221.9
7100-363.7-491.7--236.1
7300-345.3-479.9--239.8
7500-325.1-464.3--233.4
7600-312.6-452.4--226.1

Avg=>406.5-464.9--206.0

--------------------------------------------------------------------------------

with #041x Heads back-to-back on same Short Block
same basic Flow CFM Numbers, same valves, same CC's
but with Port Velocity slower and more acceptable
throughout the entire Intake Port

RPM---TQ----HP----Fuel Lbs
4500-449.5-385.1--166.1
4700-444.2-397.5--164.5
4900-455.2-424.7--177.0
5100-456.2-443.0--158.3
5300-464.1-468.3--169.6
5500-471.1-493.3--192.9
5700-470.2-510.3--199.2
5900-468.2-526.0--199.3
6100-465.0-540.1--204.5
6300-459.8-551.5--209.7
6500-456.6-565.1--216.3
6700-442.6-564.6--223.1
6900-432.8-568.6--217.2
7100-426.6-576.7--215.3
7300-418.3-581.4--224.5
7500-401.8-573.8--238.2
7600-394.1-570.3--231.0

Avg=>445.7-514.1--200.4

================================================== =

with #462 castings 1.940/1.500 162.0 CC Ports
differences just 3 CCs can make when ground out in the
correct places, again FlowBench CFM between the
#462 and the other 2 #041x Heads were very close
and CFM numbers don't indicate the HP/TQ differences observed
and Ports had different Velocity Profiles.
Same ShortBlock and all pieces the same.

RPM---TQ----HP----Fuel Lbs
4500-443.0-379.6--168.3
4700-441.8-395.4--159.8
4900-450.6-420.4--164.4
5100-456.9-443.7--169.8
5300-459.2-463.4--183.9
5500-465.9-487.9--190.6
5700-464.1-503.7--192.0
5900-463.0-520.1--195.2
6100-460.6-535.0--196.6
6300-454.9-545.7--206.5
6500-446.8-553.0--216.1
6700-438.0-558.8--225.1
6900-428.4-562.8--220.8
7100-422.0-570.5--223.9
7300-410.1-570.0--219.5
7500-395.3-564.5--226.4
7600-388.8-562.6--231.1

Avg=>440.6-508.1--199.4


Quote:
Very well put - I have thought for some time that "Choke" is actually a
misleading term here. David Vizard has called it "Power Limiting Port Area",
a more accurate description, but unlikely to catch on.


i just use the word "Choke"
because sometimes the Engine will be Choked by an Area
and sometimes by the same cross-sectional, but now has one of the walls
with too much local velocity FPS and/or diverging too quickly on 1 wall

in the above Dyno Test examples the
one extreme hi-velocity #041x SBC Heads
is using more Fuel, but if you try to lean it out, you loose even more Torque
and HP...notice it makes Peak TQ and Peak HP lower and runs out quickly
with rapid rising BSFC numbers as rising RPMs show Choke problem even more.

the 2nd pair of #041x heads
make more Peak TQ & HP and at higher points,
and don't lay over top end.

the #462 castings with 3 less CC's
make Peak TQ at same point, but past Peak HP point start to layover
more than the #041x

Fuel consumption is about identical

Same FlowBench CFM Numbers
but different Intake Port Pitot Probe profiles/velocities



note thats a 117.9 HP "LOSS" for the extreme hi-velocity Heads at 7600

yet..on a steady-state FlowBench test,
"BOTH" Heads flowed almost as exact CFM as you could possibly
make them be equal on both Intake + Exhaust sides.

even used and swapped the same exact Valves out of both Heads
for those tests

same #041x castings , both same Chamber+Port volumes


what i call the extreme velocity FPS #041x Heads were;

every possible portion of that Intake port that could have
Epoxy added to it, and that Flow CFM was not reduced at all,
was epoxied up.

and the rest of that Port was enlarged just enough
to hold the same Port Volume CC's

the Short Turn Apex speed was to the moon
and so was the pushrod area...and just about every where else in the
Port....the Floor had some "Ski-Jump" shape to it also...as it kept
the CFM Numbers up and the velocity sky-high

i guess you could call it an experiment to see how far
you could "shrink" certain CSA areas of a Port
and not reduce the FlowBench CFM numbers .

pretty evident from Fuel Consumed Numbers -vs- Dyno HP/TQ Numbers
that Intake Port could not handle that much speed FPS
without Choke or Separation

you can also see why just about everyone i know
will Run the #041x heads over the other Legal #462 castings,
those 3 more CC's can be used to "SLOW DOWN" the already
too fast FPS

one other thing that stood out in some of the Tests, was the very hi-velocity
too fast FPS Heads that had a choke problem,often liked "more" low to mid
lift flow.The engine's being fed sooner and more, so the cylinder depression is
lesser until Choke occurs...and you still have good low-lift to take advantage
of high velocity at end of stroke

also the velocity FPS is slower in the smallest CSA areas, in the low to mid lift
portions of the Flow/Cam Lift Curve...pumping losses working thru rod angle
leverage in early and latter parts of stroke are going to be lesser than at Peak
Piston CFM demand point where leverage is great and Choke makes more losses.

a Closed Intake Valve has "ZERO Port Velocity FPS"

at Max-Lift , typically the Cyl Head has its best FlowBench CFM Number
or about in that vicinity...so Port Velocity FPS is highest at Peak Lift or
so. as the valve starts to move towards max lift, Port FPS is increasing...
also the minimum csa area FPS is starting to really increase or any too
fast FPS area is also increasing in FPS (add to that max Piston CFM
demand in vicinity of 70-80 deg ATDC and volume CCs increasing till
BDC, + Flow Lag Times, pumping losses working thru Rod Angle
leverage/velocity, etc.)


FPS = (CFM * 2.4 ) / CSA

if Head Flows 127 CFM at .200" Lift = 156.6 fps @ 1.948 csa

if head flows 260 CFM at .700" Lift = 320.3 fps @ 1.948" CSA

but in reality there will be CSA spots in Heads that will be
smaller than 1.948 sqinches, so the FPS will be higher than 320.3
other CSA will be larger than 1.948
and other localized spots can have too high FPS
even though your Average CSA of 1.948 says its only 320.3 fps


the Port Volume is the same in both cases,
the FPS changes up or down inside the Port
in relation to the Lift/Flow Curve -vs- Piston CFM demand

picking up the Low to Mid lift flow in the too-fast-velocity heads
helped...but it still didn't run as fast down the DragStrip.
the best way i've found so far is to slow the FPS to as close
to reasonable speed as possible, as long as its not too slow,
take the choke CSA out of the picture as much as possible.


As I understand it, ports don't actually go into sonic choke at .55 Mach -
but at this point (approx.) we reach the trade off where the energy required
to move the air through the port becomes higher than the power increase
(cylinder filling) that comes from higher velocity.

[FlowSpecialist]

Originally Posted by automotivebreath

here's a very good quote from STEVES
that explains the general idea and reason why Choke
or too fast FPS hurts HP+TQ
just read rest of Posts with that in mind .

As I understand it, ports don't actually go into sonic choke at .55 Mach - but
at this point (approx.) we reach the trade off where the energy required to
move the air through the port becomes higher than the power increase
(cylinder filling) that comes from higher velocity.
---SteveS

Where did this figure of 0.55 Mach come from?

Dave

[Devious]

Direct link to articles - thanx
The Mototune site has not been updated in several years, and I believe the writer is no longer building race engines. But, I could well be wrong.

There are a lot of performance bike engines with ports that are too large for their intended use and rpm range. However there has been a trend in recent years towards smaller ports, or the same ports with larger capacity engines.

Also, many performance bikes built within the past 8 years are using a secondary butterfly in the throttle body bores. These secondaries are controlled by the ECU and do not open under a given rpm. This keeps the engine from seeing too much throttle opening until the intake velocity has reached a given point.

On a road race bike with ports that are too large, reducing the port volume and throat cross section can increase velocity - adding broader torque and throttle response. For many riders/racers, this leads to quicker lap times compared to an engine with more peak power, but less average power. And more importantly, it can make a small capacity bike easier to ride well - very important for club level racers.

[Cammer]

This thread stands as evidence of the many faces of porting.

Too often we are caught up in the waves of internet gurus proposing certain parameters for cylinder heads.

Great cylinder head artists refine their craft by hundreds to thousands of hours spent working on heads.

Class racing forces a person to make the most of what can be done under specific rule structures. Small gains separate winners from losers!

Use your grinder like a surgeon uses his scalpel!

[automotivebreath]

Originally Posted by FlowSpecialist

Where did this figure of 0.55 Mach come from?

Dave

Dave, I don't know where STEVES came up with his information; however it is
implied in "The Internal Combustion Engine" published by the MIT press, when
port velocities exceed 0.55 the speed of sound a limiting condition exists.

[FlowSpecialist]

Originally Posted by automotivebreath

Dave, I don't know where STEVES came up with his information; however it is
implied in "The Internal Combustion Engine" published by the MIT press, when
port velocities exceed 0.55 the speed of sound a limiting condition exists.

I was pretty sure this was what was being referred to and I know C.F.Taylor's work has been quoted by other authors (mentioning no names - cough) as indicating that port velocities should not exceed 0.6 of the speed of sound but this is a mistake stemming from a basic misunderstanding of what Taylor did.

Taylor did try to correlate theoretical port velocity assuming incompressible flow(bore area/valve area x piston speed) with volumetric efficiency and found there was little correlation to the data.

Then he came up with another measure which he called the 'Z factor' which was based on the steady state valve flow discharge coefficient (relative to the head area of the valve) interpolated against the inlet cam profile and then averaged over the cam duration. He called this averaged flow coefficient Ci. For a well developed port and valve this might be about 0.5 or in extreme cases even higher because poppet inlet valves can achieve discharge coefficients of 0.6 to 0.65 quite easily, higher in extreme cases with very high valve lifts but obviously don't spend all their time at full lift. 0.5 would be a good result for Ci for a non drag race engine though.

He then turned this averaged discharge coefficient into a pseudo velocity, the Z factor, by taking into account piston area, valve area and piston speed again as in the basic incompressible flow approach above.

Z = (b/D)^2 x S / (Ci x A)

Where b = bore diameter, D = valve diameter, S = piston speed and A = the speed of sound

He found a very good match against volumetric efficiency with this Z factor and that VE started to drop when Z exceeded 0.6.

However Z is not a true port or valve or valve curtain area velocity, nor was it ever meant to be one even though he called it a Mach index which is where the confusion has originated from. Z is just a measure which gets smaller as either valve lift, cam duration, valve area or valve flow coefficient increases and bigger as piston speed increases.

Obviously the things that make Z smaller are good for VE and the things that make Z bigger are bad for VE.

Let's try some numbers. I'll pick something akin to a small block Chevy race engine out of deference to the colonial readership in here

Assume b= 4 inches, stroke = 3.5 inches, D = 2 inches, Ci = 0.5, A = 1129 ft/s (yes I know it isn't really that in real engine operating conditions)

The constant part of the equation is (b/D)^2 / (Ci x A) = 0.00709

We need to multiply by piston speed in ft/s to get Z.

At 5000 rpm PS = 48.6 and Z = 0.34, well within limits.

Z hits 0.6 at 8700 rpm.

Now you can make what you will of how accurate or relevant this approach is to highly developed race engines as opposed to lowly tuned laboratory ones but clearly it does take into account factors which you would expect from first principles to limit VE.

What it does NOT say is that ports become choked at 0.6 of the speed of sound and frankly why on earth should they? What would be special about Mach 0.6 anyway? At Mach 1 you could obviously expect problems though.

All it does is refine the very basic (and clearly unrealistic) incompressible flow approach to include the actual efficiency of the valve and port and the effect of the cam profile. However the erroneous assumption that because it was called a Mach Index it actually referred to the real gas speed in the port has propagated into tuning books for 30 years or more and confused an entire generation of engine builders.

If you exclude the Ci part of the equation above you get back to the incompressible flow Mach Index which in the above case would be 0.3 at 8700 rpm because dividing by Ci of 0.5 doubles the result. Does this mean that ports get choked at 0.3 of the speed of sound? No of course not any more than they get choked at 0.6 of it just because the Z factor has Ci built in.

Where the Z factor approach falls down is with cam duration because insufficient port area in a highly tuned engine can limit power like a brick wall and fitting longer duration cams won't make a scrap of difference. However in the Ci calculation more duration would lead to a higher average Ci and lower Z factor because the valve is spending a proportionately greater part of its cycle at high lifts. This lower Z factor would lead you to think that VE should improve but in reality it doesn't. Of course Taylor didn't test with race engines and very long duration cams so he probably never got round to this part of the deal.

So what's the real story behind the minimum port cross section area and its effect on power? Well that's for another day

DB

[automotivebreath]

DB, it's obvious you gave this subject more than a little thought. I appreciate the
information, however I will refrain detailed comments until I better understand
what you are saying.

Going back to a previous quote:

"the best way I've found so far is to slow the FPS to as close to reasonable
speed as possible, as long as its not too slow, take the choke CSA out of the
picture as much as possible"

Using a formula previously published by D.V.; I calculate minimum CSA for a
particular SBC combination in attempt to keep FPS at a reasonable level for
the intended engine RPM. The example below calculates 6920 RPM potential for a
MCSA of 2.2 ....comments?

(MCSA * 177780)/(Stroke * Bore sq.) = RPM

(2.2 * 177780)/(3.48 * 4.00 sq.) = 6920

"So what's the real story behind the minimum port cross section area and its
effect on power?"

Does this have anything to do with the fact that in a running engine the valves open
and close meaning the flow stops and starts? Isaac Newton once said "Every
action has an equal and opposite reaction".

[FlowSpecialist]

Originally Posted by automotivebreath

DB, it's obvious you gave this subject more than a little thought. I appreciate the
information, however I will refrain detailed comments until I better understand
what you are saying.

Going back to a previous quote:

"the best way I've found so far is to slow the FPS to as close to reasonable
speed as possible, as long as its not too slow, take the choke CSA out of the
picture as much as possible"

I'd basically agree with that.

Using a formula previously published by D.V.; I calculate minimum CSA for a
particular SBC combination in attempt to keep FPS at a reasonable level for
the intended engine RPM. The example below calculates 6920 RPM potential for a
MCSA of 2.2 ....comments?

(MCSA * 177780)/(Stroke * Bore sq.) = RPM

(2.2 * 177780)/(3.48 * 4.00 sq.) = 6920

I'm not familiar with these formulae but then I haven't read DV's book or books on Chevy engines. Not engines we deal with much here in Blighty. I did by chance read Bill Jenkins excellent Chevy book many years ago but that didn't go into this sort of thing anyway.

"So what's the real story behind the minimum port cross section area and its
effect on power?"

Does this have anything to do with the fact that in a running engine the valves open
and close meaning the flow stops and starts? Isaac Newton once said "Every
action has an equal and opposite reaction".

No, not as far as I'm aware. IMO ports become sonic choked when the gas speed reaches Mach 1 and at that point only the absolute value of the upstream stagnation pressure has any impact on flow. The pressure drop across the port
ceases to have the usual square root effect on flow because the signal of that pressure drop can't traverse the port any quicker than the flow is already going. This 0.55 or 0.6 Mach thing is just a red herring IMO.

In simple terms the minimum cross sectional area (MCSA) of both inlet and exhaust ports has a direct limiting effect on power output. Equations taking engine size and rpm into account are, I think, not really necessary. Whether the engine is large and slow revving or small and high revving the percentage of any given period of time available for flow to take place is the same in all cases and is determined by the cam duration. The number of cycles that take place in that time doesn't alter this. X bhp requires Y CFM to be processed per minute. Obviously small high rpm engines will have different mechanical efficency than large low revving ones and CR, combustion efficiency and other things also have their effect on power so any equation needs tailoring for its application.

However basically you can just equate the total MCSA of an engine for either inlet or exhaust ports with a power potential for that engine. Whether the engine then reaches that power potential depends on the port flow being sufficient i.e. just opening up the ports but getting no more CFM won't help you if CFM is already the limiting factor. Conversely getting more CFM from a given MCSA also won't help you if MCSA is the limiting factor.

So designing the perfect engine combo is a two stage process.

1) Work out the power potential of the flow you are getting.

2) Open up the ports to the MCSA required to supply that power potential.

You'll then have both port flow and port size matched to the peak bhp the engine can be expected to reach.

What I'm not prepared to do at this stage on a public forum is give away the equations I've refined to do the above. Let's just say they are of the form that if you calculate the total MCSA of both inlet ports and exhaust ports for the whole engine then power will be limited to X bhp per sq inch for the total inlet MCSA and Y bhp per sq inch for the total exhaust MCSA where X and Y are different numbers.

This of course means that the ideal ratio of inlet MCSA to exhaust MCSA is given by the same equations and then that has further knock on effects on the ideal ratio of inlet valve area to exhaust valve area which is a different percentage because exhaust ports operate at higher discharge coefficients.

Phew. I hope all that was clear and makes some sense.

Dave

[FlowSpecialist]

Ah go on then. I suppose for the sake of completeness I can chuck some numbers away. They aren't going to be universal and I'm more used to dealing with 4v engines and straight round ports rather than curved rectangular ones but you can play with these and see how they fit your experience.

On the inlet side bhp will be limited to approximately 5.0 bhp per sq cm or 32.3 bhp per sq inch of total engine MCSA.

On the exhaust side bhp will be limited to approximately 7.3 bhp per sq cm or 47.1 bhp per sq inch of total engine MCSA.

Provisos as previously about mechanical efficiency, CR, combustion efficiency etc. Also where a port curves sharply then it will not have a uniform flow pattern or flow speed so it may become velocity limited on one side despite having an area that is theoretically sufficient. This is actually no more than basic common sense that area needs to be increased around curves to slow the gas speed and help maintain flow efficiency. However most ports will have their MCSA in the straight sections anyway so this can usually be fairly easily measured.

Dave