Porting School #5 Identifying Primary Restrictions

[automotivebreath]

David, Here's some relavent information that may intrest you:

"2-Valve Heads
So far my Tests show increasing Low-Lift Flow always
"Hurts" Torque "below" the RPM point of Peak TQ
and sometimes increases top-end HP
...just the opposite of what most people think.

most will "equate" increases in Low-Lift Flow = increased bottom-end
or low RPM Torque......but i've never seen this to be True yet,
even with a smaller duration Cam like in the series of Engine Master tests.

The 2 Cyl Heads=> AFR and the TricFlow 's
had the best .100" Lift Flow to .300" + Flow
but the TQ output was not as good or any better at 2700 RPM to 3500
as the worst low-lift Dart Head
(especially at 2700 RPM)
i wonder what was happening below 2700 RPM ??
along with gas mileage MPG ?

the 2 worst Low_lift Heads (Dart + Edelbrock)
made as good or more low RPM TQ.

the better test would have to change Low-Lift Flow on the same exact casting
one at a time..and repeat those Tests studying Low_lift Flow effects.

There are times you can increase Low_lift Flow then use an even shorter
duration Cam (like 4-Valve designs)
and Pickup HP and TQ at low to midrange RPM,
but usually always looose top end HP cutting down duration to achieve that.

Also Heads with CSA Choke problems respond favorably to increased
Low to Mid-Lift Flow so far in my Tests.....but overall the best method
is to fix the Choke ...and not rely on Low-Lift Flow so much."
_________________
Meaux Racing Heads

"increasing Low-Lift Flow is effectively like increasing OverLap Period,
increasing Duration, and increasing chances of reverse flow or reversion".

[Dusty]

2-Valve Heads
So far my Tests show increasing Low-Lift Flow always
"Hurts" Torque "below" the RPM point of Peak TQ
and sometimes increases top-end HP
...just the opposite of what most people think.

most will "equate" increases in Low-Lift Flow = increased bottom-end
or low RPM Torque......but i've never seen this to be True yet,
even with a smaller duration Cam like in the series of Engine Master tests.

I think I hear Davids keyboard cringing at the thought of how hard the keystrokes will be responding to that one

[Cammer]

GFN is doing a great job of covering cylinder head modification!

GFN members will have an easy to access guide on cylinder heads.

Pistons are sitting by patiently waiting to get thrown into the mix!

Spend your money close to the valves!

[Rick360]

Originally Posted by DavidVizard-GFN

You obviously reading word for word what is being said here and throwing in liberal doses fo your own experience - great stuff. The subject material you are speaking of is going to be covered in the near future in this series so whatch this space - and see in detail what you are taliking of in terms of valve to port geometry, sizing, shrouding etc.

I look forward to that.

Originally Posted by DavidVizard-GFN

There is one point thought that I would dearly like some input from you on if you have it. You mention the supposed effect that low lift flow can have on hp. I have been trying to get other people to show their dyno tests indicating that too much low lift flow for a race engine costs power. Do you know of any good back to back tests conclusivly proving this?
DV

No, I don't have any dyno tests to prove it. It would be a VERY difficult thing to PROVE. There are many different ways to change the flow characteristics of a port that could be used to reduce low lift flow. If you only made one change to affect low-lift flow, how could you know it was because the flow was less that caused the change in power? Anything that affects flow will also cause some other differences, such as wet flow, pressure recovery or the duration affect of low-lift flow. How many other things would need to be changed to find the ideal combo again after making one change. I think it would take a dedicated study to isolate the low-lift flow as the "cause" of any power difference, not just a single test.

There have been several engine builders and head porters who have made comments about this and their belief in it from their dyno tests. The post automotive breath made of Larry Meaux is but one. Meaux also has some dyno numbers he posted here is another. Not proof, but more evidence...

Originally Posted by maxracesoftware from Speedtalk

Joe just within the last Month flow tested a pair of SBC Heads
that had a 2.225 OD Intake valve.
These Heads had the worst Low-Lift .200 to .300 Lift Flow
i've ever measured on my Bench !! in fact so terrible,
my SS #041x Heads with 1.940 intake valve have a bunch more
.200" flow , and the 1.940 ties the 2.225 valve at .300" lift.

by the time you reach .600" lift flow those 2.225 Heads
are about the same Flow CFM i get out of Track 1 or Dart Pro 1
Heads with a 2.100 or 2.125 valve,
then at .650 Lift..the FlowBench CFM numbers finally start to take off.

So basically those Heads have only .650 lift to .950 lift flow numbers
over a pair of Track 1's or Dart Pro 1's.

SF-901 Dyno test results=> the highest HP + TQ numbers so far
for that Class

DragStrip Run=> the very first Run was .02 hundredths ET
faster than the Record !!

the 1/8 mile was more than 2.5 MPH faster than Record Run !!
indicating pretty good mid-range TQ + HP

The above Engine Combo is one-way to get down the DragStrip,
its by no means for everyone....but pretty good realworld test Data
on the particular importance of high-lift flow numbers (.650 to .950) over
the terrible low to mid lift flow number were on this particular Combo !

There is no question that most of the valve jobs used in high-end race heads today provide very poor low-lift flow compared to more conventional designs. Are these used because they hurt low-lift flow? I doubt if any of them are 100% sure that is why they help, but they know what works on the dyno. Maybe its a side-affect of designing the port/VJ to improve high-lift flow or improving pressure recovery that makes them work. It is my opinion that at least some of the benefit is less low-lift flow.

When some of the heads that make the MOST power have the WORST low-lift flow makes me think there is something there.

Rick

[automotivebreath]

Originally Posted by Dusty

I think I hear Davids keyboard cringing at the thought of how hard the keystrokes
will be responding to that one

I don't have a personal opinion on this; although I do respect what Rick and Larry
Meaux are saying.

When thinking about low lift flow promoting reversion. I personally would need to
see test data for different camshaft profiles. I would expect much different results
comparing a cam with 280+ @ 0.050" to something more along the lines of a
street performance engine at say ~ 230 @ 0.050" because of the diffrence in overlap.

[FlowSpecialist]

Originally Posted by Rick360

Originally Posted by maxracesoftware from Speedtalk
Joe just within the last Month flow tested a pair of SBC Heads
that had a 2.225 OD Intake valve.
These Heads had the worst Low-Lift .200 to .300 Lift Flow
i've ever measured on my Bench !! in fact so terrible,
my SS #041x Heads with 1.940 intake valve have a bunch more
.200" flow , and the 1.940 ties the 2.225 valve at .300" lift.

by the time you reach .600" lift flow those 2.225 Heads
are about the same Flow CFM i get out of Track 1 or Dart Pro 1
Heads with a 2.100 or 2.125 valve,
then at .650 Lift..the FlowBench CFM numbers finally start to take off.

So basically those Heads have only .650 lift to .950 lift flow numbers
over a pair of Track 1's or Dart Pro 1's.

SF-901 Dyno test results=> the highest HP + TQ numbers so far
for that Class

DragStrip Run=> the very first Run was .02 hundredths ET
faster than the Record !!

the 1/8 mile was more than 2.5 MPH faster than Record Run !!
indicating pretty good mid-range TQ + HP

The above Engine Combo is one-way to get down the DragStrip,
its by no means for everyone....but pretty good realworld test Data
on the particular importance of high-lift flow numbers (.650 to .950) over
the terrible low to mid lift flow number were on this particular Combo !

Rick

This is all well and good but it makes the assumption that the power and torque came because of the lack of low lift flow rather than despite it.

How do we know that with more low lift flow that same engine wouldn't have produced better figures everywhere in the rpm band? The only way would be to test it and see.

I can certainly understand some of the arguments that people have been raising since Bill Jenkins did in the 70s that lack of low lift, or even mid lift, flow means you can run more cam duration without hurting low rpm power. It makes a certain amount of sense on initial consideration but there are counter arguments.

The single biggest difference you can make to low lift flow is to substitute one large inlet valve for two small ones of the same area. The peak flow in a well developed port will be similar but the low and mid lift flow will be much higher in the 4V head. At low lift by a factor of 1.41 or root 2 which is the ratio of the two small valve's total circumference compared to the single large valve. Two 32mm inlet valves have the same area as one 45.25mm one. Those are convenient numbers because the former is a 2 litre Ford Zetec 4V engine and the latter is a 2 litre big valve Ford Pinto one.

The usual big valve choices for the Pinto are 44.5mm or 46.0mm of which the average is exactly 45.25mm. Now regardless of which of these sizes you choose it's a non-trivial task to build a 200 bhp Ford Pinto engine. It requires top notch head work, full race cam, very good induction and exhaust systems and high CR. Most engines fail to break 180 bhp. A moderately well known motoring hack who posts in here from time to time even had a crack at it 30 years ago and did beat 200 bhp by a small margin after filling in the inlet ports with Devcon and other spurious ruses.

Getting 200 bhp from a Zetec is like falling off a log in comparison. The standard engine puts out 130 bhp to the Pinto's 105/115. Add a decent exhaust and carbs or TBs and you're up to 165. Port the head and fit fast road cams and 200 bhp is there for the taking. It will still be tractable at that output unlike the Pinto. In full race tune 230 bhp is on the cards. With extreme development nearly 250 bhp should be possible.

Of course the 4V engine wants less cam duration than the 2V one but that isn't an issue that actually hurts its power output. It's simply a function of the flow per cc and the effect that has on ideal valve opening time.

Other things also differ between the 4V and 2V engines. Chamber shape, swirl pattern and burn speed. Do these make 50 bhp difference, or even 30 bhp difference? I think not. What makes the difference is low and mid lift flow.

Dave

[Rick360]

Originally Posted by FlowSpecialist

This is all well and good but it makes the assumption that the power and torque came because of the lack of low lift flow rather than despite it.

How do we know that with more low lift flow that same engine wouldn't have produced better figures everywhere in the rpm band? The only way would be to test it and see.

I can certainly understand some of the arguments that people have been raising since Bill Jenkins did in the 70s that lack of low lift, or even mid lift, flow means you can run more cam duration without hurting low rpm power. It makes a certain amount of sense on initial consideration but there are counter arguments.

The single biggest difference you can make to low lift flow is to substitute one large inlet valve for two small ones of the same area. The peak flow in a well developed port will be similar but the low and mid lift flow will be much higher in the 4V head. At low lift by a factor of 1.41 or root 2 which is the ratio of the two small valve's total circumference compared to the single large valve. Two 32mm inlet valves have the same area as one 45.25mm one. Those are convenient numbers because the former is a 2 litre Ford Zetec 4V engine and the latter is a 2 litre big valve Ford Pinto one.

The usual big valve choices for the Pinto are 44.5mm or 46.0mm of which the average is exactly 45.25mm. Now regardless of which of these sizes you choose it's a non-trivial task to build a 200 bhp Ford Pinto engine. It requires top notch head work, full race cam, very good induction and exhaust systems and high CR. Most engines fail to break 180 bhp. A moderately well known motoring hack who posts in here from time to time even had a crack at it 30 years ago and did beat 200 bhp by a small margin after filling in the inlet ports with Devcon and other spurious ruses.

Getting 200 bhp from a Zetec is like falling off a log in comparison. The standard engine puts out 130 bhp to the Pinto's 105/115. Add a decent exhaust and carbs or TBs and you're up to 165. Port the head and fit fast road cams and 200 bhp is there for the taking. It will still be tractable at that output unlike the Pinto. In full race tune 230 bhp is on the cards. With extreme development nearly 250 bhp should be possible.

Of course the 4V engine wants less cam duration than the 2V one but that isn't an issue that actually hurts its power output. It's simply a function of the flow per cc and the effect that has on ideal valve opening time.

Other things also differ between the 4V and 2V engines. Chamber shape, swirl pattern and burn speed. Do these make 50 bhp difference, or even 30 bhp difference? I think not. What makes the difference is low and mid lift flow.

Dave

Those are excellent points and ones I can't dismiss. I haven't done any 4V head testing myself, strictly 2V pushrod V8's, so my knowledge is very limited in that area.

There are other things that a 4v head benefit from, pressure recovery being one of the biggest as far as flow is concerned. Fuel distribution (wet flow) in the cylinder should be better too. They will flow better at full lift also for the same csa. I don't have a good feel for how the flow at low-mid-high lift are on 4V heads or what valve jobs work the best in these heads. Maybe the best ones are also using valve jobs that discourage low-lift flow? I don't know.

Some very well done tests related to low lift flow would be interesting.

Why is everybody in Nascar, P/S, Comp running steep valve angles (50-60º)? They must make more power, but why? IF you want good low-lift flow, do the gains at high lift offset the losses at low lift?

Thanks for your insight, I appreciate good discussion on these subjects.

Rick

[FlowSpecialist]

Originally Posted by Rick360

Those are excellent points and ones I can't dismiss. I haven't done any 4V head testing myself, strictly 2V pushrod V8's, so my knowledge is very limited in that area.

There are other things that a 4v head benefit from, pressure recovery being one of the biggest as far as flow is concerned.

I covered pressure recovery in some detail in another thread as far as it relates to flow testing of components on a flow bench. I'm not sure if you mean the same thing but even so I can't see why a 4V head would differ in this respect from a 2V one.

Why is everybody in Nascar, P/S, Comp running steep valve angles (50-60º)? They must make more power, but why? IF you want good low-lift flow, do the gains at high lift offset the losses at low lift?

Thanks for your insight, I appreciate good discussion on these subjects.

Rick

In very highly modified engines such as you mention the valve lift is extreme compared to that in most engines. In standard 2V road engines it's usually about 25% D. In normal race ones perhaps 35% D. In these classes you can be up to close to 45% D. In effect the valve is almost no longer a part of the port at high lift and what you are trying to do is shape the port to maximise flow without the valve being in it. The ideal shape for that is a venturi tube with gently sloping upstream and downstream cones.

What you don't want in such a shape is rapidly divergent angles such as a 45 degree valve seat whose main purpose is to redirect flow between the throat and chamber for a valve at medium lift. So yes it's a trade off between low and high lift flow and what that tells you is that the ideal valve seat angle varies with the L/D ratio of the cam.

Low lift cams benefit from a 30 degree seat which generates a larger curtain area at low lift than a 45 degree one but tends to suffer at higher lifts. That's why many diesel engines use them. 45 degrees is a good compromise for most uses. Steeper angles than 45 degrees benefit very high lifting cams. Very steep angles tend to be self locking so there's a limit to how far you can go.

None of this actually proves that low lift flow is a bad thing though. It's just something that has to be sacrificed to get ports to flow better at very high lift.

If you want to consider something else it's flow just as the inlet valve is closing as the piston rises up the bore. What determines whether flow continues to flow into the cylinder or out of it is cylinder pressure versus the kinetic energy of the gas coming through the rapidly closing inlet valve. The better low lift flow you have the faster the gas speed through the valve seat. Kinetic energy is proportional to the square of speed so better low lift flow gives you a very big boost in the ability of the port to continue filling the cylinder and increase VE until the valve closes.

It's this late cycle flow that lifts VE from the theoretical 100% that a valve closing at BDC could achieve to the 130% that well developed race engines with long duration cams can achieve. The key to all of this is flow when the piston is actually rising back up the bore and trying to push the gases back the way they came. The better you overcome this effect the more power you make.

Dave

[Furby]

Originally Posted by FlowSpecialist

If you want to consider something else it's flow just as the inlet valve is closing as the piston rises up the bore.

This would assume flow is still going into the cylinder, instead of out.

With any given combo, there would be an rpm point/port speed/ve, where increased low lift flow will be flowing better backwards.(any increase in foward flow will most likeley increase flow backwards also).

I would think this point would be before peak TQ/VE, therefore I can see where increased low lift flow would be similar to more duration/overlap, and would reduce power down at some rpm, unless a smaller cam was also used.

Furby

[MaxRaceSoftware]

Originally Posted by automotivebreath

I don't have a personal opinion on this; although I do respect what Rick and Larry
Meaux are saying.

When thinking about low lift flow promoting reversion. I personally would need to
see test data for different camshaft profiles. I would expect much different results
comparing a cam with 280+ @ 0.050" to something more along the lines of a
street performance engine at say ~ 230 @ 0.050" because of the diffrence in overlap.

i'd have to go back and find that Magazine Article that did the Flow + Dyno tests
with the different LS-style heads...but in those tests...the Heads with the best
Low-lift flow made the worst bottom-end Torque,
and i think the Cam's were in the 230's to 240's ??? i'd need to check that out
to be certain, but the original post was on SpeedTalk


Originally Posted by Rick360
Originally Posted by maxracesoftware from Speedtalk
Joe just within the last Month flow tested a pair of SBC Heads
that had a 2.225 OD Intake valve.
These Heads had the worst Low-Lift .200 to .300 Lift Flow
i've ever measured on my Bench !! in fact so terrible,
my SS #041x Heads with 1.940 intake valve have a bunch more
.200" flow , and the 1.940 ties the 2.225 valve at .300" lift.

by the time you reach .600" lift flow those 2.225 Heads
are about the same Flow CFM i get out of Track 1 or Dart Pro 1
Heads with a 2.100 or 2.125 valve,
then at .650 Lift..the FlowBench CFM numbers finally start to take off.

So basically those Heads have only .650 lift to .950 lift flow numbers
over a pair of Track 1's or Dart Pro 1's.

SF-901 Dyno test results=> the highest HP + TQ numbers so far
for that Class

DragStrip Run=> the very first Run was .02 hundredths ET
faster than the Record !!

the 1/8 mile was more than 2.5 MPH faster than Record Run !!
indicating pretty good mid-range TQ + HP

The above Engine Combo is one-way to get down the DragStrip,
its by no means for everyone....but pretty good realworld test Data
on the particular importance of high-lift flow numbers (.650 to .950) over
the terrible low to mid lift flow number were on this particular Combo !
Rick

Rick and Automotivebreath,
those Heads are on Craig Bourgeois's B/ND
they had the worst Low-Lift i've ever measured for a SBC on my FlowBench,
yet Craig set the NHRA B/ND Record at 7.000 ET but just recently lost that Record,
and Craig's # 1 in Comp Elim in NHRA
2008 NHRA POWERade Championship Point Standings

so Craig's proven you can "Fly" with terrible Low-lift- Mid-Lift Flow !

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

On the NHRA Chevy and Chrysler SS Heads,
i was privileged to be at a Time when NHRA changed the Cylinder Head Rules
allowing you to do anything to the Valves execpt change the original seat angles,
so when NHRA changed the Rules, i instantly ground 30deg Backcuts
on the Intake Valves on the Chevies and Chrysler SS Heads.

The Chrysler SS 318/340/360 SS Heads had a Tulip-shaped intake valve
...so the Chrysler ended up drastically gaining Low-Lift Flow Numbers
going to a Nail-head Valve shape w/30 deg Backcut.
Back on the Dyno the effect of ONLY the Valve shape change w/30 deg backcut
hurt the very low RPM Torque numbers a lot ,
and even hurt peak TQ a little...but gained hi-rpm HP

Likewise the SS #462's and #041x Heads grinding just only a 30deg backcut
and increasing Low-lift Flow Numbers "again" lost the very low RPM TQ numbers
and picked up the hi rpm HP just a little.

those SS Cams are in the 280's @ .050" on the Intake Lobes

Basically you can see this very same "TREND" looking at
Phillip H Smith's Data in his Book.

you need to have a certain amount of Cylinder depression
to create the proper Flow velocity to achieve the necessary
Ram-effect at the Intake valve closing point.

if you fill the Cylinder too easily too quickly,
the necessary depression is lost, as well as the ram-effect.
To compound this even further,
increases in Low-lift flow almost always results
in an increase in reverse Flow allowing greater amounts of mixture to be reverse
pumped backout the Cylinder before the Intake valve shuts/closes.

its also the same "Basic" reasons or part of the reasons why Engines
have certain RPM ranges. Example-> 500 CID ProStock Engine,
they can make around 820+ Peak TQ at 7800-8000 RPMs,
so why don't they make 820's TQ at 4000 RPMs ??

if the Heads can feed the Engine between 8000 to 10000 RPMs,
how come they can't effectively operate at 3000 or 4000 RPMs
and make 820's TQ ?...they lack Intake and Exhaust System velocity
and proper Wave tuning effects,
and a majority of this is due to lack of enough Cylinder depression to create
the necessary pressure differentials to create the System velocities !

you need pressure differentials to create Flow velocities,
if for a "given RPM range" if you reduce pressure differential by increasing
low-lift flow, you loose the necessary intake system velocity.

the Cylinder depression rate and amount need to occur in the 40 to 80+ deg ranges
ATDC on the Intake Stroke to give the mixture enough time
to get-back at the intake valve closing point.

the cylinder depression trace curve should look like a "Check-mark",
the peak depression should be around 40-80+ or so degrees ATDC.
to get great VE % it should be minus - 3 psi to no more than minus -5 psi
..anything more than a negative -5 psi causes too much pumping losses
and way too late ram-effect to be of enough gains.