[uneasyrider]

Too much to read since I last posted...

Think of the fuel as a little grain of sand in the air stream and lets say it's laying on the bottom of the runner. As the velocity increases the pressure will drop until the grain of fuel is lifted off the bottom of the runner and pulled into the air stream (Bernoulli). If the velocity gets to high (sonic region) pressure waves form and flow reduces and you get something like what happens when water is poored too fast out of a jug and the void can't be filled behind it (blurp, blurp, blurp). Don't misunderstand me, there are pressure waves in the intake manifold but sonic pressure waves aren't good. The pressure waves that are good are the subsonic versions that are taken advantage of for ram tuning effect. Think of it like a spring and a weight bobing up and down. You tune the runner length to the rpm range of the engine and take advantage of the harmonic (like an organ pipe) of the valve opening and closing and the momentum (don't forget that the fuel/air mix has weight) of the fuel air charge behind the valve and time it all so you get greater volumetric efficiency by packing the runner full under greater pressure so when the valve opens the next time there will be more air and fuel rushing in faster. Sort of a mini blower in each runner. The area of the runner looking down in the direction of flow is flow rate the length would add to your "ram" effect. Any added plenum and runner volume would add to the avalable fuel for on demand throttle opening and peak hp. In the end there is no one runner right for the whole operational range of the engine that is why we see the dual runner intakes in the new cars. You can have that runner with the area and volume to give optumal flow and "ram" effect at WOT and still have one small enough for putting around town. With the new cars you don't have to worry about keeping the fuel suspended for the length of the runner though. If you looked at the manifold of a carb engine in slow motion you would see these pressure waves of fuel and air go by as the intake opened and closed and the fuel droplets (really a fog of atomized fuel) spred out in there. It would look like those pictures of locusts flying by in sucssesive waves.

That's the way I have understood it anyway. I have been wrong before though.

[Skip Fix]

Since I don't have a handle on physics and neither did the Pontiac engineers please enlighten me! They used BIG heads on HO and SDs in the same power range. Did your HO or SD have less bottom end than your current BIG D port motor?

Larry several folks here,yourself included,routinely post how larger cc heads be they KRE or Edelbrock heads HAVE to kill velocity and bottom loss, making the motor a high race motor "because it's physics". Period no other factors involved,no actual measurement. Yet when we have hard data contradicting that fact, even different rpm ranges for the same size head, or even the factory's Big head motors not doing that we get no explanation how that can even happen with strictly physics Larry. Head experts agree there can be too much velocity for fuel to stay suspended.

These heads can match the low end and be way over on the higher end of street rpms as documented routinely because they flow more air. Most 260 cfm D ports like yours Larry aren't 160cc ports, and some aren't shifted at 5500 tractor rpm.

Many look here for decisions on motor parts and if all they see is big is bad. There are lots of factory round ports, Edelbrock and ported KRE heads making similar low end numbers and higher 5800 numbers defying physics! I also find it funny that E heads are considered "expensive race pieces" by many even with coupled with RPMs or Torkers and 4150s, yet D ports on race gas, Victors and Dominators(find me a cheap Dominator) are considered street tractor motor pieces to compare to. As Brian said in the post about iron vs aluminum the better shape of the same size ports is why it made better HP. So not just simple size. I don't care what type heads some one used to go fast, but when peolpe make blanket statements that aren't backed up by all the data something is wrong with the physics theory-at least that's what my engineer buds say.

And then posting a time for my car that had a definite mismatch in parts to compare to Mike's second combination and not the one that was on the same day and almost identical time. So who is biasing the info out there.

[BruceWilkie]

Big, big enoughfor the combo, too big? IMO if it is too small it chokes the motor. I'm thinking that in most of the examples we see in the Pontiac big port small port debate is all in the combo. I dont think it is all flow or all velocity. It is in the overall balance. Best average power and torque in the rpm range you are running is only part of the story though. Motors with peak power from 5000 - 7000 rpm will spend more time above 5252 rpm(the point where rpm and torque are equal) requiring optimum port velocities for maximum hp near that 5200-7000 rpm point. Motors that peak hp around 5000- 5500 rpm are going to be mostly in the 3- 5000 rpm range requiring optimum velocities in that range. The low rpm motor will have a bias for the torque curve, the high rpm motor will be biased to the hp side of the curve. The average torque and average power COULD be the same! Cam, gear and convertor will be different. With our Pontiac small port vs large port the velocity change isnt as drastic compared to a Ford 302 windsor vs 302 boss head or a stock D port vs ported Tiger head. There is a lot of overlap in our Pontiac applications as MOST Pontiac builds seem to be only about 1000 rpm(and 70 cfm) apart between "tractor" vs "race" (displacement equal).

[uneasyrider]

The velocity and turbulence of the air stream is what keeps the fuel suspended. It's just like the lift generated by a wing. The higher the velocity the lower the pressure in the stream. You can think of the air as a fluid for this discussion at least. Look behind a dam or in a pond and you will find silt on the bottom. The flow slows and the dirt drops out of the water. Put a bunch of sugar in a glass of water and then stir it. When the water stops moving the sugar falls to the bottom of the glass.

There is NO perfect size port. You have to size it to the application. You have to stop thinking about specific combos to see what is happening. Think of making the port as big as the cylinder then think about it the other way like as small as a pencil. The little port will work at idle at best and the big port would work at 20,000rpm or something it all depends on the application. In the end the greater the port area the greater the capacity for peak power but everything else has to be there or it's just a big hole that can't be filled. That is why there are dual runner intakes. The volume of the port and the plenum give a reservoir of fuel and air to draw from to fill the next charge. Below the carb you have a "packed" runner ready to fill the cylinder.

[uneasyrider]

Originally Posted by BruceWilkie

...With our Pontiac small port vs large port the velocity change isnt as drastic compared to a Ford 302 windsor vs 302 boss head or a stock D port vs ported Tiger head. There is a lot of overlap in our Pontiac applications as MOST Pontiac builds seem to be only about 1000 rpm(and 70 cfm) apart between "tractor" vs "race" (displacement equal).

There you have it! Thanks Mr. Wilkie.

We don't live in the Chevy world where there are 4,500rpm 400cid engines and 10,000rpm 400cid engines. We run in a "narrow" rpm range with similar size engines and you build them as much to get drivability characteristics as hp. What generally is happening is the "race" engines as with most race engines the rpm range they work well in is narrower to optimize peak hp. Since Poncho's run below 6,500rpm or so and usually below 6,000rpm and the are in a similar cid range the port size it's as "critical". Not that it doesn't matter. The big thing is the piston velocities in each engine are in the same range and all you are ever trying to do is fill the void left by the piston as it goes down in the stroke so if the void on all these engines expands at close to the same rate (piston velocity) the flow rate is about the same [Flow rate = velocity (piston) x the area (smallest hole)] the thing you optimize is the "ram tuning" and plenum volume to optimize the "packing" of the cylinder. Basically choose whether you want a cammed up "undrivable" on the street 6,000rpm engine with 700hp or a mild cam "streetable" 6,000rpm engine with 500hp if you see what I mean.

[johnta1]

Why are they usually run below 6000/6500 rpm?

This is the race section right?
Should have some good parts in there.

Ask Scott Rex or John Langer what rpm they run.

[uneasyrider]

Originally Posted by johnta1

Why are they usually run below 6000/6500 rpm?

This is the race section right?
Should have some good parts in there.

Ask Scott Rex or John Langer what rpm they run.

OH CHIT!!! HERE WE GO!!! Ah... johna1 IDGAS what rpm they are running. IT'S ONLY HYPOTHETICAL. I was trying to make a point not be EXACT. Do they run 10,000rpm? Do they run 8,000rpm for 500 miles? Quit trying to discuss someones combo and start looking at the physics of what's happening and WHY that combo works or doesn't. He said, she said... blah blah blah... Time to get out the bones and the vodoo doll I guess.

Originally Posted by johnta1

...This is the race section right?...

...But Bob stood on his head at midnight and sucked the hind leg of a frog and his engine turns one billion rpms and...

[Larry Navarro]

Originally Posted by Skip Fix

.....I don't care what type heads some one used to go fast, but when peolpe make blanket statements that aren't backed up by all the data something is wrong with the physics theory-at least that's what my engineer buds say.

Engineer "buds" need to get with the folks at Edelbrock who DESIGN and ENGINEER for the specific area of debate....

Skip, I'm no expert but to make it easier for you to understand, I have copied
the pertinent comments from Edelbrock about the
effects of port size and velocity. One would have to
assume they should have a pretty good understanding of
what their products do and how they work best. On
the other hand, maybe not - maybe you do know more
about their business then they do!

Here is one of the paragraphs in the current catalog
at the address listed at the end of this post:

"2. Bigger is not always better!"

A large port doesn't always mean more power. This is
especially true with STREET heads and in some cases,
RACE heads. Velocity is just as important as flow.
A smaller port volume generally equates to higher
velocity for better street performance. The speed of
the mixture determines how tightly the combustion
chamber is packed. The more tightly packed the
combustion chamber, the more pressure is developed
when the mixture is ignited, pushing the piston with
more force for more power. For example: A large port
and a big flow nuumer at 0.600" lift means low
velocity (especially off-idle to 3500 RPM) and results
in less throttle throttle response. For the street,
velocity is the key to overall performance."

That paragraph is copied directly from the current
Edelbrock catalog!
Now we know from past posts why Jim Hand lost performance with the
bigger KRE D-port heads. The power and engine response
below the converter "hookup" point determines how fast
the engine is accelerating and therefore how hard it
"hits" the converter hook-up RPM, for a hard launch.
Skip, we also have an answer to your recent comment on
an earlier "port vs. velocity" debate:
[QUOTE=Skip Fix] "Jim has been able to coax out more airflow with less
ccs than most on a D port iron head by doing careful
work to get both air flow and good filling velocity
for his motor." Jim obviously understands the
importance of smaller ports and great low lift flow on
moderate RPM performance, regardless of the engine
displacement![\QUOTE]

As many have said, port size must accomodate the
required airflow for the RPM to be run, and higher RPM
engines obviously need more airflow then those
shifting at 5300-5500. But to infer that one size
head can efficiently provide the best performance
regardless of RPM is obviously wrong - assuming that
Edelbrock Corp knows anything at all about head
design!

Well, there it is.
Now you can either AGREE with the ENGINEERS at Edelbrock about the effects of port size, or continue to DIS-agree and bring forth with what your engineering "buds" tell you.

http://www.edelbrock.com/automotive_...ds/specs.shtml
and then select: "Cylinder Head Flow Data (286 KB)"

[johnta1]

Since Poncho's run below 6,500rpm or so and usually below 6,000rpm and the are in a similar cid range the port size it's as "critical".

I believe you're the one that said this.
Got your proof?

[Skip Fix]

Larry I very well understand the general theory on size and velocity.Jim's car is so far the only car I've heard of that lost time with the KRE's due to their "bigger size". Cliff's "generally similar" combination(don't want to say that they are the "same" that makes some folks mad) picked up signifigantly and stayed in the same rpm range-smaller initial D ports than Jim has since his were not ported-please have the "engineers" explain that one!! That is where I get "confused" how it is set in stone. Same range more power bigger cc just like Scott's E heads did. This is always skirted around, if that theory is so air tight Cliff's car should have fallen off like Jim's, even worse since there was more size difference , Scott's short block should have had less power even at 3500 than the D ports did-NEITHER reacted that way.

Please document some dyno data where there were losses going to "big heads"!!

The HO head 455s only increased 400 rpm made 10-50 hp more still below 5000 rpm and the used a bigger cam Larry-REAL engineers designed them! You had one of those in your car was it a pig in the low end?

The added air flow trumped any theoretical velocity for the combinations.As I've said before anyone measured the velocity in the entire port to document it is worse?

Those contradictions to your "theory" never get explained out Larry. That's where we beat that dead horse. Real life examples that question that theory on a 455 Pontiac that never get explained other than that's the way it has to be


"A large port doesn't always mean more power. This is
especially true with STREET heads and in some cases,
RACE heads. " Since Edelbrock makes a 215 cc street/strip head for a SBC I bet even their engineers would have a hard time calling their Pontiac head a race head. If you look it is in their street/strip category (Performer RPM) no a Victor head. So let's not take one general statement out of context and apply it to a 215cc head on a 470 ci motor!!

If you also remember Edelbrock tried to generally copy the street RAIV head that Pontiac engineers had with it's HUGE 185cc ports only a 5500 power peak on a little 400 with a cam similar to what most folks run in 455-470s! So from the onset these were not and are not RACE heads from conception to production, now comparing a BBC 320-340cc rectangle port head that IS listed in the race section to a 280-290 cc oval port or a Boss 302 to a Windsor head yea then we're comparing race to street.

If you were comparing a 750 cfm carb and an 800 cfm carb would you use different intakes with the different carbs and then say all the data was based on just the carb size? Simple yes or no there.

[Steve C.]

Bio listed below for one head honcho at Edelbrock, he recently gave a speech at the Advanced Engineering Technology Conference. His presentation on port-flow efficiency against the theoretical "ideal" port-flow numbers was reported to be very intriguing. Noted, his "coefficient of flow" chart indiciated a consistent dip in almost all intake ports at around 0.300 inch of valve lift, which might lead to ....

changing some people's ideas on designing and evaluating intake-port flow characteristics.


Rick Roberts, PhD of Edelbrock (www.edelbrock.com)
Development of a High Output Cylinder Head for Small Block Ford Drag Racing
This talk summarizes the engineering effort behind Edelbrock’s new Glidden Victor SC-1 cylinder head. Topics discussed include: Valve and spark plug layout, port configuration and flow studies, flow comparison with other racing heads, preliminary CFD results and their implications, and valve train stability and strength considerations
Born in East Liverpool, Ohio on July 22, 1953, I grew up in a time and place that was encouraging for a burgeoning auto enthusiast. One of my earliest memories was accompanying my father to go look at the neighbors ‘57 Chevy. It had two carburetors. I thought that was just coolest thing ever. There were many Hot Rodders in my neighborhood. As children, the sound of a car without mufflers signaled us to jump on our bikes and go see what was going on. Then as now, to my ear there is nothing quite like the sound of a performance engine.
In 1968 my family moved to northern Illinois. I went off to Chicago in the fall of 1971 to study engineering at Illinois Institute of Technology. I graduated from IIT in 1975 with a degree in mechanical engineering and a principle interest in fluid mechanics. I was fortunate to be accepted at California Institute of Technology for graduate study in their Aeronautics department, a department of international renown for its research in turbulent fluid flow. I spent far longer at Caltech than I should have because it was such a great place to learn and it was easy to get sidetracked in the pursuit of new knowledge. I did come to grips with something while at Caltech and that was that I wanted to engineer products for performance cars. Most of my colleagues at Caltech went on to be professors at universities, both teaching and doing research. I chose instead to try a product development environment at IBM in San Jose, Ca.

During my final year at Caltech and during my time at IBM, I developed a friendship with then owners of Air Flow Research Company, Ken and Phyllis Sperling. They became mentors for me in the aftermarket performance automotive world. In the fall of 1986, I resigned my position at IBM and accepted a job with Ken and Phyllis at Air Flow Research. I worked in the machine shop, ran the flow bench, helped in the dyno room, and tried to do relevant research on a very limited budget.

In early 1988, my work at AFR attracted the interest of Vic Edelbrock and I entered into and agreement to share information and resources between Edelbrock and AFR. In the fall of ’88, AFR decided to purchase Brownfield company, a cylinder head manufacturer, and offered me the opportunity to buy into the new company. Brownfield’s foundry process was unique and I was given the responsibility to set it up and make it productive. It was a great learning experience for me.

By early 1991, I had gotten my fill of the foundry business and was looking to do more design work so I accepted a position as Director of Engineering at Edelbrock Corp which I still hold today. My time at Edelbrock has been a mixed bag of projects. The last five years have been better than the previous ten due largely to working on true race oriented cylinder heads. This is my passion and I more or less get to pursue it on a daily basis. I feel very lucky.

[uneasyrider]

Originally Posted by johnta1

I believe you're the one that said this.
Got your proof?

Oh... my... god! I... think... I'll... suck... on... a... shot... gun... I'm... so... hu... mil... ia... ted. You've... nailed... me... there. My... whole... ar... gu... ment... has... been... shot... all... to... heck. I... have... no... proof. I'm... screwed! I... give... up. Thank... you... for... show... ing... me... my... err... or. LOL!!!!!!!!!!!!!!



My brothers '03 Mach I has a factory redline at something like 6,800rpm. Think of what that little engine would do in "race" trim. MOST Pontiac engines on the street or raced here are approaching or beyond the limit of their rpm range at that point. It's all relative. We've taken that little Mustang out for hours and ran it to the red line many times durning the drive and it's bone stock and it didn't skip a beat, got ok milage, etc., etc. Not long ago that would be considered nearing "race only" rpm ranges for an engine and that little car will do that easy. I'll stack that little DOHC engine up against any traditional factory production Poncho on here with like for like mods and lets see who wins. I'll let someone else put up the money for that test thank you. Stock street engines that spin in the 6-9,000rpm range aren't all that unusual anymore. GENERALLY all of the engines built on here are "tractor" engines compared to many street engines today as far as RPM range goes. Lets face it, unless we highly modify a "traditional" Pontiac beyond anything the factory ever even thought of doing other than a few (VERY FEW) all out race, never seen the street as a factory engine stuff we can't run in the rpm ranges of a Honda S2000 so they are ALL tractor engines if you look at it that way. We build antique engines because we like them and it's fun to run something different not because they are the best and easiest and most efficient choice out there. It might be more appropriate to call this "Race, considering that it's a Pontiac and not a flat head Ford". I'm not sure if you could get any traditional Pontiac engine to run a full 24hrs at LeMans today and also be competitive. OR, how about building a traditional Pontiac power plant that will run in the top 3 in NHRA Pro Stock or how about the big time NHRA Top Fuel and I don't mean Nostalgia. The "Hemi" took that over a long time ago. How about running a traditional Pontiac in Grand Prix or Indy. So lets take a break on the "RACE" BS. As far as street or race goes you'ed be better off building a new LS1 engine and sticking it in your Poncho but IMO what would be the point, I WANT A PONTIAC!!

I mean heck, put Duntov heads and a blower on a Ford flat head and you will see a hot little engine but... LOL!

[Steve C.]

Reminds me of a recent article titled "Max Street Power". The question was posed, how much power can you actually make on the street and still remain driveable. They asked the experts...

the majority recommended building as big an engine as possible, using radical cylinder heads, and installing a mechanical roller cam.

They had a few engine builds for examples and the starting point, and low man on the totum pole, was "only" 600 hp with a very doctile 454 Chevy with a mild 248/254 solid roller and a set of aluminum heads with a 220 cc runner volume and 10.5 compression. Stated the combo would make 600 hp and 575 lb-ft of torque, peaking at a reasonable 6,200 and 5000 rpm respectively. Oh, and it carried a two year, 24,000 mile warranty.

Some would wimper at the thought of using this "race" engine on the street !

[Ron H]

In most of the findings of people who step up to larger volume heads and had an increase in power throughout. The engine needed more than it had before the swap.
I also think that the intake port is designed to keep the velocity high for the size of the port.
If the CI is there the velocity of a large port will be enough that it makes plenty of torque and HP throughout the rpm range making it streetable or not. The cam , converters and gears also help to put the power range where applicable for the application.
A 340 cfm flowing large port head will run very well on a 482 but not on a 350 in the same rpm range. But the 350 is able to spin up to a higher rpm and therefore able to use the larger port at higher rpm. So the cam converter and gears can be changed to make up for the lower rpm power losses.
The more CI and higher CR the less need for high rpm. But the port volume must be there or it will choke the engine.
If there is enough CI the larger port will always win if the rest of the combo is designed to take advantage of it.

[uneasyrider]

Originally Posted by Steve C.

Reminds me of a recent article titled "Max Street Power". The question was posed, how much power can you actually make on the street and still remain driveable. They asked the experts...

I would totally agree. As has been said since before I was born, "There is no subsitute for cubic inches." IMO, for the "street" an old OHV BB is GREAT. As you said the "experts" agree and as you said the "race" thing is relative.

The point of this thing was port size of course and I think that Mr. Wilkie said it well in stating that in general we are all running with 1000rpm of each other street or race so that is why the port size debate comes up becuase it isn't obvious where the cut off point is. If we were trying to spin these 467cid engines to 10,000rpm it would be totally obvious you have to have MUCH LARGER than stock ports. There is no perfect port, it's all about matching the port size to the cid, rpm, etc. to get the max power for the given application. All these engines people are spouting off about work not because they have a "big" port or a "small" port it's because the port they have works with everthing else. A good old example of the wrong port for the rpm range and use was the stock 351CJ engine. WAY to big a port for the stock cam and manifold for street duty that most of them did but when used on the drag strip where they could stick a tunnel ram and dual quads on them and spin them to 9,000rpm they flat SMOKED.

[Skip Fix]

"I also think that the intake port is designed to keep the velocity high for the size of the port" AH HA!!!! SHAPE! What a concept! Ron hit right on it.

Larry if we are going to quote Edelbrock engineers as knowing what they are doing why do they as well as GM engineers make 170 and 210cc ports for STREET 305-400 ci SBC that have peaks at 5500 or below? A 400 SBC has the basic B/S as our 400s-so yes we can compare them, same theory on heads for all motors right? It's not just a Pontiac theory? Quote on using a 175 cc head on a 305 "the volume is in the bowl so the CSA can be smaller for better velocity". Gosh bigger than D ports on a motor 150 or more CI smaller and peaked at only 5100! Where is that "race rpm"??

New 210cc GM HEADS on a 350 over "plain heads" picked up 44 hp 27 ft lb and at 5500/4000- same as a 185cc RAIV on a 400. "We knew the improved ports,chambers, and valve size would make more power".

[uneasyrider]

Shape is critical of course. Shape manages the boundary layer. The larger the boundary layer for the given port area the lower the flow. Why a teardrop shap to the engine cowling on a P-47 Thunderbolt and not a round cowling? It was because they found they could get more air through the given space with a teardrop area than an round because it reduce the boundary layer. Why a rectangle port and not a round, same reason. Why vortex generators on the leading edge of a wing, to pull the air down over the wing and reduce the turbulent boundary layer. Why don't most of the "Ram Air" scoops on the old Muscle Cars actually produce "Ram Air", because they aren't tall enough to get out of the boundary layer that sets on the hood, cold air yes ram air no. Why do you need a little roughness left in you intake port on a carb engine, to keep some turbulance on the boundary layer so the fuel doen't stick to the port walls. Shape and texture manage the boundary layer. Think of the port as your toilet and the fuel as number two. You want #2 to go down ("Who does #2 work for?") so you need some swirling to keep #2 from sticking to the walls. BUT to much swirl and #2 is flung out (maybe to the ground! ) and never goes down. I hope this helps.

[goquick]

Does anyone here realize that even our best heads avalible at this time out of the box are only good enough to properly feed about 400 - 420 cid? But they are a vast improvement over the heads we've had that were not enough to correctly feed a 300 inch engine.

[goquick]

Uneasy, I'll never be able to think of air and fuel the same way again without holding my nose.

[uneasyrider]

Originally Posted by goquick

Uneasy, I'll never be able to think of air and fuel the same way again without holding my nose.

LOL!! Sorry.

In the world of fluid flow it doesn't matter if it's sewage or fuel you are trying to move you just have to figure out what velocity will keep it all floating. If you look at the old sewers of London the engineers had it right WAY back in the day when they made them upsidedown teardrop shaped (egg) so that as the flow increased the area became greater to keep the velocity in the right range and the "matter" suspended (flow rate = velocity x the area). Look at some of the modern ports and also weren't the RAV ports egg shaped? Boundary layer control! When you look at the vortex generated by the water in the tub as it goes down think of the air in the intake port trying to do the same thing. The "hole" in the middle of the water whirlpool sucking air is like the nonturbulent area in the airstream going into your intake port. The water is like the bounary layer. The closer you can pull that water to the edge of the port wall the more air you can suck in. That's just a rough representation. But that is why round ports don't generally work well as intakes and you see most high flow ports are something other than round. Round allows the fluid to rotate easily and makes that undeveloped (the area where the vortex is formed) flow region larger. With a oval or rectangle the flow has to change direction as it falls into the port so the rotation is reduced. There is some swirl needed but just enough to keep the fuel from sticking to the walls and in full suspension in the air stream. To much and the fuel is slung out and also you waste energy rotating the airstream rather than letting it go down the port. It's no different than why you put lighter rims on your car so you don't have to waste energy rotating that extra mass. Same reason some of the new artillary rounds are smooth bore so energy isn't wasted spinning the shell in the bore. Look at the shape of the new LS1 intakes. Some of you might have even seen ports or pipes that have blades put in them to counter the rotation of the flow and straighten it out.