I figured that I would start a thread about some of the misconceptions going around about cylinder heads since most people do not know enough in this area and are going by what is force fed to them. The few people that actually KNOW about cylinder heads either do their own work or are having Larry Meaux, Air Flow Development, Trevor Johnson, etc, etc, do their heads and are dropping big $$$ to get what they want. The other 95 % of the people on this board will gain some knowledge by reading this.

The first thing that people ask is "what can you get them to flow?". This is a VERY confusing question for a few reasons.

1- flow #'s are NOT AS IMPORTANT as runner shape and measurements in key areas of the port.
2- most people inflate or lie about #'s since that is what most customers wanna see.
3- it will vary depending on what valvce size we are using and what the port NEEDS to be shaped like.
4- more CFM on a flow bench at 28" of depression will not always make more power. The engine will have the air traveling MUCH faster than this and find alot of problems with the port that a 28" flow test will not show. Flow testing at a higher depression and LOOKING for problems is a better way to design a port, even if this means shaping the port different so that it flows LESS at 28" of depression.

The next thing being thrown around is that a large runner volume kills velocity and will make the car accelerate slow. Velocity where? If you have a good flowing valve job, and the right measurement at key areas, the port will have plenty of velocity to fill the cylinders well. Velocity is not something that you want to be "highest". It is something that you want to control. The port needs to be small enough and shaped right to keep the air moving fast enough to fill the cylinders BUT it also needs to be large enough to SLOW DOWN the air and allow it to stick to the port and valve job under the conditions that it will see when the engine is operating. The higher the HP, the faster this air is moving so you need to adjust this and make certain areas larger to keep the air stable.

Runner volume is a bi product of getting the port shaped like you want it. Once you determine the valve size and venturi diameter of the valve job, get the measuerments that you want over the short side and at the pushrod pinch that allows the air to travel the speed you want it that will feed the cubic inch/RPM that you want and then get the port taper where you want it, the runner volume just "happens".

This is NOT a lesson in air flow going out to Air Flow Development, Larry Meaux, Trevor Johnson, Yelvi, etc, etc,. . . . . lol . . . . this is just a brief overview to arm the average cylinder heads consumer with some better knowledge than "what do they flow", "that runner volume is too big", etc, and put things in words so that most people understand so they will not just keep repeating the bad info going out there. It seems once this stuff is repeated several times, it becomes "fact" and then "common knowledge", even if it is wrong.

If you have the $$$ to send heads to ANY of the people mentioned in this thread, do that. If you are working on a tighter budget, you WILL NOT find a consistantly better working head than here at Elliotts Portworks for the $$$ spent.

Lloyd Elliott
972-617-5671
Eportworks.com

 

100% TRUTH!!!

 

Another very informative thread. Now you have a PM.

 

Does this mean velocity has a "happy medium" persay? Kind of like a graph that would go up diagonally with increase of HP compared to air moving.

What do you mean "stick" to the port and valve?

Also, maybe you could better answer my question here, since you were the one who got me going.

 

you want the air to move fast enough to "fill the cylinders well" but if it is moving too fast, it will NOT stick to the walls of the port and just go turbulent. Once it starts bouncing around, the flow drops dramatically. This means the cylinder fills with less air and makes less power.

Air does not wanna change its cross sectional area or make any turns so the more gradual you make the turns, the better. Making certain areas wider and larger (short side, etc) will allow the air to slow down and make the turn as opposed to "jumping" off of the port and killing flow. If it MUST change cross sectional area, you want it to remain as stable as possible so the taper needs o be slow.

Most porters know this but it is easier to remove less material and say "a big port kills TQ". This is true when talking 240-250 cc ports but a 200 cc port is NOT big on a 6200 RPM 355 engine with an LT1 intake.

After calling a "competitor" and gearing a bunch of nonsense, I figured that I would set the record strait. These are the same people that want people to believe "we could work for NASCAR but we like working for less $$$ and dealing with the street crowd" LOL.

Lloyd

 

So basically, with a certain lift and duration, you want the cylinder to fill as much as possible, but not OVER FILL it correct? Once it "over fills" with air it bounces back out of the cylinder into the head again creating turbulance, right?

 

My box was full i sent you another one again.

 

it will not "over fill" that is the thing, it will not fill as much. You are not gonna get 100% filling due to all of this and you are pretty much just trying to figure out what % will be filled and at what RPM.

When the port goes turbulent, less air enters the cylinder and you make less power. You are always trying to get closer to that 100% mark. If you have evrything worked out right and the air enters like the cam wants it to, you start out at 85-95%. Once the port goes turbulent, this drops the filling % by a good bit.

You have the intake valve open for just a certain amount of crank degrees and if the air can stay stable, you can get more in the cylinders than if it goies turbulent and starts bouncing around.

Lloyd

 

Thanks for that Lloyd.

Steve

 

why did warren johnson say if choosing between two set of heads of equal flow he would choose the one with the smaller ports.

 

I can ASSURE you that Warren Johnson is not testing his heads at 28" of depression either. He knows what he wants his cylinder heads to do and he wants them to feed to cylinders as well as posisble. I am sure that the flow #'s are not the only thing he is looking at.

He probably cranks the depression well past any thing the average porter is used to (maybe 80", maybe 100" or more . . . .???) and simulates what the enigine will see. He is also measuring certain areas in the port and making sure the air will not go sonic on him. You would probably be better off asking Warren what he is looking for and just take for granted he is telling you everything (which we will not).

My post was more in relation to the LT1 community and the average 370-450 RWHP in a 3500-4400 lb car turning 6000-6800 RPM. obviously something more along the lines of a Pro Stock head would fit in a different catagory.

Lloyd

 

Damn Lloyd.... you used to be able to read Warren Johnson's mind. Are you slipping???

 

So it is like pouring water into a bottle, you want to control it as much as possible (water simulating air movement) and pour it straight into the bottle's opening, but if you hit the rim it sprays everywhere (rim being whatever and spraying water being the turbulance in the air). Correct?

 

so given 180 runner or 200 runner that flows the same# which would you choose on a lt1 turning 6200rpm and why?

 

Great post Lloyd. I really appreciated it when we talked last about maybe going from the LE2 to the LE3 heads on my Impala SS. As we talked about on the 205cc runners and the flow and volosity of the heads vs valve size and certian areas of the ports being worked on.
I am very very impressed with the work done on my LE2 heads and will again use you down the road when I decide to upgrade to a stroker. I am still realing about my dramatic gains over my previous setup done by another well know porter. I will continue to tell all other LT1 friends about your services and incourage them to give you a call and let you explain the advantages of your heads. Again thanks for everything. Lloyd rocks
HVY SS Frank Staton