Intake closing...Effective displacement vs Intake charge.

The Can of worms maybe not everyone (including me) completely understands,,,,,

General theory states that timing your Intake centerline to allowing the valve to approach maximum lift at or near the the point of maximum piston velocity (where the connecting rod is just passing the 90 degree right angle to the crank throw) is very beneficial for torque output. Note: NOT the same as 90 degrees past TDC but later. This point where the Right angle is achieved is a constant but will vary depending on rod length (for any given stroke), but it is calculable through Trig.

But if you can maintain a strong unrestricted optimum air/fuel ratio charge flowing past your intake valve at high piston speeds ,The fact that your intake is closing earlier (relative to a later Intake centerline) might actually cost you some power in terms of cylinder filling as the piston is coming back up the bore.

When you get it right, the ramming effect of a strong intake tract will overcome the loss of displacement as the piston is coming back up the bore past BDC which effectively increases dynamic compression. the issue (if you can visualize it) is that as the piston is bottoming and heading back up the bore, the intake valve is rapidly closing the flow window for the port to keep filling the hole.

Where the charge keeps filling as the piston volume is reducing/passing BDC and fully closing is in effect 'supercharging' the lower effective displacement.....that's the key fascination for me....and for any motor and head combination (within the limitations of whet your working with) is what I'm always seeking to achieve is the best balance of both. If you don't have enough intake charge, the piston will push (reversion) the mixture back toward the intake, but if the charge is high enough, you trap more mixture than the cylinder (at that instant where both valves are closed) can hold statically...before actual mechanical compression begins.

I've been doing a lot of research on what Bob Glidden was doing in the 70's with the Cleveland fords and the W2 mopar wedges. It fascinates me how the intake charge, the cam centerline and the intake closing all work together. And also how the torque and power peaks interact and where valve overlap can be (and is) both beneficial and detrimental....depending on what part of the power curve you are looking at.

It was also how I figured out how the F.A.S.T. cars could be getting the amazing outputs they were achieving.

I'm sorry for rambling but I'm sure a lot of you will know what i'm getting at.

I'm just seeking additional insight and understanding from guys with a lot more depth of knowledge than I have.

I MET BOB AT A RACE IN THE SEVENTIES. HE WAS A GREAT GUY TO CHAT WITH AND WOULD ANSWER MOST ALL OF YOUR QUESTIONS.

What about IVO and piston demand, If the pressure in the cylinder is still high at IVO what does that do to the intake charge?

I met Bob several times, the last time was when he was crew-chiefing for Larry Morgan, super cool guy and he seemed very amiable and humble and loved being focused on the task at hand.

His work ethic was so evident in his hand shake and his demeanor and he was living proof that hard work pays off. He used to build his engines on the floor and I would love to see a display of all of his many cylinder head and intake manifold innovations.

What amazes me today is the technology of Todays CHI Cleveland head (that anyone can now buy off the shelf) incorporates many of the port innovations (and beyond) that Glidden first envisioned back in the 70's.
He spent 100's of hours brazing and epoxy filling factory heads and manifolds trying to achieve those same types of innovations. He understood port shape, velocity and Air/Fuel MASS allowed the cylinders to trap and burn more mixture and achieve much higher VE than his competitors.

if you want to see something related and interesting watch the youtube channel "driving 4 answers' regarding offset bore cylinders, it looks in depth on how the effective intake stroke increases by several degrees and the compression stroke shortens by several degrees. Kawasaki and other manufacturers have already incorporated it into several of their in-line engines. This means you could effectively fill the cylinder more with less total cam duration and there is somewhat more of the natural "level effect" from the crank on the power stroke, and you can imagine the turbo supercharging possibilities.

The downside is that it upsets the natural primary and secondary counter-balance and the natural maximum stroke of the crank (mechanical stroke) the isn't fully realized.

it's just interesting

I like your thinking and, yes, this might be a little heady for some folks.

My feeble little mind says that maximum intake opening should occur just beyond maximum peak piston velocity. Air is rather elastic. It takes time to get up to speed. Having the valve at maximum opening as the intake charge is at peak velocity would likely be more effective. The delay will be small but heavily dependent upon the target RPM.
Tuning this for peak hp would likely be less effective than timing it for a plateau. Spread it out for more area under the curve but based on the port velocity, not piston speed.
Again, a fine example of building a combo. Change anything in the incoming air's path and you have to start all over again.

I am surprised Polyspheric hasn't jumped in hear yet.

My first thought when reading the post was the intake ‘manifold’ ??? then after reading I finally saw it was the valve. Sounds real close to having high velocity in the intake manifold and intake port, reason the Hemi don’t make power till 5000 but wedge at 2500, stock stuff mind ya.

Something to think about:


Amazing Video: Jon Kaase Tests Airflow Dynamics With His Finger

Chrysler engineers worked with this when they developed the Long/Shortrams manifolds. The Shortrams used a special cam gear that was 2° retarded to optimize the ram effect.

That was a fascinating video!

What year are you calling the short ram intake?

Cab, they were available from 60 to 64. Hp ratings were 390 and 400. Mike at Nikes Garage rebuilt a 64 413 out of a 300k that was factory equiped with the 390 Shortrams motor, it also featured a pair of factory cast iron headers. His final hp and torque numbers fell way short of what they should have been. He bored it to 426ci and replaced the factory flat tappet solid cam with a hydraulic. Either the cam was ground wrong or was installed incorrectly.
He's got a YouTube show that's pretty good. He also dynod a 440 with a set of Long rams and a mild hydraulic roller cam. His single rotor dyno couldn't hold the motor at a low enough rpm to record the maximum torque figures. If I remember correctly, the lowest the dyno would hold the motor was 28-2900 and the peak torque was something below that, it was around 570ftlbs at 2800.

Learning how to effectively use ENGMOD4T will show you the optimum cam timing events but there is not only the learning curve of learning the software but lots of physical measurements that need to be taken.

The big thing against its use is that it doesn't natively have a decent camshaft profile set of functions, so it needs a plug-in for realistic camshaft profiles.


It's more than lots of enthusiasts are willing to tackle, but its use will allow a much deeper understanding of things like the cylinder ramming effect. There's lots to learn, but some study and a flexible camshaft profile plug-in are required for best results.

It's based on Gordon Blair's equations, so it's really accurate given good inputs.

You mean this guy:
http://www.profblairandassociates.com/pdfs/Back_to_basics.pdf

Ever heard of a guy called Larry Widmer?

The math to calculate the percentage and actual charge mass captured, the "dynamic" CR, and effective displacement when the intake valve closes ABDC is fairly simple trigonometry based on the engine's rod to stroke ratio. Read my article for more content as well as the formula: http://victorylibrary.com/mopar/cam-tech.htm
However, there are too many variables remaining that are difficult to quantify or reconcile as to their relative contribution to obtain anything like a linear solution. It will predict a trend, not a result.

I wrote an Excel program to do these calculations automatically.Use the sliders to select number of cylinders bore, stroke, rod length, intake valve closure, static CR, atmospheric pressure (Imperial & Metric).
E-mail for a free copy.

I have heard of Larry widmer and I believe I have read everything he’s ever published

Guess that makes 2 of us. Here's Larry discussing some of his stuff on another forum.


Now I'll address your head related questions: With the exception of blown applications, ports don't just flow one direction. Intake ports pulsate back and forth, and exhausts flow backwards too. This occors primarily at overlap, when the cylinder still has positive exhaust trying to exit the exhaust port ...where header back pressure is pushing backwards. Now the intake valve (which is larger in diameter) opens, and exhaust gasses seeking the path of least pressure take the easy way.....the intake port "exit". This is not a good thing because besides turning the intake port black "reversion" also contaminates the intake charge with inert gasses which will not burn again. My studies showed a direct correlation between low lift intake flow and reverse flow.....The better the low lift flow on an intake port, the better the tendency for reverse flow, or sucking exhaust. I designed my intake ports to not flow worth a [censored] at low lift, and also to not flow backwards.


Its obvious that if you can create enough inertia early on in the intake cycle then it will continue well past BDC. The irony here is some engines need more exhaust residual to improve the burnable mixture by increased vaporization so airflow dynamics are one thing and the chemistry of the burn is another.

Are you familiar with UDHarold?


At low engine RPM, an early exhaust opening HURTS bottom-end power. It could extract more torque from the crank, instead of blowing power out the exhaust pipe.
At low engine RPM. an early exhaust closing HELPS bottom-end power. It helps prevent reversion from contaminating the intake, and reduces fuel loss during overlap. At low-RPMs, it is the TIME of the exhaust overlap, not the number of degrees it has.
At high engine RPM, an early exhaust opening HELPS top-end power. The most important thing becomes the necessity of cleaning exhaust gasses out of the cylinder, to allow the maximum intake charge to get in.
Peak engine horsepower occurs when the exhaust cam can no longer let ALL the old exhaust gasses out, and some remain to hinder cylinder filling.
All these things occur with the intake on the same ICL.

I remember Larry Meaux discussing a Hemi engine once that had the most VE he had ever seen on his dyno. The problem was the intake charge was heading straight the exhaust port so it wasn't reflected in the power it was making or should have been making had it been contained in the cylinder and utilized.



Just more stuff to think about.

Its been a while since I posted, but a good subject.

Before all of the computer programs, we found on max effort tunnelram, Carbureted NA engines, that a 278 degree @ 0.050" intake was pretty much optimum starting point. Didn't seem to matter who's name was on the heads if they were decent. Dyno time to move the centerline around a bit. Very aggressive ramps only gave minuscule gains at the cost of quick VT destruction. Bigger bullets liked the cam timing retarded. Even now, some of the best grinds in our day when put into the program predict the most torque area over the RPM band. you could test 25 cams all around that VT and maybe chance 10HP.

As a side note, taking old racing heads and putting them into street service; I put a tiny HR in the engine and still make great power in the upper RPM ranges of the valve springs.

0.02.

Thanks Polyshpheric!

I'd love to have a copy I'll PM you my E-mail.

Hysteric: Yes I was very early follower of Harold at Ultradyne with his asymmetric lobes as 102 Intake centerlines, I learned a lot about camming stroker from a compilation of cam theory and lots of experimentation.

Also, BTW there is a GREAT youtube presentation where they interview 93 year old (and still working) Ed Pink talking about the 427 Cammer and the struggles with adapting it to Top fuel racing.

I'm sure you've watched these videos, but in case you haven't.

https://www.youtube.com/@darinmorgan3520/videos

Covers a lot, I watch them every six month or so

Sometimes we take air for granted because it is the environment we live in, and we forget that it has mass, density, and inertia when moving.
David Visard has a way he calculates port energy (I think that is what it is called?) which I think is flow and velocity combined.
I still don't understand how McFarland uses 1/2 Mach speed (around 563 feet per second) to estimate peak torque RPM?

I've always found that because a stroker (particularly one with a shorter rod) makes more average torque when I run a proportionally bigger intake lobe combined with an earlier (say 102 vs 106-108 ) ICL. because when you stroke the motor the amount of "give back" past BDC per degree of intake duration consumes a proportionally higher amount of effective displacement.

I think this is of dual benefit if you are seeking highest average torque (primarily a street strip or a torque monster bracket motor) because #1 the added stroke initially draws a bit harder on the intake port so the added duration (say 8 degrees vs a standard stroke) doesn't upset the drivability and the early opening gives you the same intake closing event as a +8 degree cam going in at 106. When you stroke a typical wedge engine it's hard to even get enough port on the motor to begin with and since you are generally RPM limited (due to higher net piston speed for a given rpm) the "supercharging" effect of packing the cylinder above its effective displacement is going to occur sooner in the RPM range anyway.

Above the torque peak (Peak VE) many people don't understand that the main reason the HP curve goes up but the torque moves down is because past peak VE the internal friction within the motor is increasingly becoming a "brake" (rising levels of piston ring drag, valvetrain spring rate loads, etc) and the port flow/velocity is trying it's best to overcome those parasitic losses. I think/believe this is why for most strokers the torque and HP peaks tend to be closer together and the HP falls off proportionally quicker. I think this is readily apparent with small block wedge strokers when people accidently discover that short shifting (say at 6400 vs 6800) has a lot less effect on the ET than a similar standard stroke motor....because the shorter stroke would have a proportionally less "Brake effect" per 100 RPM gain above the torque peak.

Of course this is a bit of an over-simplification, with some of the bigger race heads (like the CHI Ford heads) they can keep 'packing the holes' way up in the RPM range....even with very long strokes.

I think for any given/desired combo there is a "sweet spot" and I think understanding the cause and effect of the Intake closing plays a huge part in getting it optimized for whatever you are asking the motor to do.