ptuomov

If this is in reference to what generates the high-pressure wave propagating upstream in the intake tract for high VE engines, I would make the following claim. It is possible to generate an intake pulse by closing the intake valve early enough. This will however hurt the volumetric efficiency and power, and losses will be much bigger than any potential benefits.

If the valve is closed only slightly too early, the local air speed at the valve is very slow and no appreciable pulse will be generated by valve closing. The pulse does nothing worth mentioning, as it's weak. The pulse generated by the piston near BDC will however still be in play.

If the valve is closed much too early, the local air speed at the valve is fast and a stronger pulse may be generated by the valve closing. This pulse will not result in a volumetric efficiency over or even near 100%, however, because the volumetric efficiency losses from closing the valve too early are much larger than any potential benefit from the pulse generated by closing the valve too early.

Therefore, I believe that it's simply impossible for the pulse generated by intake valve closing to lead to volumetric efficiency greater than 100%.

Here's the hardware and software package I've been thinking about buying that allows for direct measurement of many of the things I've claimed here: http://www.tfxengine.com/software7.html . I found these actual empirical measurements useful for helping my understanding.

For example, this graph shows how the pressure wave is already there in full force before the intake valve closes:



The pressure wave peaks at intake port before the valve closes, so the valve closing can't be causing the wave. The zero gauge pressure is exceeded slightly before the piston BDC, supporting the theory that the pressure wave is caused by decelerating piston. Also, interestingly, the benefit from this reflected wave is visible with the pressure being high at the port at intake valve opening point.

jeff spahn

I'd also like to know how this would work on a stock 5.0L or what the implications of this intake would be to a supercharged engine. I am not an engineer nor did I stay at a Holiday Inn Express last night. The engineering talk on the forum sometimes goes way over my head. That's why I hire engineers to work for me.

TexasDude74

Ptuomov, whether the pressure wave is generated by a valve slamming shut or a piston coming to a stop, would it make any difference in the development of this manifold? In regards to runner length, diameter, taper, cross section, material, temperature or plenum volume? Or any other aspect of a engine under Gregs' control?

ptuomov

I have no idea about the approach that Greg Brown has taken to decide the runner lengths, so my speculations about how his manifold was developed would be a waste of everyone's time. He'll share if he wants to.

Speaking entirely in general terms of manifold design, not specifically about any manifold project:

The difference between the two explanations is a lot of crank degrees so _in theory_ it makes a difference to the runner length. You can eyeball the pressure wave shift in percentage units from the TFX graph.

In practice, I assume that one has to do a lot of cutting, welding, and testing anyway to empirically find the correct runner length, in which case it doesn't make any difference to the end product what one's theory is. The better theory may at best get you to the correct runner length with fewer cuts and welds.

Mongo

In theory, if flow is improved and equally distributed to the cylinders, power would be improved since there are certain ports that are restricted in the factory setup. A while back, someone had invented intake spacers to see if this would improve the flow to the ports restricted, gains were negligible on naturally aspirated (stock) applications. Supercharged and stroker motors showed gains though. I can only think that there has to be some sort of gain if this intake manifold is installed on a stock application, especially if it is sharktuned.

Tom. M

Ignoring all the details ... I am assuming it's a fixed length runner.. so in theory, you are tuning for a particular rpm band (assume higher end)....so the engine will lose some low end torque in hopes of gaining significantly in the upper end.

Gone will be the double hump torque peak of the S4...and in it's place you will make way more power at the top end? Again assuming the intake is designed for your big engines (6.5 liters), the loss of low end is inconsequential...and the gains on the top end are probably pretty good ..

I suspect on 5 liter the loss of the low end would be much more noticeable??

GregBBRD

Now someone is getting it....

We've got a completely different manifold for a 5.0....that engine has different requirements than a 6.5 liter engine.

mickster

6.5>5.0

Mongo

I don't have my book about intake manifolds in front of me right now, but I take it with the 5.0 manifold the runners are longer to maintain or gain torque?

GregBBRD

When you find that book, please have Amazon send me a copy....

Mongo

It was in a book about engine management systems. The chapter is not very descriptive but did provide calculations for runner length and volumetric efficiency. I think you may know more than what that book tells us lay people.

BC

Four-Stroke Performance Tuning by A. Graham Bell

I can loan Greg my copy of that and his forced induction book.

But I think he already knows most of that.

mickster

Mongo

This is the one I am talking about:

BC

Read that one cover to cover several times. More questions than answers now.