Well,along with my fabulous 60 word per hr typing speed,I make typing mistakes,too.

Glad I don't build engines with a keyboard.

 

Not so fast cowboy!

Current MLA writting style dictates the following:
Anyways, i love this thread. Learning a bunch of stuff i never knew before.

 

I am still waiting for LR to whip his dick out

 

I would have to sell tickets to that show,and you probably wouldn't get your monies worth.

 

Don't want to see that Ellis.

Let's look at some of the stuff that's been thrown up in this thread.... some of it is really out there when you think about it.

Hmm, won't "feed itself". Well that was definitely a deeply technical answer. It's all clear as mud now.

The charge will go out the exhaust?

Hmm, where does maximum port velocity take place and when are piston speeds highest?

You've gotta chuckle at this one when you figure out that the exhaust valve is CLOSED.

Yet everyone who's in the know says it is.

And LR knows that WJ and Andersons ports aren't doing more than .5 Mach? Must say, this retired crane operator has some connections.




Anyone else see a contradiction in terms here?

They "aren't worried about MACH numbers. All they want is more air and fuel in the chamber".

Looks like someone doesn't understand the effect of air speed on cylinder filling (VE). Oh yeah... I forgot, it's all gonna go out that closed exhaust valve or perhaps it's going to go right by the rings? Who knows what's going on in there...

Now this is the question I'd really like an answer to...

Now, LR if you can answer this question with the slightest inkling of technical bravado I'll shut up. Don't think you can do it cause I'm gonna checkmate you til the cows come home bubba.

-Mindgame

 

Well, I have never PAID anyone to build my engines,as you have.
You can say what you want the .5-.55 was a guess.Thats it bottom line.
You can't figure port velocity from a VE number and that's what you said.You can poke holes in whatever you want,but all the formulas in the world won't make that right.
After you do the formulas you have to make it happen and I don't PAY to have it done,I am smart enough to do it myself. Figure that.

The exhaust valve is not closed on the overlap cycle.Anybody should know that

 

Nothing magical happens at 4-4.3 MACH.IMO and some others(not on this board) it's when you get over that things start going wrong with the flow. I can make plenty of power below .5 MACH so why put up with the flow problems any higher.I am not rules limited or have to run unported heads so why go there.
If you had have put up the whole statement I said for the "average" builder.
I build engines with short rods and big ports.If you don't believe that theory get in touch with Billy Glidden and he will build you one.He is another one that don't believe in the over .5 MACH.(probably learned it from his dad)

Since you "paid" for your engine to be built and all you brought to "that" party was your checkbook,you are now an authority with these formulas.Didn't say right or wrong either.Formulas are good but you can out engineer yourself.

 

actually I have built all my motors and in my old age I have gotten lazy. much easier to pay someone for there time when I can save mine

I know some of the other people here are in the same boat. It is easier to pay someone to do it WHILE others are paying me to do what they do not want to do

So I for one am offended by that statement. I build my own motors for 25 years and now I let someone else do it am I am a looser.

Damn I am going to have to work on the 28 hour day!

 

No offence intended toward you,and I am still building them after I retired from my regular job.(40+ years on Manitowoc lift cranes)I get to do what I like to do and don't have the money or the trust in anybody else to build mine or my customer's engines.I can't see spending the money for something I do well myself and enjoy it.
When I was working I also built engines/cars in every off minute that I had.It's much easier to work only one enjoyable job.
It's about time this old fart slowed down,but there is always someone looking to go faster.

 

Well after reading this most informative post, I must say this. I am no engineer, and don't know how to apply some of the formula's mentioned here. But I do know the basics of operation of the internal combustion engine.
Please correct me if I am wrong.

A basic fact of physics is if velocity goes up, volume goes down, to get higher velocity the port has to be small(er) and would have trouble either at higher rpm or more cubic inches feeding the engine..right? You can't have both, velocity AND volume.

If the air IS IN FACT moving faster on the overlap portion of the stroke where the piston is on "rollover" at TDC and has no bearing on helping the charge enter the cylinder, the air fuel charge on the 1/2 of the intake valve FACING the exhaust is already turned to go out the exhaust valve by the hitting backside face of the intake valve as it opens and the exhaust scavenge is the only thing pulling the charge in the cylinder, stands to reason that the faster the air fuel charge is moving, the more would go out the exhaust valve, negating the high mach number?

Stands to reason that most of the A/F charge is coming in the cylinder closer to the exhaust valve side of the intake because the other side is crowded by the cylinder wall..right?

Mach number in theory can't really be applied to a running engine anyway...right? How you gonna measure how much pull the piston has on the intake tract AS A WHOLE?

So in reality MACH numbers are really like head flow numbers, you really don't know anything until you put it on the rollers or the track.

Just had to ask.

David

 

BTW just to make this relevant to the LT1 guys reading this.....

With the amount of cross section that you can get out of a LT1 head at the pushrod area a 383 will easily overspeed the port at RPM that the motor will see.


Forumla: (Min Cross Section x 185,000) / (Stroke x Bore ^2) = HP RPM Peak

2.10 x 185,000 / 3.75 x 4.03 ^2 = 6379rpm Max Power for a LT1 headed 383
2.10 x 185,000 / 3.48 x 4.03 ^2 = 6875rpm Max Power for a LT1 headed 350

Now If you do a bunch of welding on that area and play with it you can get the min cross sectional area big enough to run a 383.

So.....

The 383 with LT1 heads @ 7000rpm....
(.00353 x 7000 x 3.75 x 4.03^2)/2.10 = 716 fps or around .59 MACH!

The 355 with LT1 heads @ 7000rpm....
(.00353 x 7000 x 3.75 x 4.03^2)/2.10 = 665 fps or around .55 MACH!

BTW The forumla for that is.....

(.00353 x RPM x stroke x bore^2)/min cross sectional area = Max Port Speed

Now if the cross sectional area is not that big it will easily get .55+ MACH at lower RPM.

This is the easy way to explain why they fast LT1 headed guys have 355's not 383's!

I hope that helps make this thread more applicable to the average guy.

Bret

 

Ohh, you got me there LR.

Contrary to what you might think, given so little information, I do build my own engines and the only one I haven't put together was Sonny's 504 ci small block I mentioned in one of my other posts. Have any idea what goes into building a 504 ci small block? Not many people do, so I guess if I had it all to do over again, I'd let Sonny do his thing.

You are right though... I don't port my own heads, I don't do my own machine work, hell... I don't make my own nuts and bolts so I must not know much of anything about engines.


If you know how to copy and paste then could you please do me a favor and paste the reply I made where I said you could calculate Mach directly from VE.

I said they are directly related, nothing more.

And anyone who knows anything about this subject, will know that the highest port velocities DO NOT occur anywhere during the overlap period. May have a bit of carbide precipitation of the cranium going on here.

And I though this was about PEAK port speeds or am I the only one who understands what this whole cluster**** is all about?

David,

There are technical answers to your questions but I have pretty much given up on trying to get them across as I may be dubbed a paper racer or something along those lines.

If you want to look at the basics then you can break it down to "relationships". If I gave you an equation that you didn't understand, let's say

A x B = C

then you could see that any higher value of "B" is going to increase "C". Simple enough?

Now look at the things that effect the potential output of an engine. If you look at restricted Nascar engines in particular, you will see that one of the key reasons they don't make the power they could is due to a reduction in volumetric efficiency thanks to the restrictor plate.
In our examples we're talking about a restrictor plate that's in-the-port so to speak. Doesn't matter where the restriction is in the intake tract, because wherever it is, it's going to govern when airflow speeds become too high to help power.

Regardless of what you may have been told, guys are spending a great deal of time trying to get as high a velocity through the port cross section as possible given a given operating range. Why? Because these engines will make better power across that rpm range at higher % of VE. VE and port Mach are directly related as every paper from Taylor and others will suggest. The point being that as the piston comes around from BDC and starts to ascend, the higher port velocities are, the better the cylinder filling will be. The higher the port velocities are, the later the intake valve can be closed. If you really want to understand this, do a search for "pressure crank angle diagrams" on google.
They paint a very vivid picture of what's going on. They also suggest that the correct intake valve closing point is not just some random number. An engine combination can be simulated, inertial effects can be seen and ways of capitalizing on this phenomonon can be utilized. This is the whole basis behind software packages like Dynomation Wave Action Simulator.

Either way, the port cross section is best when it is sized such that port velocities can be highest at peak torque and nearest peak Mach for that port design. WHERE you want that peak torque determines the size where it will become sonic... so there really isn't that much mystery involved here. Just good common sense will get you a long way.

OS, that Chopin is sounding real good about right now.

-Mindgame

 

BTW, here's a good article on Dynomation, what you're looking for in the graphs and what all of the information tells you. Pay attention to the airflow speeds they're "looking for" to capitalize on inertial effects in the system. A bit higher than .4 at peak.

http://www.racetech.com.au/faqinertia.htm

-Mindgame

 

You're right. And no one is arguing against this. What IS being discussed is what the optimum size of the cross section area is and what speeds we should target for best power.
Any size port cross section area (csa) can go sonic given enough rpm. Where you run into problems is when you size that csa to go sonic at say a 6000rpm torque peak and you only cam the engine to make tq peak at 5000rpm. You then have a port that produces low velocity and it will never capitalize on the inertial effects it would have produced had it been sized properly.

First off, scavenging is all part of the process. At low rpm you get alot more of what you're describing then at high rpm.

What you ARE erroneously assuming is that you know how the air travels into the cylinder. From everything I've read (I don't do engine r&d, just read about it) is that flow is predominant towards the center of the cylinder bore at low to mid lift. At high flow it is moving across the back of the intake valve, but look at the ports..... they're parallel to each other. I could see more of this happening on a true hemi style head and maybe that's why those camshafts are typically ground with a bit less overlap? Just an observation.

Mathematics and simulation.

Anything can be simulated to some degree of accuracy. Thermal compensation algorithms, friction coefficients, you name it, it can be used in a program. If you take a look at some of the best suimulation software on the market you could see some pretty amazing trends when you start overlaying graphs.... simulated vs measured. How else would we know how much stress a component could handle before failure in a complex mechanical assembly? All about simulation and mathematical models.

The guys that do this stuff on a serious level, have all these tools at their fingertips. They can simulate running conditions, including inertial effects and wave ineractions, then determine pressure oscillations in the port. Then they can flow the head at a depression that is very close to what's actually seen in the engine. All about resolution in a non-steady state simulation but you can get extremely close.

They do the same thing anytime a venturi is designed. Jet engines too.

Good questions.

-Mindgame