Thread: Curious Question..Long

Hey guys.

Well for those of you who are experienced with internal combustion motors and more importantly the physics and dynamics of how combustion happens inside the motor. I figured I would put this up and see if anyone has anything to say about it. I would like to have a stable and informative discussion, yet don't hesitate to tell me this is BS and WHY you think so.

I have been doing some considerable reading in preparation for my college courses down the road, and also to keep me from going crazy whilst taking BS classes in preparation for my actual major's classes.

In some of the literature, it was talking about combustion chamber design, in regards to burn patterns on the piston, and the head of the motor. The article described your basic ideal for coloration and pattern on a piston, as well as swirl and tumble techniques to encourage proper atomization and prevent mechanical separation of atomized fuel once in the combustion chamber.

To the point, it mentioned if you have a motor that requires allot of timing (and fuel), not only is that not an indication of a good and fast burn, but the more timing you add, the more negative work is applied to the crankshaft before TDC. With that, it got me thinking, has anyone or any company worked or examined the ve's relative burn speed and combustion pattern? It occurred to me that perhaps the motor could be loosing allot of power with an incomplete burn and also the need for increasing timing BTDC. This also translates to the fact that more timing indicates a need for a "longer" burn, which would point towards a slow burn. Not good.

I also have not really seen any after market pistons, that might provide a faster burn towards the exhaust valves? We all know that the ve does not have the best intake velocity, however we also know intake velocity is not as important as a faster burn, allowing a motor to make more torque and use less fuel, all the while, causing EGT to be lower and that is a great thing indeed. Perhaps the secret to getting more power out of this motor is not in porting, or improving flow bench numbers, but finding what is going on inside the combustion chamber. Because many experts point out, intake velocity is not as important as the retainment of atomization of fuel once inside the combustion chamber, as well as the reduction of fuel pile up inside the intake runners after the intake valve has closed.

This brings me to another point, that one of the members on this forum who had a valve angle job on his ve head, managed to make considerably higher numbers then most members on the forum with the same bolt ons. Perhaps this further emphasis's the need for a look at the chamber dynamics of the ve.

Again, give it some thought, let me know what you think. I just figured some might have some feelings about this, because we all know the VE is miles behind any Honda motor as far as R&D. And those doing R&D at this time don 't give a crap about us. Lets hear it guys.

Cheers,

Dudeman

If you have any friends in college that are going for an engineering degree you can get them to pull as many SAE papers as possible on the exact topic you are talking about.

It's all a compromise is what you will find

The best piston design will match your best head work will match your best cams

A slow burn is fine if you have a piston that dwells at TDC and BDC longer

Here is what went into my motor build
I wanted to have the highest streetable compression possible with the flattest piston possible. A flat top piston promotes even heat distribution and keeps hot spots to a minimum so that there is no detonation or preignition.

Headwork
Port matched everything and rough honed everything. This helps promote tumble

Swirl polished and back cut valves with a 3 angle valve job. This helps swirl and pulling the air into the cylinder with the best possible mixture

Cam
Custom for this motor but DEGREED
everyone forgets to degree their cams but its as important as cam gears

Dual staged injectors
There is a reason the N1 has 8 injectors

Ideally you'll mix it all together to get every last bit of power possible

The bottom end is another story that keeps all that power reliable.

I'm not entirely sure what you mean? Pistons with a surface pattern that encourage turbulence in the inflow? If so I would agree as a more turbulent flow will help to keep fuel atomized. You do want to avoid areas that might cause fuel pockets that can cause knock though.

In regards to the intake velocity, it also has an effect on the atomization. While you're right and the atomization is the most important for a fast and more complete burn, this is also directly affected by the intake velocity (higher velocity should give you a better retention of atomization).

I think the best you could do would be to both increase intake velocity and reshape the piston face (if that's what you meant).

Additionally, more powerful spark is a plus and if it's a big improvement should allow you to retard the timing a little more towards TDC.

All I really know about the combustion itself is that it's complex enough that you really can't predict it too well. I am familiar with the basics, but its some crazy stuff (interesting though).

I think you're right about the VE though... not as much R&D as the hondas and I don't think there's been much done yet on it as far as things like that.

Great point I'll check it out!



Is that so? Interesting. Because from what I have read, it was saying the slow burn would cause a need for longer burn time, or more timing, which is less power on the down stroke of the piston. It also seemed resoundingly evident a faster burn is always better. I could imagine what you mean though.

Some very interesting points, thanks for sharing what you did, the neat thing is I understand most of what you said...reading is a good thing i guess??

And just to make things clear, my main point, was that fact that perhaps the VE could GREATLY benefit from the proper alterations to piston design, and head and runner design, similar to what you mentioned. Make sense?



Yea you got what I meant! Alterations to the piston/chamber to encourage and enhance combustion. My main point is, perhaps the ve is lacking in this area?




I'm not sure if i can completely agree with you there. While intake velocity is very good and important, it is also much more important to have proper atomization regardless of velocity. If reducing intake velocity for say more tumble effect, causes a larger gain in torque, then maybe thats what the ve needs? (By reducing I mean converting velocity into tumble). Again just thinking out loud... Fire back at me



No argument there, especially since none of us have the means to test how well our engines create a decent combustion environment. One of my books talks allot about "reading" the piston and the head, for indications of poor design. I am on the hunt for "used' ve head photos maybe that will shed some light as to if I am beating a horse that doesn't exist?



Dudeman

What I meant was from a fluids point of view: any increase in the intake velocity is going to make the flow more turbulent which should encourage better mixing conditions and keep the fuel atomized. Not sure what you mean by tumble effect? Again though it's all theoretical and I think you'd really have to run tests probably.

Right, air will act as a fluid when entering the combustion space.

However, excessive intake velocity can actually be detrimental to performance. This is when the velocity actually causes the mechanical separation of the air and fuel.

This can happened when entering the combustion chamber, because fuel is heavier then air, it will not follow the same path. With too much velocity it can aggravate the separation, because the fuel is heavier and will not follow the shortest path like air will.

Also when entering the chamber, it can come in to fast and separate in some conditions, which is said to be more so with shaped pistons and large valve reliefs.

So the question is, how much is too much? That is supposed to be designed around ideal peak power rpm. So, that means it needs to be developed on the flow bench...

Tumble is a term given to a design that will cause the atomized mixture to physically twist into small dimples on the piston, head or intake manny. Maintaining an accurate mixture, and helping to create a faster and more complete burn. It was pointed out that allot of times builders will look at the pistons and heads and use dimples where there are signs of wash on the piston.

Dudeman

Actually that had not crossed my mind haha, I was thinking of the charge in terms of a normal fluid (oops ). Makes perfect sense now that you've mentioned it. So you'd just have to find the optimum balance then for the RPM range you're aiming at.

i don't necessarily think you are after a "faster" burn, What you want is a controlled burn.

with flame propogation happening in a controlled and predictable manner.

Interesting post. The higher the velocity the better IMO. think of it this way, it does not seem to bother forced induction. Just got to find the right combination.

Check this out. http://en.wikipedia.org/wiki/Cylinder_head_porting

What you want is a more complete burn in any case. A faster burn will put out more torque though.