I like the discussion about detonation and testing an engines detonation limits. I do most of my testing at the drag strip, with my combination detonation shows up first at the launch. It's easy to be unaware of it because of the noise and as piston speed goes up the problem can quickly go away. If it's severe enough it comes back when I put it in high gear, piston speed goes down, VE is very high and the engine is heavily loaded.

One of the problems I have with testing detonation limits is when I find something that works and the detonation goes away I then must find a way too raise the compression while maintaining the same basic configuration before resuming testing.

Another confusing issue is when combustion is improved ignition advance requirements are less. Both the modification and the new timing settings reduce detonation, and then you have to tear it down, raise compression with out changing critical specifications and start over.

Anyway people locally want grooves in their cylinder heads, here's some of the projects I'm working on

[QUOTE=automotive breath]I like the discussion about detonation and testing an engines detonation limits. I do most of my testing at the drag strip, with my combination detonation shows up first at the launch. It's easy to be unaware of it because of the noise and as piston speed goes up the problem can quickly go away. If it's severe enough it comes back when I put it in high gear, piston speed goes down, VE is very high and the engine is heavily loaded.

One of the problems I have with testing detonation limits is when I find something that works and the detonation goes away I then must find a way too raise the compression while maintaining the same basic configuration before resuming testing.

Another confusing issue is when combustion is improved ignition advance requirements are less. Both the modification and the new timing settings reduce detonation, and then you have to tear it down, raise compression with out changing critical specifications and start over.
QUOTE]

Interesting. Not everyone has access to a dyno but any one of us can put some mufflers on the exhaust and either run it down the drag strip or up a steep hill with a rubber hose and Styrofoam cup on the end of it placed close to the engine to listen for detonation.
Your right about the ignition advance, the better the combustion becomes the less advance you need up to a certain point, I was reading something like 15 degrees is around the minimum.
Another interesting thing about efficient combustion and Nox levels is the Oldsmobile engine. I read that the reason it was the last American V8 to remain carburetor was because of of its efficient and flat combustion chamber. However if you ever saw an Olds combustion chamber it is huge. Of course there are reasons why the chamber worked.
One more thing, I don't think those grooves are adding that much more surface area to the chamber to add to the causes of detonation.

Looking at the first picture in post 106.I can see where the grooves come toward the valves.There are four points.I would think these points would get hot and stay hot.Right across is the spark plug.I wonder if the reason you are seeing a decrease in your detonation is because the four points are staying hot and igniting the mixture more evenly along with the spark plug.In other words instead of detonation knocking the piston sideways the four points are remaining hot and almost igniting it from both sides.Or do you guys feel they would not remain hot enough?

That would not make sense. With those areas getting hot they would promote preignition.

I think we need to define detonation and preignition.

Detonation: When a ember or heat generated from compressed gasses begins to burn the A/F instead of the plug initiating the flame. Sometimes detonation can happen when gasses on the other side of the chamber begin to burn the A/F and then the plug fires, creating another flame from that collides. This is very uncontrolled.

Preigntion, Anytime the A/f is burned before the plug initiates the sequence. Controlled but at the wrong time.


Turbulence helps by creating a "draft" that helps cool the hot spots.

Turbulence will not help Preigniton.


The only way to reliably test detonation is with EGT's and knock sensors. Drag strips are to varied in atmosphere and track conditions. Fuel, timing devices, wind speeds, all have an effect. You aren't controlling your control. Negating any reasonable testing. Since your are finding positive results with your grooving, I'd be looking at other things that might cause a similar result. Don't wear blinders...

That definition sounds a little crossed up. First detonation is spontaneous. Detonation always happens after the the spark plug initiates normal combustion. You are correct with the heat or ember (I will assume by ember you mean perhaps a hot exhaust valve, hot spot in the combustion chamber within the head or piston top/crown. Now your example of "Sometimes detonation can happen when gasses on the other side of the chamber begin to burn the A/F and then the plug fires, creating another flame from that collides." belongs in your pre ignition definition. Thats not detonation. Also pressure can cause detonation. The main thing you want to remember is that detonation occurs "after" the spark plug propagates normal combustion.

I am not sure what you mean by turbulence creating a draft. As far as I know turbulence is caused by the intake port/system or by the rapid decrease in volume near a quench area.
As far as testing with a EGT or knock sensor that would be out of the budget of most people here since you would need a data acquisition system therefore a drag strip is the closest controlled testing ground most average blue collar workers have to test at.
If the guy has everything else the same except the grooves, what or where else should he look to that is causing his results?
I kind of think the guy took his blinders off and tried something in left or right field and it is working for him.

I doubt this'll clear up the issue considering the fact that both of those definitions sound exactly the same.

Perhaps that was a little dumbed down. I meant only to clarify the terms.

I might agree that timed runs are a distant second to dyno runs but if if the changes are small and minute, than with any kind of variable, the results are affected. My small list of variables are already posted.

Judgement results, and that all we have with timed runs, because of the variable involved, are often skewed because a person opinion greatly influences what they feel. Circumstantial evidence at best.

johnsongrass1,

As pointed out by others, your understanding of pre-ignition and detonation are very weak and full of inaccuracies. In addition you have no understanding of the testing I perform, how well I control variables and what benefit the testing provides.

IMO you are not in a position to make statements like “don't wear blinders”.

Can you tell me the post number so I can read over those variables?

It is very simple and very easy to dumb down. This isn't rocket science.

Detonation, a collision of flame fronts in the combustion chamber.

Pre ignition, ignition occurs prior to spark.

Here's a quote from another forum, this member has a very clear understanding of combustion, detonation, pre-ignition and the importance of turbulence during the combustion process.

Earlier I mentioned one of the cars that is running grooved cylinder heads.

It's important for people to understand I am not claming the grooves are the only reason this car runs well. The modification is one of many things that were done to this car and engine to improve performance.

It's a late 80's Camaro with a 355 SBC and a T350. Last time out the weather was good and the car was working great, here's the times it ran.

60 ft. 1.299
330ft 3.997
1/8 6.258
Mph 108.63
1000 ft 8.221
1/4 9.895
Mph 134.22

My involvement was porting the dart heads and cutting the grooves, the remainder of the combination was the work of the owner. Here,s some pictures:





If you look in the background the blue dodge is running grooved 340X heads, and I'm porting and grooving a set of SBF edelbroock heads for the yellow truck, I'll post pictures later.