Grooved Cylinder Head Analsys

[crazyman]

Another aspect as to why it might work, just one, is the fact that the in cylinder swirl tumbles over the ridges and mixes better.

[trmnatr]

Well if the theory is correct, I will say it again, this is nothing more than a fireslot

How about doing a .500" tall dome on say a GM head, run it 50 dyno runs, pull it down, have fire slots machined in and run it then put the grooves in and see what you gain then install a second set of same pistons without fire slots and see if the grooved head / domed piston is the same power as the fire slot piston / std head

I suspect it will be the same

[SWB]

Just changing the angle of the edge of the squish pad on the piston, or in the head, can change the knock threshold by 15% or more. The reason is not just changing the angle of the squish gas flow OUT of the area, but significantly increasing the turbulence of the gas flowing BACK into the area. Reverse Squish Flow plays a key role in how likely a region is to detonate, because the squish pads are often the area of the combustion chamber from which detonation originates.

Getting as much flow in there (perhaps by the direction the gas initially flows OUT?) as possible as the combustion progresses has a huge effect on whether or not there will be a detonation event in the "end zone".

As far as I'm concerned, this all makes perfect sense ... but it's all before/after results, which are always hard to prove ... and I'd like to see more real fluid simulations about the change in reverse squish flow, and perhaps some more-scientific analysis with very in-depth analyses. Until that happens, I think this will remain a subject where we just have to make an educated guess on why it works, and possibly still a leap of faith on THAT it works.

Just my two cents though.

-Adrian

So Adrian, do you feel that a flame front that rapidly enters the squish zone on the power stroke will help eliminate detonation? I've seen in-cylinder photographs from GM research and they showed detonation happening some time around 20*ATDC and yes, it happened in the squish zone.

My original thought was the groove was allowing liquid fuel to be re atomized into the squish area. In the first photo, there is some obvious fuel wash running around the cylinder bore and the groove might be making use of that liquid fuel somehow. I saw some piston tops Jim Mcfarland had developed in CT magazine some years back that had dimples and such on them. I can't find that now, but I remember the idea was similar.

Now I'm wondering if the groove isn't just pulling combustion into the squish area faster ATDC however?

[FastFourierTransportation]

Just changing the angle of the edge of the squish pad on the piston, or in the head, can change the knock threshold by 15% or more. The reason is not just changing the angle of the squish gas flow OUT of the area, but significantly increasing the turbulence of the gas flowing BACK into the area. Reverse Squish Flow plays a key role in how likely a region is to detonate, because the squish pads are often the area of the combustion chamber from which detonation originates.

Getting as much flow in there (perhaps by the direction the gas initially flows OUT?) as possible as the combustion progresses has a huge effect on whether or not there will be a detonation event in the "end zone".

As far as I'm concerned, this all makes perfect sense ... but it's all before/after results, which are always hard to prove ... and I'd like to see more real fluid simulations about the change in reverse squish flow, and perhaps some more-scientific analysis with very in-depth analyses. Until that happens, I think this will remain a subject where we just have to make an educated guess on why it works, and possibly still a leap of faith on THAT it works.

Just my two cents though.

-Adrian

So Adrian, do you feel that a flame front that rapidly enters the squish zone on the power stroke will help eliminate detonation? I've seen in-cylinder photographs from GM research and they showed detonation happening some time around 20*ATDC and yes, it happened in the squish zone.

My original thought was the groove was allowing liquid fuel to be re atomized into the squish area. In the first photo, there is some obvious fuel wash running around the cylinder bore and the groove might be making use of that liquid fuel somehow. I saw some piston tops Jim Mcfarland had developed in CT magazine some years back that had dimples and such on them. I can't find that now, but I remember the idea was similar.

Now I'm wondering if the groove isn't just pulling combustion into the squish area faster ATDC however?

There's a lot of research showing that faster, and more turbulent, reverse squish flow helps abate detonation. Whether that is the primary function of these grooves, or not, is subject to debate ... but it's certainly possible.

-Adrian

[williamsmotowerx]

When you say reverse squish, do you mean more clearance at cylinder bore walls... and tighter towards bore center?

[Warp Speed]

What if the combustion chamber / dome is properly designed per the combo? It wouldnt be needed???????????

X2

I would think that proper design and blending would negate the need!?!

[falcongeorge]

Well if the theory is correct, I will say it again, this is nothing more than a fireslot

How about doing a .500" tall dome on say a GM head, run it 50 dyno runs, pull it down, have fire slots machined in and run it then put the grooves in and see what you gain then install a second set of same pistons without fire slots and see if the grooved head / domed piston is the same power as the fire slot piston / std head

I suspect it will be the same

I agree, sorta. But the idea behind the original fire-slot concept was to help the flame front get around to the backside of a large dome with a low plug position, not necessarily direct it into the quench. Of course, when you would run a piston with a fire-slot, the burn would go deeper into the quench than it did without, but it usually wouldn't go all the way back. Not in a typical big-dome sbc application anyway. When I was young, I worked for a guy who did alot of sbc MP motors, and even with the angle-plug heads, he spent a TON of time & effort trying to get a burn like what you see in these photos. I DO agree with what you said about a really good chamber/piston top making these slots un-necessary...I think...

But, yea, this is an upside-down fire-slot.

[ZoRG]

Right, no need to get offensive, just putting things into perspective. Maybe here is a better example:
I've been told to put on of those magnets on my cars fuel lines to improve the fuel consumption and make more power, the salesman couldn't put a number on that either and could not explain exactly why it happens, but he said it works, and other people said so too! - get the point?

If you want any sort of peer review then you need to be able to give more specific information than, "you can run higher compression for a given amount of octane", something more along the lines of "On this X-type of chamber we are able to run 2 compression points higher without detonating and here is a link to the dyno run with and without the grooves and one with the grooves and higher compression ratio". Be a little scientific about it, I drew them into my profiles so when I rebuild some chambers again I "might" give it a try, BUT, I definitely will give it a try if someone can actually put numbers down, and then add my own numbers and so on and so forth grows everyone database of information and understanding... I suspect once you get into a system where people are willing to share more complete information the groove development will properly take off, if it works.

Glad to see you are taking my advice, Zorg. That having been said, you have given me a few suggestions, I will respond with a few of my own.
1) Read what was posted. Clearly, you havent read my post, as you are asking me for "numbers" on what effect cutting the grooves had on octane tolerance. If you had bothered to read what I had posted, you would have noted that I have no experience with cutting the grooves. My experience relates to the more conventional methods of progressively re-shaping the chamber/dome.
2) Frame your question in a way that shows you have put some thought into it. You want a number? 5 points. The way your question was worded, you didn't ask any specifics. My posting was the pertaining to the effect chamber/dome shape had on octane tolerance, NOT on the grooves. 5 points? Based on the difference between an f-head with a large dome, and a modern heart-shaped chamber with tight quench & a flat top. Next time, be a little more specific, and maybe people will take your question a little more seriously.
3) Get over the idea that anyone owes you proof of anything. They don't. I am here to learn from my peers. Part of that process is bouncing things off each other, brainstorming, and READING (you might wanna work on that one, but I have already suggested that.) other peoples ideas. You seem to be about the only one on here that feels there is nothing to be gained by re-working the domes/chambers to get a good burn over the entire piston top(as that's what I was talking about, you might have noticed that if you had taken the time to read my post). Thats fine, thats your opinion, and you are welcome to it, and I have no interest in trying to change your mind or anyone elses.

You seem to feel that I would put a great deal of importance in changing your opinion over to align with mine. Nothing could be further from the truth. What you believe to be true or untrue is of absolutely no concern of mine, and is of no benefit to me whatsoever. A wise man once said "what others think of me is none of my business", and I try to keep that in mind.

As far as I'm concerned, I am done with this little exchange, I will gladly give you the last word. Cant say I will bother reading it, but...

I'm still not sure why you are getting excited, I was merely trying to point out why people would say it won't work and what it would take to stop the "yes it does, no it doesn't" arguing that's been going on since these were made public some years ago, I never took any sides as to will it work or will it not, and can't without testing. But before testing it would certainly be nice if there was a true understanding about how it works, what to do to see the benefits etc Then we can look at manipulating it more to perhaps have greater benefit.

Here is an example, for instance, how can we optimize the grooves, what is the difference between shallow wide or deep round grooves? How about drilling a hole through instead of a groove?

[Cudafever]

First off i have no experience with this stuff at all, so take that as you may.

the "hole" or tunnel theory i like! In the "piston going up" part as i feel there would be a lot more air speed there to mix things up!

But when the mixture fires, Now you have a torch affect that my damage a head or cylinder bore.

With the groove, in my minds eye you have a flame all across that groove lighting off extra fuel

with a hole, there is only flame at the end........................

[ZoRG]

I just tried to go all extremes with something in the middle to understand it better... maybe it helps someone else a bit to understand what is at work as well.

I probably won't try these, because of the type of engine, the goals, and the direction I've already taken, with the second motor I'll probably just develop the current system further, but even then, without grooves. But I would still like to really understand how they work!

Here is why I don't think they will work for us, it is a honda head, so on the primary cams the inlet valve lifts/durations are staggered, so there is extra motion there, the valves I use has a turbulence generator, the motor is a high rpm motor so the low end effects are not that important, and due to the vtec system idling and low down performance is good for a high rpm engine. The pistons also have some small cutouts that should help a bit already.

My current understanding is that these grooves only work at low rpm / part throttle.

[dwilliams]

looks like it could be of benefit on the 461's I want o use,

You might want to sonic check the quench area or make some calipers to reach in there and check before grooving. 461s are a bit thin there; I've seen detonation break chunks out of 461s that had been milled heavily.

Angled and/or relocated plugs used to be the hot setup for 461s, back in the day. I never saw any real detail on how it was done; I'm assuming a taper plug of some sort, and drilling a new hole.

[falcongeorge]

looks like it could be of benefit on the 461's I want o use,

You might want to sonic check the quench area or make some calipers to reach in there and check before grooving. 461s are a bit thin there; I've seen detonation break chunks out of 461s that had been milled heavily.

Angled and/or relocated plugs used to be the hot setup for 461s, back in the day. I never saw any real detail on how it was done; I'm assuming a taper plug of some sort, and drilling a new hole.

Yes, I have the same concerns. To be clear, are you saying you have seen these heads break in the quench pad across from the plug, or the pad under the plug? I have heard of them cracking under the plug, but not so much in the area across from the plug. IF I do use these heads, I will be angle milling them in the area of .100-.120, so they will be thinnest under the plug. I was considering putting a slot in the quench pad acroos form the plug, but I do have the same concerns about putting a stress raiser in that area of the head. IOf I where going to do this,I would grind a slot with a rounded bottom, rather than a v-shaped slot, that just seems to asking for trouble on a head that is prone to cracking anyway.

[automotive breath]

Interesting discussion. I'd like to thank WFOLarry for sharing his
experiences with the Harleys.

For those of you that don't know me, I bracket racer at No Problem Race
Way. I have grooved over 100 set of heads mostly for race cars (8-9-
10&11 second range) and an occasional street strip car. Like Larry its all
been good, I have never had any complaints.

I don't have any "proof" so to speak. The best I can offer I have run
grooved heads on my cars for five years now and I race with a dozen or
so people that have been running these for several years. The consensus
is the same, cleaner running engine, improved idle and throttle response.
Occasionally a detonation problem is eliminated. Some cars run about
the same ET after, some show as much as 2 tenths improvement with the
grooves alone. Most of them I port the heads at the same time as I cut
the grooves so there is no way to tell what is responsible for the gains.

One thing I have learned, if you cut the grooves too narrow (<~0.080"),
they will carbon up. I don't know what would happen if they are cut wider
than about 0.125", I have never done that.

Many of us run inefficient combustion chambers. The 23 degree SBC
wedge design is over 50 years old. Sure the manufacturers have done
what they can to improve them. There is only so much you can do with
the antique design. For example if you wanted to increase the squish
to bore ratio on a optimized SBC head what would you do? As a result
many of the chamber improvements are for increased flow (thats where
the big gains normally come from anyway; improvements in combustion
efficiency appear vague in comparison).

Some one said something about cracking. I cut three groves in these
chambers right up to the exhaust valve seats. I was concerned about cracks
and sure enough I'm starting to see some at the seat. Otherwise this
layout worked well, one of the best running engines I have been involved
with (notice I didn't say fastest)



ZoGR, I would take the center drawing and cut the groove deeper at the
chamber cavity.

[falcongeorge]

Interesting discussion. I'd like to thank WFOLarry for sharing his
experiences with the Harleys.

For those of you that don't know me, I bracket racer at No Problem Race
Way. I have grooved over 100 set of heads mostly for race cars (8-9-
10&11 second range) and an occasional street strip car. Like Larry its all
been good, I have never had any complaints.

I don't have any "proof" so to speak. The best I can offer I have run
grooved heads on my cars for five years now and I race with a dozen or
so people that have been running these for several years. The consensus
is the same, cleaner running engine, improved idle and throttle response.
Occasionally a detonation problem is eliminated. Some cars run about
the same ET after, some show as much as 2 tenths improvement with the
grooves alone. Most of them I port the heads at the same time as I cut
the grooves so there is no way to tell what is responsible for the gains.

One thing I have learned, if you cut the grooves too narrow (<~0.080"),
they will carbon up. I don't know what would happen if they are cut wider
than about 0.125", I have never done that.

Many of us run inefficient combustion chambers. The 23 degree SBC
wedge design is over 50 years old. Sure the manufacturers have done
what they can to improve them. There is only so much you can do with
the antique design. For example if you wanted to increase the squish
to bore ratio on a optimized SBC head what would you do? As a result
many of the chamber improvements are for increased flow (thats where
the big gains normally come from; improvements in combustion
efficiency appear vague in comparison).

Some one said something about cracking. I cut three groves in these
chambers right up to the intake valve seats. I was concerned about cracks
and sure enough I'm starting to see some at the seat. Otherwise this
layout worked well, one of the best running engines I have been involved
with (notice I didn't say fastest)

Myself and another fellow have expressed a concern with cracking, specifically as it applies to angle-milled #461's as they are fairly prone to cracking anyway. I had asked Larry (I believe) if he was running 14/1 in his HD with pump gas, and never recieved a response. Do you know if this was on pump gas? If so, WOW.

[wfolarry]

Falcongeorge it was on pump gas. 89 octane.
Almost all the bikes that I've grooved the heads on come in at 13.8-14:1. Usually with 26-28* timing. This is on mild builds.
I also do some high compression builds with dome pistons. These are either 20 or 30*. The grooves don't have as much of an effect on these. Very little actually.
I also have tried a 3* taper on the heads. One thing nice about the HD heads is you can chuck one up in a lathe & cut anything you want. The taper seemed to help the burn some but it didn't do anything for fuel or timing.
All in all the grooves are the easiest to do & work the best. I have seen better results with 87 or 89 octane than with 93. I have never really seen an increase in power but the motors definitely run cleaner. I always had to run premium gas before. Now I hardly ever do.