Which one of these combustion chambers you like the best?

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Re: Which one of these combustion chambers you like the best

Post by williamsmotowerx »

#3 if you take out the shaping between intake an exhaust.
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Re: Which one of these combustion chambers you like the best

Post by af2 »

ptuomov wrote:The head #2 flows a lot more than head #1. In all fairness, #2 has bigger valves.

Here are the graphs. They are not in comparable units (different day, different pressure, different bench). However, both of them have the stock head flown, and those should be pretty close for the 3R and 4R castings. So the percentage improvements over stock should be comparable.


Head #1:
HeadNo1.JPG
Head #2:
HeadNo2.JPG
Does flow make more HP?

The head #3 looks good..
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Re: Which one of these combustion chambers you like the best

Post by CREngines »

Head 3 looks to me like the valves are canted making it more of a 4 valve hemi instead of a pent roof. The Honda 400EX atv engine uses that arrangement, and they are not really in the same league as the newer non canted 4 and 5 valve bike engines.
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

af2 wrote: Does flow make more HP?
Yes? Maybe? Probably?
af2 wrote: The head #3 looks good..
I think they all look gorgeous. Different but all gorgeous, like my three daughters! ;-)
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

CREngines wrote:Head 3 looks to me like the valves are canted making it more of a 4 valve hemi instead of a pent roof. The Honda 400EX atv engine uses that arrangement, and they are not really in the same league as the newer non canted 4 and 5 valve bike engines.
I believe the person who ported that bike head actually "decanted" the intake valves a bit to fit in bigger intake valves, or so the rumor goes. But I know nothing about the heads, really, I just copied out the coolest and most "race" looking head from the google image search as the thrid, control option for my poll.
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Re: Which one of these combustion chambers you like the best

Post by SWR »

Number 1, with the intake squish pad slightly slanted to remove the step.
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

SWR wrote:Number 1, with the intake squish pad slightly slanted to remove the step.
#2 flows gangbusters, and has more squish area. Why not like that for a normally aspirated or low boost high compression engine?

Also, here's a more general question:

Suppose that the 4-valve head squish area is in four small pads and the piston has a shallow spherical dish with rim for the squish and big valve reliefs. Suppose further that we have a little bit of taper in the head or pistons and some sensible clearance such that nothing gets trapped in there. Let's quote "boost" in volumetric efficiency units, so that say an engine that fills naturally at 108% VE seeing 5 psi boost is quoted to have 145% "boost."

What is the ideal squish area to bore area ratio as a function of boost (let's quote "boost" in volumetric efficiency units) for a pump gas engine?

Does it go down with boost about linearly? Or is there a cliff, below which you want a lot of squish area and above which you want very little?
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Re: Which one of these combustion chambers you like the best

Post by Erland Cox »

The side squish pads on number 2 restrict the flow a lot more than no 1.
Look how little space there is between the intake valves and the chamber.

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Re: Which one of these combustion chambers you like the best

Post by SchmidtMotorWorks »

#2 flows gangbusters, and has more squish area. Why not like that for a normally aspirated or low boost high compression engine?
That #2 is close to what the Honda Indy engine had but the valve angles were something like 11.5 & 13.5 degrees and the chamber was a bit smaller, to the point that the valve seat bores formed the corners of the chamber and it had a slight clover leaf shape from that (without the valve seat pockets the chamber would have been sort of square).
It looked horrible with the seat running out into the seat bore with no blending, an open pocket about 0.150" deep. They never did any CNC chamber cutting to blend it or any kind of hand work like die grinding, in fact I don't think there was a die grinder in the building. That was the Honda way.
Some of the american guys brought in a flow bench (Honda didn't have one) and made some changes to the chamber, but it didn't perform any better. The real marvel about the Honda engine wasn't the exotic features it had, rather it was how many things they didn't do and still made power.
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Re: Which one of these combustion chambers you like the best

Post by SWR »

ptuomov wrote:
SWR wrote:Number 1, with the intake squish pad slightly slanted to remove the step.
#2 flows gangbusters, and has more squish area. Why not like that for a normally aspirated or low boost high compression engine?

Also, here's a more general question:

Suppose that the 4-valve head squish area is in four small pads and the piston has a shallow spherical dish with rim for the squish and big valve reliefs. Suppose further that we have a little bit of taper in the head or pistons and some sensible clearance such that nothing gets trapped in there. Let's quote "boost" in volumetric efficiency units, so that say an engine that fills naturally at 108% VE seeing 5 psi boost is quoted to have 145% "boost."

What is the ideal squish area to bore area ratio as a function of boost (let's quote "boost" in volumetric efficiency units) for a pump gas engine?

Does it go down with boost about linearly? Or is there a cliff, below which you want a lot of squish area and above which you want very little?
I'd say it's not linear. Depends on chamber temps you'll see and the fuel you run, evaporative qualities does more than octane does. But in general, I dislike any large - wide - squish between the intake valves where it's "cold"..
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

SchmidtMotorWorks wrote:That #2 is close to what the Honda Indy engine had but the valve angles were something like 11.5 & 13.5 degrees and the chamber was a bit smaller, to the point that the valve seat bores formed the corners of the chamber and it had a slight clover leaf shape from that (without the valve seat pockets the chamber would have been sort of square). It looked horrible with the seat running out into the seat bore with no blending, an open pocket about 0.150" deep. They never did any CNC chamber cutting to blend it or any kind of hand work like die grinding, in fact I don't think there was a die grinder in the building. That was the Honda way. Some of the american guys brought in a flow bench (Honda didn't have one) and made some changes to the chamber, but it didn't perform any better. The real marvel about the Honda engine wasn't the exotic features it had, rather it was how many things they didn't do and still made power.
Funny that you mentioned that. I think the guy who welded and ported that head #2 was involved in the Honda-Ilmor IRL program in some capacity.

They did kick ass and take names with that engine, though. Wonder why it was so successful? Do you happen to have any photos of that engine's guts?
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

SWR wrote:But in general, I dislike any large - wide - squish between the intake valves where it's "cold"..
Why? What bad things happen if you "squish" the cold area between and behind the intake valves?

I have to confess something. I never understood exactly what that squish area really does inside the engine. This may not come as a total surprise to those who are reading my posts.

In think the squish doesn't have much impact before the spark. So the squish is probably moving burned, burning, and unburned mixture. Is it more beneficial to move burned mixture, unburned mixture, or currently burning mixture?
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Re: Which one of these combustion chambers you like the best

Post by ptuomov »

SchmidtMotorWorks wrote:Based on valve size and location I would choose to begin with #2
The combustion chamber shape was informed by what was learned during a project relating to one Honda IRL engine.
I was thinking that. If you have small ex seat throats with huge radius you will have it very similar.
Jon -- Sorry missed your post there earlier. Tell me more what the exhaust port looked like on that Honda IRL engine?
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Re: Which one of these combustion chambers you like the best

Post by hoffman900 »

Is that the head off the 190E, or a later Mercedes DTM car?
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