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Which one of these combustion chambers you like the best?

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Which one of these combustion chambers you like the best?

Postby ptuomov » Sun Jun 02, 2013 8:35 pm

Three combustion chambers, all 4v designs.

(1) Squish pads behind the exhausts and behind intakes, but not on the sides
(2) Squish pads in all four sides
(3) Clover leaf, squish pads protruding into chamber from all four sides.

Assume pump gas motor with at most a little boost (less than 10 psi) and that you can design the piston to be ideal for the head.

4r-heads.jpg

3r-heads.JPG

cloverleaf-head-026.jpg
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Re: Which one of these combustion chambers you like the best

Postby axegrinder » Sun Jun 02, 2013 8:45 pm

I have no 4 valve experience but I like #3.
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Re: Which one of these combustion chambers you like the best

Postby swatson454 » Sun Jun 02, 2013 8:48 pm

I don't either but #3 sure is purdy :D
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Re: Which one of these combustion chambers you like the best

Postby axegrinder » Sun Jun 02, 2013 8:53 pm

If nothing else, #3 looks like it would take good care of the intake charge as compared to the others.
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Re: Which one of these combustion chambers you like the best

Postby mike22l » Sun Jun 02, 2013 9:32 pm

Less valve shrouding on 3.....
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Re: Which one of these combustion chambers you like the best

Postby MadBill » Sun Jun 02, 2013 9:53 pm

Also #3; good for pressure recovery/flow as well as squish.
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Re: Which one of these combustion chambers you like the best

Postby ptuomov » Sun Jun 02, 2013 10:06 pm

"hot or not"

I have the heads #1 in an engine that will go in probably some time in July. The combustion chamber is very close to stock 928 chamber, so no surprises expected. The only combustion chamber difference is that there will be a bigger dish on the piston to lower the compression ratio.

I just bought the heads #2. Those have some welding effort in the combustion chamber, and the biggest valves that one should fit in (without putting in oversized valve guides and offset boring the intake guides to move valves further from each other and offset boring the exhaust guides to change the exhaust valve angles to get them further away from the intake valves). The combustion chamber shape was informed by what was learned during a project relating to one Honda IRL engine.

Heads #3 are a random picture from the internet, it's some motorcycle head, probably some 750 cc single cylinder. It appears to have slight radial valve angles as well.

If cylinder heads are ranked based on voting, someone else got the winner! ;-)
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Re: Which one of these combustion chambers you like the best

Postby pdq67 » Mon Jun 03, 2013 2:07 am

2-valve here!!!

The Jag "May head" and the early MOPAR "318 Poli-Head" but modern "ball stud" designed.

4-valved, I wish GM would have let Buick finish their "nail-head" into the 4-valve head that it as supposed to be.. Damned car frames weren't wide enough for it back then is all.

And btw, I'm of the opinion that if you blow whatever head hard enough, that it doesn't matter.... Up it to whatever psi and watch the power build... He, he!!

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

Postby Erland Cox » Mon Jun 03, 2013 2:16 pm

Number 3 kills tumble when the piston nears TDC and needs a lot more ignition lead.
Number 1 is best of those 3.

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

Postby SchmidtMotorWorks » Mon Jun 03, 2013 2:24 pm

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.
Last edited by SchmidtMotorWorks on Mon Jun 03, 2013 2:27 pm, edited 1 time in total.
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Re: Which one of these combustion chambers you like the best

Postby MadBill » Mon Jun 03, 2013 2:26 pm

Erland Cox wrote:Number 3 kills tumble when the piston nears TDC and needs a lot more ignition lead.
Number 1 is best of those 3.

Erland



Really? So those four triangular squish areas count for nothing? :-k

When you say "kills tumble", where does the tumble energy go?
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Re: Which one of these combustion chambers you like the best

Postby Erland Cox » Mon Jun 03, 2013 2:42 pm

When the piston nears TDC the tumble breaks up in several mini tumbles.
All ridges in the combustion chamber supress the chamber motion.
The extra area only makes the surface to volume area worse.
An example from the motorbike racing world.
A 1000cc superbike with its longer stroke versus bore can have a 15:1 compression ratio
but a shorter stroke supersport 600 can only have 13:1 without loosing power.
A good 4 valve combustion chamber must be unobstructed to have good combustion.

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

Postby MadBill » Mon Jun 03, 2013 2:48 pm

That would be a good process for Jon to model in CFD for us!
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Re: Which one of these combustion chambers you like the best

Postby Erland Cox » Mon Jun 03, 2013 3:06 pm

I have helped a guy with a Husaberg with several billet heads.
He has a big problem with too high compression so the next head I will make totally without any ridges.
The CNC head looks something like head no.3 but I smoth the ridges out a lot.
The side squish pad lowers intake flow in most cases, round against the cylinder on the sides flows best.

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

Postby ptuomov » Mon Jun 03, 2013 3:17 pm

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
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