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Old 09-18-2021, 12:53 AM   #1
Brian
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Default combustion chamber design

Combustion chamber design is possibly one of the most debated subjects when it comes to flathead performance...and I think it plays a very important role. The major issue is flow versus compression; to increase flow rates we need to open up the passage between valves and cylinder; in doing so we automatically lower compression. Also there is the heat conductivity factor of head material; aluminium, by virtue of it's higher heat dissipation, allows higher compressions with out spark knock, but the heat dissipation takes out some of the effect of the same cr in iron heads.
I've built numerous flatties, in varying styles during my lifetime. One advantage of building flatheads for customers is one can incorporate different ideas at customers cost, knowing, whatever one builds will run, but how well?
So. after untold expense [not all mine], I have sort of an idea as to what works in combustion chamber design. My favourite engine to build, for the performance gained is still the little 221....
I fully understand people, such as Ronnieroadster, wishing to keep their hard earned secrets to themselves, and I respect that immensely. Others, such as Ol Ron, freely give of the discoveries they've made over the years I admire what individuals such as himself, [and others] have achieved, but I'd like to start a discussion about cylinder head design.
What, in your opinion, is the ultimate flathead combustion chamber design?
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Old 09-18-2021, 12:58 AM   #2
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Default Re: combustion chamber design

We could get into pop up pistons, relocated spark plugs, who knows?
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Old 09-18-2021, 01:07 AM   #3
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Default Re: combustion chamber design

Or even Harley WR head design...
I agree with Ol Ron, that the majority of aftermarket heads available, whilst looking pretty, with their fins etc, the combustion chamber just resembles stock Ford heads, so there is obviously no performance to be gained from running such eye candy
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Old 09-18-2021, 01:14 AM   #4
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Default Re: combustion chamber design

Like, for example, this recent thread;
https://www.fordbarn.com/forum/showthread.php?t=303408
illustrates two totally different Stock ford Combustion chambers; whilst they both apparently have approximately the same cr, which design flows the best?
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Old 09-18-2021, 02:36 AM   #5
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Default Re: combustion chamber design

Brian the heads that went the best on our dragster were cast iron truck heads but we have a 4-71 to help with the flow
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Old 09-18-2021, 03:58 AM   #6
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Default Re: combustion chamber design

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Thing is, around 60cc chambers allow a pretty good cr. However, if the combustion chamber design follows the head gasket profile, 60cc chambers turn out pretty shallow, with the corresponding reduction in breathing. So, if the combustion chamber shape is altered to become narrower between the inlet valve to cylinder, [which is where we want to enhance breathing], it could be deepened, giving the same 60 cc volume. The exhaust side of combustion chamber, because it's not relying on atmospheric pressure for flow, rather, the positive displacement that occurs from the rising piston, does not need the same flow enhancements.
if you look at the photos in the first post in this link;
https://www.fordbarn.com/forum/showthread.php?t=303408 you might see sort of what I'm on about. One combustion chamber follows the head gasket profile, the other is longer and narrower, and favours the inlet charge. Both are approximately the same volume, but I'll bet flow is different in each head. So, from a performance point, which head is of the better design?
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Old 09-18-2021, 04:00 AM   #7
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Default Re: combustion chamber design

Lawrie, And there I was thinking your Hogan heads were the go!!
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Old 09-18-2021, 09:48 AM   #8
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Default Re: combustion chamber design

I think the tapered wedge chamber is the only design that could increase breathing performance of a normally asperated engine. Weiand made a set of cast iron heads with Wedge pistons I saw at bville back in 03. I tried to have Egge make a set of pistons for me back in the 80;s with extra head thickness for the same use. Unfortunately I couldn't afford them and I found out the heads weren't thick enough to clear them. The chamber I make now improves low and mid range power and economy and saves $$$$$$$
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Old 09-18-2021, 10:29 AM   #9
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Default Re: combustion chamber design

There is one exception in aftermarket heads. Edmunds (at least the three sets of 8BA's I have) have the sparkplug relocated just enough so that it clears the exhaust valve and allows the use of extended tip plugs. I have had a set of them milled and machined down to have .050" clearance over the piston on the '51 Merc in my club coupe for the last 5 years and am very happy with them. The car has required no maintenance and runs fine. I am very satisfied with the performance (it also has a 2G and a Mallory dual point). One of these days, I may get around to installing a set of seat belts so I can take it to "Run what ya' Brung" at BIR to get an actual time.

I believe "Ol' Ron" has touched on the relocated spark plug in the other thread currently running.
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Old 09-18-2021, 12:19 PM   #10
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Default Re: combustion chamber design

As a competition engine, against other L heads, I like the 21 stud better than the large cube 24 stud applications and I like FT pistons, over domed.

With FT pistons, you can, potentially get a higher CR and totally evacuate at least 1/2 of the cylinder area, using .035-.040 piston to head clearance. With domed pistons, matching the piston dome to the combustion chamber shape, is much harder.

A asymmetric chamber shape, over the valves, sounds like it could be a great benefit but, would take a lot of development. I don't think any modern speed manufacture would invest in that, because of the low market potential.

Don't forget about the block side of the combustion chamber. Air doesn't flow very well over sharp edges and I think, rather than relieve a block, that you would be much better off, producing a radius of 3/16 - 1/4" around that side of the cylinder.

Another idea that comes to mind, is having a radius or tunnel, above each valve, with the area between them, down as close to the block as possible, say .010, trying to isolate the valves and smooth the flow, into and out of, the cylinder, as much as possible.

You don't get much cross section area (CSA) or curtain area, with a L-head so, that "tunnel" doesn't have to be to big.
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Old 09-18-2021, 04:41 PM   #11
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Default Re: combustion chamber design

Brian , I got Garth to cast me up some heads, but solid with no chambers or water jackets,I machined the chambers myself.
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Old 09-18-2021, 08:39 PM   #12
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Default Re: combustion chamber design

Brian I have found each time I opened up the combustion chamber to assist in unshrouding the valves performance improved. How one goes about doing this will vary depending on how brave one gets. Now when it comes to the flathead the word economy has no place. My time spent with the many flatheads I have been involved with the one thing that's pretty consistent the more hydro carbons feed the better the engines would run.
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Old 09-20-2021, 06:36 AM   #13
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Default Re: combustion chamber design

Brian there is a whole book written by Vizard on modification of cylinder heads for performance. One of my friends has it and used it to modify his Austin 7 Head -With the power that engine develops any increase is gladly received.!! There are firms who coat the inside of inlet manifolds and exhausts with slippery coatings that are supposed to improve flow - but it might be all pyschological -Karl
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