Comnbustion Chamber Design


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Greetings Inliners, just received my Performance Handbook. A wealth of info that is helping me make those final decisions so I can start getting some rebuild parts.

The changes I will be making to the intake will be to use an existing intake manifold design from another inline six. The point is that the stock intake log will no longer be used so I am free to choose from any of the heads from the 65’ 170ci and up.

So here is the question. Is there an advantage to the Kidney Bean combustion chamber on the 65’ and later 170 head?

Thanks in advance, Ric.
Hi Ric,

I'm glad you've liked the Handbook so far.

We (Dave and I) have not had a chance to do a flow test of the later 170 head against the 200/250 head. I've got a 70 Maverick 170 head lined up to play with this summer (in N.Dak that means three days in July and then it is winter again) I hope to find out if it IS a kidney bean, the cc's, the manifold volume, and if it flows better or worse than a wedgie.

But none of that helps you right now. So some history of OLD car magazine articles. Way back in a 1962 HotRod they reported that a 170 head flowed 30% better than a 144 head. (It figures, bigger intake and exhaust valves).

Later, in the late 60's (maybe '68) Ak Miller wrote that the 170 kidney bean head made more power (I don't recollect that he said if flowed better - what I remember is more power. If any can correct me, I'll appreciate it) than the 200 wedge head and recommended it for a hp boost. The hp may come from the shape, or from a smaller cc chamber - we just don't know for certain.

BUT, (don't you hate butts) the '75 head hadn't been cast yet. Even if you chop off the log, you'll still have to add the 1.75 intakes to your '65 head.

So.... I've given you absolutely no answers here - just more to think about.

Good Luck
8) the kidney bean shape tends to encourage the air to swirl as it enters the cylinder creating a sort of tornado effect that other combustion chamber designs do not. this encourages a bit more cylinder filling and more complete combustion thus creating more power. the effect is marginal but measureable enough to not be a dyno error.
Howdy Ric:

I thought I'd add my two cents.

The kidney been chambers offer two distinct advantages; 1, a higher quench to bore ratio and 2, a smaller volume at about 52 ccs.

The down side is less room to effectively add larger valves, and severe shrouding of the stock size valves.

The flow bench will tell on the amount of flow. As for swirl, it is an unknown as there is no easy way to assess that factor. Improved quench requires quench area and a tight deminsion, say .020" to .030". Any less and you're at risk of the piston and head coming into contact. Any more and quench, or squeezing mixture out of the tight places, into the chamber doesn't happen with any significance.

For what it's worth.

Adios, David
The swirling and mixing is basically what I remember about the advantage of this shape. I only have about two weeks to find where I had read about this and make a decision. If anyone can find or remember where this info is please add a post. I will be digging through all my old Hot Rod’s.

This idea is to completely remove the log and add a mating surface. The mating surface can be designed any number of ways to accommodate any off the shelf manifold.

We shall see, Ric.
Hi everyone.

Ric I've just asked this question in the "Another manifold to fit crossflow" message in this same forum.

How difficult will be to cut off the stock manifold and then prepare the head to accept the other "better flow" manifolds.

I think I saw something about swirling way back when I was checking some "gizmos" for fuel economy. One of them had to do with the swirling of air at the intake thus helping combustion and power. Of course that's what the product ad said to do. The name of the product was ....something "Tornado".

Now is it nessesary to think about all these modifications (eg head, manifolds, ignition, bla, bla, bla) can be easily done using some of these "gizmos" like the "Tornado" or the "magnet?" fuel economy device? (These two devices claim that they save fuel by acctually burning fuel more efficiently which in turn produce more power or same power with less fuel.)

Well I don't think so.