Monday, August 8, 2011

Another Dual Carb Manifold

It's not every day that somebody walks into my shop with a really cool piece of vintage speed equipment ....but it did happen recently. My friend Teach came in to finish assembling a set of Knuck heads that I had reworked for him, and with him he had a Seeley manifold that had recently found its way to him. To be perfectly honest I had never heard of a Seeley manifold, and at first glance I thought it was the same as a manifold that I had built 15 or 20 years ago. At the time, I assumed that I was the first one to come up with the idea. Of course the truth is, there is no new thing under the sun (a very wise man said that a very long time ago).

Judging by this vintage ad someone beat me to the punch by about a half a century!

Closer examination of the Seeley manifold, however revealed that it was indeed different than what I had built. You see, the Seeley has the clever addition of a diagonal plate which separates the manifold into two equal individual runners, whereas mine was simply open so that both carbs fed each cylinder.

It's little difficult to photograph the actual divider (as shown above), however in the photo below, a straight edge placed on the outside of the manifold shows the orientation of the internal wall that separates the two intake tracts.

So, how well does the Seeley manifold work? Well, the proof will be in the pudding, so to speak. The vintage advertisement claims a 20% increase in horsepower. Is that accurate or is it hype?

It is obvious examining the manifold that the cross section is visibly smaller at the divider wall. Not that there is anything that Mr. Seeley could have done about this; there's only so much room between the heads. So, while Teach was installing the rocker boxes on his heads, I took the opportunity to put the Seeley manifold on the flow bench. The bench confirmed that there was a restriction in the Seeley manifold. How much of a restriction? Well, comparing it directly to a stock Linkert manifold, (each checked with a velocity stack directly attached to the manifold - no carb) the Seeley is 22 cfm down. That's not the whole story though. Flow testing both manifolds with an M35 carb attached showed it was only down by 5 cfm (because the carb was more of a restriction than the manifold).

Now, 5 cfm at a 28 inch test pressure is not a huge amount. It could very well be that a better "tuned length" effect of the individual runners on the Seeley manifold could indeed lead to more power despite the slight loss of cfm. Or not. We'll just have to wait for a report back from Teach as to real world performance!

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