Volume II, Issue 12, Page 2

Accidental Discoveries...

here are times we find something quite by accident.  In the world of R&D, that’s occasionally what happens, and the benefits can be immediate and far-reaching.  Such was the case when I was brow-deep in attempting to resolve a testy intake manifold design problem a number of years ago.  It went like this.

I’d been pouring over a raft of flow bench numbers and dyno sheets, trying to make some sense out of why a particular prototype manifold had caused a notable shift in the engine’s torque peak.  Specifically, at peak torque, port flow is never at an “optimum” (maximum) value, although my sense was the problem might be flow velocity related.  Simply stated, peak torque had shifted upward by about 500 rpm, compared to baseline data.  We’d made no other changes in the engine’s configuration.

Back on the air bench, it appeared that at a flow rate consistent with engine speed (at peak torque rpm), whatever flow rate had occurred at this point during baseline testing didn’t happen until the higher rpm was attained on the dyno.  So, on the premise that it was velocity related, manifold runner crossection area was in play.  In fact, I reckoned, if this was the case then maybe (at peak torque), a certain section area was required.  Further, on the chance this hunch was on target, I thought maybe the notion could be turned around and used as tool to influence where we wanted a torque boost to occur.
Keep in mind, this was during a time when such development technology as real-time, in-cylinder pressure measurement (Engine Cycle Analysis) was not even on the horizon, and the analytical means we had at our disposal were of the “chisel and hammer” variety.  Frankly, you had to devote more time understanding why certain problems were created than can today be resolved from more contemporary methods that do a lot of the investigative work for you.  We called it working smarter.

Concurrent to this exercise, I’d been working with a friend of mine, highly skilled (even at the time) in computer programming.  He was also a gear-head, which helped.  I began feeding him some of the data streams with the intent he might conjure up a math model that would begin to define what was going on in the manifold, with respect to mean flow velocities and the engine’s volumetric efficiency (torque) characteristics.  Ideally, I wanted to see if we could come up with a process that provided some predictability about how an intake manifold could materially affect torque characteristics (curves).

Then the curtain parted.  In a “what if” session with my friend, we talked about the possibility that in virtually any engine (operating at peak torque) the value for mean flow velocity in the intake track might always be the same.  I mean, why not?  If you compare an engine’s volumetric efficiency (“pumping” efficiency) curve with its torque curve, they’re vastly similar.  In fact, up to the point of peak volumetric efficiency (typically peak torque), there’s not sufficient crankshaft speed to adequately fill the cylinders.  And,

beyond this point, there’s not enough time to sustain the highest level of v.e.  It made sense but we had no evidence.  Then came the “accidental discovery.”
I decided to place a high-resolution pressure transducer in one of the prototype intake manifold’s runners and connect its output to a garden-variety oscilloscope.  The purpose was an attempt to quantify the amount of reversion pressure that could be upsetting calibration of the carburetor.  This step had nothing to do with the mean flow velocity issue previously discussed.  A couple of dyno pulls were made, the pressure/time traces photographed and we began dissecting the reversion pressure information.  I’d also done the same thing in the stock manifold being compared.

The imprint of an open palm on my forehead probably didn’t disappear for several days.  When I matched the pressure/time traces from the stock and prototype manifold, the slope of the traces (rate of change in pressure or flow) and the same shape occurred at peak torque rpm…for both engines.  This meant that the mean flow velocity in the intake track, at peak torque, was the same (although at different rpm) for both manifolds.  More importantly, it revealed that we could select an engine speed at which a volumetric efficiency (torque) boost was desired, and size the flow passage (crossection area) to produce the “correct” flow velocity at that speed! 

I couldn’t build the next prototype manifold quickly enough.  Runner crossection area was chosen to produce peak torque flow velocity at a specific rpm, a set of headers that would peak at a much higher rpm were installed (taking them effectively out of the rpm range we were using) and the manifold tested.  And there it was; a torque boost at the predicted rpm.  What followed was an entire “family” of intake manifolds, targeting lower engine speeds for towing and fuel economy.  The new “tool” quickly became useful in designing high performance and race-bred manifolds.  And on the exhaust side of the engine, we began crafting “collected” header sets to produce companion torque boosts at other points in engine speed ranges.

Cascading down from this point, we discovered the benefits of sizing runners (within a given intake manifold or header set) to produce multiple torque boosts at desired points.  In two-speed, drag race applications we’d place a boost at the rpm at which an engine would drop on the 1-2 gear change.  Down came the elapsed times.  We almost reduced one cam grinder to a “mumbles” stage because of the cams we wanted that had different intake and exhaust lobes (tied to differently-sized intake and exhaust header passages) on equally different lobe centers.  We found that we could “tune” every other cylinder in an engine’s firing order, thus broadening and flattening its net volumetric efficiency (torque) curve.  Without realizing the evolution, we’d bridged into “individual cylinder tuning” and its benefits. 

We passed the notion along to a couple of NASCAR engine builders and they even went so far (with the “two V-4” concept) that they juggled rod/stroke ratios in accordance with the multiple-sized intake/exhaust passages.  It was nuts…but it truly worked…and all because of an “accidental discovery” when studying some simple little wiggly lines on an oscilloscope being used for another purpose.  Actually, we weren’t that smart.  Just dumb lucky. 

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