S14 Cylinder Head Flow Bench Results

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S14 Cylinder Head Flow Bench Results / Evo 3 Intake vs. Honda S2000 Intake

Evo 3 Intake vs. S2000 Intake Port Flow Results

This chart is interesting. The Honda S2000 cylinder head is very highly regarded among Japanese engine tuners. It is sometimes referred to as the "King of Heads" in those circles. It is easy to see why this is so when you look at the flow results.

Consider that the S2000 head has only 36.0 mm intake valves, compared to the 38.5 mm intake valves of the Evo 3 head. And yet the S2000 head greatly outflows the Evo 3 head at valve lifts beyond 0.325" (8.26 mm). But we should not overlook the fact that at lower lifts the Evo 3 cylinder head flows better (though by a smaller margin).
So one has to ask which is more important; high-lift flow or mid-lift flow? As the camshaft rotates through 360° the valve lift goes from zero, to max., and back to zero. Perhaps the intake valve spends more time in the "mid-lift" zone, so that flow at mid-lifts contributes more and therefore allows greater cylinder filling? This question is answered by the next chart:

Flow results compared to time-at-lift for Schrick 284° camshaft

Using carefully measured lift vs. cam rotation data for a Schrick 284° cam, it is possible to compare the "time at lift" vs. the flow capability at that lift. Jim Butterworth provides the cam lift data. With this data in hand it is possible to graphically divide this curve into *regions* of lift. Each region of lift is examined to see how long it lasts, in degrees of cam rotation (divide by RPM to get time in seconds). Click here to see how this was performed.

By doing this we can address the question of how long the intake valve "dwells" at a certain lift value. If we have great flow capability at high lifts, but spend very little time in this region, then the high flow numbers might not seem as important. The chart shows quite the opposite to be the case.

Starting out, the valve spends a comparatively long time in the very low lift regime. But this is the camshaft "ramp" which is used to gently accelerate the valve off the seat (and set it back down). So although the valve is in this lift area for a long time, the flow numbers are quite low and the effect is not too important (probably). We say "probably" because this ramp area ends up defining a good portion of the critical overlap period where the exhaust and intake flows communicate. A lot of what goes on during overlap is governed by pressure waves due to pulse tuning of the intake and exhaust tracts. Since pressure waves move at the speed of sound it is unclear if volumetric flow numbers are relevant during this time.

Moving on to the intermediate lift region, where the Evo 3 head outflows the S2000 head, we see that the valve dwell time is relatively low. So although the Evo 3 head flows well here, the valve rushes right past this region on its way to the peak of the cam lobe.

Which brings us to the high lift region (0.325" - 0.450" / 8.26 mm - 11.43 mm). This is where the S2000 cylinder head really shines in terms of intake flow capability. And if the S2000 head had a Schrick 284° intake camshaft, then this lift region is also where the intake valve would spend the bulk of its time (it sort of "hovers" here). The combination of good flow and long dwell in this region make the S2000 cylinder head quite impressive.

It's probably unwise to say for sure that an S14 head with S2000 intake ports would make more power than an S14 with an Evo 3 head, but based on the very high performance of the S2000 engine (240 HP from only 2 liters) it might an interesting thing to try. The dyno would be the ultimate judge.

Do not forget: "A flow bench is only a tool".

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