The Honda S2000 hit the world like a missile. Here was a car in which Honda engineers had almost nonchalantly achieved the incredible triple - the world's best power per litre of any naturally aspirated engine, excellent economy, and the LEV cleanliness of exhaust emissions for which Honda is fast becoming famous. And with the shapely coupe capable of a 0-100 time of 6.6 seconds and a 14.8 standing quarter straight out of the box, what would there be left to do in the aftermarket? Surely a new exhaust and a chip wouldn't do much for this engine - not when it was already so incredibly good?
That's where the conventional wisdom has stayed - until now. For we have just seen with our own eyes Bob Romano Performance Motors in Brisbane (Australia) achieving a no-bullshit improvement in power of 27 per cent from what are really relatively mild mods. Yes, you read that right - 27 per cent! Technically, that should give the mighty 2-litre NA more than 220kW at the flywheel!
So where does all of this magic come from?
Honda's S2000 uses an 11:1 compression ratio on its over-square (B&S - 87 x 84mm) DOHC four cylinder. A reduction in internal friction, revised VTEC actuation methodology and normal hi-po breathing mods has resulted in a massive 176kW (236hp) at 8300 rpm, with torque chiming in at 208Nm at a sky-high 7500 rpm. However, as can be seen in this Honda engine dyno graph, the torque curve isn't as peaky as the 7500 rpm figure could suggest.
So as you might expect, this isn't the sort of engine where you can get a back-yarder to grind up a set of cams - not if you want good results, anyway! However, it has been found that there are two tried and traditional avenues to power that work incredibly successfully on this jewel-like dynamo. But firstly, don't get too excited about changing the airfilter. Romanos has had the local Honda club put a series of S2000's through their paces on the workshop's Dyno Dynamics dyno, and it was soon found that the factory cone-shaped filter working in its standard box was pretty hard to improve upon - and there was certainly no power gain just by changing the filter, anyway.
But what about the exhaust? Incredibly, it appears that the S2000's exhaust is quite restrictive - specifically the dual (one each side) rear mufflers. Those in the Honda club that had modified the exhaust were getting a very good power gain from the mod - a no-pain gain in fact. So what sorta numbers are we talking about then? OK, a dead standard car puts out about 152hp at the wheels. (Because our dyno sheets are in hp, we'll use those units from now on.) With a flywheel figure of a (claimed) 236hp, 152 at the wheel represents a 35 per cent drivetrain and tyre loss - a bit more than the 30 per cent often quoted for this dyno but not that far from the mark. And with the rear exhaust boxes upsized a little and replaced with free-flow designs? The dyno has shown that peak power jumps from that 152hp to more like 173hp, a very substantial gain of 14 per cent. So, pretty obviously, Step #1 for S2000 owners is to ditch the rear mufflers for something better.
And that's just what the owner of the S2000 shown here had already done. Two 2½-inch Magnaflow mufflers were hung under the tail, with the new exhaust in front of that being of the cat-back variety. That's the way that the car lobbed into the Romano workshop, so Chris Romano's baseline power-run with this car was already well up over stock. But what could be done to extract even more?
The first step was to piggy-back a MoTeC M4 programmable ECU (complete with ignition expander) onto the standard computer. That way, Honda electronics could keep running the dash and performing all those other factory tasks, while the MoTeC could work the injectors and control the ignition timing... places where power could be found. Chris Romano used nearly all the factory loom, accessing it under the dash for the injectors, ignition drivers and most of the sensors.
However, he chose to add a new sensor to measure coolant temp, locating it in a fabricated stainless steel fitting placed in the top radiator hose.
In addition, he disabled the factory idle speed control air bypass passage - otherwise the Honda ECU would keep trying to control idle speed, just as the MoTeC tried to do the same via ignition timing variations! The idle air bypass passage passes through the Honda throttle butterfly gasket, and so making a new gasket that simply lacked that hole was an elegant way of blocking the opening. (Incidentally, Bob Romano Performance has more tools than I have ever seen in a single workshop... When making the new gasket, Chris casually got out the complete set of gasket material hole punches...)
But where was this further power improvement going to magically come from? Replacing a factory ECU with a MoTeC does not of itself make grunt, y'know. Well, in this case it was easier than it should have been - the Honda ECU at full throttle runs the mixtures very rich indeed. Obviously the guys at the workshop do not want to give away all that they have learned, but we can say that the leaning out required to give best power was very substantial - enough in fact that colder plugs could be fitted because their likelihood of fouling was substantially reduced when there was so much less fuel being mixed with the air. So with a leaner air/fuel ratio, some timing tweaking, the colder plugs, and a VTEC changeover point shifted by only a small amount, Chris Romano found himself looking at a power graph that peaked at 187hp - a gain of 8 per cent over the car fitted with the new mufflers.
But there was still more to come. While the people who had previously played with new filters had thought that they were onto something, as we've shown time and time again at AutoSpeed, it almost always works better if the factory filter is retained and a new cold air intake duct placed into the airbox. And that's just what Chris Romano did, removing an internal baffle in the box, leaving the standard over-bonnet intake in place and adding large diameter convoluted tube picking up air in front of the radiator. And the power responded again, rising to a rousing 195hp at the wheels, a further improvement of 8hp, or 4 per cent.
Isn't that absolutelybloodyamazing - a dyno recorded power output of 195hp at the wheels on a Dyno Dynamics - and all from just 2-litres of NA muscle?
Contact:
Bob Romano Performance Motors
07 33958255
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The Dyno Results
The top three lines on the graph show the steps carried out at Bob Romano Performance Motors. As the car arrived at the workshop already equipped with new rear mufflers, the bottom line is from another completely standard car. So the bottom (red) line is from a standard S2000, the light blue line (second from bottom) is for 'our' car when equipped with Honda management, the standard airbox and the new rear mufflers; the next up (black) line shows the results of the additional engine management tinkering; and the final top (pink) line shows the combined result of the MoTeC, intake mods and (of course) the new exhaust. Very impressive numbers, aren't they?
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