Luis

My other experiences with dual lobe dual cam VTEC engines include the 160HP 1.6L Civic engine and the 190HP 1.8L integra engines. On both, the change in torque when switching lobes was quite dramatic. It was truly dr jekil & mr hyde behaviour.

I contend that this is not the case with the F20C engine. It's still a peaky engine, that is, torque is well sustained at the top of the range (instead of the camel hump you see on most street engines), but it is reasonably smooth. People that claim that the S2000 has dual character (below 6Krpm and above 6Krpm) are being fooled by the engine sound.

I offer a g plot as sustaining evidence. Gs are what you really feel, not horsepower nor engine torque. The data for this plot was obtained with an accelerometer held squarely in the direction of travel. In the graph you can see 2 lines for 2 different runs:
1) the raw data
2) a 4th degree polynomial interpolation of all data points.

Please note that the raw data is not smooth because pavement imperfections are detected by the accelerometer, that is hitting a small bump is perceived as an acceleration, and coming off it as a deceleration (it all evens out in the end).

This test was done in 1st gear where variations in torque are much easierly detected. Any higher gear will produce even smoother results.

Elistan

Actaully, engine torque is the root of what you feel, since that directly translates into wheel torque which directly translates to the car's linear acceleration.

Luis

I agree (sort of, the real root is combustion inside the cylinder ), but what you feel are Gs (acceleration) not torque. That was my point.

Tox

Very interesting analysis, Luis. But how did you pair the RPM with the acceleration data? Was the accelerometer also hooked to the tach, or did you correlate them some other way?

I guess I'm surprised by a couple things. First, obviously, I'd have expected more of a change. I'm substantially deaf, so I don't think I'm being fooled by the noise. (I don't hear much either way.) IMO there really is an obvious surge -- but perhaps a 0.1 or 0.2 g increase (20-40%, after all) really makes that big a difference to the inner ear.

Second, I'd have thought the S2000 would pull more than half a g. (Pause -- sound of brain starting up...) On reflection, though, that's 16 ft/s2, which gets you to 88 ft/s (60 mph) in 5.5 seconds, so I guess that's about right. 0.55 g would get you to 60 in 5 seconds flat.

Thanks for posting that.

statueman

Interesting thought. Good post. If I get the drift, your making a compararison between the F20C and the 1.6/1.8 VTEC Hondas. The first VTEC, and only other VTEC, I've experienced was a 1992 GSR (1.6l w/160 hp). That was a while back, but thinking back on it I don't think it was any more pronounced than the F20C. I guess we would need a 1st gear g-graph on one of the other motors for an objective comparison.

Prelude

Another good comparision is the Prelude's H22A engine, similar amount of torque and weight. I've driven the GSR and the Civic Si both are pretty boring compare to the pull on the Prelude.

This is such a great post, thanks for starting it!

Luis

Tox,

No Tach hookup. The unit integrates velocity from acceleration. Then it is just a question of dividing velocity into velocity/rpm (a constant on a given gear, I used 4.65 mph/krpm).

I was also surprised by the low G numbers.

But then if you calculate force from engine torque multiplied by overall gearing ratio divided into the wheel radius, you get something like 1000kgf peak in 1st. Divide 1000kgf into 1400kg (weight of the car with driver and fluids) and you get a=.71g. If you assume you've got 20% drive line inefficiencies then a=.57g, which squares nicely with what I measured.

E30M3

>>If you assume you've got 20% drive line inefficiencies then a=.57g, which squares nicely with what I measured.<<

The gs are always lower than you might expect in first and second gear. Higher losses due to gearing and the more rapid revving accentuates any MOI issues. That's why a light flywheel helps the most in the lower gears yet is basically unnoticeable when in the higher gears.

If I plot road HP for each gear on my m3, 1st is the lowest by far, 2nd a bit higher, and then third and fourth are nearly the same. On that car 4th is the very highest (least loss) cuz the gearing is 1:1 in that instance.

Having said all that, the results are the results. The Ap-22 is very "real world".

Another thing about drivetrain losses..some are pretty fixed and "paid once", some vary and not always as a straight percent at all revs.

Stan

Ludedude

Cool "scientific" analysis.

I'll tell you this, from a purely "seat of the pants" feeling...my previous car was a 1999 Prelude (H22A I believe)and the VTEC changeover was much more pronounced, almost brutal, by comparison to the S.

I hear it, I feel it, but in the Prelude there was no mistaking what just happened.

Now, ask me if it matters?

Luis

[QUOTE]Originally posted by E30M3
[B] ...
If I plot road HP for each gear on my m3, 1st is the lowest by far, 2nd a bit higher, and then third and fourth are nearly the same.