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2 things I noticed

3K views 27 replies 10 participants last post by  padgett 
#1 ·
First of all. Have any of you guys noticed where they rear view mirror is for this car...take a look and u might find it interesting. and the nother things is, i dont know how the miata is gonna be able to beat this thing cause has better power/weight ration that the miata. if anyone knows the power/weight ratio for the miata let me know cause as fas as i can tell....the miata will not even touch this thing.:cool :cheers
 
#27 ·
padgett said:
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One of my experiments at GMI ...

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GMI? As in the GMI in lovely Flint, MI?

Did you graduate from GMI-EMI, Gen Motors Institute, or Kettering U? Are you a GMTE?

What year? (don't mean to hijack thread topic, but found this interesting)
 
#28 · (Edited)
Sorry, will try to back it down a bit. Basically it is HP that makes trap speed but torque that determines how fast you get there.

They are related: HP=Torque*RPM/5252. Obviously the higher the rpm for a given torque value, the higher the HP.

Further, what a dyno measures is Torque (the classic ones even look like a big scale). To get HP you apply the above conversion.

Where it gets confusing is that peak HP only has a meaning at a specific RPM. Acelleration OTOH is how fast you can *change* the rpm. Apples and Oranges.

Now if you could just keep the engine at peak revs the whole time then it would have meaning but in a car you can't (as a sidelight you might look up Continuously Variable Transmissions which tried to make it possible but generally were only successful in cars under 1 liter (61.5 cid)).

Since you can't, what matters is the torque available while you re in each gear. Diesel trucks have a very narrow operation range which is why 10, 12, 15, and even 20 speed transmissions are common. - Not really 15 speeds but a 5 speed connected to a three speed with over, under, and sideways drive and both hands with an elbow hooked to the wheel needed for speed shifting...

Meanwhile a typical five speed has a starting gear often good for about fifteen feet and one bounce out of the gate, three accelleration gears, and a long mpg gear. (In my Sunbird V-8, first gear was so low that the engine could not rev fast enough with the stock flywheel and would acellerate faster starting in second).

OK, you take the jump in first and pull (or push depending on the linkage) hard on the shifter and bat the clutch. Right foot flat on the floor (or forget the clutch and bat the throttle, depends on technique - personally I do not care for the "hit the rev limiter and pull" style, feel like the limiter upsets the engine for too long).

Initially you get a jump from the engine inertia at 6500 grand suddenly droping to 4k but after that it is how much torque you have *at every point* from 4k to 6500 again that determines when it is time to row your boat again. (Honda S2000 owners multiply by 1.5).

Now you may not care but the general does how much is available at 2000 rpm as well because that is important from a CAFE and emissions standpoint. Internal friction goes up by the square of the RPM so economy and "gas guzzler" tax avoidance demand the RPM to be kept as low as possible during normal driving.

Ideally the toque would be flat from 1200 rpm to 6500 but it does not work that way. While there are tricks you can play on an engine to spead the curve, it remains a curve. Further combustion parameters (a whole 'nother semester) being failrly fixed for pump gas (93 PON burns slower than 87 PON, it doesn't have any more "power") and various losses increasing with rpm, this means that a longer stroke engine will peak at a lower rpm than a short stroke engine

Just to mention the Honda S2000 again, for 2004 the stroke was increased from 84 to 90 mm to make the car "more streetable" at the expense of a few rpm.

In comparison with an 86 mm stroke, the s/c 2.0 l Ecotec is really going to wind (though boost can correct a lot of issues) while the 98 mm stroke of the 2.4 positions it much more as a low rpm torque engine. That stroke difference between the two engines is really going to change the character completely.

Must admit I find the 12 psi claimed peak boost for the s/c version incredible for a street engine particularly with 9.5:1 cr and a 6500 rpm cutoff, will be interesting to see what it does on the road.

Does this make more sense ?

BTW yes spent a number of years commuting from Anderson. IN (home of Delco Remy) to Flint when it was still GMI and we were employees, not students. Once dropped a loaded Suzuki 750 water buffalo on glare ice in the middle of I-69 during a commute. Didn't know I could pick it up until then but an oncoming semi made a number of things possible.
 
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