Miata Mailing List: December 1997, Message #175
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From: 	GibbP@aol.com

Subject: Re: More HP or More torque (nerdish)

Date: 	Tue, 2 Dec 1997 09:49:22 +0000



In a message dated 97-12-02 04:10:18 EST, curtis.j.wiseman@lmco.com writes:



<< 

 First, thanks to Mike for the explanation, however nerdy it may be.

 (Some of my best friends are nerds.)

 

 Second, I have some questions:

 

 After examining two scenarios (torquey and peaky), Mike concluded:

 

 >So, it seems that the solution is to have a motor that is some balance

 >of torque and horsepower.  The relative "size" of the figure is just an

 >artifact of the measuring system (as discussed earlier), what is really

 >important is the shape of the torque curve.  If the curve is huge but

 >falls off too quickly, you can't do the work fast enough to capitalize

 >on the power.  If the curve peaks very late, but is not high enough

 >early on, then the power is too low at low rpms to motivate the vehicle

 >effectively.  So much so that you may never actually get the car moving

 >fast enough to reach the power band.

 

 Okay, then, back to the "controversy" thread.  There is often talk of 

 which is better, a turbo or supercharger.  We also often hear that 

 torque makes acceleration.  Now Mike brings up the shape of the 

 torque curve.  Well then....

 

 So let's put some limitation$ on the equation: if one does not 

 change from the stock ECU but is allowed an ignition retard (say 

 a J&S), larger injectors, an auxiliary fuel pump, and a variable 

 fuel pressure regulator, which is "better," a turbo or supercharger?  

 Let's also confine the discussion to street driving (to eliminate 

 optimization for track conditions and keep it "real-world").

 

 I have had the pleasure of riding as a co-pilot, er, passenger in 

 Shiv's F'stein and, sure enough, there is no lag and lots of boost, 

 torque, and power.  Unfortunately, I am not currently allowed to 

 write checks to be drawn on Shiv's account.  I have also driven 

 a 1.8 Autorotor and a 1.6 BEGI System III (kudos down San 

 Antonio way).  To me, the instant boost/torque of the Autorotor 

 made it more driveable than the higher ultimate hp of the 

 System III (although either one beats the pants off a normally

 aspirated Miata.  Blindfolded.  With one hand tied behind its

 bumper.  Uphill.  Both ways.).  Autorotor boost jumped up as 

 soon as you asked instead of building up.  

 

 I also realize there are drawbacks to belts and pulleys as 

 opposed to good old energy-laden exhaust but, for now, 

 I'm just asking about driveability to keep the discussion

 bite-sized.

 

 Any opinions?      :-)

 

 Curtis Wiseman & Zonker >>







Well.......with the stock ECU and using the stock compressor housing I think

that a stock Autorotor will build boost lower down than a comparably sized

turbo. Unfortunately, I don't have any data regarding boost threshold and

rate of change on an Aerodyne.....any volunteers?



While Max power is sure fun, it is imediate power in the midband, and off the

line that make a car drivable. MOST of the time when you are tooling around

you need immediate boost around 3-4k. Both a turbo and a supercharger will do

this. Where MOST superchargers are better is off the line......Shiv's

Frankenstein excluded!!!



What you really want from the car is a broad, flat, high torque curve.

Indeed, this is exactly what my 92 Autorotor Plus is tuned for. You will find

that extending out the torque curve, or rather plateau, will give you IMMENSE

benifits in real world driving situations. You can achieve this in two ways.

Either by brute force, e.g. more boost, or by sophisticated tuning, e.g.

aftermarket ECUs and lots of dyno time. It is my experience that the more

sophisticated way is by far the better way to go.



Within the limitations of the stock ECU something like the J&S can GREATLY

improve the drivability of your car. By advancing the base timing of the car,

and using the J&S to retard it at the detonation threshold you can reall add

torque to the bottom of the power curve. Indeed, from my various dyno runs I

should think you could net about 15 ft/lbs of torque below 3000 with a

properly set up J&S. This is a SUBSTANTIAL difference, and will greatly

enhance the drivability of the car.



Gibb Phenegar

92 Autorotor Plus 13 winter psi