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Got me thinking...........

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In response to Nial's comment about the supercharged M1 Miata, in my region of the SCCA, one guy was giving me some driving tips (I was driving my dad's automatic 99 miata b/c the midget's clutch was again malfunctioning). Turns out that he races his C Street Prepared Miata (with '99 engine and 13X7 wheels with yokohamas) quite successfully. Previously he'd had the supercharger kit and said that he actually turned faster times without it because of the excessive wheel spin it introduced. He also said the throttle was harder to control. In the end, he runs it without the supercharger (stock HP=127)
 
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No, I think you are thinking of a turbro. If you look at the dyno graph of a superscarged car there is a smooth increse in power even from idle because you are getting boost at all time.

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All boosted, pumped, turbo charged, mechanical supercharged engines work on the demand principle. If the throttle is closed or only partially open, manifold pressures will still be at the non boosted levels, ie, normal engine vacuum. It is entirely usual for a boosted engine to cruise at normal vacuum levels. It is only when extra throttle opening is used that the normal manifold vacuum levels transition to boost levels & extra power is available. The only time the turbo or supercharger is effectively in operation is at the higher throttle settings, note not necessarily engine rpm settings. You only get boost when the throttle opening is higher than the un- boosted engine would be able to put out.

Most dyno graphs only show the extra power available under full throttle conditions. These power & boost presures are only available when the throttle openings are higher than the non supercharged engine can put out. They are still demand sensitive systems which will put out according to throttle settings.

It is easy to put a vacuum/pressure gage on the engine & observe these conditions under various throttle, engine power output conditions.

A supercharged engine may have more boost pressure, at lower rpm under full throttle, than a turbo charged engine, but this is a function of turbo A/R design, & many turbos have as much boost available at a given rpm, as supercharged engines for the same engine/load combination.
D
 
Dave - excellent! Never saw the "boost" function explained so well.

When I want/need to pass someone on the interstate, I don't go full throttle - I just press down a bit to "give it more gas". What type of boost system (if any) would give me just an extra kick w/o going full throttle?

Thanks.
Tom
 
Tom,

Any supercharger system will give you boost on demand that is proportional to throttle opening, just open the throttle more for more boost. You don't have to use full throttle/full boost if you don't want to.

Many folks can't resist using full throttle at every chance, just for the fun of it. It's kind of fun to pass in five seconds, a car going 60, when you could just have well taken 15 seconds to do it. Of course by the time the car is passed you are going 90 & usually have to slow down again.

You can say that you will only use full power when it is really needed, but few drivers actually do this. Hence the warnings about having the rest of the engine in perfect condition to start with. It's likely to get run harder. Extra power is addictive.

Have fun,
D
 
Dollars to doughnuts.......I can put more reliable, useful , horsepower on the ground by building a normally aspirated engine, using nothing more exotic than head work, piston selection, cam and valve train matching, lightening and balancing of critical components, etc., than you can ever do by adding a turbo or a blower to an LBC engine.
I'm not for a moment suggesting that a blown motor won't put out more power than a normally aspirated engine will, but face it. With a "B", you have 1800cc to work with, a 5 main bearing engine, and what can you hope to accomplish with a turbo or a blower?
Buy a Honda, put a 6000 watt stereo in it, a chrome fart can muffler, and go play with the boys.
Jeff
 
If the main idea is more power, how about more displacement? Isn't there a Rover V8 swap that can be done for a lot less than the supercharger? (or for that matter, maybe you can get a deal on a V8/tranny combo from a GI's yank tank if you live close to one of the bases)
 
Heh, you sure would get more power out of the V8 conversion, but even a passingly decent v8 conversion would probably run you more than the cost of 2 supercharger systems. =)
 
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