Theo, et Listers,
While I think you are generally correct Theo, you've managed to hit at
least three of my "hot" buttons with your latest posting. In the order in
which they appear, let's start with your statement: "Any piston engine
built to develop maximum power "well above" 5000 rpm is not going to
perform worth beans at 2500 rpm and below." Now I haven't ever driven the
Honda 2.0L/240HP screamer, but the 3.0L DOHC Yamaha motor in my SHO is
probably the sweetest engine I've ever driven. You can rev it up to 7,000+
rpm and still lug it around at ridiculously low rpms, way below 2500,
without it ever complaining. It puts out 220HP at 6,400 rpm and max torque
at 4,800 rpm; probably not too far different from the rpm points of the 289
in my Tiger. And, cruising at 75 or so with the air conditioning running it
gets pretty close to 30 mpg. The SHO engine is naturally aspirated, has
four valves per cylinder of course, and has two intake runners for each
cylinder; a long one, and a short one that opens up above 4,000 rpm. I
don't think the valve timing changes with rpm, but I assume there's some
dual pattern setup at least. This whole package comes about as close as I
can imagine to having your cake and eating it too. And, of course, this is
not the only modern engine out there with these kind of manners. To get my
289 to run this well over the whole rpm range I'd probably want to start
with a set of Gurney-Westlake heads, fuel injection, dual runners, etc.,
etc., and lots of $$$$$. BUT, it could be done, and be very driveable, and
make 400+ horsepower, and even get decent mileage too (20+). So, in
summary, I think you're way to pessimistic with the referenced statement.
Even just a roller cam will give you a motor that runs well over quite a
broad rpm range; i.e., just like a new 5.0L.
On to hot button #2: What's this about the toploader being a farm
implement? Hey, I love this brutish piece of machinery. Can't imagine
having a wussy tranny behind a big bore motor; just doesn't fit. Kind of
Zen thing you know. And hey, this tranny is so good, they even make
adapters to put it behind Chevys! Sure, it takes a firm hand to use it, but
it downshifts a 7000+ rpm just as easy as at 2500. And, of course, it's
probably the most rugged tranny you can find in a passenger car or truck.
You're absolutely right about the Mazda tranny though; that's what's in my
SHO. BTW, the new 5-speed boxes are a lot smoother shifting, although I
haven't tried the Tremec which I believe is more like the toploader (so of
course this is the one I want).
And finally, I'll bait you with this question: Just where in the rpm range
does the important parameter go from being horsepower to torque? The answer
is nowhere, but for some reason most people talk about torque in the low
rpm range and horsepower in the high rpm range. Just seems unnecessarily
confusing to me. Just look at the horsepower versus rpm curve and it tells
you everything you need to know.
Just tryin' to stir up some trouble in San Diego,
Bob
At 11:07 AM 2/4/99 -0700, Theo Smit wrote:
>The funny thing about engine power is that you can't make it everywhere. Any
>piston engine built to develop maximum power "well above" 5000 rpm is not
going
>to perform worth beans at 2500 rpm and below. And that means you can't use
2.88
>gears anymore. Not having 2.88 gears means you get to row the gearbox driving
>around town, and let's face it: The toploader shifts like a farm implement
>compared to any Japanese transmission (okay, not Mazda's :) built in the
>last 30
>years.
>
>And what's GOOD power in a V-8? 1 hp / cu.in? You won't get much over that
>using
>factory heads, even with porting and oversize valves. Even making 400 hp
out of
>a 302 only gets you 1.3 hp / cu. in., and I would like everyone who has a real
>400 hp Tiger that is pleasant to drive around town to share their secrets,
>please. The only thing that saves high-RPM V-8's is that even if they are so
>tightly tuned that they only make 60 ft-lb of torque at idle (compared to say
>300 at peak), that's still enough to move a Tiger off the line with reasonable
>vigor. With a smaller engine, having that kind of peak to idle torque ratio is
>going to make the car hard to drive. Not that it can't be done, you just
>have to
>drive like you're on a mission everywhere you go.
>
>Theo Smit
>tsmit@novatel.ca
>B382002705
Robert L. Palmer
Dept. of AMES, Univ. of Calif., San Diego
rpalmer@ames.ucsd.edu
rpalmer@cts.com
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