Warning, pedantry ahead. I'm going way back to basics on this.
FWIW, Vizard's book on the A series is an excellent primer on
engine tuning in general.
First of all horsepower is torque * RPM (1). So you can not
affect one without the other. I believe that what you are
complaining about is that you are noticing the lack of torque
at lower RPM.
Burning petrol releases energy. The more petrol that you burn in a given time
means more energy per second, or more power. The limiting factor is air. The
more air that you can pump into your cylinder, the more petrol that you can
burn and the more power that you can make. Higher altitude means less air,
means less petrol that can be burned. The complete solution is to figure out
how to get more air into the cylinder, hencenifty items like superchargers.
There's another factor involved and that is combustion efficiency.
assuming that you don't have $4,000 to drop on a supercharger and you
just want to get the best performance you can for a minimal investment,
you need to look at your SUs. This is one area in which SUs shine.
It takes only a few minutes to recalibrate their mixture curve.
I reccomend getting a copy of the Haynes book on SUs. On page 94 is
an applications list which lists several possible needles. Appendix 2
has needle charts listing the profile of the needles. The book reccomends
going to the leaner needle for high altitude driving.
Do you have your SUs tuned so that they idle a bit on the lean side?
Do you need to use a bit more choke to get it started than you would expect?
Were the carbs adjusted at high or low altitudes?
The quick and dirty solution would be to buy an assortment of needles and just
try them out to see what works. Of course, you would want to start with the
lean needle reccomended for your application. A much better solution would be
to spend a few hundred dollars on a dyno tuning (2). Use the exhaust analyzer
to see where in the power band you are running rich or lean and choose new
needles (preferably out the the bunch you bought ahead of time) accordingly.
On Wed, Aug 04, 1999 at 11:07:15AM -0600, James Nazarian Jr wrote:
> Does anyone know any tricks for tuning a stock 71 for more torque. I am
> living in Co and loose about 15-18% power because of altitude but it all
> seems to come out of torque, horesepower seems unaffected. Stock SU's
> were completely rebuilt 18 months ago, air pump belt has been removed but
> nothing has been sealed (it is functional with a belt), and I have a
> 1&3/4" thrush exhaust. The car runs like a bat out of hell at sea level
> but the torque is definately lacking at 6000 feet.
>
> James Nazarian
> '71 B roadster
> '74 BGT bastardization with big alluminum heart :)
(1) energy = work = force * distance = lb * ft.
torque = lb * ft
power = work / time = lb * ft / sec
RPM = 1 / time = 1 / sec
torque * RPM = lb * ft /sec = power
(2) IMHO, the *only* proper way to tune for performance is on a dyno.
It allows you to monitor what is really happening inside the motor
and to correlate it with torqe & power. Properly tuning your motor
can result in a several horsepower boost in performance, without
buying any new parts. Once you have done so, you can note the baseline
adjustments at idle and return to them when you tune up, without needing
to rent a dyno every time you tune up your car.
--
The person who dies with the most toys doesn't win. The winner is the
person that has the most fun playing with toys, whoever they belong to.
lrc@red4est.com http://www.red4est.com/lrc
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