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TUNING FOR SPEED ON THE DYNO
by Kelvin Palmer
Chicagoland MG Club
I
had the experience of attending a new seminar offered by MG technical
specialist John Twist of University Motors Ltd. of Ada, Michigan. John
regularly offers (usually during February) a series of MG-related technical
training seminars ranging in topic from rebuilding engines and gearboxes
to basic maintenance and restoration. This new September seminar titled
"Tuning for Speed" caught my attention as I race a MGB in vintage
racing events.
John Twist was joined by associate Carl Heideman in teaching the seminar.
Carl operates "Eclectic Motorworks" in Holland, Michigan where
he offers body and frame fabrication and restoration as well as "go-fast"
work on a wide range of vintage sportscars. Carl also writes technical
articles for a variety of auto enthusiast magazines, notably including
Grassroots Motorsports, a high quality and believable source of hobby
racing news and ideas that I read regularly. Carl has been endeavoring
to sort out the effects of various bolt-on performance gadgetry for MGs
and report accurate results to the readers of these magazines.
Over the last several years I have spent considerable time reading and
re-reading a book by Englishman Peter Burgess titled How to Power Tune
MGB 4-Cylinder Engines. Although not literally used in the class as a
textbook, the seminar followed most of the tried and true recipes offered
by Mr. Burgess for extracting the most from an MG engine in the way of
power and performance. The book certainly prepared me to better understand
almost everything we would eventually discuss in the class.
Mr. Burgess promotes the idea of "Rolling Road" tuning. The
rolling road or "chassis dynamometer" is a large scale test
instrument where the powered wheels of a car drive a set of heavy rollers.
The instrument measures torque and horsepower at various RPMs. The performance
recipes offered in his book are documented with accurate data collected
from one of these chassis dynos displaying the horsepower one could expect
from different component and tuning choices on MGBs.
The real draw of John Twist's seminar for me was that on one of the three
class days we would gather at Baker Engineering in Nunica, Michigan, a
local business that operates a chassis dynamometer. We could learn the
basics of what these remarkable test instruments can accomplish. At a
small extra cost, we were offered the opportunity to place our own car
on the dyno and perform some tuning and parts swapping experiments. The
beauty of working with your car on a chassis dyno is the opportunity to
make instant, reliable measurements of exactly what the tuning or parts
change accomplished in the way of power increase or loss. Four of us seized
the opportunity to try this with our own cars.
Carl Heideman has performed hundreds of dyno "pulls" on numerous
MGs at the Baker dyno, so performing these tests on our four different
cars went smoothly and safely. Carl also confirms that the results of
his MG tests very closely match the results and figures quoted in the
Peter Burgess book. The dyno is housed in its own shed building with a
garage door.
Your car is backed onto a car-size elevator which raises it to the level
of the big rollers. The car is then further backed onto the rollers, tied
down and chocked in place. The first car tested was a TF. The dyno is
sized for typically larger cars and careful attention had to be paid to
the very narrow wheel track width of the TF. Any inches smaller and the
car would not have straddled the ramps on the lift.
A "pull" on the dyno consists of gently running up through the
gears to third or fourth and then briefly holding at about 2000 RPM. When
the dyno operator signals, you stomp the accelerator to the floor and
let the RPMs rise as high as you dare. Through this acceleration, the
rollers apply a known load to the wheels. Measuring the time it takes
to reach various RPMs allows torque and, ultimately, horsepower to be
determined.
The dyno is computer assisted and prints out the familiar horsepower and
torque curve graphs for you to keep and study.
The TF owner simply wanted a baseline peak horsepower number which proved
to be around 40 or so. The "rear wheel" horsepower figures measured
on a chassis dyno are always lower than what an engine dyno would find
when testing the engine only. Higher engine-only horsepower is what typically
gets quoted when publishing power specs for a vehicle. The power losses
in the transmission, differential and the mass of wheels and tires all
come into play in reducing the figures when testing this way. We were
told to typically expect a 25 or so horsepower loss from engine horsepower
for a car like a MG. Another owner tested his MGB GT and experimented
with different air cleaner setups. The K&N filters he swapped on proved
to produce a 3 or 4 HP boost over the stock factory units. John Twist
himself tested his MGA for power and found some air flow changes resulted
in higher output. The dyno also identified some intermittent crossfiring
in the ignition which disappeared with a different set of ignition wires.
My car's turn was last. My "butt-dyno" (a technical term we
learned from Carl during the seminar) had told me that I had significantly
increased my engine's output last year when I sent out the cylinder head
for a porting job. I was sold on the benefits of porting the head after
reading the Burgess book. I had no idea what kind of horsepower numbers
I had before and no idea what I might learn today. I knew my engine was
hotter than stock with the easier breathing and somewhat milled head,
an exhaust header and a mystery fast-road type cam. I knew it still has
low compression, slightly over-sized deep dished pistons and runs real
nice on pump premium fuel. Carl explained that most stock or near-stock
MGBs register peak rear wheel horsepower readings in the mid-60s to low
70s. He asked me what I expected from my car before we started and my
best guess was 75 or so, based on what the Peter Burgess book suggested
for engines with tame modifications like mine.
Well, our first, right-out-of-the-box pull registered 81.7 HP @ 5400 RPM.
Cool! We measured the ignition timing and realized that it was about 4
degrees retarded from my usual setting of 32 degrees of full advance for
some still unknown reason. We set it to 33 degrees and pulled again. This
time 84.4 HP. Cool! So what if we tried 35 degrees, or 37? Result: 85.8
HP! Way cool! I gained 5% in power in ten minutes by turning the distributor.
You can't just keep dialing up spark advance and 35 degrees of full advance
proved to be the sweet spot for my engine. There was no evident spark
knock due to excessive advance and the dyno loading does sort of mimic
climbing a hill where spark knock would be likely to show up.
All the while, a "sniffer" was inserted in the car's tailpipe
sensing fuel mixture. The dyno can show the richness or leanness of the
mixture at all these various operating speeds. The Burgess book suggests
that best power is typically made with an air/fuel ratio of around 12.5:1-considerably
richer than settings made for fuel economy. My air/fuel ratio started
out a bit lean (13.5:1) at lowest RPMs (we guessed due to my known to
be worn and leaking SU throttle shafts). It went a bit rich (11:1) in
the 3000 to 4000 RPM range and then settled at a nice, safe value of 12.3:1
in the race operation range above 4000 RPM. Based on these observations,
mixture setting changes were not called for.
We had a bit of dyno time left and Carl wanted to try some airflow experiments
on my engine. I have always run a set of K&N air filters on my race
car. Practically nobody else at the track does. I just figured it was
safer and K&Ns were known to be pretty good at not impeding airflow.
We tried a different set of K&N filters but without my usual "sub
stacks" which are short but very smooth mouths at the carb throat
openings that fit inside my air cleaners. That lost us 1 full HP. We then
removed the air cleaners entirely and fitted a very trick looking, $90
set of TWM brand stacks to the carbs instead. These are the trumpet shaped,
horn-like things I see on a lot of race cars (apparently for good reason).
My final dyno pull with those stacks registered 87.6 HP. Almost another
2HP! Needless to say, those stacks were staying where they were.
Better yet, Moss Motors had donated them as a door prize for the seminar,
and I got to keep them. Moss and Advanced Performance Technology (APT)
provided several other valuable freebies to seminar attendees.
Overall, my horsepower gain after arriving at the dyno was 6 HP, an Increase
of over 7%. I wasn't sure at the time if everything translates exactly
from dyno results to street or track results but the value of the chassis
dyno as a test instrument was obvious. I've now returned from a race weekend
at the four mile Road America circuit in Elkhart Lake, Wisconsin. I consistently
turned laps 2.5 seconds faster than I had there earlier in the year. Doesn't
sound like much? You'd be amazed what racers will pay for 2.5 seconds.
Metropolitan areas typically have several shops that operate a chassis
dyno. I highly recommend the experience. John Twist may run a similar
tuning seminar again in the future. Watch for it. John Twist can be contacted
at University Motors Ltd., (616)682-0800 or johntwist@universitymotorsltd.com.
Carl Heideman of Eclectic Motorworks is at (616)355-2850 or carlheideman@yahoo.com.
In the meantime, if tuning for speed is your thing, the Peter Burgess
book for MGBs is invaluable.