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Tuning For Speed
What's New Now?
"TUNING FOR SPEED" ON THE DYNO
by Kelvin Palmer
I recently 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, MI 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 to John Twistís seminar for me was that on one of the three class days we would gather at Baker Engineering in Nunica, MI, 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 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 raise 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 to be determined and ultimately horsepower. The dyno is computer assisted and prints out the familiar horsepower and torque curve graphs for you to keep and study.
Carl Heideman makes adjustments to the MGB race car engine on the chassis dyno during the University Motors "Tuning for Speed" seminar.
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 cross firing in the ignition which disappeared with a different set of ignition wires.
My carís 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 engineís 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, 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 canít 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 carís 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 starts 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 goes a bit rich (11:1) in the 3000 to 4000 RPM range and then settles 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 wasnít 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. Iíve now returned from a race weekend at the four mile Road America circuit in Elkhart Lake, WI. I consistently turned laps 2.5 seconds faster than I had there earlier in the year. Doesnít sound like much? Youíd be amazed how much racers pay for 2.5 seconds.
The dyno in Nunica, Michigan is a long way away but several exist in the Chicagoland area if you are interested in trying such a thing. 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 firstname.lastname@example.org. Carl Heideman of Eclectic Motorworks is at 616-355-2850 or email@example.com. In the meantime, if tuning for speed is your thing, the Peter Burgess book for MGBs is invaluable.
We had a brief discussion at the September CMGC meeting about possibly organizing a club "Dyno Day" somewhere in our area. A certain level of participation would be necessary to make it feasible and there would be an as yet unknown cost to each participant. The club officers NEED to hear from those interested to investigate further. Please let them know what you think.