Alfadyno

In June, after covering 1100 miles on the new motor, I booked a tuning session at the local dyno facility which is equipped with a Dynojet 248C. I used that opportunity to get some baseline power numbers and also to experiment with jet and timing changes. It was a productive day that ultimately ended with the car producing 126.2 hp @ 6000 rpm and 116.2 lb/ft @ 4900 rpm. Five months and 3200 miles later, I returned to that same dyno facility for another session. During the intervening 5 months the following changes had taken place:

Installed a bigger, more open exhaust
Put an additional 3200 miles on the engine (4300 vs. 1100)
Switched from dyno motor oil to Redline synthetic
Raised the float bowl level to improve drivability at low rpm

Those four changes resulted in a car that felt faster across the board -- from the 3000 to 7000 rpm. Given that most of the above improvements (particularly the bigger exhaust) should have made noticeable improvements on the top end, I expected to see higher peak horsepower numbers on the return trip to the dyno -- I was dreaming. My first dyno run of the day showed 5.6 fewer hp (120.6 @ 6000 rpm) although the torque had increased by 5 lb/ft at 600 fewer rpm
(4300 rpm). The increase in torque, particularly the huge jump in the midrange, accounted for the perception of increased power, but didn't explain why the car now felt a little faster above 6000 rpm. After all, I would think that
comparatively speaking the big bump in midrange torque would make the upper end feel softer even if the actual high rpm numbers were the same.

One theory for the perceived disparity in numbers is that the dyno was having trouble that day and thus produced artificially low numbers. There were several Alfas present during the November session and all the final numbers seemed a little low. The dyno also unexpectedly shut down several times and prematurely triggered my Electromotive's rev limiter on all but one run, lending further credence to this theory.

With regard to tuning changes, when I dyno'd the car back in June, it ran really rich. In fact by leaning the mains from 150s to 145s, we picked up 5.5 hp. However, in November the car was running really lean at high rpm (the bigger exhaust at work?). After the first run we began to make some changes and by increasing the mains back to 150 and upping the air correctors from 185 to 175, the final run of the day produced: 127.1HP @ 6000 rpm and 124.9lb/ft @ 4800 rpm.

The changes I made during the last run of the day reduced low-end torque by just a small amount over the initial run (below 3500rpm), but brought back all the
missing top-end power from my first visit to the dyno. Torque was higher from 4000rpm on and peaked at a 7.3 lb/ft increase at 5700rpm. As it now stands, the
car produces 90% of its peak torque from 3400 to 5900rpm. Click on the graphic to the right to see how the horsepower and torque curves from the June and November sessions compare.

Note: Those dyno runs were made with 38mm chokes in the Webers. According to several Weber sources, a 2.0L 4-cylinder engine with a 38mm choke per cylinder

should produce peak power at 6000 rpm. Because my power peak was only 6000 rpm with the 38mm chokes, I suspected that the motor wasn't making full use of the larger units and so I replaced them with 36mm counterparts. The difference? Well, by the seat of the pants the car is faster. There is no perceived difference in how quickly the car pulls from 6000 - 7000 rpm, and if feels much stronger below that figure. The next dyno trip should prove interesting.