My street S4se had been waiting a few years for that day, but eventually
I did not build this engine (the original one, Stromberg head, is stored), just swapped the unknown cams (probably CPL2 reground) for known Q420, Weber 40DCOE with 34mm chokes. It is believed to be a 1700cc (old build invoice from the 80s), running on RON 98 gas.
I had previously sorted a bit the carbs on the road with the help of a lambda wideband sensor (Innovate), though the electronic ignition (123.nl) or other electrical gremlin makes the tacho recording chaotic (rpm signal lost at high revs), hence not as usable as it should… so a reason more for dyno fine tuning…
The day started with a decent compromise with the carbs jetting (conclusions from road test in parenthesis)
Emulsion F16 (F2 too rich)
Main 135
Air 170
Pump 35 (40 too fast)
Idle 40F8 (45 or 40F9 too rich)
the first goal being to fine tune the ignition timing
first pull gave 126.8 @6300
Initial 123.nl curve was maxing out at 33?, but to my surprise this was still not enough (32? was dropping the power at least 2.5hp in the concerned zone), so after a number of pulls the following compromise was adopted
1000 12? (not tuned)
1400 18? (not tuned)
2000 25?
3500 32?
5000 34?
6500/6800 34?
8000 19? (acting rev limiter in case rev limiter does not work)
I prefered not to push beyond 34? on this street engine: this curve provided a 129HP new reference, from which the carbs jetting were optimized (Main mostly between 130 and 135, air over 155-190) to
Main 135 Air 180
final street result 130.5HP (about 164Nm torque @5150 - ~121 ft.lb that is)
(Main 130 Air 190 was marginally better by 1/4HP but a bit lean at high revs 13.5-13.6 right at the cut - torque was a bit better by a couple Nm, too)
I may come back to try the leaner setting after I recalibrate the lambda sensor, to check if indeed it is too lean at high revs or still ok, not that much of a difference anyway. The curve appears quite flat from 5300, I suppose this is admission limited since I have a road TTR exhaust line supposed to take up to 160HP (stock big valve head, not ported).