There is no substitute for real facts. I had convinced (finally) my mate Bruce Marston to outlay $500 for a custom made set of 2 into 1s. To get baseline figures we put his bike on the dyno exactly as it came off the track from the Victorian Titles (He won by the way). The first set of runs showed 84 HP. This was much better than Bruce had hoped for as he thought the number would be 10 less than that.
We then went to the 4 plug setup and got another set of figures but the results (for me at least) were a little disappointing as we didnt increase anything. What it did do was to fix an occasional mis-fire that was present on the first set of runs.
We then installed the 2-1 and did another 4 runs. This showed an increase of about 2 HP but the tailpipe length (after the collector) was obviously too long and reversion was killing the upper mid range.
After chopping 11.875 inches from the tailpipe we got the best run of the day and the engine actually hit 89 HP on one run.
A couple of minor afjustments produced the final set of 4 runs which all showed a fairly smooth curve peaking at a little over 87 HP.
The last set of runs had everyone in the workshop pretty stunned. They were used to seeing nothing but Evos and had never heard a racing Ironhead engine in full flight.
The dyno operator said the motor was still pulling very hard at 6500 and had more in it but the vibrations were starting to worry him. Hes more used to Evos which are a lot smoother at 9 than an Ironhead is at 7.
There is more to be had from this engine as we hadnt knocked the ignition timing far enough for the 3 plug heads, hence the lack of improvement there. It was at 42 degrees not 40 where it needs to be. Also the air fuel ratio is now too rich by at least one main jet size. So this engine will pull well over 90 HP at the next meeting.
Some facts to explain these numbers:
S&S 4-1/2 stroke stock 3 bore. (1026ccs)
Stock pistons, compression around 10 to 1 (Not measured)
Running on Methanol through twin 38mm Amals on separate intake runners.
Stock Fairbanks Morse firing 4 plug heads with no port work.
A copy of my 2-1 exhaust.
Andrews Y cams.
So, yes, there is more power to be had from this engine. The stock Y cams and twin Amals are limiting air flow through the engine.