Terry Crocker's 996

This is a long story so I'll skip a lot of the non-performance details. For whatever reason, Terry couldn't get his bike to run properly. For whatever reason he sent it 1/2 way across the country.

The engine;

The engine is a 996 with high compression pistons, 996 SPS cams, ported big valve heads, 54mm bored stock throttle bodies, and a 54mm Arrow exhaust system.

The heads were done by Vee Two, as were the throttle bodies.

After completion, the bike never ran right, surprising, since it's a barely pumped SPS.

At one point Terry sent a dyno sheet and it showed both 118 HP with one chip and 122 HP with another iteration.

The particular chip was a single-injector-per-cylinder version. Not surprisingly, one injector per cylinder can only flow (at 3 bar fuel pressure) enough fuel for, roughly, 118 HP. It's obvious, from these results, that one can extract a little more power than the injectors will support, but it will be going lean, as this chart shows.

The person who did these dyno charts, told him that the bike wouldn't make any more power. The parts wouldn't support it. Terry thought that the A/F ratio could be improved significantly, and the might make more power.

Interesting that the A/F ratio on the chart goes lean above 9000 RPM. Because of the slight delay in the system it's actually going lean before that. What did I just say about single injectors?

Needless to say, the first thing I did was connect the second injector and start with a map I had created for a very similar bike.

Within a couple hours of dyno runs and map changes I had a pretty good map and over 133 HP. All of this was good, because I didn't want to take this engine apart. I had reason to believe that the people who assembled the engine are competent, and the results confirm this. The only problem with this engine was the tuning or lack of it.

After I confirmed that the engine could make the expected power, I continued to optimize the entire fuel and ignition mapping. That takes a while. The charts below are after considerable refinement of the mapping.

The chart below shows the difference between the bike with a stock air-box, without air-filters and with the filters.

When the filters were installed there was a greater loss in power, but a little tweaking recovered most of that.


You will notice that the X-axis of the chart is in MPH. That's because the run for the blue trace (#.019) didn't have very good RPM data.

I had finished the mapping before I left Manley's. We had wanted to map it with the Vee Two air-box, but it was several months late. During 'the move' Terry contacted me and told me that he had recieved the air-box. Shipping was scheduled for August 29th so I told Terry to send it and I'd see if I could get it done.

The job was finished weeks ago, and now we're in 'emergency mode' again?!?!!

More on that, in a later report.


You don't get your moneys worth until it's tuned!!

Plus, you don't know if your engine work is any good until it's tuned!