H-D 'B' Motor Power-Quest

Initially, I thought this might be a candidate for an addition to the collection of excellent results with Mike Roland's Andrews TW11G cams. TW11G cams Instead, it turns into an excuse to fire away at several subjects, among them; Screamin' Eagle's Delphi fuel injection software, and the culture of pseudo-performance.

Howard Boever expressed an interest in the 'buzz' about the new Rinehart pipes. Since I had this 'mapping' session coming up, I said I could write the report on the results. I don't feel that I can come to any strong conclusions, because we have two variables, a cam change and a pipe change.

So, if you're looking for the definitive report on Rinehart pipes, it ain't here.

Let me tell the story.....

Mankato H-D has been utilizing me for fuel injection calibration for over a year now. Late in December '02, Jeff brought an '02 Softail that had been built with Bob Wright/Lee's Speed Shop ported heads, domed 95CI pistons, SE 257? cams, bored throttle body, and Vance & Hines Long-Shots pipes. By dumb luck, I had just finished a Softail with flat-top 95CI pistons, stock heads, stock throttle body, Roland's TW11G cams, and a V&H Pro-Pipe.

Both of these where using the new Screamin' Eagle Delphi mapping software.

When I finished mapping Baldy's, the result was 91.4 HP vs 93.5 HP for the earlier, milder, one.

Like a fool, I showed the customer the comparison. He asked me what I thought the difference was, and I told him that I thought the TW11G cams and the Pro-pipe were the biggest factors.

They took it back to Mankato and replaced the cams with the TW11Gs (Roland had just recieved a shipment, and more folks were beginning to realize how well they work, so they went, fast) But, when it came time to purchase a new pipe (Pro-Pipe or Thunder-header had been my suggestion) he couldn't make himself do it, and with the recent onslaught of advertising for the Rineharts, he purchased the Rinehart Flush-style pipes.

Here is where I get side-tracked a little.

The Culture

I don't know where or how people's expectations are formed, but clearly, performance doesn't have any influence on the appearance of Harleys. This customer expected his Harley to have two extremely large pipes with no mufflers. That's why he first purchased the Long-Shots and then the Rineharts.

Both of these are pipes with a baffle stuffed inside. My experience has been, that doesn't work. Putting the baffle inside, functionally shortens the pipe by the length of the baffle, and restricts and raises the temperature of the gases.

Shortening the pipe length, raises the tuning RPM. Since no-one makes a pipe long enough for a 6000RPM engine anyway, shortening the pipe doesn't seem to be the right direction to go.

As far as stuffing a potato in your pipe; the pressure wave travels the length of the pipe, and when it reaches a large volume increase (such as an open pipe or a well designed muffler) the pressure wave changes from positive to negative (or vice-versa) and returns to the closing valve. At the torque peak, the negative pulse does a great job of extracting the last of the exhaust gases, as well as starting the inlet cycle.

When the pulse doesn't have an increase of volume, I'm not sure what happens. Probably it acts like a closed end pipe, where the pulse doesn't change sign.

I think that makes it act like an even shorter pipe. Even if that happens to have a frequency that works out OK, the strength of the pulses is smaller with a shorter pipe (higher frequencies), so you can't expect the benefits of a properly designed long pipe. To be fair, you also, can't expect the negatives (big dips in torque) of a long pipe.

Since 'style' is so arbitrary, I can't understand why there isn't some sub-culture that accepts whatever-makes-power to be 'stylish'.

Back to the story

Last week (late Feb. '03) the bike returned with TW11G cams and the Rinehart 'Flush-style' pipes.

The baseline dyno run netted a whopping 79 HP. The first thing I did, was call Roland to tell him his cams 'suck'. Both of us know that there are infinitely more ways to loose power than there are to gain power. In this case the process had just begun and the changes had put the 'tune' way out in left field.

I've done a lot of tuning and I'm beyond getting depressed about poor power numbers. My experience tells me that it 'ain't over 'til it's over' and there was  long way to go.

Although the air/fuel ratio appeared to be OK at the upper part of the power band, I realized that the rear cylinder wasn't being checked and there is one other variable introduced by the Delphi fuel injection system.

The Delphi system monitors some aspect of the ionization of the sparkplug gap. I don't know much about it, but, obviously there is some characteristic that precedes detonation and can be detected. When this condition exists, the timing is retarded. It appears that the computer retards quite a bit then advances to the point of the re-occurrence of the condition, then the process repeats. The power curve appears as a very jagged line when this occurs.

I changed the fuel a little and disabled the anti-knock and gained 10 HP. The chart shows the start of the anti-knock process at 4100 RPM.

At this point, things don't look so bleak. After all, I haven't checked the rear cylinder A/F.

I proceeded to properly map the front cylinder using the Delphi recommended procedure, then switched the exhaust probe to the rear cylinder.

During the front cylinder mapping, the power was around 90 HP. When I checked the rear cylinder the reason for the low power was obvious, it was too rich on the rear.

As I got the rear cylinder fuel into the right range the power increased to high 90s. All of this testing was done with the anti-knock disabled, so the final part of the testing is to get the ignition timing to the point that it doesn't introduce the anti-knock mechanism.

The chart below shows 4th and 5th gear runs with the anti-knock enabled. Run # 053 (red) shows the anti-knock kicking in near the top of the run, while run # 055 in 5th gear, shows signs of the anti-knock working quite a bit earlier in the run. The yellow trace, run # 058, is accomplished by retarding the WOT timing another 1.5 degrees.

This illustrates another variable. There are differences in power, depending upon the gear you choose and the weight of the rear wheel.

The example bike has a Baker 6-speed gear-box. Just as in the stock box, 5th gear is 1:1 with the mainshaft running the power straight through, while 4th gear uses a gear reduction transferring the torque through the layshaft and back to the mainshaft. This uses two pairs of gears.

On most bikes, top gear will give the highest power numbers, but the 'Big-Twin' Harleys don't usually give this result. This phenomenon is a result of the inertia dyno. More energy is stored in the drive train (primarily, the crankshaft since it has the highest RPM in the system) at higher acceleration rates. In top gear the engine acceleration is considerably slower than it would be in 1st gear, therefore it stores less energy in top gear.

The only reason Harleys appear to go against this law of physics, has to be the weight of the rear wheel. In top gear, the rear wheel has the greatest rate of acceleration, and when it's heavy, it absorbs more energy rather than transmitting it to the dyno drum, thus the lower power in top gear.

In the chart below you can see the difference between 4th (red) and 5th gears. I didn't try 6th gear because the rear wheel on this bike is a huge cast aluminum flywheel.


If you've read the report about the TW11G cams, you'll know what the performance expectations are. Below is a comparison of Nelson's 95CI Twin-cam and Baldy's, both with Bob Wright heads, Nelson's with a 42mm Mikuni carb and Baldy's with a 48mm throttle body, Nelson's with a Thunder-header and Baldy's with Rinehart 'Flush-style' pipes. These have similar torque with the Thunder-header producing it's torque almost 500 RPM higher, and holding torque farther out the top.

The cam change worked pretty well, but the pipes haven't pitched in to produce the peak power numbers.

Go to the mapping software report to continue. mapping