More HP from plug wires?

[REXX]

Just read an article where a slightly modified Harley gained 2.1 HP from installing a pair of Sumax Thundervolt50 plug wires. The tests were supposedly done by an independant speed shop, Carl's Speed Shop in Daytona. Now, if a tractor motor can gain 2.1 HP...what would the Blackbird gain?

[Iceman_40]

My guess is nothing.....

Honda was smart enough to put a real set of wires on our XX....lol

[REXX]

Good point!

[jrdxx]

The stock H-D motor is at such a low state of tune that practically anything you do will net you a small increase in power. I had Carl's Speed Shop in Daytona (they're just up the road from me) port and flow the heads on my '94 FXR, resulting in an increase from 56 rear wheel HP to 87 as measured on a dyno, an increase of about 55%, and not too shabby for a 80 inch motor with stock compression. The Blackbird motor is already at a sufficiently high state of tune that many mods to the engine (such as a slip-on exhaust, for instance) individually could actually result in a net decrease in peak horsepower. A good point of reference might be to ask the guys running nitrous or turbocharging their engines. If they can run using the stock ignition, then the stock setup is already delivering peak performance for a normally aspirated engine.

[XX4me]

From what I understand the XX ignition is somewhat under powered.

On my Hahn kit instructions they suggest decreasing the plug gap to .025.

This presumably keeps the spark from being blown out under boost.

I think I've heard of other turbo owners changing coils to get stronger more consistent spark not sure about the wires.

[Pete in PA]

Motorcycles are STILL putting on weak ignitions, as evidenced by our .035 gap versus my 99 Monte Carlo's .060.

Cars get 80-90K volts versus our 32-40K volts.

The biggest improvement would be larger coils since our wires are actually wire, not a carbon string like auto wires.

I BTW remove the resistors in the plug caps on all Honda bikes I've owned.

[Northman]

Plug gaps aren't an indication of spark power available, but other factors.

Engines with lower compression ratios, for instance, will use a larger plug gap as the gap is easier to jump.

GM used the same coil for 20 years (HEI). On a Chevy, your plug gap was .045". The same application in an Oldsmobile used the .060 gap. I've also seen gaps as high as .080.

Gapping the plugs is like tuning your spark. The larger you gap them, the more spark will be needed to fire the plug.

It works the same way with compression. The higher the squeeze (or the more boost), then the smaller the gap required for a hotter spark.

Car DIS systems run about 40-50K max, with about 15-20K measured at lower speeds. I don't know what bike systems produce, but there are 500hp bikes out there, running stock ignition systems.

I asked this same question to my engine builder, BTW, and his answer was leave it alone. No race kit he's ever fitted included a better ignition system, including Duhamel's RC, which was running over 13:1 compression.