Myth or Fact: Will Ground Wiring Add HP's

[align=center]Myth or Fact:
Will Ground Wiring Add HP's[/align]

Got into some long talks with nakedchef about ground wiring... regarding additional sumo style wires that are used to improve the ground connections between various points, and hopefully improve the performance of the ignition. If poor grounding exists, it is quite possible for the sparks to be lower in energy, resulting in less desireable combustion.

Here is an example of ground wiring...


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So I thought it was worth putting it to the test! :dance:



THE BASIC THEORY


First… a bit of basic theory that shouldn’t put you to sleep!


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To generate a spark, you need tens of thousands of volts :newspaper: Typically, 40,000 volts is used... it bites! To get this sort of voltage, a transformer is used... referred to as the "ignition coil". Put in low voltage one side, and get high voltage out the other. To make it work, usually a 100:1 transformer is used, so you need to pump in 400V on the primary "low side" to get the 40,000V on the secordary "high side".

Given only 12V, we still need 400V... so the primary coil is charged to 12V, and then LET GO at the right time! The coil discharges the energy stored in its inductance very very quickly and spikes to the needed 400V. During the charging phase, approximately 4amps is drawn.

The problem is… a wire will drop a bit of voltage… which gets worse the higher the current! So you lose a volt here and there, and your 40,000V spark can drop by thousands of volts. Less volts, colder spark, slower combustion, less power.

To overcome this problem, thicker wires that runs the shortest path is used, hence ground wiring is born!

There are essentially 2 components to the CBR250’s ignition system to look at…
1. The primary of the coil, supplied by the CDI(-ve) and the battery (+ve)
2. The secondary of the coil, getting the high voltage energy into a spark.


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Ideally we want a nice long hot spark for a long time to burn the fuel/air mix. Picture the spark causing a flame ball, that combusts like an explosion while being pushed around. If the spark is nice and hot, then the flame ball is intense from the start. If the spark is long, then it ignites more mixture as it’s pushed around in the cylinder.

So spark energy needs to be maximised to get that intense fire ball thats gonna burn everything with a bang :dance:

On the primary, getting the most energy into the coil is achieved by getting the most voltage across the coil. So the battery feed has to be good, and so does the CDI pulling the other side to ground.


THE ELECTRICAL INVESTIGATION

So I investigated if there was a problem…


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I found that the battery voltage dropped 1.2V… 10%
The CDI only pulled the coil close to ground, at 0.75volts.
So almost 2 volts in total lost!

So to improve the CDI’s performance, I installed a direct thick wire link to the frame and battery. This gave a much shorter ground path for the CDI to the battery than the existing wiring loom does. However, I did not see any significant improvement.

The 0.75V drop is really due to the transistors used in the CDI… and this was seen on the oscilloscope. It's a characteristic of the transistor used that is causing this voltage drop. I added additional wiring up to the coils, and reduced the voltage drop to 0.5V, but the CDI was the limitation on this side of the coil, not the wiring.

So what makes the battery volt drop by 1.2V to the coils… lets go for a trip around the bike From the battery +ve, we go through the main fuse, through a connector, to the key barrel at the front of the bike, then from there to another connector and then to a 10A fuse in the panel on the left hand side of the bike. Now it goes through yet another connector and to the kill switch on the right hand side of the bike. Through yet another 2 connectors and it arrives at the coils… hence 1.2V are lost!

So… I installed a hugh 10 gauge mother of a wire from the battery, through a fuse, through a relay and then to the coils. The relay is controlled by the ignition, so when the bike is off, so are the coils, and the kill switch still cuts the power. The result… the voltage drop was reduced from 1.2V to around 0.1V… major improvement opcorn:

Primary coil spike did not show an increase, however my equipment wasn’t suitable to capture such small width pulses, and I made a little circuit to protect my oscilloscope from blowing up that also inhibited a clear picture of the 400V spike.

For the secondary… I saw nothing that could be done except for putting in high quality spark plug leads. Better yet, would be coil-on-plug technology. The coils on the CBR250's are dual packs, and deliver a spark to two cylinders at once. This approach does however mean that a spark is wasted, as one of the cylinder will be on the exhaust stroke (although it's weak as it's low pressure with less dense ions). The spark plugs are screwed into the engine head, where this contact provides the ground reference. Engine is bolted to the frame and the battery negative is bolted to the frame... that's a rather descent ground path! So I’m not sure how providing more ground path could improve this system… perhaps it may provide a better reference point to keep the spark potential between the two spark plugs even. If anything, any additional ground should be connected to the engine head, not the coils… as there is no permanent ground connection on the coils anyway :huh:!!!

But… just because I don’t understand it, doesn’t mean that there can’t be some trickery at hand. So I installed two big 10 gauge wires from the battery to the coils holders… keep in mind, I still have the battery to frame link installed attached. Took some measurements on the oscilloscope… I could find no difference in the spark primary waveforms.

Below is what I ended up with. At the battery, you can see 3 big arse black leads on the negative, and a red one on the positive. You can also see the ground wires to the frame, bottom centre bolt. One for the battery, and the smaller two wires go straight to the CDI ground. The inline fuse is on the bottom left… red battery line.

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Below is the new wiring to the coils. You can see the grey ignition relay used, and the red wire from the battery connected to it. This relay switches the battery line straight to the two coils. Also notice the two big wires going to the bolts closest to the coils… these are the two big ground wires from the battery.

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All up, 3.13 metres of wire, 1 relay, 14 terminals and 2 full days of work from net searching through to typing this sentence :newspaper:

The additional wiring weighed a total of 378grams :-/


THE REAL RESULTS!


So I can’t afford a dozen dynos to prove what works and what doesn't . So I chose another method to compare… I strapped a video camera on the bike, and went for 16 rides to collect the needed info. Each test was performed at least twice to ensure consistency. I set the shift indicator to turn on the first light at 6,000rpm, and the last at 14,000rpm. I crept the bike in 2nd gear until the first light was lit, then snapped the throttle wide open until I hit the shift point.

I then ripped all the footage to an AVI, and stepped frame by frame through to capture the time stamp between the 2nd light and 7th light turning on. This method proved to be very consistent, though very tedious :dodgy:

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It all comes down to six numbers!!! How long did it take to accelerate a further 6,000rpm!

1. With no mods… it took 1.81 seconds.
2. With just the battery and CDI grounded to the frame, 1.82 seconds.
3. With #2 and one extra ground cable to the coils, 1.85 seconds
4. With #2 and two extra ground cables to the coils, 1.84 seconds.
5. With just the +ve ignition feed to the coils installed, 1.80 seconds.
6. With all the mods installed, 1.82 seconds.

So stuff all difference :lol: and any variation was probably due to the change in air temperature if anything!!!

The only mod that I found on the oscilloscope to have made a difference was the +ve battery feed to the coils. The bike certainly started easier, which is to be expected with an extra volt available. The CBR250’s don’t spark well at low voltage (like cranking with a low battery).

Even so… these results are for the CBR250’s. Other bikes which have poor grounding etc… could see real benefits. I’ve heard the TLR’s can get an extra 4-5HP from improved grounding, simple because their wiring is not well designed. But I think seeing some of the pictures showing an obsessive number of wires from some bikes are with good intention, but unfortunately, not all required. Actually just adding additional weight :lol:

Based on these results… I’d say if there were to be a noticeable benefit, it would be from the +ve feed to the coils, and a direct ground path from the battery to the CDI. Next time I take my tank off, I’II be removing one of the coil ground wires (remove 95grams), and probably fit two low gauge wires for the CDI coil drives.

Nakedchef gave it a go, and installed the ground wires. Reported easier engine starting and better performance... well worth it. So we may find differences between models! Will be interesting to see how he goes with the +ve feed to the coils.

Another thing to consider… we lose at least a volt for the headlights and horn. A project for another day! Until then, wakeup, your finished :sleepy: