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paris

Fri May 24 2013, 01:35AM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
Location:
Posts: 121

I never knew there was such a thing = learning some thing every day

swear to god Im not going off topic ...... Pendine sands (UK) is happening june 22 , 3 x Indians so far .

Ash Small

Fri May 24 2013, 09:30AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Thanks for that info Paris. The link to the official website for the event is here:

Will you be there?

EDIT: There is also this event for cars coming up in September:

EDIT: Paris, are you FLH on HAMB?

EDIT: There is a post (dated 5-11-06) in this thread comparing 90 degree and 76 degree cranks in the same parallel twin engine. The 76 degree crank was smoother. Offhand, I think the cylinder angle on a Harley is also 76 degrees. There is another thread on the same forum discussing the theory involved, somewhere.

EDIT: Here's a theory thread....not sure if it's the same one I read before, but loads of info:

Steve Conner

Fri May 24 2013, 04:06PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

What's the deal with the 180 degree crank? Does it make the firing times of the two cylinders close enough together that in a wasted-spark system they would both have ignitable mixture in them when the spark goes off? If this is the case, you could be shooting some impressive flames out of your carbs.

Ash Small

Fri May 24 2013, 04:21PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

What's the deal with the 180 degree crank? Does it make the firing times of the two cylinders close enough together that in a wasted-spark system they would both have ignitable mixture in them when the spark goes off? If this is the case, you could be shooting some impressive flames out of your carbs.

I think the theory goes something like 'because the two pistons aren't going up and down together, you don't need so much counter-ballance on the crank, so the crank is lighter, so acceleration is quicker. The 90 degree and 76 degree cranks mean you can go lighter again, as one piston is stationary while the other is at maximum speed'. The current discussion is over whether 90 or 76 is better.

I was reading yesterday that, if running on methanol with a wasted spark, the cylinder 180 degrees behind would also be ignited, but, according to that article, if running on petrol/gasoline, it wouldn't be a problem. I think I read earlier today that someone is running a 90 degree crank with wasted spark, but I'd have to check again.

So I may be able to run a wasted spark system after all. (but do I really want to waste sparks?...I might if I'm running a 'conventional' ignition system, but it may to too much for what I'm trying to build here.)

Steve Conner

Fri May 24 2013, 07:19PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Well, if you're willing to go to the extra complexity of two timing pickups, two amplifiers and two coils, there is no reason to use a wasted spark system. You'll get more power because each coil only fires one gap, and they have more dwell time to charge.

I still don't believe that a bigger spark can provide the same benefit as a knock sensor. Having a knock sensor to regulate the timing means the engine can run right on the edge of detonation all the time, giving the maximum fuel efficiency and torque.

Without the knock sensor, you have to set the timing so it won't detonate excessively at full throttle and low RPM. This can mean it ends up too far retarded for maximum power output. Retarded timing means the mixture gets ignited too late, and never gets a chance to do its work on the piston before it is thrown away down the exhaust. This is why the centrifugal advance was invented.

This probably doesn't matter a great deal in a racing engine that will always be revving in its powerband, and probably doesn't like running at low RPM anyway because of its racing cams. It is probably OK to set the timing for max horsepower and leave it there, but don't expect a smooth ride to the shops.

The only time a more powerful ignition system helps is as mentioned earlier, when high compression or supercharging give a charge so dense that a standard ignition system can't force a spark through it reliably.

paris

Fri May 24 2013, 09:18PM

Registered Member #3042 Joined: Wed Jul 28 2010, 12:36AM
Location:
Posts: 121

Ash = yep! I have a FLH , thats why Im interested in the out come of this . Theres 3 indians running at Pendine , one is Grizz on 27 Chout (chief Mot / Scout frame) be great to be there. Im building a 26 scout at the mo.
Im not gonna ask what your bike is I want to figure out the mystery in time, a who done it ? thread

Ash Small

Fri May 24 2013, 11:05PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve, firstly, mechanical advance/retard with bob weights and springs never worked, not as intended, anyway. At low rpm the ignition would be retarded (mostly), above 300rpm they'd be at full advance, and in between, where you want a smooth advance curve, they'd be all over the place, due to power pulses through the crank, and everything else that's going on. Electronic advance/retard is another thing though.

Secondly,while you are correct about most of the points you make, initially, I'll fit a manual advance/retard lever, which, in my opinion, is much better (in some applications) than any mechanical system. You are correct about the racing cams and high compression ratio, which is why I'll keep the ignition retarded so that it will be rideable around town, etc, where you don't require anything like full acceleration. This should also take the edge off of the exhaust, which will be 'anti-social' at the best of times. I've also not yet completely ruled out fitting a supercharger, although I have no short term plans to do this. (I would need to fit a 360 degree crank and cams first, unless I fit two blowers).

I'ts not so much the 'do I need it?' (who NEEDS a bike like this anyway?), but the 'can it be done?' and the 'What difference will it actually make?' that are the reasons for this thread. (and the other one on 555 timers, etc.)

And what was the reason you gave for building a Tesla coil?

I've built several points and coil based ignition systems in the past, it's time to try building an electronic unit.

Paris, It's only a couple of hours from here, I'll look out for the Chout.

EDIT: Steve, How would you drive the Z-FETS I mentioned in the 'other' thread?

EDIT: Paris, What is it with you New Zealanders and 'the world's fastest Indian'?

Steve Conner

Sat May 25 2013, 02:00PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

This reminds me of years ago when my dad and I finally figured out the ignition timing (or lack of) on the family Vauxhall Nova. It was never quite right since the conversion to unleaded fuel, which basically involved turning the distributor a bit to retard the timing.

Eventually we figured out that the timing was changing as the points wore down. At one extreme it would pull like a (1.0 litre

) train accompanied by loud knocking. At the other extreme it would buck like a kangaroo when accelerating away from traffic lights (no doubt due to the centrifugal advance) and refuse to start on cold mornings. Somewhere in between was a sweet spot, shrunken by the unleaded conversion.

The method we eventually came up with was to fiddle with the points and then razz up and down a steep hill to see how much power we were getting. If it knocked, the gap was too wide, if it bucked the gap was too narrow.

After 134,000 miles of this "tuning" method the car was a rust bucket but the engine was still going great.

Ash Small

Sat May 25 2013, 02:25PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Yep. that's the beauty of a manual advance/retard lever, you just adjust it to suit the conditions. I'm not saying it's better than a properly mapped electronic system, but it does give you more control.

This engine will need to be retarded, just to make it drivable around town, etc.

Steve Conner

Sat May 25 2013, 02:41PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I agree, a manual timing adjustment would certainly have been better than the random timing on the old Nova.

Might be tricky to implement on an electronic ignition system though. Maybe you could have a pickup that gave, say, 10 pulses spaced evenly over the range you would want to adjust the timing, a digital counter that would fire the ignition after N pulses, and a 10 position rotary switch to set N.

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