Engine project

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maccas
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Re: Engine project

Post by maccas » Sun May 22, 2016 8:05 am

That looks quite a good result to me Doug!

Sort the clutch, play with the ignition curve some more to get it revving on and it may hit 60+ which is very respectable.

Dan

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bozbridge
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Re: Engine project

Post by bozbridge » Sun May 22, 2016 10:05 am

Thanks for the tip on clutch springs, I hadn't realised there was a stronger option and I've just ordered all the plates and springs. Hopefully that will sort it but if not at least there's more I can do!

Im really pleased with it as well Dan, thanks for the advice and help, it sounds really sweet and the fuelling is looking safe so hopefully next run we can coax some more from it ☺

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Re: Engine project

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JanBros
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Re: Engine project

Post by JanBros » Sun May 22, 2016 11:13 am

you should retard the ignition after 10.000 rpm, to get more overrev.
more retard means less heat used to push down the piston and more heat goes into the pipe. that again makes the waves go faster through the pipes, acting like a shorter pipe and extend the working of the pipe to higher revs resulting in more overrev :wink:
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bozbridge
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Re: Engine project

Post by bozbridge » Sun May 22, 2016 4:24 pm

Thanks Jan, I'll give it a go.. Hopefully if the clutch is sorted! I've copied some figures from Saturn's post just to compare (I appreciate the engines are very different) and put some curve figures in:
Image

I'll put the new curve on and see what difference it makes, just don't want to melt the front off a piston either :?

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Re: Engine project

Post by stevo135+ » Sun May 22, 2016 4:31 pm

I'm learning every day. This is interesting as I always thought that retarding the spark timing at high Revs was a feature used by manufacturers as a sort of soft cut rev limiter.

So what your saying is that retarding the timing is actually due to the temperature difference, fooling the engine into thinking it has a shorter pipe for better cylinder filling at high rpm past the natural peak power rpm?

Does this flatten off the peak power point and spread it over a wider rpm range, or is the peak still the peak, but the engine is capable of running past this rpm even with the power dropping away?

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bozbridge
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Re: Engine project

Post by bozbridge » Sun May 22, 2016 5:33 pm

I'm still figuring most of this out as well! As far as I get it the shockwave can travel faster through hotter gas, so if the ignition is closer to tdc (retarded) the gas exits hotter and allows the shockwave to return quicker so effectively shortening the exhaust and allowing to give more top RPM.. I could be wrong, Jan might explain it better.

Downside is headers get hotter, piston edge temp is higher and you can lose the front of a piston at the exhaust port if you go too far with it.

I tried retarding it a lot on the last engine playing on the road and after 1 run I could smell the paint on the headers, they'd already done a thousand miles since the repaint so I think it gave them an extra little bit of "curing", I backed it straight back down to where it had been. It did seem to rev out nicely though :shock:

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Re: Engine project

Post by JanBros » Sun May 22, 2016 10:47 pm

bozbridge wrote:I'm still figuring most of this out as well! As far as I get it the shockwave can travel faster through hotter gas, so if the ignition is closer to tdc (retarded) the gas exits hotter and allows the shockwave to return quicker so effectively shortening the exhaust and allowing to give more top RPM.. I could be wrong, Jan might explain it better.

Downside is headers get hotter, piston edge temp is higher and you can lose the front of a piston at the exhaust port if you go too far with it.

I tried retarding it a lot on the last engine playing on the road and after 1 run I could smell the paint on the headers, they'd already done a thousand miles since the repaint so I think it gave them an extra little bit of "curing", I backed it straight back down to where it had been. It did seem to rev out nicely though :shock:
nope, couldn't have explained it better.

if its only a roadbike, no real use for overrev of course. it only is needed on a track to get that bit extra without having to go up a gear before the next corner.
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Re: Engine project

Post by maccas » Sun May 22, 2016 11:35 pm

Personally i don't think you'd ever damage an engine by retarding the ignition. Starting the burn later means there is less time for the combustion to heat up the piston, meaning damage is less likely. Advancing the ignition is the dangerous one to try!

Dan

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Re: Engine project

Post by scooble » Mon May 23, 2016 8:08 am

in my experience testing fully instrumented engines (mainly 4 strokes), there was always a danger of damaging the exhaust valves or turbo if ignition was to far retarded due to the excessive heat.
Typically on a two stroke, the engine tends to sieze on the exhaust/thrust side, and retarding will also contribute to this.
It was always a balancing act though at full load and high speed, because although advancing it reduces exhaust temperatures, it did increase the likelihood of detonation as you could see the cylinder pressure increase, and then if your not careful, can lead to self ignition were it doesn't even need a spark before going on to spitting the engine contents all over the test cell

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Re: Engine project

Post by JanBros » Mon May 23, 2016 9:39 am

a better way to get more heat in the pipe to get more overrev , is to reduce the spark energy when the power starts to drop. But I don't think a Zeel can do that ?
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Re: Engine project

Post by maccas » Mon May 23, 2016 11:20 am

In 4 strokes I totally get that it could cause issues.

On my 3xv i'm igniting at TDC at 12k. No issues. I'd have gone negative advance if I could but the zeel doesn't allow that.

h***a on some of their race bikes went to as much as 3 degrees after TDC. I still don't think retarding the ignition can cause a seizure, quite the opposite surely?

Dan

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Re: Engine project

Post by scooble » Mon May 23, 2016 3:37 pm

maccas wrote: I still don't think retarding the ignition can cause a seizure, quite the opposite surely?

Dan
having seen exhaust temperature shoot up to over 1100 Deg C, I suspect that kind of heat for any engine isn't good for it

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Re: Engine project

Post by bozbridge » Mon May 23, 2016 4:17 pm

Is anyone willing to go to 0 degrees to find out for me :lol: :lol:

It's a balance all the way up through I guess but I'm going to try an advanced and retarded curve on the Zeel next time and switch straight between the 2 to see what affect they have.

Spoke to Mick today and I can likely get some more time pretty soon after the bank holiday, he's not sure if it was clutch slip on all the runs (def on one or 2 when the gearbox wasn't fully up to temp as you could hear the revs peak up) but it suggests the clutch isn't great so might as well change it and see. He said the software might just make the curve look like a step drop but I was hoping peak power might be closer to 10,500.

More news when I get some results :)

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Re: Engine project

Post by maccas » Mon May 23, 2016 6:45 pm

scooble wrote:
maccas wrote: I still don't think retarding the ignition can cause a seizure, quite the opposite surely?

Dan
having seen exhaust temperature shoot up to over 1100 Deg C, I suspect that kind of heat for any engine isn't good for it
Was that in a 2 stroke though Tricia? Not sure exhaust gas temps get that high in a two stroke?

Dan

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