The building of my vintage racer

[bmweuro]

Originally Posted by pommie john

I'm not disputing your power outputs, I'm asking if you have direct comparison dyno charts for single and dual plugs.

Sorry, I do not. I have never been a fan of dual plugging.

Originally Posted by FreeTheBeast

I'd like that kind of power... :~)

It's not cheap.

[Airhead Wrangler]

Originally Posted by pommie john

I'm asking if you have direct comparison dyno charts for single and dual plugs.

I doubt you'd see much difference in HP just between single and dual plugged. The addition of another plug in and of itself doesn't really bump power up much if any. It allows a faster and more complete burn with less advance. This will result in an engine producing less waste heat and which will run cooler. Because it runs cooler it allows you to bump up compression with less likelihood of pinging. Bumping up compression WILL increase your power. So in short it's not the plug that gives the power, but the higher compression the additional plug allows that'll give you power. Also, as BMWeuro stated, twin plugging is more useful in 1000cc engines as the flame front has farther to travel in the wider bore of these engines and thus a second ignition point and two flame fronts will show a greater improvement there than in smaller 750 and 800cc bores.

[supershaft]

And then a strict comparison of just the additional plugs wouldn't make much if any difference at all more than likely. The whole point of dual plugging is raising the compression even higher and getting the setup to make peak power running a more retarded ignition timing. Both generally net more power. Hell, if I set up a racing engine I would reverse offset the piston bores Smokey style for closely related reasons. It does work! But I would long rod one too. That works big time again for closely related reasons. It's granted that generally larger displacements have more detonation issues because flame front travel times remain relatively constant despite displacement but there are still advantages to be had there in a 750 IMO as well as many others but to each there own.

[bill42]

Is it any wonder that a guy who calls himself SuperShaft is such an expert on DP'ing?

Oh oh. FLAGGED.

Originally Posted by supershaft

And then a strict comparison of just the additional plugs wouldn't make much if any difference at all more than likely. The whole point of dual plugging is raising the compression even higher and getting the setup to make peak power running a more retarded ignition timing. Both generally net more power. Hell, if I set up a racing engine I would reverse offset the piston bores Smokey style for closely related reasons. It does work! But I would long rod one too. That works big time again for closely related reasons. It's granted that generally larger displacements have more detonation issues because flame front travel times remain relatively constant despite displacement but there are still advantages to be had there in a 750 IMO as well as many others but to each there own.

[supershaft]

Originally Posted by Airhead Wrangler

I doubt you'd see much difference in HP just between single and dual plugged. The addition of another plug in and of itself doesn't really bump power up much if any. It allows a faster and more complete burn with less advance. This will result in an engine producing less waste heat and which will run cooler. Because it runs cooler it allows you to bump up compression with less likelihood of pinging. Bumping up compression WILL increase your power. So in short it's not the plug that gives the power, but the higher compression the additional plug allows that'll give you power. Also, as BMWeuro stated, twin plugging is more useful in 1000cc engines as the flame front has farther to travel in the wider bore of these engines and thus a second ignition point and two flame fronts will show a greater improvement there than in smaller 750 and 800cc bores.

As I understand it, there is less pinging because the twin flame fronts allow less time for the unburned portion in FRONT of the flame front to overheat and detonate versus burn. That unburned part of the mix in front of the frame front gets super compressed and the molecules break down. That is what causes detonation. That's why you can always see the piston melting around the very edge first. What's going on behind the flame front is a burn. You don't want the remaining fuel for that on coming flame front and burn to disappear in a bang right in front of it. It cuts way down on the push and PUSHING that piston is what makes torque and torque times rpm is HP.

I forgot to add ignition timing. That is a big part of the extra power too. You can generally determine the efficiency of a combustion chamber by it's peak power ignition timing. The more retarded it is, the more efficient it is. Peak power ignition timing drops dual plugged 750 or 1000cc's. Perhaps not as much with a 750 versus a 1000 but gains are there for the taking IMO.

[ericrat]

I wish I had the time and money to test more of this stuff... I sure many of you do to. Last time I went from singles to dual plug it was also from worn out head to fresh seat and guides. Not much of a test. It is so very hard to truly do one thing at a time.

I have a hypothesis that dual plugging is more of an advantage at lower RPMs when there is less turbulence to spread the flame front then at high RPM where turbulence assist with rapid combustion. Couple this with the idea that spark advance is stopped at higher RPMs because turbulence takes over and spreads the flamefront more quickly for us.

I wish I had more to add than that, but that is what has been rolling around in my head as I think about buildin my next race engine.

Eric

[supershaft]

Originally Posted by bill42

Is it any wonder that a guy who calls himself SuperShaft is such an expert on DP'ing?

Oh oh. FLAGGED.

I got that moniker from an old girl friend I had while I was working at San Jose BMW. Some of my friends don't believe me and I let them go on for a bit at my shop and then I take a well done drawing of a beemer off my shop wall and show them the back of it were I am fondly referred to as "Supershaft". The hand writing is obviously a women's. She is a tattooist. Anyway, they usually then go into ultra-denial. I got out of that relationship without a single mark!

[supershaft]

Originally Posted by ericrat

I wish I had the time and money to test more of this stuff... I sure many of you do to. Last time I went from singles to dual plug it was also from worn out head to fresh seat and guides. Not much of a test. It is so very hard to truly do one thing at a time.

I have a hypothesis that dual plugging is more of an advantage at lower RPMs when there is less turbulence to spread the flame front then at high RPM where turbulence assist with rapid combustion. Couple this with the idea that spark advance is stopped at higher RPMs because turbulence takes over and spreads the flamefront more quickly for us.

I wish I had more to add than that, but that is what has been rolling around in my head as I think about buildin my next race engine.

Eric

The only way I can/could afford to do most of this stuff is doing it for hire. I have never had my own TIG welder, my own dyno, my own machine shop or my own real sheet metal equipment! Get out there and do some good work! Listen and learn along the way! And READ!

[Voltaire]

Originally Posted by Airhead Wrangler

I doubt you'd see much difference in HP just between single and dual plugged. The addition of another plug in and of itself doesn't really bump power up much if any. It allows a faster and more complete burn with less advance. This will result in an engine producing less waste heat and which will run cooler. Because it runs cooler it allows you to bump up compression with less likelihood of pinging. Bumping up compression WILL increase your power. So in short it's not the plug that gives the power, but the higher compression the additional plug allows that'll give you power. Also, as BMWeuro stated, twin plugging is more useful in 1000cc engines as the flame front has farther to travel in the wider bore of these engines and thus a second ignition point and two flame fronts will show a greater improvement there than in smaller 750 and 800cc bores.

Nicely explained

[moorespeed]

more compression in a race engine only gives extra power up to a point, after that the engine just starts to get harsh. and as for twin plugs, i have never seen any gains, so i stick with single plug even on my bored and stroked engines.

[Voltaire]

Originally Posted by moorespeed

more compression in a race engine only gives extra power up to a point, after that the engine just starts to get harsh. and as for twin plugs, i have never seen any gains, so i stick with single plug even on my bored and stroked engines.

Are you Moorespeed as in http://www.moorespeed.co.uk/ ?
Can you tell us about your racebike?

Is it time for me to bin my 336 cam and move on?

[pommie john]

So what is the consensus of a good power figure from a single plugged 750 full race engine?

[pommie john]

Originally Posted by Voltaire

Is it time for me to bin my 336 cam and move on?

I would say not. The 336 is a good cam.

[bmweuro]

Originally Posted by pommie john

So what is the consensus of a good power figure from a single plugged 750 full race engine?

If you talking about horse power high 50's low 60's.

[pommie john]

Originally Posted by bmweuro

If you talking about horse power high 50's low 60's.

You want to try dual plugs, high 60s.