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#620530 - 10/04/15 10:42 pm What effect does compression have on timing? plugs  
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441/R3cafeSteve Offline
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Just fishing for peoples opinions and tips relating to compression and timing and or mixture effects. Does high compression benefit from hotter plugs? I am running a NC3 after having issues at lower revs with B8ES plugs.
S


The 441, most versatile BSA of the 60's
#620555 - 10/05/15 4:00 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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More compression usually needs less advance. I've been running two grades hotter plug in my A65 Steve, otherwise it can soot them, maybe related to less adv at low RPM, because it moves back as well. I'll go a grade colder when I put the new head on. The thing runs probably half on the idle circuit a lot of the time. Its the same stroke as a Commando running about 28deg total adv. I think they run hotter plugs. I can run more advance and get better economy but it then loses top end power.


mark
#620557 - 10/05/15 4:57 am Re: What effect does compression have on timing? plugs [Re: Mark Parker]  
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Triless Online content
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OZ
Well, this is pretty old school from years back, and as such I will be decimated by some of the cognoscenti who consider me a no hoper.
Now, as Mark Parker said, with high compression, the combustion, flame propagation, and all that stuff, happens quicker But, in my case with a highly compressed metho burner BSA ZB 33, alcohol, having a higher latent geat of evaporation, therefore being slow burning, this had a bit of a negating effect, so I settled on 36 degrees. This was also running fixed ignition, with a Lucus SR 1 magneton ( but initially, with a BTH TT mag, with variable ignition.)
Now, heres the rub, initially I used a very cold Champion retracted gap racing plug. That was the advice given way back then ( 1971).And I forget the actual nomenclature of that plug, but it was so cold it would practically stick to you fingers( joke! ).Now, in light, that plug should have been warmer.So, Marks comments are interesting.
So, the reason for all this bullshit, yes, compression does affect igntion timing and plug heat range considerations.

Last edited by Triless; 10/05/15 5:01 am. Reason: spelling
#620570 - 10/05/15 6:38 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Hillbilly bike Online content
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Running from demons in WNY
Did the 11-1 compression Triumph TT use the same timing as the 9-1 compression T-120?

My 10.5 compression 650 Triumph LSR bike makes best power at 39 degrees advance. NGK B9EG plugs never foul even after low speed running..030 plug gap with a Pazon Smart fire ignition. I use VP C12 leaded race fuel that is fast burning along with lean jetted Mikuni flatslides...
A wider plug gap can have the same effect as advancing the timing slightly.

Yes, I believe more timing enhances mid range, a bit less for top end power.
With autos,higher compression engines runner cooler at part throttle than the same engine with lower compression...


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#620675 - 10/05/15 7:40 pm Re: What effect does compression have on timing? plugs [Re: Hillbilly bike]  
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Originally Posted By Hillbilly bike

A wider plug gap can have the same effect as advancing the timing slightly.



The same effect as Retarding the timing by mili-seconds. You now have to wait for the coil to charge to a higher voltage to bridge , and you also have to account for the gap size to be bridged, and the time it takes to bridge that gap.

This in effect will dump heat from the cylinder into the pipe. BUT it can also reduce detonation in a higher compression engine

The answer to the question is really, as pressures increase so does the voltage required to bridge a set gap. At least in our applications.
This is set by Paschen's law...

#620678 - 10/05/15 8:00 pm Re: What effect does compression have on timing? plugs [Re: Zombie]  
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Running from demons in WNY
Originally Posted By Zombie
Originally Posted By Hillbilly bike

A wider plug gap can have the same effect as advancing the timing slightly.



The same effect as Retarding the timing by mili-seconds. You now have to wait for the coil to charge to a higher voltage to bridge , and you also have to account for the gap size to be bridged, and the time it takes to bridge that gap.


This is set by Paschen's law...



The wider gap acting like advancing timing is a statement made
by many professional engine tuners.It's got to do with the time it takes for the spark to ignite the mixture.


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#620682 - 10/05/15 8:28 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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For what its worth I've used Champion G57R plugs in my Weslake pushrod engine. 540cc single. 13:1 comp. with 36 deg. fixed advance. I use VP 110 or ERC 110. I tried going beyond 36 deg. but the engine didn't want to know about it. No problems so far and no plans to mess with what works. 134 on gas works for me.


God rides a Triumph but wishes it was a Norton.
#620684 - 10/05/15 8:52 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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I think the results you guys are getting regarding advance/mid and low range power is due to dynamic compression variation but i am probably talking crap eh?

As for sparks, the time taken for a plug to ionize with a 35 thou gap rather than a 25 thou gap (providing there is sufficient energy to do the job) is microseconds or decimal points thereof.
The fact that the spark has a higher energy will give you the effect of advancing the ignition as the gas will be ignited faster. HEI ignition systems impart the largest energy into the spark (at present) and use the required very low impedance primary coils with monitored charge current. Once the spark has been generated it's the design of the chamber etc that governs the burn rate but the largest energy spark will ignite the gas faster and more reliably at the required time.
Using a large accelerator pump in a carb will effectively retard ignition in use as the over richened mixture when it is operated will slow combustion, this method was used to prevent pinging by many race bikes/cars. (In times of old anyway.....)



#620701 - 10/05/15 10:13 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Florida PanHandle
I absolutely can see how this is correct, and combines the facts behind both sides of the same coin.

Same for Noisy Nortons post... By slightly retarding the timing you are dumping heat away from the piston, and preventing detonation.
At the same time you have enough inertia in the piston to negate the later than 14* ATDC prime velocity.

In essence you could/would make more power at the Std. timing if you had the fuel to handle the higher compression ratio but the difference is still better (more usable power) than a lower compression set up.

Thanks for tying that up NickL.

#620703 - 10/05/15 10:32 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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One thing I noticed when retarding the points yes points and putting in hotter plug the slight drop at throttle blip disappeared. If I just lifted slide slightly it had been dropping idle even cutting out (this made me think at sub 800rpm the inertia was not there to fire against the compression, it would chuff/bog to a stop). Before buying a new carb I wanted to try the plug and timing. I bent the advance spring T's on ATD out to increase spring pressure as well. I'll add a rev video tonight. Plug chops next if I get some daylight hours to do it. LOL! Excellent technical points guys!
S


The 441, most versatile BSA of the 60's
#620711 - 10/05/15 11:40 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Florida PanHandle
Originally Posted By 441/R3cafeSteve
One thing I noticed when retarding the points yes points and putting in hotter plug the slight drop at throttle blip disappeared. If I just lifted slide slightly it had been dropping idle even cutting out (this made me think at sub 800rpm the inertia was not there to fire against the compression, it would chuff/bog to a stop).
S



To me that just sounds like an idle mixture problem.

Retarding at or near idle will simply drop the rpm more than have any other effect.

Plug chops are a great idea at this point.

Have you put a proper timing light on it to verify the correct timing before making this change? I only ask because near idle is where so many potential issues can overlap that it is easy to compensate for the problem with the wrong solution.. I'm thinking that if a hotter plug helped it may be oil fouling or too rich at idle, and the initial timing may have been too far advanced anyway.

If a twin cylinder bike is too far advanced it will sound like a drummer on a slave ship. Lump, Lump, Lump, and increasing the idle just increases the beat. It will often die with a burst thru the carb when you snap the throttle
Too far retarded, and it sounds like muffled hum with no real "crack" at the throttle/slower revving.

You may well be correct, and have the issue nailed. I'm just putting in 2 cents from another point of view.

#620733 - 10/06/15 4:16 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Always makes me think of a great tuners comment.....

'Wouldn't it be lovely if all engines required the same advance curve eh?'



#620741 - 10/06/15 6:36 am Re: What effect does compression have on timing? plugs [Re: NickL]  
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I don't know much but I will say what I know.....I thrashed the 650 Triumph LSR bike for hours on the dyno...It made best HP on lean jetting and 39 degrees advance @7250 rpm. ..The torque peaked @5100 and stayed within 90 percent until 7050 RPM when it fell off rapidly
At the one track I geared the bike for for the HP peak and it ran very well..Then at the 1-1/2 mile track I regeared the bike figuring it would run 5 mph faster.....
It ran about 3.5 mph faster on the longer track...But what was more interesting, the one mile speed increased 1.5 mph although the engine was turning about 7000 rpm rather than 7250....
So...it's torque that moves the bike on the track ....


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#620743 - 10/06/15 7:06 am Re: What effect does compression have on timing? plugs [Re: Hillbilly bike]  
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Triless Online content
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OZ
Well,Tony, it seems when its all said and done the track is the crucial dynometer!

#620744 - 10/06/15 7:20 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Can't argue with that, the type of racing i was involved in was very different, mid range power was far more important than dyno busting flat out performance. Tuning my bike for more HP and torque (which i know could be done) would have made it even more difficult to make the amount of meetings a championship required. It's all about compromise and money! The time i spent on a dyno was really to get venturi sizing and jetting correct between 3.5-6.5k at different ambient temperatures.



#620749 - 10/06/15 7:51 am Re: What effect does compression have on timing? plugs [Re: NickL]  
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Running from demons in WNY
The famous drag racer Grumpy Jenkins said something like this
Quote:
Tune all day Saturday on the dyno and lose on Sunday at the track.


The dyno is just a tool and helped me to get the tune up sorted out.On the track I always ran the timing and jetting from the dyno except for the last run at 1-1/2 mile track...Went up one jet size and the bike went about .5 MPH faster
The bike does not have the long pipes and megaphones used by the competitors...Unknowingly,I built and tuned the engine for torque rather than top end power but never fully realized this until the runs at the 1-1/2 mile track....


650 Triumph modified production LSR record holder 133.1 MPH... Twin 650 engine Triumph LSR that goes sorta fast...
#621123 - 10/09/15 12:07 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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It's close to fixed now, I had a carbon core spark plug lead and maybe an issue with crimps so I put on a lead from an outboard with copper core and starting is easier. Chocolate brown tip on the Nc3 and this plug is a BP7es NGK. Turn up volume! :o) It loads up after start with pops and blue flame but then as you can hear it clears it's throat and runs clean. I need a new battery for revving at night but I should not be up in this range doddling home.

I know where an RT450 is but the 441 still sounds a bit sweeter, this one starts at 2:00 in and this guy's owned it 23 years. If you pause each clip at revs the sound is very similar despite valvetrain set-up. I get a lot of Italians in the area that swear it is an old Duc when they see or hear my 441. Cocktail Campbell muffler with 4- 1/2" holes drilled in end cap.

S


The 441, most versatile BSA of the 60's
#621154 - 10/09/15 11:48 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Florida PanHandle
I'm no expert but it sounds to me like the timing is a bit retarded.

I would mess with timing, idle mixture, and then reset the idle speed.

I think it will start easier, and rev more freely. The big bonus for you is in the solid core wires. I would go to stainless steel, and IF required... resistor plug caps.

side thought... 7's are pretty hot plugs. They do well in hot climates or high altitude for bikes that run well at sea level or are tuned for moderate temps. I tend toward 9's, and leaner jetting to avoid fouling, and get a bit more "pep" out of the engine.

Base line tuning at moderate temps is best done with 8's, and as your season gets colder you can switch to 9's, and keep your jetting as is.
7's are more for hot summer months, high altitude, or racing with richer mixtures/on-off the throttle that causes cylinder loading.

Before anyone asks, "Hot plugs, and hot months?" The air is less dense in hot months or at higher altitudes so the fuel/air mix is richer. The hotter plug burns that rich mix better.

Since you are at a coffee color now, going to an 8 will show darker... Maybe too rich but I believe too far retarded on the timing.
Just my thoughts on the vid.

#621347 - 10/10/15 9:08 pm Re: What effect does compression have on timing? plugs [Re: Zombie]  
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Thanks Zombie, I an working with used points and very worn carb so may improve those now to have a better start at tuning but with the miles on these compensating may be the best I can do. Cheers,
Steve


The 441, most versatile BSA of the 60's
#621348 - 10/10/15 9:20 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Florida PanHandle
A work in progress then...

It's like getting a whole new bike when each new part makes a notable difference.

Now lot's of systems will cross over, and give good or bad results when trying to dial it all in. It's easy to get false positives as in advancing the timing to compensate for a rich carb at idle...

Plug chops, and a pocket full of new plugs are your best friend for initial set ups. Compression tester, timing light, coil gap tester are my number 2-3-4 buddies.

I may be a million miles off in my "diagnosis" over the net so tools to verify everything are needed. You're obviously on the right path tho.

#621484 - 10/12/15 6:51 am Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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My thoughts, the Beesa sounds flooded when it starts up, lots of exhaust woofing suggests unburned fuel. How bad is the carb? a new slide may fix it, I have fitted the plated brass slides from Surrey cycles to my fairly worn carb bodies ( as found the pot metal slides were finished), the bike idles very well and is pretty much fuss free now.
I had the same HT fault last year, Silicone HT leads , what is the point of them?, the copper cored restored normal performance.


71 Devimead A65 750
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#621502 - 10/12/15 11:57 am Re: What effect does compression have on timing? plugs [Re: gavin eisler]  
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Florida PanHandle
Originally Posted By gavin eisler

I had the same HT fault last year, Silicone HT leads , what is the point of them?, the copper cored restored normal performance.



The silicone is only the jacket-ing material.
The core is the issue. It's a combination of graphite, and strand fiberglass.

The composition is set so as to have a predetermined resistance over a given length. Just far example, 500-Ohm per inch.

The main reason is to eliminate electrical noise. That noise you used to hear in AM radios that buzzed up, and down with the engine's rpm.
Today they (resistor wires) are mandatory on engines that use micro processors to control the engines. Those micro processors are sensitive to this "noise", and will not run correctly, if at all without resistor wires.

For non electronically controlled engines/ignitions, resistor wires are NOT recommended.
Now here's another twist... Many electronically controlled engines including most late model motorcycles (mid 1970's, and up) will use resistor spark plug boots , and solid metal HT wires. The resistive boots alone are enough to knock down that noise. Usually in the 5k Ohm range.

All that is really done is the HT voltage is reduced to a point where the plug can fire without having excess voltage, and larger, noisier spark.

#621505 - 10/12/15 12:28 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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John Healy Online content
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On motorcycles resistor wires are not recommended by people who make Old British bike Electronic Ignitions This is because they are prone to cracking internally. In cars this type of wire is supported every few inches and isn't left flapping in the air. Of course if you wish to support your resistor wire plug cables every 4 inches you probably wouldn't have a problem.

What they do insist on wither the units that are digital (not analog like Boyer MKIV - black box) units are 5,000 ohm resistor caps. Failing to use some form of RF suppression and the units will not work!


#621508 - 10/12/15 12:40 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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Unless you are looking for problems you always select the grade spark plug by the factory recommendations or based upon any change you made that would require a colder plug. Raising the compression is just one of those factors.

Unless you are looking for a good case of pre-ignition never select your grade of spark plug to solve a fouling issue whether it be gas or oil.

If the manufacturer recommended an N3 (B8ES is the NGK equivalent) and you have raised the compression and the bike is having plug fouling problems FIX the reason it fouled. Do not change the grade of plug and think you found a solution!


#621520 - 10/12/15 2:36 pm Re: What effect does compression have on timing? plugs [Re: 441/R3cafeSteve]  
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The only thing I can add with the suppressed cap issue is this:

My strobe like is the Gunson all singing and dancing with Rpm read out etc.

Using non resistor caps and EI and the read out consistently gave me BS readings. With resistor caps it read correctly.

However, when I ran points ignition with no resistor caps the read out was fine. If it wasn't for the strobe light read out I probably would be using non resistor caps, although now we are using digital tv signals and not analogue the electrical interference no longer effects the TV. - which as a youngster was quite funny.


beerchug
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