Spark Plug Gap..

[PJFZ1]

 What is it supposed to be?  I used the search and didn't find the gap.

[werase643]

i figured it would be in the wiki thingy


might be....


0.031-0.035 inch
0.8-0.9 mm

[ben2go]

I use 0.030 for cheap gas and 0.038 for premium.I really don't think it makes a difference as long as it's +/- 0.005 from 0.032.Correct me someone if I'm wrong.

[ohgood]

when you go to autozone for your plugs they can look up the spark gap for you.

that's a new one on me about a bigger gap for a higher octane gas. funny.

[ben2go]

when you go to autozone for your plugs they can look up the spark gap for you.

that's a new one on me about a bigger gap for a higher octane gas. funny.

It's one of those old racer secrets from days gone by.I don't really believe it works,but I haven't had problems doing it either.I also index my plugs on my automobiles.So maybe I'm just strange,wierd or some sort of an odd ball. 

[PJFZ1]

Higher octane = longer slower burn, and normally less overall power unless the motor has the copmression to require it. (I've tested this on the dyno)

Larger gap is better only if you have the coils and plugs to support it.

[kml.krk]

Higher octane = longer slower burn, and normally less overall power unless the motor has the copmression to require it. (I've tested this on the dyno)

Larger gap is better only if you have the coils and plugs to support it.

are you saying that by using 94 octane fuel I'm losing power? It doesn't sound right to me.
Can someone confirm that?
so far I've been using only the ultimate fuel (94 octanes I think)
what are you guys using?? regular, premium or ultimate??

[elric8467]

Octane, if I'm not mistaken, describes combustability. The higher octane the more combustable the fuel, the more easily and completely it burns, also helps deter detonation?

[Kerry]

I understand it to be almost the opposite.  The higher the octane, the higher the "flash point" (or whatever they call the temperature/compression point at which the fuel combusts).

Detonation occurs when the fuel combusts sooner than it should ... before it has been fully compressed and maybe even before the spark plug has "sparked".  Going to a higher octane prevents this from happening.

So ... an engine with a high compression ratio (volume of uncompressed fuel mixture / volume of fully-compressed fuel mixture) will need a higher octane fuel to keep the fuel from igniting too soon.  Our GS engines don't fall into the "high compression" category, to say the least.

Except when traveling through other states, I have watered Ole Yeller exclusively with 85 Octane for her whole 35,000 mile life.

[Kurlon]

Octane is a measure of how fuel burns in a test motor compared to two control fuels.  A 100 octane is equivilent in when it starts to knock to a 100% mix of one of the control fuels, 0 octane 100% the other, 50 would be a 50/50 mix of the two.  (I don't remember the control fuel names off the top of my head.)  Basically, a test motor is run until it starts to detonate on a given fuel blend.  Those results are compared against control fuel mixes, and that determines the octane rating.

To make things even more fun... there are two different ways to run that test, in the US we take the results of both and average them.  This is why you see the R = M / 2 math on gas pumps, Research and Motor Octane added together, divided by two equals the rated Octane.

Generally speaking, higher octane fuels require higher temperatures to autoignite, burn slower, and contain less energy per unit compared to lower octane fuels.  For any given motor, the lowest octane fuel you can run in it without detonation will produce the highest power.

Aha, but why do high performance vehicles require higher octane if it's a crappier fuel you ask?

Lets say our random 500cc low comp motor runs just ducky on 87 octane.  Pulling numbers out of thin air, we'll say 93 octane 'high test' has 4% less energy per gallon compared to that 87 octane fuel, so if you run it, you'll be down on power 4%.

Now, take that same motor, and lets bump the compression up from 9:1 to 12.5:1, high end sport bike territory.  You normally can estimate a roughly 2% power bump for each point of compression.  This puts our lowly 500 up by 7%.  Now you NEED 93 octane for this motor to keep from detonating, so by improving the combustion capability of that motor via compression, you're able to get more overall output by requiring higher octane fuel.  Your new, more efficient motor would turn it's internals into shrapnel on 87 octane.

[kml.krk]

I'm speechless My english does not allow me to absorb the data you've presented. Can you just write a conclusion in plain english? poor me I know...

Just say: -stay with ultimate
                                          or:
            -duuuude You gotta be usin' regular for better ride 

thanks

[PuddleJumper]

Here's a real easy way to remember:

Low compression engine........Use Low octane.

High compression engine........Use High octane.

BeSafe.

[Kurlon]

Try premium first.  If it doesn't ping, go down a grade.  If it still doesn't ping, go down a grade, repeat until it starts to ping, then go back one step.  If you get all the way to low test and it's not pinging, pat yourself on the back for being able to run cheap gas. : )

[ohgood]

1) install the proper heat range plugs.
2) 'install' 83 octane unleaded.
3) change the oil/filter every 3,000 miles.
4) adjust the valves every 4,000 miles.
5) install new rubber every 15,000 miles.
6) repeat steps 1-2 as needed, keeping steps 3-5 in mind.

Oh, and if you really think 105 octane is getting you more HP from your gs, or better fuel economy, or 'burning cleaner', you should get out more.

only 18,800 measly miles on the gs. ((top speed about 105))
only 143,000 on the camry. ((top speed about 110))
only 164,000 on the hilux (installing new timing chain stuffs) ((top speed dunno, it's a truck))
only 211,000 on the vtec accord wagon ( 30 MPG on the last 2000 mile trip @ 70-80 MPH sustainted ) ((top speed still about 120))

All of mine burn 87.

[CndnMax]

Try premium first.  If it doesn't ping, go down a grade.  If it still doesn't ping, go down a grade, repeat until it starts to ping, then go back one step.  If you get all the way to low test and it's not pinging, pat yourself on the back for being able to run cheap gas. : )

what exactly does pinging sound like?

[ohgood]

a very quick (frequency) 'pingity-pingity-pingity' that sounds somewhat metallic, but in the middle of the engine, top to bottem, usually immediately after opening the throttle fully, on a hot day.

think older ford V-8, and some blackish smoke coming out of the tailpipe on acceleration.

don't confuse it with valve lash noises. it's not that heavy.

nor do you want to confuse it with a piston wrist pin, it's not that expensive.

hope I helped.

[Kurlon]

a very quick (frequency) 'pingity-pingity-pingity' that sounds somewhat metallic, but in the middle of the engine, top to bottem, usually immediately after opening the throttle fully, on a hot day.

The other description I've heard, think of someone taking a screwdriver and dragging it across the cooling fins really fast.

[CndnMax]

got it  time to check the valves 

[bobthebiker]

IMO, the ONLY time high octane fuel is needed, or beneficial, is when you're running something like a really high compression muscle car engine, say a chevy 396 with a supercharger,  a GSXR1000 or busa,  or anything really that has a turbo.   

our little 500's are great, for a few reasons,  we can run em on the cheap(yeah right) gas, get fair fuel milage, and still have plenty of fun riding em.  they arent performance monsters, they dont go 150+, and therefore, dont require high octane fuel.

[kml.krk]

OK. I got you now. But I have one more question: what if you have tweaked your ignition advancer? customized one or V&H? whatever?? what then?? isn't higher octane fuel needed to avoid motor detonation?