180lbs. compression. what octain recommended.

[jcs003]

i know some will say 180 is borderline race fuel. what are you fellas facts and opinions?

[troybilt]

Opinion... race fuel VP110, MRX01, or C12 if cost is an issue, VP RED or just 97 octane fuel.

[atvmxr]

I hate to type this but I think the oil:fuel ration makes a difference too. I run 50:1 in my LRD National motor with 93 octane for 15 years or so... I think the 32:1 pulls the octane down to where you need race fuel because LRD would swear up and down that the motor needed race fuel - but it didnt

its probably best to run race fuel, but you might be able to get by with pump gas - just watch your coolant temps, check the plug, and listen for deto...

[jcs003]

what are symptons of detonation? im in the break in period and know temps will be slightly higher typically.

[derby]

Originally posted by jcs003
what are symptons of detonation? im in the break in period and know temps will be slightly higher typically.

I would not be too concerned just yet. I ran my 67mm stock stroke with 200lbs compression on 91 octane for nearly 5 years. Actual compression check is not an accurate measurement for saying whether a bike needs race gas or not.

Detonation will make a distinct sound. The spark plug will start backing out no matter how tight you get it. You can usually see metal fragments(aluminum from the piston) on the the spark plug.

[jcs003]

Originally posted by derby
I would not be too concerned just yet. I ran my 67mm stock stroke with 200lbs compression on 91 octane for nearly 5 years. Actual compression check is not an accurate measurement for saying whether a bike needs race gas or not.

Detonation will make a distinct sound. The spark plug will start backing out no matter how tight you get it. You can usually see metal fragments(aluminum from the piston) on the the spark plug.

my plug is gray not brownish and i have been only cruising as im breaking in the motor. according to pics i have seen light gray and light brown is a good sign.

[fearlessfred]

Originally posted by atvmxr
I hate to type this but I think the oil:fuel ration makes a difference too. I run 50:1 in my LRD National motor with 93 octane for 15 years or so... I think the 32:1 pulls the octane down to where you need race fuel because LRD would swear up and down that the motor needed race fuel - but it didnt

its probably best to run race fuel, but you might be able to get by with pump gas - just watch your coolant temps, check the plug, and listen for deto...
x2 more oil does lower octain i use to run 32 to 1 and 50 50 100 octain and pump gas , so that would make it about 96 .i ran about 180 pounds with the 89 cr head gasket. i would suggest running a colder plug also

[jcs003]

Originally posted by fearlessfred
x2 more oil does lower octain i use to run 32 to 1 and 50 50 100 octain and pump gas , so that would make it about 96 .i ran about 180 pounds with the 89 cr head gasket. i would suggest running a colder plug also

cooler plug??? br9es?

[fearlessfred]

Originally posted by jcs003
cooler plug??? br9es?

yeap,any time u raise combustion temps by raising compression or any other means u would want to run a colder plug.i use to run a 10 when i use to race up comp hill at dumont on a three wheeler.

[troybilt]

Originally posted by fearlessfred
yeap,any time u raise combustion temps by raising compression or any other means u would want to run a colder plug.i use to run a 10 when i use to race up comp hill at dumont on a three wheeler.

Wonder if I should go up to a 9. Makes me worried. I'm running 215 psi with 110 octance 32:1 with br8es

[fearlessfred]

i wouldnt worry,but would definitly go with the 9. and then recheck wot plug readings,because it will require over all jetting to be more spot on. go on ngk site and search around,and some were on there it will tell u the same things i have just told u. i believe one step colder is good for around 60 degrees colder combustion temps. most people confuse plugs heat range with how strong the spark is,and of course the heat range has nothing to do with how strong the spark is.u could possi. run slightly less octain after going to a colder plug.my reason for saying this is because detonation and pinging are two diff. things. if your need for that high of octain was because of detonation then a colder plug could help reduce detonation ,but if the need was because of ping ( the flame front meeting the piston before it starts its downward travel ) then your need for that high of octane has not changed. when we run to high of octain than what is needed for that perticular motor than we actualy paying good money for less performance

[atvmxr]

so if your running lower compression you could go with a hotter plug? I have been meaning to start a thread on the subject of hotter vs cooler plugs and what they are doing and such...


the LRD motor I was referring to earlier, I also ran a Champion N4C, same heat as a BR7. like I said, it was a purple squirrel, high compression on pump gas, 50:1 oil ratio, champion plug, hotter plug, all the things you arent supposed to do. but it ran hard and was super reliable

[troybilt]

Originally posted by atvmxr
so if your running lower compression you could go with a hotter plug? I have been meaning to start a thread on the subject of hotter vs cooler plugs and what they are doing and such...


the LRD motor I was referring to earlier, I also ran a Champion N4C, same heat as a BR7. like I said, it was a purple squirrel, high compression on pump gas, 50:1 oil ratio, champion plug, hotter plug, all the things you arent supposed to do. but it ran hard and was super reliable

Its a good topic there is lots of theories out there. See around my neck of the woods we ran hotter plugs, Br8es, even B7's depending on fuel mixture. My stock motor was mixed at 20:1 and I ran a B7. Don't have a particular reason other than that's what I was told at the time.

[fearlessfred]

Originally posted by troybilt
Its a good topic there is lots of theories out there. See around my neck of the woods we ran hotter plugs, Br8es, even B7's depending on fuel mixture. My stock motor was mixed at 20:1 and I ran a B7. Don't have a particular reason other than that's what I was told at the time. well think of it like this,for what reason would u want higher combustion temps.the only one that comes to my mind is to keep the plug clean and i do believe that is the only one. i guess im asumming that anyone that is pumping his motor up is running wide open most of the time.mabe im wrong.so if u are puttin around u dont need a colder plug and if u are running more oil i would guess u might need to stay with an 8. i would try the 9. the oil recommendations was 20 to 1 with the standerd 8 plug. the only time u would need a 7 is with slow warm ups in the cold and for putting around.i have never heard of an engine builder of any kind recommend a hotter plug for a high performance motor,most two stroke builders do have s tendency to set them up fat on the main

[derby]

Back to the original question that I did not get a chance to answer completely. In my opinion the decision to run pump gas or race gas is dependent on your compression ratio. With that said you can usually get away with 91-93 octane with comp ratios of 12 to 12.5:1 and lower. Anything higher than that with the ignition setup on the 250r you need to jump to at least 108 or 110 if you have anything 13:1 up to 14.5:1. Of course methanol can usually be run up to 17:1.

If you are good with your math then you can do some calculating to find your comp ratio.

This has always been the method I have used for uncorrected comp ratio as this makes more sense to me instead of the Japanese corrected ratio nonsense.

1st you have to have to find total cylinder volume:

Cylinder volume = [(πD2 x S) / (4000)]

π= 3.1416
D= diameter of the bore in mm(you must square this # not multiply by 2 the forum will not do a superscript for some reason)
S= stroke in mm

Now you should have the cylinder volume you will use that in the next equation

Compression ratio = [(CV + CCV) / (CCV)]

CV = is the cylinder volume you calculated in step one
CCV= is the combustion chamber volume in cc’s (with the piston at top dead center). Usually measure this using a dial indicator, vegetable oil, and a syringe. Once you get the piston at top dead center, torque the head down with the gasket then fill the head with vegetable oil all the way up to the base of the plug threads taking note how many cc’s of vege oil you used. That should give you a pretty accurate CCV.

[fearlessfred]

http://www.ngk.com/charglossary.asp?kw=Heat+range

[derby]

Originally posted by troybilt
Its a good topic there is lots of theories out there. See around my neck of the woods we ran hotter plugs, Br8es, even B7's depending on fuel mixture. My stock motor was mixed at 20:1 and I ran a B7. Don't have a particular reason other than that's what I was told at the time.

Man you guys are talking about my favorite topics tonight.


The difference is just what it sounds like. A hot plug transfers combustion heat slowly and is used to avoid fouling in engines with relatively low combustion temperatures. A cold plug, on the other hand, transfers heat rapidly from the firing end. It is used to avoid overheating where temperatures are high.

The length of the insulator nose and the composition of the electrode are the primary features in a plug that change heat rating. Hot plugs have long insulator noses, and hence a long heat transfer path. Cold plugs have shorter nose lengths to transfer heat more rapidly from the insulator tip to the cylinder head to the water jackets via the metal spark plug body

For all of my engines I have always run a colder plug just because I am a duner and there is a lot of wot on the flats. But not just any cold plug, but especially the fine wire plugs like the iridium or palladium versions for the sole reason that they are type of plug that have a very wide heat range to resist both fouling and detonation. The small diameter electrodes in the iridium plugs require less voltage to fire than a regular electrode. I have a much easier time starting most of my 250r’s. The voltage available at lower cranking speeds is lower so the idea is if I use a plug that needs less voltage to fire it will start easier. The insulator nose is a special 'open' design which allows more clearance within the firing end of the plug for better scavenging of deposits. That is why I choose the BR9EIX.

If I was running motorcross which is tight short bursts of acceleration I would run a std or one step hotter on the plug where temps are not as high as running wot for long periods plus the less chance of fouling the plug especially in competition is important.

[fearlessfred]

the information is always the same on any plug site, but heres 1 more http://www.densoplugs.co.th/denso_spark3e.htm

[troybilt]

This is good stuff, I think we kind of high-jacked jc003's thread... sorry bud!

I'll start another one for spark plugs. I'm learning something here... :D

[fearlessfred]

Originally posted by troybilt
This is good stuff, I think we kind of high-jacked jc003's thread... sorry bud!

I'll start another one for spark plugs. I'm learning something here... :D
well u are both enginerds and im a wannabe ,so he prob.cool with it.