can a 2003 banshee use 87 octane?

[ehall1]

Originally Posted by 370banshee

cars are 4 strokes. compresion ratios vary between 2 strokes and 4 strokes.

yeah i know but hell even a shitty old 80s gutless motor had like 81/2 to one compression. stock banshee is 61/2 to one that really seams low. cant 2-strokes deal with higher compression. and if so do you have any idea how many thousands i can shave off my stock heads as soon as i get pipes of course and still use 93 octane? but i work in a machine shop so milling heads wont cost me anything? thanks ahead of time, ed
ps. i will get a cool head sooner or later but the head plus pipes is out of the question financially right now.

[blaster2000]

Originally Posted by 370banshee

cars are 4 strokes. compresion ratios vary between 2 strokes and 4 strokes.

Hey wouldn't it be great if they started making 2-stroke cars?

[ehall1]

Originally Posted by blaster2000

Hey wouldn't it be great if they started making 2-stroke cars?

believe it or not ive kicked my car plenty just not to start it!!! and ive used mixed gas right out of my banshees gas can too a lot!!! never smoked or nothing, but i sure didnt have 2 stroke power either. the only time 4 strokes are better is when your jerking off

[J.J.]

Originally Posted by 370banshee

cars are 4 strokes. compresion ratios vary between 2 strokes and 4 strokes.

I thought I'd chime in here, as most of you completely missed what 370banshee said
Speaking strictly 2-stroke:

There are two commonly refered to methods of stating a given engine's compression ratio:
1) Corrected Method, which refers to the volume above the piston at the point on the upstroke that the exhaust port is fully closed.

At first glance this seems to be the obvious way, since compression cannot start before all the exit points are closed. This is not strictly true in the case of a high performance 2-stroke (AKA Yamaha Banshee )

At high RPM's, the piston speed is so great that on the upstroke it will actually outpace the rate at which the fuel/air mixture can escape out of the exhaust port. Ofcourse some of the mix will escape, but once past the exhaust port, the piston will trap a much larger volume of fuel/air in the upper cylinder than just the static volume above the exhaust port. This trapping efficiency improves as the RPM's increase.
To get to the point, under actual running conditions, our true compression ratio dynamically increases with the rpm.

It is rare to approach 100% efficiency at any rpm in a stock motor, but with some porting and a matched pipe, (I'm sure you all know the next bit,but I'm on a roll here) a suction or scavenging pulse is created to assist in complete evacuation of exhaust gases AND a slight vacuum to pull extra fuel/air mixture up through the transfer ports, this is followed by a return or pressure pulse from the exhaust pipe just before exhaust port closing which actually stuffs some of the escaped fuel/air mix back into the cylinder.

This means that your XXX cc motor over a narrowly defined powerband can actually trap more than XXX cc's of fuel/air in the upper cylinder and then squeeze it into the much smaller volume above the piston just prior to ignition. Sounds great, but the problem here is that this all works in a very small RPM range. If the RPM is out of this range, the planets are not aligned anymore, and the pulses in the intake and exhaust sytem can actually work against each other. (Lightswitch power band and no over-rev, should sound
familiar to all you T5 lovers :p, sorry couldn't resist )

So, if the above ramblings made any sense, it is obvious that there are limitations to using the corrected method of compression ratio calculation...
For example, you can raise the exhaust port in your two stroke and find that without touching anything else, due to less cylinder volume above the now higher exhaust port, your ratio has dropped.

If one really wants to speak compression ratio to compare oranges to oranges, one should look at:
2) Uncorrected compression ratio:
This ratio compares the total cylinder displacement which is the bore area x stroke length + the volume in the combustion chamber, (The TOTAL volume above the piston at BDC) with the volume above the piston at TDC.

Now we have a datum to compare engines of similar size and state of tune... We still have to consider trapping/scavenging efficiency, bore size, rpm, etc, but it gives us a much more consistent reference value.

Generally, mild 2-stroke motors on pump gas run with uncorrected compression ratios in the 10:1 to 11.5:1 range.
Small, sub-70 mm bore engines can often tolerate as high as 13.5:1 uncorrected.
"One run" drag bikes on 110 octane or better with well designed combustion chambers to discourage detonation can tolerate 15.5 or 16:1 and sometimes higher. Methanol motors and those using a blend of methanol and nitromethane can tolerate 17:1 and higher.

Can it be calculated? Sure, it is (volume of cylinder at BDC + volume of combustion chamber at TDC) / (volume of combustion chamber at TDC).
Sounds easy you say.
The calculation for the cylinder volume can be done by most 10 year olds, but, how to calculate the volume above the piston at TDC?
Factors to consider here are the shape of the piston crown, the shape of the combustion chamber, the thickness of the head gasket, the deck height, the volume taken up by the spark plug, blah blah blah.

The only way the average backyard mechanic like me could come close to finding this volume is to actually fill the space above the piston with a viscous oil through the plug hole (if you could manage to prevent the oil from draining past the rings, heh) and accurately measure the volume in cc's.
Not that I've ever tried it.

Well Ed, if you've read this far without falling asleep, well done!
To answer your question on milling the head, yes, you can safely take .030" off the gasket sealing face of the head, without having to correct the squish band and still run pump gas.

Cheers
J.J.

[Banshee]

Wow that was a mouth full

Anyway to the person how said it would be cool if 2-strokes were in cars. Well they were. There is a period where the Cummings Diesel was a 2-stroke motor. Here is a link that talks about how a 2-stroke diesel works.

http://auto.howstuffworks.com/diesel-two-stroke1.htm

I actually say that they had a Cummings 2-stroke on the TV show Trucks.

So now you can say they do make 2-stroke trucks.

[ehall1]

Originally Posted by J.J.

I thought I'd chime in here, as most of you completely missed what 370banshee said
Speaking strictly 2-stroke:

There are two commonly refered to methods of stating a given engine's compression ratio:
1) Corrected Method, which refers to the volume above the piston at the point on the upstroke that the exhaust port is fully closed.

At first glance this seems to be the obvious way, since compression cannot start before all the exit points are closed. This is not strictly true in the case of a high performance 2-stroke (AKA Yamaha Banshee )

At high RPM's, the piston speed is so great that on the upstroke it will actually outpace the rate at which the fuel/air mixture can escape out of the exhaust port. Ofcourse some of the mix will escape, but once past the exhaust port, the piston will trap a much larger volume of fuel/air in the upper cylinder than just the static volume above the exhaust port. This trapping efficiency improves as the RPM's increase.
To get to the point, under actual running conditions, our true compression ratio dynamically increases with the rpm.

It is rare to approach 100% efficiency at any rpm in a stock motor, but with some porting and a matched pipe, (I'm sure you all know the next bit,but I'm on a roll here) a suction or scavenging pulse is created to assist in complete evacuation of exhaust gases AND a slight vacuum to pull extra fuel/air mixture up through the transfer ports, this is followed by a return or pressure pulse from the exhaust pipe just before exhaust port closing which actually stuffs some of the escaped fuel/air mix back into the cylinder.

This means that your XXX cc motor over a narrowly defined powerband can actually trap more than XXX cc's of fuel/air in the upper cylinder and then squeeze it into the much smaller volume above the piston just prior to ignition. Sounds great, but the problem here is that this all works in a very small RPM range. If the RPM is out of this range, the planets are not aligned anymore, and the pulses in the intake and exhaust sytem can actually work against each other. (Lightswitch power band and no over-rev, should sound
familiar to all you T5 lovers :p, sorry couldn't resist )

So, if the above ramblings made any sense, it is obvious that there are limitations to using the corrected method of compression ratio calculation...
For example, you can raise the exhaust port in your two stroke and find that without touching anything else, due to less cylinder volume above the now higher exhaust port, your ratio has dropped.

If one really wants to speak compression ratio to compare oranges to oranges, one should look at:
2) Uncorrected compression ratio:
This ratio compares the total cylinder displacement which is the bore area x stroke length + the volume in the combustion chamber, (The TOTAL volume above the piston at BDC) with the volume above the piston at TDC.

Now we have a datum to compare engines of similar size and state of tune... We still have to consider trapping/scavenging efficiency, bore size, rpm, etc, but it gives us a much more consistent reference value.

Generally, mild 2-stroke motors on pump gas run with uncorrected compression ratios in the 10:1 to 11.5:1 range.
Small, sub-70 mm bore engines can often tolerate as high as 13.5:1 uncorrected.
"One run" drag bikes on 110 octane or better with well designed combustion chambers to discourage detonation can tolerate 15.5 or 16:1 and sometimes higher. Methanol motors and those using a blend of methanol and nitromethane can tolerate 17:1 and higher.

Can it be calculated? Sure, it is (volume of cylinder at BDC + volume of combustion chamber at TDC) / (volume of combustion chamber at TDC).
Sounds easy you say.
The calculation for the cylinder volume can be done by most 10 year olds, but, how to calculate the volume above the piston at TDC?
Factors to consider here are the shape of the piston crown, the shape of the combustion chamber, the thickness of the head gasket, the deck height, the volume taken up by the spark plug, blah blah blah.

The only way the average backyard mechanic like me could come close to finding this volume is to actually fill the space above the piston with a viscous oil through the plug hole (if you could manage to prevent the oil from draining past the rings, heh) and accurately measure the volume in cc's.
Not that I've ever tried it.

Well Ed, if you've read this far without falling asleep, well done!
To answer your question on milling the head, yes, you can safely take .030" off the gasket sealing face of the head, without having to correct the squish band and still run pump gas.

Cheers
J.J.

hell yeah that was a mouthfull. but ya learn something new every day, sometimes two or three things on this sight. but thats great. one more thing when i mill the 030." off will a stock new head gasket work or will i need something aftermarket (stronger). dont wanna find out like i did on my chevelle when i jumped up on compression that stock gaskets suck. thanks ed

[J.J.]

Originally Posted by ehall1

hell yeah that was a mouthfull. but ya learn something new every day, sometimes two or three things on this sight. but thats great. one more thing when i mill the 030." off will a stock new head gasket work or will i need something aftermarket (stronger). dont wanna find out like i did on my chevelle when i jumped up on compression that stock gaskets suck. thanks ed

Ed, to be honest, I haven't done the head mod myself, but I know many people who have. I asked one of them last night and he has not had any gasket problems. He fitted a new stock gasket after the mod.

I am using an aftermarket head, that's why I haven't done it.

As for the "mouth full" comment, it's even worse when you only have "divebomb" two finger typing skills...

[370banshee]

damn J J i';m glad sombody else knew what i was saying. i just didn't wanna type all taht out. even thought i''m not a divebomb typer. and you actually knew more about it that i did.

[ehall1]

try typin all that with one finger!!! ok gotta go my hands crampin ed

[throttle_lock]

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i am really stumped.87 octane.here in Australia we dont know of anything less than 95.i run my yz250 on 98 octane.
I would not go anything lower than what you usually run....the octane boosters are the best option