Change fuel. Why this?
- Thread starter wscycle
- Start date
In most cases, this is good advice. If you're ever going to deviate from the manual's recommendation, then you better know what you're doing or you better know the consequences of changing things up.
And then, don't gripe about it when things go south on ya! :
:--Wag--
They run massive compression in their engines, normal gas wouldnt cut it.
DevilDawg1
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On a Gasoline burning engine - Wouldn't a 12.5:1 be considered and EXTREMELY high compression ration - Diesel engines run 15:1 - 18:1.
If not; what would be considered a massive compression ration.
Not talking about the alcohol burning engines, but the very large cubic engines that are normally aspirated.
1. What is the compression ratio on a Pro Stock engines? Probably more than 12.5:1
2. What is the compression ratio on a MotoCross Bike? Probably less than 12.5:1
3. What is the compression ratio on an AMA race bike? Probably right at 12.5:1 but less than 14.0:1
4. What is the compression ratio on a NASCAR? Probably right at 12.0:1
give or take a point up or down.
Not sure but some can correct my answers to the above:
Your turbo and super charged gas burners are a much lower compression engine (minus the boost of the turbo/super charger).
Most all the Mechanics/Technicians I know will tell you that when you bust the 10.0:1 Compression ratio and it is gonna be a daily driver you should use the 91+ octane.
In an engine with a greater than 10.0:1 Compression ratio, running to low of an octane fuel can and will cause detonation. The pinging a person hears is the wall of the flame slamming the top of the piston and the face of the valves at the wrong time. This pinging is just like hitting these surfaces with a ball peen hammer. Hit the surface long enough and hard enough and parts will start to brake and this can be catastrophic to the internals of an internal combustion engine.
DevilDawg1
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The key words here being "Some road race bikes".
I agree the 13:1 can run on pump fuel, but it should be 91+ octane to prevent detonation.
And yes the competion diesel motors run these astronomically high compression ratios. But they also spit about 1/3 of their fuel out the exhaust system. And a diesel uses "glow plugs" when it first cranks and then it uses compression to ignite the fuel.
justa-busa-girl
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ine always used 87 or 89 and never had a problem with my bike!
justa-busa-girl
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im not saying that im right by doing it, ive just always been told that it was ok and it runs well with it but i need to stop using it i will!!
DevilDawg1
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The GenII Busa engine should not be considered a low compression engine, it should be considered a high compression/high performance engine.
It should be considered one of the highest performance engines in the motorcycle world. In this status it is comparable to the lamborghini, ferrari, porsche, (my favorite - the Z06 Corvette), and even the Carol Shelby KR Mustangs. Now about all of these cars would be considered 190-200MPH cars, and not one of them reccomends 87 octane, they all recommend 91+ octane fuel. It is because of the compression ratio of these engines.
Detonation inside the engine is not a good thing, it is a BAD thing.
memorex
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Draco1340
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This is driving me crazy... There is a hell of a lot of oversimplified info flying around. Detonation is only partly due to Fuel octane and compression ratio. The third variable that is just as important is heat. Even a low compression engine with high octane fuel will ping like crazy under the right circumstances such as the following:
-Carbon build up on piston and head surfaces
-Sharp corners and surfaces on head and piston (such as piston valve reliefs)
-overheated engine or insufficient cooling
-large bore diameters and hemispherical chambers with long flame paths.
Back in the days of cast iron cylinder heads and large hemispherical combustion chamgers., the car guys were forced into having to use 100+ race fuel at the track, but our GenII is not a car. It has a very smooth relatively small flat top piston with a flat smooth aluminum cylinder head with excellent cooling. If the engine is in good condition with no carbon build up, and if it is well tuned at 13 to 13.3, it will not detonate on a high quality 87 octane fuel. Walk through the pits at any regional or national race and see what the fast guys are running. They are not running high octane unless they are spraying.
The manufacturers specify 91+ octane because they assume that many riders would lean their bikes out with pipes and not tune them. Or they would put 50k miles on the motor with all sorts of carbon build up.
-Carbon build up on piston and head surfaces
-Sharp corners and surfaces on head and piston (such as piston valve reliefs)
-overheated engine or insufficient cooling
-large bore diameters and hemispherical chambers with long flame paths.
Back in the days of cast iron cylinder heads and large hemispherical combustion chamgers., the car guys were forced into having to use 100+ race fuel at the track, but our GenII is not a car. It has a very smooth relatively small flat top piston with a flat smooth aluminum cylinder head with excellent cooling. If the engine is in good condition with no carbon build up, and if it is well tuned at 13 to 13.3, it will not detonate on a high quality 87 octane fuel. Walk through the pits at any regional or national race and see what the fast guys are running. They are not running high octane unless they are spraying.
The manufacturers specify 91+ octane because they assume that many riders would lean their bikes out with pipes and not tune them. Or they would put 50k miles on the motor with all sorts of carbon build up.
justa-busa-girl
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hey draco i pm'd ya!!
DevilDawg1
Registered
You left out proper timing as well.
And in alot of ways everything you say is correct.
Burning gasoline weather in a car engine, lawn mower engine or a motorcycle engine is burned in the same manner.
You are right again the pistons are much smoother today than many years ago, this means that there is many times more machine marks in the same square inch as yesterday.
And as you walk through those race pits on any given race, ask the guys that are running the 87 octane what their compression ratio is and ask if the bike is tuned for the 87 octane, and as for the guys that are spraying you can bet that they are not running a 12.5:1 compression ration.
I believe that you are correct on your assumptions as far as the manufacturer recommending 91) octane. But you left out that the GenII Busa motor is considered a high compression engine and that the factory MAP for the bike is set to run on 91+ octane fuel.
Overall their are many factors than can cause detonation, with this statement I am sure that we all can agree.
But one of these many factors is definitely running to low of an octane fuel in a high compression engine. And everyone who has turned a wrench on a high compression engine will state that this can cause detonation. I assume that we all agree that this is not the only factor that can cause detonation, but it is a factor that can cause detonation by itself.
It is not true that lower octane gasoling produces more power. It "depends" on that motor with its specific tuning. For general street use in all temps and humidity, use 91 or more octane. If you are dyno tuning it, and have a way to measure detonation, and A/f ratio, then you can tune that motor to specifically use 87 octane, if your that cheap! There is a reason that we have race gasoline sold by VP of all kinds of octane and oxygen blends..... For everyday riding, use 91+. But, you can of course do whatever you want.....
afterhours
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wow all this....and nobody has yet answered the question the OP asked....
Draco1340
Registered
It was answered in the very begining. It didn't shift because it was pulling harder on 87. Adding kill time would fix this.
best define "detonation" there is a big difference between "pre-ignition" and "detonation" although they do similar damage and have similar causes, they are in fact two completely different issues..
We found on the dyno that when going with aluminium heads, we had to bump the compression 1 full point to "break even" on HP with like "configured" heads due to heat rejection issues..
for the average "joe" run the fuel you are supposed too.. they typically have good reasons for this..
Also, the BTU difference from "regular" to "premium" typically do not exist.. They do however exist for "cafe" blends.. Winter/summer mixes also vary by around 5-8% due to winter additives (alcohol being a main one)
If you want faster, hotter or more efficient fuels, you need to go up on naptha ratios and blend other exotics in (F1 cars are the kings at this game).. I like nitromethane myself
I just put in what the maker wants myself..
We found on the dyno that when going with aluminium heads, we had to bump the compression 1 full point to "break even" on HP with like "configured" heads due to heat rejection issues..
for the average "joe" run the fuel you are supposed too.. they typically have good reasons for this..
Also, the BTU difference from "regular" to "premium" typically do not exist.. They do however exist for "cafe" blends.. Winter/summer mixes also vary by around 5-8% due to winter additives (alcohol being a main one)
If you want faster, hotter or more efficient fuels, you need to go up on naptha ratios and blend other exotics in (F1 cars are the kings at this game).. I like nitromethane myself
I just put in what the maker wants myself..
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