92 vs. 110

shawngr · Apr 3, 2009

What are the disadvantages or advantages to running 92 octane vs. 110 octane? And how would you change from a 92 to 110. Or maybe even running AV Gas? And how do you convert?

78 Continental · Apr 3, 2009

This all depends on what your motor is built for. Low compression you will see no advantages to running 110. Disadvantage 110 way more money than 91 and Av-gas. If the motor is built for 110 it will make more power than pump gas because of Compression ratio. This all has do to with, heads, carburation, ignition, etc...

shawngr · Apr 3, 2009

78 Continental said:
This all depends on what your motor is built for. Low compression you will see no advantages to running 110. Disadvantage 110 way more money than 91 and Av-gas. If the motor is built for 110 it will make more power than pump gas because of Compression ratio. This all has do to with, heads, carburation, ignition, etc...

Thank you

78 Continental · Apr 3, 2009

No problem

RiverDave · Apr 3, 2009

Contrary to popular believe you actually want to run the lowest octane possible in your motor before detonation. This is when you will make the most HP..

Running higher octane levels for motors that aren't intended for it, is a waste of $$.. Doesn't do anything for you, and no some microscopic level will actually cost you HP.

Octane is a measurement of what temperature the fuel will light off at. Detonation is when the fuel / air is compressed in the cylinder it gets hot enough that it "pre-ignites" before the spark plug lights it. The piston is still in the upward motion of compressing and it starts to light off and expand and that is the "detonation" that you are hearing. Very hard on motors.

When the piston is on it's upswing it is compressing the fuel / air mixture.. It should be compressing it to the point of just about to light off but not quite. The spark plug then gives it that last little bit to "combust" the mixture, expanding the gasses and pushing the piston back down. This happens at or just befoer TDC (Top Dead Center) I'm not an engine expert by any means so I'm quite sure someone will come on and say theirs engines that do it after TDC as well but for the life of me I couldn't think of why.

With a higher compression motor and octane level you can squeeze the gasses harder letting that temperature before "ignition" go even higher before the spark plug ignites it. Because you squeezed it harder and you will get more energy in return when the gasses expand. (I'm not 100% if this is accurate so if there's a fuel expert on here feel free to correct me)
Higher octane fuel also takes longer to burn the mix then lower octane fuel..

Without changing major parts of a motor, from my understanding running higher octance fuel would allow you to advance your timing a bit, but that's about it. (Timing is in reference to when the spark plug fires in relation to where the piston is at from TDC.) Advancing your timing means the spark plug fires earlier on the upswing of the piston.. Retarding the timing means it would fire later on the upswing to TDC, to potentially even on the down swing.

Hope this helps.

RD

shawngr · Apr 3, 2009

RiverDave said:
Contrary to popular believe you actually want to run the lowest octane possible in your motor before detonation. This is when you will make the most HP..

Running higher octane levels for motors that aren't intended for it, is a waste of $$.. Doesn't do anything for you, and no some microscopic level will actually cost you HP.

Octane is a measurement of what temperature the fuel will light off at. Detonation is when the fuel / air is compressed in the cylinder it gets hot enough that it "pre-ignites" before the spark plug lights it. The piston is still in the upward motion of compressing and it starts to light off and expand and that is the "detonation" that you are hearing. Very hard on motors.

When the piston is on it's upswing it is compressing the fuel / air mixture.. It should be compressing it to the point of just about to light off but not quite. The spark plug then gives it that last little bit to "combust" the mixture, expanding the gasses and pushing the piston back down. This happens at or just befoer TDC (Top Dead Center) I'm not an engine expert by any means so I'm quite sure someone will come on and say theirs engines that do it after TDC as well but for the life of me I couldn't think of why.

With a higher compression motor and octane level you can squeeze the gasses harder letting that temperature before "ignition" go even higher before the spark plug ignites it. Because you squeezed it harder and you will get more energy in return when the gasses expand. (I'm not 100% if this is accurate so if there's a fuel expert on here feel free to correct me)
Higher octane fuel also takes longer to burn the mix then lower octane fuel..

Without changing major parts of a motor, from my understanding running higher octance fuel would allow you to advance your timing a bit, but that's about it. (Timing is in reference to when the spark plug fires in relation to where the piston is at from TDC.) Advancing your timing means the spark plug fires earlier on the upswing of the piston.. Retarding the timing means it would fire later on the upswing to TDC, to potentially even on the down swing.

Hope this helps.

RD

God damn, Thanks for the schooling!

RiverDave · Apr 4, 2009

No problem.. LOL Might as well know how it all works together right?

RD

DaveH · Apr 10, 2009

I agree that buying higher octane fule is nothing more than a waste of money. you only need enough octane based on what sort of compression you are running (or in the sace of a turbo/blown engine, cylinder"density").

When the piston is on it's upswing it is compressing the fuel / air mixture.. It should be compressing it to the point of just about to light off but not quite. The spark plug then gives it that last little bit to "combust" the mixture, expanding the gasses and pushing the piston back down. This happens at or just befoer TDC (Top Dead Center) I'm not an engine expert by any means so I'm quite sure someone will come on and say theirs engines that do it after TDC as well but for the life of me I couldn't think of why.

ideally, the spark ignition point is a moving target. there are many reasons for this. a big one is it does take TIME for the fuel to burn. this burn time, without factoring in other things, stays CONSTANT. This means that the faster you rev the engine there is LESS physical time to burn the fuel. that is why a traditional spark curve ADVANCES with engine RPM. you simply need to light it off sooner so that by the time maximum cylinder pressure is built up from the burning of the mixture, the piston is not already PAST TDC and you efforts are wasted.

another BIG factor is cylinder density. not so much in boats, but in cars you can coast down a hill or generally run the engine at higher speeds with very little throttle. this "vacuum condition" (read as less dense cylinder filling) will need MORE timing as the weaker mixture takes longer to burn. conversly WOT high engine loads that "packs more mixture" into the cylinder will burn faster, needing less timing. this is the basic premise as to why forced induction engines make more power on LESS timing.

other factors come into play also. high engine temperatures premote quick cylinder "burns" this requires less timing. other factors, but to a lessor degree, also contribute. things like air intake temps, bore diameter, cylinder head/combustion chamber design all have a role.

but back to the basic question of pump vs. 110, it is a waste of money unless you are running right near the ragged edge of detonation. if you are 11:1CR and getting away with it by keeping engine temp COLD, one hot day could push you over the edge. in that case higher ocatne fuel is cheap INSURANCE. You could also BLEND your fuel, a 50/50 mix of 110 and 92 would yied a octane of 101, giving you a much wider window and somewhat costs under control.

92 vs. 110

shawngr

Well-Known Member

78 Continental

Well-Known Member

shawngr

Well-Known Member

78 Continental

Well-Known Member

RiverDave

In it to win it

shawngr

Well-Known Member

RiverDave

In it to win it

DaveH

Well-Known Member