Originally Posted by MyNameIsNick

I've never heard of premium actually being "harder to burn". I'm pretty ignorant on the actual differences in fuel other than higher octane has a higher resistance to knock and detonation. Aside from that, other specifics are all new to me and it's hard to tell what's truth and what isn't in this thread. Everyone seems to think they're right and others are wrong so I'll hunt for answers elsewhere.

Originally Posted by 1991Jeep_Man

You just gotta be EXTREMELY careful when going through the TB. You can easily hydrolock your engine.

Originally Posted by (*~*)lost

Yes directly into TB But like was stated earlyer must be VERY careful, when injecting it this way allowes proper distrubtion throughout intake ports. tube diameter that of WD-40 red straw im using hobby hose from nitro rc truck. Do your own reasearch for what is right for you good luck

Originally Posted by thelaststarfighter13

you'll find it, for a fact it's "harder" to burn. It will take a whole helluva lot more heat and compression before it pings off.

Originally Posted by cdeal28078

I don't know by how much it would affect it but I have torn down high mileage engines that were not taken care of and seen at least .020 or more build up in the combustion chambers and on the underside and tops of the valves. So build up in the head side and on the piston side I can see where it would add to the compression ratio. Then any parts of carbon that are sticking out so to speak will get hot and hold that heat until the next cycle will cause pre-ignition. I can see where premium would lower the chances of the pre-igniton or detonation in an engine in this shape or condition. I have used premium in engines with low compression from the factory and never saw any increase in fuel mileage. Was the lead in the old leaded fuel called an additive? I don't know. I do know it aided a mechanical part by keeping the valves from beating themselves into the heads.
clint

Originally Posted by MyNameIsNick

I've never heard of premium actually being "harder to burn". I'm pretty ignorant on the actual differences in fuel other than higher octane has a higher resistance to knock and detonation. Aside from that, other specifics are all new to me and it's hard to tell what's truth and what isn't in this thread. Everyone seems to think they're right and others are wrong so I'll hunt for answers elsewhere.

Originally Posted by djb383

.......and on most old engines with some carbon deposits, the old rings/cylinder walls and valves don't seal up as they did when new, thus lowering the actual cylinder pressure at TDC. This will have an offsetting effect on the slight increase in compression ratio. Remember, compression ratio is just a mathematical calculation. If things don't seal up real good, compression ratio can be a mute point because cylinder pressure can be very low even in a high compression ratio engine.

Originally Posted by MyNameIsNick

I've never heard of premium actually being "harder to burn". I'm pretty ignorant on the actual differences in fuel other than higher octane has a higher resistance to knock and detonation. Aside from that, other specifics are all new to me and it's hard to tell what's truth and what isn't in this thread. Everyone seems to think they're right and others are wrong so I'll hunt for answers elsewhere.

Originally Posted by No4x4Yet

Knock or Detonation is a premature burning of the fuel, the pressure and heat built up in the cylinder is enough to cause the fuel to ignite with out spark. When the piston is still on its upward stroke this is VERY BAD! A high octane fuel requires more heat and pressure to burn, so its is harder to burn. This is why diesel engine needs a lower octane fuel, since they rely on the heat and pressure to ignite the fuel.

Originally Posted by Diesel

Diesels are around 15-25 octane rating, and around 40 cetane. Higher Cetane=Less ignition delay, Higher octane=More resistance to pre-detonation(or ignition)

Originally Posted by superj

and aren't diesels some crazy compression ratio? not a good thing to bring in to this thread as diesels run off totally different requirements then gasoline, for the purpose of our discussion.

a bit of interesting info for you. you can usually turn your hose on to a little less then half flow and put it into you tb without hydrolocking your engine. in the old days, this was how your chambers could be cleaned and it would be done with either a garden hose or a container of transmissions fluid. when i used to buy bmws really cheap and fix them up, if they didn't require a head gasket, that is how i would clean the chambers.

i hear it can make your o2 sensor go crazy but it never messed with the bmw ones

Originally Posted by superj

and aren't diesels some crazy compression ratio? not a good thing to bring in to this thread as diesels run off totally different requirements then gasoline, for the purpose of our discussion.

a bit of interesting info for you. you can usually turn your hose on to a little less then half flow and put it into you tb without hydrolocking your engine. in the old days, this was how your chambers could be cleaned and it would be done with either a garden hose or a container of transmissions fluid. when i used to buy bmws really cheap and fix them up, if they didn't require a head gasket, that is how i would clean the chambers.

i hear it can make your o2 sensor go crazy but it never messed with the bmw ones

Originally Posted by cdeal28078

I do that still on anything old that I work on. Works great on small engines also. It is pretty hard t hydrolock an engine. I have heard of trucks going down the boat ramp into the water at an idle and all it needed was a good drying out.
OK you sold me on the carbon build up not raising the compression enough but what about the carbon causing hot spots causing the fuel to ignite too soon. I guess this might be detonation of sorts? I wonder if that would be helped by premium?
Back to the poster's answer though I still say premium in anything that doesn't call for it is a waste.
clint

Originally Posted by Diesel

Didnt even take that into account, replaced the rings on mine being cylinder 1 and 3 were only reading 130 and the rest were close to 160 and withing 5% of eachother.

So that .2-.3 increase, is most likely lost due to components not sealing properly. Thus, demoting premium usage once again.