Fuel Thread - octanes, consumptions, what does it all mean?

donki

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Re: Fuel Thread - octanes, consumptions, what does it all me

lancer1993 said:
I do have a question about the 4G93p found in the M21 Protons, do they need the premium go go juice or will they happily run on the standard juice.
Engines that run at higher compression than normal generally require/run safer on higher octane fuels. Unless im confusing it, isnt it a decompressed backwards cm5a without turbo, and should be okay on 91, but personally id stick with 95+.

Generally speaking that is. My (carby) motorcycle has an 11.6:1 compression ratio, but can officially run on 91 (runs smoother on 98 though), however some turbo cars will seriously struggle and will ping on 95 and lower
 

ARC

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Re: Fuel Thread - octanes, consumptions, what does it all me

My CBR250RR didn't like 98, kept fouling the plugs. I think the 98 ran too rich IIRC.
Ran it on regulator unleaded and it was fine
 

rigby

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Re: Fuel Thread - octanes, consumptions, what does it all me

donki said:
Unless im confusing it, isnt it a decompressed backwards cm5a without turbo, and should be okay on 91, but personally id stick with 95+.
CM5A is the backwards engine. 4g93p runs 10.5:1 compression. Runs fine on 91, 95 and 98. It is literally a GSR 4G93T with a non-turbo head.
 

donki

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Re: Fuel Thread - octanes, consumptions, what does it all me

lancer1993 said:
What about conversion costs to run E85?
Larger injectors, possibly higher flow fuel pump, tune to suit. Same/slightly more power on NA, significant power more on Turbo, and significant less kms/tank for both.
 

peregrine

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Only cover 5000ks approx a year so why not use the top end 98 along with its super duper additives etc:. enjoy.
 

frosty7

Active Member
The drama with running e85 is that it absorbs moisture and it eats everything painted surfaces, non compatible hoses. the other drama people are having is the consitancy of the fuel one tank load might be 85 % ethanol the next tank might be 50% which changes the tune on the car massivly. v8 supercars use the e85 that is tested each batch and is a consistant fuel but the stuff at the pump is a gamble. This all being said you can buy a flex fuel sensor from AEM that will test what ever is in the tank and adjust accordingly. You the need to go AEM ecu. I dont reckon its worth the hastle unless your going major boost and change everything on and around your engine to ethanol compatible components.
 

peregrine

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A friend of mine bought a Mercedes 250E dirt cheap, reason being that the owner had stopped using it due to absolute frustration. Because from time to time, for no apparent reason and sometimes at extremely awkward times it just refused to start .He just couldn't trust it. Friend having bought the car experienced the same malady and tried tracing the problem to no avail, until he took it to a Mercedes expert In Thomastown Vic who said, no worries I'll fix it, cost I think it was $400. He told him what has happened is someone has used ethanol fuel in it and the only way to fix the problem in this particular case was to completely drain all the fuel out of the car then blow some sort of gas through the total fuel system. That done the problem solved. So here it can be said that the use of ethanol fuel was a godsend and saved him heaps!!! He then enjoyed many years of trouble free driving.
 
When I first bought my new 2015 GSR 2.4L manual I used 98 then tried 91 unleaded and it was gutless as down low esp on take off with air con on.

I found running 95 unleaded to be the better performing than the 98, the 95 just kicks in at 3500 RPM and goes like a rocket but the 98 does not do that, as all other fuels kick in and go hard at 4000RPM.

I have found running E10 is good 91 E10 better than 91 unleaded and E10 94 better than E10 91.

I find the E10 just as good on fuel economy on the highway, but with air con on she uses a bit more then the unleaded and this is tested over the same highway with cruse con on set on day after day, so it's a factual test.

She is a totally stock car and does not use a drop of oil in 10.000 KM i can't see it drop off the full mark at ever at all.
I will not run 91 unleaded in it ever now, as it gets on my goat taking off with air con on and it's not that good without air on, so i use the E10 always now.

I believe that the E10 is a better fuel nowadays then what it was when it first came out, for fuel economy it has improved from what it was in the beginning and i seen this with my other car a 2003 VY SS Commodore when Shell first came out with what they called a improved E10 for fuel economy and i found this was true and it gave better torque down low i found for sure, as before it did not respond well till it hit 1600RPM then it leapt to life, not flat out mind just driving about normal like.
 

donki

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BUMP with further information, and to make more sense to noobs and more technical minded folks. Also updated to allow us to send the link to Facebookers who really have no idea on what they're talking about.
 
Going to a higher octane does nothing, if the engine does not need it, but in fact such can lower the power.
I had a new 1999 VS stock 5.0l 179KW V8 5sp commodore ute and a mate had one just the same as well and he got a smart idea to use octane additive, mine was always just a bit faster than his and in 3rd gear runs mine would walk away from his, so he thought he had the answer and it only proved that such did not work.

Lower octane buns faster than higher as well, so one needs the correct octane to deal with what is going on in the engine, it's the dynamic compression and volume efficiency of the engine, not the static compression one truly must look at.

Their is just to much to talk about to go into everything.

If one could have their engines spark map come up, on screen like we have in modern cars that have a rev camera etc why not the same could be done, so as to show what the knock sensors are pulling out of the timing, so on screen comes up as 2 deg in red and so on, and one can see the engine is not responding to perfection, so one can see that the fuel is not good enough at a press of a button it read what is truly going on directly.
Then one can make the judgment, not to mention on colder days 91 could be just fine but on hotter days you find it she does need better, and if you drive it hard one may find it's best to use higher.

Thing is not many people have a real feel of what their engine is doing and can't pick up that it's a bit lacking one day to the next or even where in the rev range.
 

Spetz

Well-Known Member
... he got a smart idea to use octane additive....
Octane booster additive is not the same as higher octane fuel though.

As you mentioned though the ECU advances the timing and once it senses knock it retards it.
If you have higher octane fuel then the timing can be more advanced without pinging and hence can make more power.
 
Octane booster additive is not the same as higher octane fuel though.

As you mentioned though the ECU advances the timing and once it senses knock it retards it.
If you have higher octane fuel then the timing can be more advanced without pinging and hence can make more power.
It was what he thought was a smart idea as we only had 91 and 95 back in 2000, so he used 95 plus added 2 times the amount of booster, thinking that the higher the octane would make more power .

The ECU has a graph that it follows and if that knock sensor kicks in she retards the timing, on the sequential 5.0L she can kick 2 deg out from the map and 4 or 6 or 8 or 10 or all the way to 12 deg, the older EFI 5.0L just knocked back 12 deg if it had a knock sensor like the 185kw had.

A 5.0L engine like the 165KW VN-P-R-S only has 8.5:1 compression so 91 octane was fine, the sequential 5.0L was 8.8:1 and 91 was not truly correct for the last of the VS ute or Statesman or VT 5.0L they were designed to run on 95 octane but public did not like to fork out for 95, so Holden said 91 was fine to use and it was but on hot days the ECU pulled timing out and if you got up it, in came the knock sensor retarding timing, killing the power that badly that it was that gutless that a V6 could hose you off.
On a hot day running 91, on the highway I could overtake go back to 3rd in my manual or 4th pass one car and then if i was to overtake the next car soon after bang she was gutless, the temp gauge would pop up just a little bit from the 1st overtake and that was it, the VT may of been better as they have a bigger radiator.
But on 95 octane my 179kw was fine and worked out that running 95 was best for value for dollar as well, but it was only 4c a litre more than 91 and my mated dad had a 1999 Ford LTD 5.0L and he did his homework and said running 95 was just as I found.

If a engine is not efficient with low compression you will not get an advantage in running high octane at all, take a 1949 Holden for example 6.5:1 compression old grey motor they ran on what was called Standard fuel 83 octane at the time I think it was and then when that old grey motor progressed, compression went up to 6.8:1 in 1957 and then to a whopping 7.0:1 in 1958 and then to 7.25:1 in 1960 with all the improvements in heads and new camshaft grinds along the way and Standard octane progressed up to 89 octane, but running what was called Super 97 octane was worthless is such engines and forking out the extra 2c a gallon was just not worth it at the time.
 
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