98/91 fuel, how much difference?

[2DIE]

I was running my VT on 98 ever since I got it registered, yesterday I fitted a 2.5" Lukey cat back and took it for a little drive to the servo where and because I was low on cash I put $20 of 91 in it.

Now all of a sudden it feels like its got less guts than when I bought it, only major mods so far are 1:9:1 rockers and the exhaust and I'm thinking that it should still have more go than what it did regardless of fuel used.

If its the fuel that makes it feel like that then the fuel is more important to the power output of the car than upgrading rockers and exhaust?

It definitely was more responsive after installing the rockers while still running 98, I doubt its the exhaust that would have made it sluggish but I guess it's possible.

Basically I just want to hear some opinions if people notice that much difference with switching fuel to lower or higher octane as the amount of power lost for me was going backwards after spending a ton of money on parts.

I know I can just let the fuel get low and top it up with 98 again to find out but that wont be for a few days.

[Brett_jjj]

I find the same with my VSV6 if I put 91 octane fuel in it. It runs like crap compared to when its on 98 octane. I also get way better fuel economy on 98 stuff.Even when running on the standard tune I found the 98 stuff to be way better.Also I dont know if the BP ultimate around here goes stale or what happens to it,but Ive found the Caltex vortex 98, and the Shell Vpower run way better than the BP ultimate.Around here they are both cheaper than BP too.

[GothicKidd]

I dont think the exhaust would do it, I was running on a higher octane for a few hundred K's.. and went back to the normal octane, and it was running alot better on the normal octane..
The higher octane is for performance cars.. I only have used the higher octane to help clean the fuel system.. (heard it helps)

I guess once a car has been running on one type of fuel.. it gets used to it.. Well hopefully once you get some higher octane back in it.. it goes back to normal..

[Mirkz]

I switch between 91-95 & 98.
I used to only swear by 98, but for my 5L, I don't actually feel much difference. My engine may need a good freshen up though. Feels like it's sluggish most of the time.

[Brett_jjj]

The V8's run a fairly low compression ratio of 8.4 : 1 ,its probably why you dont notice much difference between the different octane fuels.

[DLFHUB666]

As far as i know unless your car it tuned to 98 you get no benifits from using it, your just wasting your money.

[Brett_jjj]

As far as i know unless your car it tuned to 98 you get no benifits from using it, your just wasting your money.

Na,I found that even running the standard tune,there is a good difference between the two fuels in my V6.Also Im not talking about driving around slowly like granny.I do a lot of half to full throttle take offs etc and generally drive the car hard.I think that if you do drive around like granny,you wount notice any difference between the two different fuels.

[DLFHUB666]

I say placebo effect, pretty sure even the ls1s are only tuned for 91 so running anything but 91 is a waste of time as the pcm will still see it as 91.

[Brett_jjj]

No placebo effect.Ive monitored the engine when using both fuels with a tech 1 scantool, and the ignition timing that the engine uses when running on 98,compared to when its on 91 octane is way higher,and the more ignition advance you can run on an engine-to a point,the more power the engine will make, and it will also get better economy,especially once the foot is down a bit.The ECU can actually adjust the ignition timing of the engine according to the octane of the fuel thats used among other things. 98 octane fuel also works out cheaper at the bowser too in the long run because I use less of it.I dont need any more proof than that.

[DLFHUB666]

So i found this they did a test of the vz alloytec found that running 98 with the stock tune got a gain of 2kw sorry they didnt have a dyno sheet for this, an then they gave it a 98 tune an got an impressive 12kw gain so really what you said is right but 2kw pfft. Green is stock tune with 98, blue is 98 tune.

[monkeywrench]

i agree 98 runs better i had 4wd and when i run it on 91 it wouldnt idle smooth worse fuel economy,than it did when i run it on 98 plus it ran smoother i actually tell my customers to run at least 1 tank 0f 98 every now and then as it acts like a fuel system cleaner

[DLFHUB666]

i agree 98 runs better i had 4wd and when i run it on 91 it wouldnt idle smooth worse fuel economy,than it did when i run it on 98 plus it ran smoother i actually tell my customers to run at least 1 tank 0f 98 every now and then as it acts like a fuel system cleaner

agree with the run 1 tank a month or week what ever but what im saying is there is no real benifit unless you get a tune to suit. an what kind of 4wd it may of had a standed tune that could recognise the differance between 91 / 98 where as the commodore tune dosent like i said above its not backed up by a dyno print out but they said a 2kw differance between 91/98 on a standed vz tune now if you think that is abenifit well keep buying it.

[Brett_jjj]

I wouldnt take any claims you read on the net too seriously.Theres claims that this is better or that is better.Theres thousands of them on there,most of it is just crap.Im going on what timing the ECU runs at,on whichever fuel, and the cost of the fuel over time.I know that the ignition timing that the engine uses when on 91 fuel is heaps lower,than when on 98, and the knock sensors detect knock way earlier on 91 octane whcih makes the ECU drop back to its lower octane timing table.When on 98 ,the engine hardly detects any knock,which means continuous running in the high octane timing map.This alone is one of the reasons why the 98 runs better.Especially if you have a heavy foot like me..If you seriously cant notice the difference between the two fuels,theres probably something else wrong with the car to begin with.

[DLFHUB666]

so your telling me that if you jumped in two identical cars an 1 had 91 an the other had 98 you could tell the differeance without your scan tool telling you that 1 has abit more timing advance than the other. doubt it. an with timing advance have you noticed on a hot day that the advance it a little bit less than on a cold day thats about the same as 91 vs 98 not really worth writing home about . but as you can see by the dyno read out i posted that if you get it tuned to 98 there is a considerable differance. anyway im over it . it just like ps3 vs xbox 360 everyone has there own side.by the way my car is tuned for 98 so no problem there.

[Brett_jjj]

Heat doesnt really effect the timing at all.I thought it would effect it a lot more than what it actuallly does.And I cant say this for every car,but Id guarantee that anyone who drove my car on 91 fuel,then 98 could easily tell the difference.And the timing difference between the two fuels does make a difference to how it runs.I do my own tunes,and Im always playing with the low and high octane tables for the ignition timing.A few degrees of advance makes a big difference to how the car runs.

[DLFHUB666]

Heat doesnt really effect the timing at all.I thought it would effect it a lot more than what it actuallly does.And I cant say this for every car,but Id guarantee that anyone who drove my car on 91 fuel,then 98 could easily tell the difference.And the timing difference between the two fuels does make a difference to how it runs.I do my own tunes,and Im always playing with the low and high octane tables for the ignition timing.A few degrees of advance makes a big difference to how the car runs.

sorry to keep going but you write your own tunes??? Im talking about a bog stock tune one from the factory not one that has been altered .so what your saying is you have altered a tune to better suit 98 which if you read my posts is what i have been saying the whole time to get the most out of 98 it has to be tuned.So yes i would probably feel the differance if i drove your car on 91/98. but i bet you couldnt feel the differance in a bog stock car from holden.

[Brett_jjj]

sorry to keep going but you write your own tunes??? Im talking about a bog stock tune one from the factory not one that has been altered .so what your saying is you have altered a tune to better suit 98 which if you read my posts is what i have been saying the whole time to get the most out of 98 it has to be tuned.So yes i would probably feel the differance if i drove your car on 91/98. but i bet you couldnt feel the differance in a bog stock car from holden.

As I said before in the above posts ,even when running a standard tune you can notice the difference between the two fuels..Of course a tune will take more advantage of the higher octane fuels,because you can add more timing advance to the timing tables.

[Daggy082]

Fuel never burns 100% in the combustion chamber so using 98 which burns better is obviously gonna burn the fuel more then 91... Thus making the car run better... It's as basic as that. This has come straight from a Holden mechanic who is my mate. So not like he is trying to prove anything or trying to get more money out of me...

[Bizmark]

Ecotecs are said to run a little better on 98, they sometimes ping on 91 under significant load so if you're having pinging problems on 91, try 95 or 98. If that fixes the problem then get the car tuned for 98 as well so you see a bit more power and more economy

[sleepa]

I used to only run 98 Octane in my Turbo 180sx as when I ran 95 it would be noticeably more sluggish, especially between gear changes. Also I would notice a lot of power loss on really hot days.

However I have only ran 91 octane in my LS1 and have had no ill effects whatsoever. I don't need any more power for cruising around, and it is after all designed to run on it.
I'd run up to 95 on a standard tune but only use 98 when I get it properly tuned for it otherwise I don't see a point running 98.

[Brett_jjj]

Hot days effect the cars power,not because of retarded ignition timing,but mainly because of the intake air temp, when the air is hot it gets thin,whereas cold air is a lot thicker or dense..The more dense the air is,the more power the engine makes because theres more air being "fitted" into the cylinder,which makes for a bigger bang..It is especially noticable on some turbo cars on a hot day..A good example is Nitrous oxide,it is a non flamable gas that makes the air going into the engine a lot denser,thats why it makes more power.

[2DIE]

Just went for a drive about 100km total, 50km on the way there with 91 and I was low on fuel so I topped it up with 98 before I drove home again.

Its back to how it was before, relived its back to normal and it was only the fuel that made the difference.

I would there be noticeable difference between 95 and 98? Its just a standard tune Ecotec.

[Brett_jjj]

Mate I woundnt even bother using 95,you may as well pay the bit extra and get 98.But its up to you really,I suggest you try them all and see what you think is the best.Also it doesnt hurt to put a bottle of injector cleaner in the petrol tank once a month or so.It seems to keep them running a bit better.

[2DIE]

Ok thanks, might as well just keep it on 98 then. I put half a bottle of injector cleaner in it a bit less than 2 weeks ago when I filled the tank.

Instead of making a new thread Ill ask something else here,

Where or who can test my speedo, will I have to get it put on the dyno to test it or can mechanics ect do it?

Only asking because I seem to be flying past every car where ever I go, I asked my bro to sit on 100 in his car and I flew past him too, when I asked if he was doing 100 he said he was doing 110km.

My tyres are fine according the the tyre/wheel size calculators, I doubt it has had the diff changed before.

I really need to get it checked and possibly recalibrated.

[Brett_jjj]

Im pretty sure some phones have GPS which can measure your speed.A dyno is another way,but too expensive just to get that done.Do you have the speed alert on the dash.Its also an electronic speedo,some speed alert units will set to the speedo mode permanently ,and some wont ,even though the units themselves are identical.The ones that wont, will still set to the speedo but the orange light will flash on and of whilst its in this mode, and when the ignition key is turned off,it will automatically go back to speed alert mode again.If you dont know how to set the speed alert to digital speedo,yell out and I will post up how.Its not very hard.