Welcome to Just Commodores, a site specifically designed for all people who share the same passion as yourself.

New Posts Contact us

Just Commodores Forum Community

It takes just a moment to join our fantastic community

Register

98/91 fuel, how much difference?

2DIE

ONEDOLLAHOLLA
Joined
Feb 8, 2008
Messages
744
Reaction score
6
Points
18
Location
South Aus
Website
www.torn.com
Members Ride
97 Acclaim
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

Well-Known Member
Joined
Oct 16, 2009
Messages
6,805
Reaction score
94
Points
48
Location
Tamworth NSW
Members Ride
vs commodore
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

ლ(ಠ益ಠლ
Joined
Dec 5, 2010
Messages
939
Reaction score
3
Points
18
Location
South Australia
Members Ride
VR S2 Exec
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

New Member
Joined
Apr 19, 2010
Messages
479
Reaction score
3
Points
0
Location
WA
Members Ride
GSXR1000
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

Well-Known Member
Joined
Oct 16, 2009
Messages
6,805
Reaction score
94
Points
48
Location
Tamworth NSW
Members Ride
vs commodore
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

GIT 'EERRR DONE!!!
Joined
Jun 14, 2010
Messages
1,375
Reaction score
20
Points
38
Age
36
Location
Nhulunbuy NT
Members Ride
VX SS, PX Ford Ranger XLS Dual cab
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

Well-Known Member
Joined
Oct 16, 2009
Messages
6,805
Reaction score
94
Points
48
Location
Tamworth NSW
Members Ride
vs commodore
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

GIT 'EERRR DONE!!!
Joined
Jun 14, 2010
Messages
1,375
Reaction score
20
Points
38
Age
36
Location
Nhulunbuy NT
Members Ride
VX SS, PX Ford Ranger XLS Dual cab
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

Well-Known Member
Joined
Oct 16, 2009
Messages
6,805
Reaction score
94
Points
48
Location
Tamworth NSW
Members Ride
vs commodore
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

GIT 'EERRR DONE!!!
Joined
Jun 14, 2010
Messages
1,375
Reaction score
20
Points
38
Age
36
Location
Nhulunbuy NT
Members Ride
VX SS, PX Ford Ranger XLS Dual cab
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.
 

Attachments

Top