After running my Subaru on shell best fuel and then going to tesco and filling up its noticeably slower and less boost is this normal and to be expected?

 

Regular or Tesco 99?

Tesco 99 seems to give same feel as Shell Nitro in mine.

 

Tesco 99 and Vpower get alternated on mine all the time and I don't feel a difference. My best dyno result was also on Tesco but that's far from scientific

 

I have used Tesco Unlimited in my car since I owned it except once where I used Shell Nitro, I felt my car was slow and sluggish on the Shell. I don't think it was any different but it was most likely in my mind!

 

It was tescos best stuff,could it be that it was so finely remapped to run at best on another fuel?because it's defo not as rapid! The same day I out that fuel in was also same day I fitted a afterburner vortex back box but surely that won't make it slower?

 

Shell petrol for me,I had the reverse effect using Tesco fuel so stick strictly with shell fuel now.SJ.

 

I recently fitted a afterburner vortex (angled exit) and noticed it ran slightly better, had a bit more response when pulling away so I don't think it can be that.

all I can suggest is go back to shell when you run out and see what happens, if it's better then don't use Tesco again!

 

I didn't think it could have been the exhaust.im gonna do what u said and run it right out and then fill it up with shell and hope I get my boost back.its still quick but just not a aggressive in 1st and 2nd

 

Mate of mine drives for Tesco tankers, (Dentressangle), says that the Momentum comes out of the same tanks at the refinery as V-Power...he used to drive for Shell.

 

That I have heard before but also read about all the different additives they use can make the difference

 

I use both Momentum 99 and V-Power Nitro with no discernable difference.

Andy Forrest himself even said to me whilst mapping my car that he can't tell between the two!

 

That's base fuel, very different to the stuff that comes out of the pumps.
They all use the same base fuel but each company use their own mix of additives to make their final product. It's said that tesco use quite a lot more silicone in their fuels than the other big names.

For me, I'll let tesco do the food and shell do the petrol.

 

Every thread I ever read about fuel in this context has somebody that knows somebody that drives a tanker or works at a refinery

 

Was it also a hot day?

 

I would say it was a average day and temp.i also fitted a boost gauge but surely that cant change its performance

 

Mine seems to perform better on Tesco Momentum than Shell vPower.

 

Seems to be a lot of mixed opinions here,I'm getting the impression that engines will run better on the fuel they are mapped with.

 

I honestly don't think that's the case. My car has been mapped a few times now at different stages of tune and I've had vPower in it for the first map when I was using T99 for 90% of my mileage, it drove fine.

I then had it mapped on T99 and spent 6 months in the US for work only coming back for weekends and trackdays. Where my car was stored, there was only really vPower available readily so I used that... no issue.

Andrew Carr certainly had the opinion that the fuel is very similar, and a map for one is fine for the other.

I think it's more likely that you've got a warmer day or a heavier car or you're just imagining the performance reduction. I'm guilty of it more than most, I'm notorious for chasing boost leaks in my sleep because my car "felt slower" on the way home from work.

With all that said, perhaps there is a problem with the Tesco fuel you used but is specific to that pump on that day. It's not unheard of for a dodgy batch of fuel to turn up at a filling station, and a tightly tuned Subaru may be one of the first cars to notice. Bluntly saying that VPower is better or worse than T99 is inaccurate though, in my experience.

 

I've run many different Impreza's I've owned from stock to modified on both fuels and have never noticed any difference when using either.

 

Tesco fuel is like rocket fuel. Love it.

 

Maybe it just my mind and I'm getting use to the power.i tapped into a vacuum line for the boost gauge and the T PIECE and pipe it came with had ALOT smaller internal diameter,could this make any difference?standed pipe is about 6mm and the boot pipe and t piece was 2.5mm

 

Not really as the smaller diameter pipe will trigger the gauge. But check to see if you have got a good seal around the T-pipe for peace of mind.

 

The map will be for the octane of the fuel, not the individual 'make' of fuel itself.

 

Defo check for leaks if you've been playing with the vacuum pipes.

I made a home-made boost leak detector a few weeks ago out of boredom, basically took induction cone off, capped off the inlet pipe and then used one of the old breather take-offs (catch can so all take-offs blanked) and stuck my compressor nozzle in it.

Only "charged" to 12psi and I had a load of leaks all around the FMIC pipework. 10mins with a spanner and my car felt a load faster.

 

Mine was a uk fuel remap back when optimax was on the go .Tried momentum had bad idle ,lacked acceleration used more fuel running it doing the same driving style when running shell .Went back to Shell v-power now nitro instant response when accelerating no more bad idle better fuel consumption .

 

Guess I will just have to burn off this tesco stuff and try v-power again and see if there is any difference

 

It certainly can if not done properly!

And double check you haven't got any boost leaks anywhere

 

if I had a boost leak surely my boost gauge would read less boost and I would know about it

 

Nope, it may be taking longer than it should to hit peak boost though.

 

...