# What petrol do you buy and why?



## Patrick_Phillips (Aug 17, 2006)

Sitting on the border between Northern Portugal and Galicia, I have listened agin to the Potuguese complaining about watery Spanish petrol and the Spanish going on about sticky and expensive Portuguese petrol. I make no comment either way...but

who buys the 98 octane stuff and why?

It is many years since I had anything to do with tuning cars - the carbs were the thing but few will even know what they are today!
Do the 98s get more miles or maybe lower maintenance bills? There has to be some reason for the two grades. Maybe 95 is less sticky or less watery???

Somebody tell me, please.
Patrick


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## Stanner (Aug 17, 2006)

What is this "petrol" used for? 

I only seem to remember using it for things like generators, mowers, chainsaws and strimmers. 
I stopped using it for anything important, like road fuel, in 1988.

Nasty stuff - Much too dangerous to have lying around in cans.


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## 113016 (Jun 5, 2008)

S U carbs, I remember having twin on a few cars.
I always thought the higher octane fuel was for higher compression rate engines.
eg 10 to 1
If you used a lower grade fuel your engine would knock, and this was called pinking!


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## cabby (May 14, 2005)

It was used mainly for higher performance engines, Jags ran very roughly on 2 star petrol, if at all.
there are still performance fuels on the pumps including diesel.

cabby

Strongberg and SU carbs, the Mk x jag has 3 x 1.1/2 inch ones The days before flow meters etc. a bugger to tune using an old screwdriver.


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## 113016 (Jun 5, 2008)

Then we had Twin Choke Webbers:grin2:
https://en.wikipedia.org/wiki/Octane_rating


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## Patrick_Phillips (Aug 17, 2006)

You guys must be as old as me - Twin choke downdraft Webbers indeed!
But there can't be many carb vehicles outside the vintage fraternity so what is the high octane used for today?
I know you are all too tight to pay out an extra 25 cents without getting a good payback - what???

Patrick


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## listerdiesel (Aug 3, 2012)

Depends on the engine, its state of tune and the engine management.

We run our Discovery V8 on basic unleaded, that suits it fine as it is 9.5:1 compression ratio, knock detectors on each bank and Bosch Motronic multipoint fuel injection.

I believe most cars from the late 90's onwards will run on the lowest octane at the pumps.

We normally run it on LPG/Autogas, but we also have the full capacity petrol tank as well for greater range.

Peter


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## 113016 (Jun 5, 2008)

Good reminder there Peter, I forgot about the difference between Leaded and Unleaded, and the damage that could be done to the valves by using unleaded :frown2:


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## Stanner (Aug 17, 2006)

Strombergs and Webers 

You also forgot the Dellortos
:wink2:

http://www.dellorto.co.uk/


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## Patrick_Phillips (Aug 17, 2006)

listerdiesel said:


> I believe most cars from the late 90's onwards will run on the lowest octane at the pumps.
> Peter


Exactly! So who is buying the 98 stuff and why?

Patrick


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## Stanner (Aug 17, 2006)

There was a test done on TV some 10years ago now using (I think) BP Ultimate and Shell Optimax.

They found that in basic standard cars (they used Clio) it made little or no difference.

But in cars with sophisticated engine management systems that could adapt to take advantage of the extra Octane it made a measurable difference - the car they used was a Subaru STX.






It seems like it's horses for courses - if your engine is sophisticated and tuned enough to make best use of the extra Octane then it pays to use it.

But this test appears to blow the theory out of the water.


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## cabby (May 14, 2005)

Those with classic cars that do minimal mileage I would imagine.

cabby


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## Stanner (Aug 17, 2006)

There was a test dome on TV some 10years ago now using (I think) BP Ultimate and Shell Optimax.

They found that in basic standard cars (they used Clio) it made little or no difference.

But in cars with sophisticated engine management systems that could adapt to take advantage of the extra Octane it made a measurable difference - the car they used was a Subaru STX.






It seems like it's horses for courses - if your engine is sophisticated and tuned enough to make best use of the extra Octane then it pays to use it.

But this test appears to blow the theory out of the water.


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## listerdiesel (Aug 3, 2012)

Patrick_Phillips said:


> Exactly! So who is buying the 98 stuff and why?
> 
> Patrick


Plenty of 70's and 80's classic cars need something better than basic unleaded, particularly those with non-electronic ignition/management and an inability to run on lower octane petrol.

You can retard the ignition, but if you're not careful you'll melt a piston crown if you go too far.

Discovery V8's came with a low compression option of 8.23:1 instead of the 9.35:1 standard ratio (not 9.5:1 as I stated earlier) so there was a need for lower CR's for countries without 95 or 98 Octane fuel.

It made 5bhp difference, 177bhp against 182bhp.

Peter


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## Patrick_Phillips (Aug 17, 2006)

OK. I think I am beginning to work this out a bit. High octane is essential to some vintage cars and gives a bit more grunt for those who have sophisticated tuned motors and are paying attention all the time to notice it...

That leads me to another question! How much "posh" petrol do they sell compared to "plebs" petrol? 
Can't believe it can be that much...

Thanks to all of you.
Patrick


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## raynipper (Aug 4, 2008)

Stanner said:


> What is this "petrol" used for?
> I only seem to remember using it for things like generators, mowers, chainsaws and strimmers.
> I stopped using it for anything important, like road fuel, in 1988.
> Nasty stuff - Much too dangerous to have lying around in cans.


Yep, my ride on mower streaks away on 95 Octane. But a friend ran out half way round his lawn and filled up the hot mower which spilled and destroyed not only his mower but his head of hair as well.

Ray.


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## Mrplodd (Mar 4, 2008)

If it is THAT much better why aren't the fuel companies advertising like mad?? 

Smoke and mirrors (but only if your particulate filter is goosed :wink2

PLEASE don't get started on super-whizzo Diesel either, the same applies.

Andy


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