PREMIUM OR NORMAL UNLEADED

[lombardi]

Can anyone out there clarify the situation with choosing the right grade fuel and whats better for carbys.i have a 1968 105 1750 veloce with fully rebuilt engine,you hear so many different things with petrol,ie is it true that 98 ron is better in cleaning carbs,i swear that with bp premium or caltex engine runs better than with shell v,but my mechanic reckons petrol is all rubbish in oz and i should just use normal unleaded,please someone with knowledge clarify the situation.kind regards angelo

[alfagtv58]

my mechanic reckons petrol is all rubbish in oz and i should just use normal unleaded

I would be worried about my choice of mechanic if they said this to me.

Personally, I use premium (preferably BP or Caltex).  On your 1750, how much compression you are running may dictate what is needed?

We have some chemists on here that may answer this with more authority than me however.

[John Hanslow]

Good points Phil.

I can say I used BP 98 with an old Ford Meteor and it made a noticable difference.  The engine was worn out and an oil burner at that - but it was hell of a lot smoother.

Got good results with my 164 and I now just use Mobile 98 ron with my 156 twin spark.  But that's a choice I made anyway.

Good advice and good fuel  is the way to go.

Cheers.

[dehne]

mobile premium is the best quality fuel i think is synergy 8000

[Barry Edmunds]

BP Premium or Mobil equivalent seems to produce the best performance. Shell has apparently acknowledged that their higher octane fuels are not as good.

I have used both Premium unleaded and Ultra in my Super but feel that Premium unleaded is the better option for my car.

Agree with Phil re choice of mechanic.

Barry

[Stuart Thomson]

Hi All,

At the island last weekend one of the guys from the Nissan camp across the road from me swore by E85, they said they were getting better performance than with Avgas!

For us mere mortals however the choice of fuel is one of those never ending questions.  Personally I think it's a bit like wine, some are better than others, but sometimes it depends on personal taste.

First the facts;
The octane rating of your fuel should be high enough to stop engine knock at normal advance.  If you've got a fuel injected car it should have maps for 95 and 98 maybe 100 RON if it's very recent, in which case use whatever you want.  If you've got carbs, the car would be jetted to a particular fuel, possibly leaded fuel still.  Newer high octane fuels have a higher density than older fuels, which can mean that your car may run rich, get it tuned properly for 95 RON fuel and use that, brand of fuel really shouldn't matter.  All Alfa motors run at relatively high compression, hence all should be run on at least 95 RON fuel, even the older ones (though the compression may be a bit down), otherwise the ignition will have to be retarded and performance will suffer.

Now the hearsay;
In Melbourne BP and Shell use the same base fuel mix, different additives turn one into V-Power, the other into BP Ultimate (from a friend of mine who works for Shell).  I use Caltex 95 or 98 depending on the pump price, I haven't noticed a great deal of difference from either in the GTA.  In my opinion Shell Optimax (now V-Power) was crap for a while, but now seems better.  I have seen a comparative dyno test where fuels were compared, the winner was Mobil Synergy 8000 which got the most advance before pinging.

Now for the myths;
High octane fuel gives more power - absolute rubbish, unless the car needs it, it's wasted.  This probably stems from the fact that many high performance engines require high octane fuel because of the extreme compression ratio's the run.  To the novice it looks like high octane = high performance.  I always get a chuckle at the people filling up their Falcodores with 95 or 98, simply wasting cash.

Cheers
Stuart
(one of the chemists)

[Sheldon McIntosh]

Now for the myths;
High octane fuel gives more power - absolute rubbish, unless the car needs it, it's wasted.  This probably stems from the fact that many high performance engines require high octane fuel because of the extreme compression ratio's the run.  To the novice it looks like high octane = high performance.  I always get a chuckle at the people filling up their Falcodores with 95 or 98, simply wasting cash.
Cheers
Stuart
(one of the chemists)

You say myths with a plural but debunk only one.  What about the claim that 98 octane fuels will clean the engine, is this a myth too?

[Ray Pignataro]

Stuart it may not give more power but seems to give more miles per gallon. whether that equates to better economy given the price difference is a different issue.

[Stuart Thomson]

Now for the myths;
High octane fuel gives more power - absolute rubbish, unless the car needs it, it's wasted.  This probably stems from the fact that many high performance engines require high octane fuel because of the extreme compression ratio's the run.  To the novice it looks like high octane = high performance.  I always get a chuckle at the people filling up their Falcodores with 95 or 98, simply wasting cash.
Cheers
Stuart
(one of the chemists)

You say myths with a plural but debunk only one.  What about the claim that 98 octane fuels will clean the engine, is this a myth too?

Nothing to do with the fuel, additives may help to remove some of the gunge.

[Stuart Thomson]

Stuart it may not give more power but seems to give more miles per gallon. whether that equates to better economy given the price difference is a different issue.

Hi Ray,

Density is higher, therefore more fuel per squirt, or shorter squirt from injected motors.  Also you can run more advance.

Cheers
Stuart

[Ash Gordon]

On the E85 - I caught some of the pre season lead up to the V8 Supercars and the comments have been that the fuel efficiency is down by approx 25% and they will require additional pit stops, particularly the endurance events.

So are the Ethanol blended fuels a benefit? Is there a power / performance benefit great enough to warrant less efficiency?

Environmental benefit, probably as it's from a renewable resource (corn / sugar cane) but if it's burning quicker is it viable?? Or is it just clever marketing ??

A bit off track - just thought I would throw it out there..

[John Hanslow]

I know that with BP my cars have always run smoother.
Muast be the clean engine.

Cheers.

[1750GT]

Stuart, if its the additive(s) (-just thought I'd get the plural in as well - stet -) that really count what about using bog unleaded with a good fuel additive in the tank? particularly with the 105's which, whilst they are carrying higher compressions than your average 1.8ltr of its era, I don't that they are carrying modern engine comprehesions, but could do with the additives more than the properties of the fuel necessarily, for the carbies?

Note: for all other than Stuart - no debunking emails required, I AM NOT A CHEMIST!

1750GT

[lombardi]

What additives are recommended and what benefits,please elaborate for our benefit,any info would be greatly appreciated,spread the knowledge,as they say knowledge is power.ciao

[Stuart Thomson]

Stuart, if its the additive(s) (-just thought I'd get the plural in as well - stet -) that really count what about using bog unleaded with a good fuel additive in the tank? particularly with the 105's which, whilst they are carrying higher compressions than your average 1.8ltr of its era, I don't that they are carrying modern engine comprehesions, but could do with the additives more than the properties of the fuel necessarily, for the carbies?

Note: for all other than Stuart - no debunking emails required, I AM NOT A CHEMIST!

1750GT

Hi,
Even though the compression of the engine may not be the same as modern engines, the cars were designed to run on leaded fuel.  The tetraethyl lead was added as a valve lubricant and octane booster, so bog standard (92) unleaded will ping unless you retard the ignition.  I believe that the octane rating of the old leaded fuel was 95, so pulp is the way to go.  Also if the heads have been shaved ever then the compression will be higher than original.  Most of the additives in fuel are detergents and such to help keep the engine and fuel system clean, as well as stuff designed to help the fuel burn cleanly.

Cheers
Stuart