Beware of Shell 98!

[LukeC]

For those of you out there still driving real Alfas with Nord engines: This trap is catching a few people out here and there...

If you are using the stock type rubber carburetor isolators: DO NOT UNDER ANY CIRCUMSTANCES USE SHELL 98!

There is something in Shell's 98 jungle juice that will turn your carb rubbers to jelly within a couple of tanks. I have been caught on a few engine builds I have done over the last few years until things clicked to me. This fuel will turn your carb mounts to jelly in short order (like a couple of tanks). When I first struck this, I though it was poor quality non-OE carb mounts, but it happened even with OE Pirelli ones. Common theme was ALWAYS the vehicle's owner was using exclusively Shell 98.

You have been warned! Like a ~$600 repair bill.

Just a quick word about 98 octane fuels in general: Unless you have a high compression ratio, you are wasting money on these fuels. A 2.0 Nord has a compression ratio of 9:1 and was originally tuned for 92 octane fuel. The actual calorific value of all petrol fuels is around 46 MJ/kg, the gains in power can only be realised when your engine has a higher compression ratio and you need the knock resistance. E.G: My Subaru has a compression ratio of 11:1 and requires 98 to run correctly. I am not going to get into why here.

What do I recommend? Anything but shell... In fact, don't even drive into a Shell service station in any of your cars. I use BP... for the purely scientific reason that it an ingrained habit.

[poohbah]

Cheers Luke, so (aside from the pointlessness of 98RON in nords generally) it is only the Shell 98 that is problematic? I thought all same-octane fuels were effectively the same?

[bazzbazz]

It's not the octane rating that's the issue, it's the different additives that each company adds to their particular blend. Obviously there is something in the Shell mix that does not agree with the rubber components associated with the
carburettors.

[vinsharp]

I've had people with the same issue & the shell98 being reported as the fuel used.
I Would imagine that if the rubber of carb mounts is affected, surely the hoses and other parts could also be damaged, as in theory the type of rubber used in both applications should be of a similar fuel-compatible type.
I'm not yet convinced that the current offerings of aftermarket mounts are really up to standard, some of the steel faces not even being flat and rubber not completely bonded around the edges. Over the years some pretty aggressive fuels and additives have been run through carb rubber mounts without any real issues. This problem now happens so fast and the degradation of the rubber is quite something.
It may well be a combination of 2 issues, both the fuel additives and grade of rubber.
Would be good to have input from anyone else's experiences too.

[Duk]

It would be interesting to see the potential reactions if someone applied ethanol and, separately, toluene, to the rubber of the carb mounts.

Any other substances that could be in fuels, that people could name as potential instigators of shenanigans?

Would silicone be a more durable material, to make the mounts from?

[hammer]

Luke, back to your comment about 98 being unnecessary in a standard Nord, would you expect that a standard Nord would run OK on 91 octane (except Shell, of course) or would you think 95 might be better? For the past 25 years I've run my old Alfas on 98, thinking I was doing the very best for them. Cheers, Brent

[poohbah]

Me too Brent, would be interested in the answer.

[vinsharp]

Very few Nords are the standard factory compression ratio these days due to head surfacing, most I've encountered have generally closer to 10:1 than 9 or 9.5:1.
Ultimately it's keeping 'pinging' or detonation at bay whilst tuning the ignition setting for best performance and drivability. While 98 may not give you any more power necessarily, it will keep the detonation margin slightly higher than 95. This will not matter with most day to day driving, but sustained wide throttle openings on hills & 'spirited' driving, it helps keep the dreaded detonation at bay: blown head gaskets, broken rings and split liners are the serious & expensive results of detonation, which often cannot be heard from inside the car at revs and wide throttle.
Keeping in mind that the old Nord's 'hemi' head is a design that is very much behind the modern standards when it comes to compact and efficient combustion chambers resistant to detonation.
You can tune your engine for 91, sure, but the reduced ignition advance required makes the (average) Nord engine very soft & soggy keeping it out of the ping range in my experience. 
For general running around I will use 95, but always put in 98 if I know there's a good chance it will get a bit of 'exercise' on a particular drive. It doesn't break the bank & I consider a cheap insurance margin.

[MD]

Admittedly it was a long time ago, possibly over 20 years or longer there was a laboratory analysis of the energy content of all petrol brands sold in Australia. Caltex 98 RON came out ahead of the rest. What composition and to what to extent fuels have been doctored since then I cannot say.
What I can report on is the apparent energy content of 98 RON versus lower octanes by personal trial using the load of an air conditioner compressor on an engine at idle. Typical rpm at idle for 91/95 was noted to be 650 with the engine laboring but functioning. A complete change to 98 RON (same brand, same engine temp) lifted the idle rpm by 150 so engine now was running smooth at 800. Putting anti knock considerations aside for the moment, my experiment clearly demonstrated to me that 98 octane has more energy content.

[poohbah]

Cheers vin, you've reminded me that the whole reason I started using 98 in my gtv in the first place was because I was told it was the best means of avoiding pinging. In which case I'll keep using it, but will make sure I never use Shell.

[Colin Edwards]

Weigh a litre of 91, 95 & 98.  Whichever is the heavier will probably have the higher energy content.

Also need to remember the chemical composition of petrol changes throughout the year.  During the summer months the brew is altered to reduce evaporation during handling. 

I'm with Vin on this one. If there is something nasty in Shell 98 that is melting "rubber", then it may also impact fuel lines, pump diaphragms, float needles etc?   

[hammer]

Good answers. Thanks lads. I'll continue to use 98 all the time. Given I live 500m up a hill, surrounded by tempting twisty roads, just about every drive is 'sprited'. Cheers!

[Craig_m67]

Is all that correct?

[ramble, back in my day]

I have always thought that the RON rating refers to a fuels ability to avoid pre-ignition.  Any increase in power is down to the higher compression engine being able to burn the fuel more efficiently/precisely.. because it can avoid pre-ignition/pinging/knock, etc.

30yrs ago (previous life) I installed and calibrated EDXRF fuel and oil analysers all over Aust. & NZ that the refineries used for quality control, ie. that the "packages" of product that were added/mixed to the base fuel or oil was correct.  The packages were just that, additives to reduce pre-ignition and detergents etc., in the oils it was Zinc, Moly, etc.  The packages were imported (at the time), the guys in the refinery were just mixing it, like post mix Coke at the pub (their words - Sunshine VIC.)

It was the (branded) packages that determined the final branded product.. the base (fuel at least) was all identical.  Several brands came from the same refinery.

I guess what I'm trying to say (or check/understand) is, I don't think one fuel has a higher energy content than another... if it's heavier, it's probably because it's got more s#hit mixed into it.  The difference is how well the engine can extract the energy.  Which is determined by the engine (compression, etal) and all the modifiers in the fuel to avoid pre-ignition etc.

Could be completely wrong though, I've forgotten more than I can remember from those days.  I was thinking of putting a polarising crystal over the ECU to improve combustion, but I understand that's a bCrock.

I always use the cheapest E10 94 in the QV.. maybe run a tank of 98 once every year or so, just to check my seat of my pants barometer..

[/ramble]

[vinsharp]

 Some years back there was a club member who had a fuel transportation business for one of the major brands.
He said that every base load of fuel was the same, then if the delivery was to be for 95 say, one drum of additive was tipped into the tanker. For 98 maybe 2 drums were tipped in. All this was carefully & scientifically blended as the truck drove over the road undulations to its destination....see, potholes do have a positive benefit!

[Craig_m67]

Yep, ^that^.

I know they blended packages into a base fuel, because I'm the guy who installed and calibrated the EDXRF process and quality control instruments in the labs (and lines for larger refineries). 

I'm sure whatever is in Shell 98 (vortex?) is available in an MSD somewhere.  Maybe a blunt social media question asking what they've changed because it's "melting" carb rubber is in order (from whomever has actual data).