I've searched and searched, but cannot find much info on what octane rating my MK2 needs. I'm pretty sure it needs premium unleaded and that's what has been going into it.

In Australia we use the RON rating system and we have two grades of premium unleaded (95 and 98). I believe that our regular unleaded (91) is the same as 87 in the States and our 98 is the same as 93 in the States.

So, my question is, should I be using 95 RON or 98 RON? It isn't a question of pricing since I've already put so much $$$ into the car that 10 cents per litre difference isn't going to break me.

I love driving the car and it puts a smile on my face whenever I get behind the wheel. A bit of history. I call it a FRANKENJAG. It's not an original numbers car, but it's all JAG. It was built in December 1962 and arrived in Australia in February 1963 so it's considered a 1963 model.

Somewhere along the line the original 3.4L engine was replaced with an engine from a 3.4L 1967 S Type and the auto gearbox was replaced with that from a Series 3 XJ6 (BW66). Three weeks ago I replaced the front seats with those from a 2003 X-Type. It's a "five metre car". From five metres away it looks perfect! It needs a complete respray but that's planned for next year.



Stu

 

I use regular, lowest octane here in Canada, 89 I believe.
It's not a high compression engine, so in that respect, regular is fine.

Even my B3000 Mazda (Ford Vulcan V6 has a compression of 175 psi and it uses regular and doesn't ping. Our Jags are no where near that compression.)

The industry will have you believe that the expensive gas has more additives in it to keep the combustion chamber clean/valve stems...

I never believed this, I always thought it was a ploy to justify the price of the higher octane stuff.

The best thing you can do for you Jag is change your oil and don't putter around town with it.
Take it out on the highway every now and then and run at 70mph, for a good hour.

If it does ping, then more then likely you have some carbon build up in the combustion chamber, so you may need higher octane.

 

These cars in that era were designed for leaded gas and thus typically have valve guides that will wear out with today's gas so to me I would not worry much as eventually you will wear the valve seats and at that time rebuilt the head with modern alloy valve seats and then it would be a good time to increase the size of the valves, maybe do some porting work and consider a better cam for higher performance. To prolong the inevitable you can spend a lot for lead additives but I am not sure if it is worth it as most likely your car engine is old and already has been worn from today's non leaded gas?

 

Not sure if valve seat/guide wear was really a factor in these engines. Very very few cars were affected.

Doesn't matter in any case, as it's not related to octane levels nor is there an effective street-legal additive that will help.

 

All of this really depends on the amount you drive your car and the more your engine is geared for performance. In my opinion most Jaguar owners drive their car so infrequently that the issues of unleaded gas are not a huge deal and when your engine wears out then just upgrade the internals for modern fuels.


Modern fuels depending on where you are located will have ethanol and do not have the lead which helped these engines valves, carbs, etc. run the way they were meant to.


If you drive your car a lot valve issues and other related issues will occur but why worry when your car is 50 years old as you will eventually need to rebuild the engine and upgrading to modern valve materials, etc. are no big deal.


There are additives but I have no experience on them as all of my classic cars have been upgraded to modern valve materials and chambers, etc. For me I want my classics fast and reliable so I upgraded my other classic original engines internals so that they look stock but now make more than double the horsepower by internal engine mods in the valve material/size, cam, cubic inches, head porting work, etc. This enables the old engine to be a reliable high compression engine that will be a daily driver.


As an example I have two Datsun 240 Z cars that have been rebuilt with modern valve design/materials and now are putting out 250 HP and over 300 HP compared to the stock 150 and they now are set up to run on today's gasoline.


FOR ADDITIVES I FOUND THIS FOR THOSE WHOM ARE THINKING OF IT; but again to me why worry your car is 50 years old and you will end up rebuilding the engine at some point...


The following additives have been tested as being effective against valve seat recession, and are approved for use by the Federation of British Historic Vehicle Clubs
Tetrosyl Automotive
Carlube Lead Substitute (supersedes potassium-based Nitrox 4 Star Lead Treatment and manganese-based 4 Lead Substitute and Octane improver). This additive is said to prevent engine knocking and pinking, in addition to preventing power loss (due to valve seat recession) in older vehicles. Tetrosyl Automotive, Bevis Green,Walmersley, Bury, Lancashire, BL9 6RE. Tel. 0161 764 5981.Website: http://www.tetrosyl.com
Castrol
Castrol Valvemaster and Valvemaster Plus Incorporating phosphorus. Castrol’s Valvemaster is claimed to protect engines under all driving conditions, to help keep the fuel system clean and to provide excellent corrosion protection. In addition, Valvemaster Plus incorporates an octane booster for engines running with relatively high compression ratios. Castrol,Wakefield House, Cambridge, CB4 5QZ. Tel. 01954 231668.Website: http://www.castrolclassicoils.co.uk
G. T. Autochemilube
GTA Power Plus Formula 2000. A potassium-based additive. GTA is now supplier of Castrol products. G. T. Autochemilube Ltd., Unit 4, Riverside Business Park, Tramway Road, Banbury, Oxfordshire, OX16 5TE. Tel. 01295 272799.Website: http://www.gta-oil.co.uk
Millers Oils
Millers produces a wide variety of petrol additives for road and track use. Millers VSPPlus is a manganese-based additive, which benefits from the inclusion of an octane booster, raising the octane number of the fuel by two (so, for example, 95 octane fuel is effectively rendered 97 octane by the use of VSP Plus). New launches include CVL and CVL Turbo; lead replacement and octane booster additives aimed at the enthusiast for fast road, track day and motorsport use which, when combined with Shell Optimax, are claimed to have the same values as racing fuel. Millers Oils Ltd., Brighouse,West Yorkshire, HD6 3DP. Tel. 01484 713201. Website: http://www.millersoils.net
Delta Oil
Red Line Lead Substitute Employing sodium to deliver the goods, Red Line Lead Substitute is said to clean intake systems, carburettors and injectors in addition to preventing valve seat recession. It was developed in the U.S.A. Delta Oil Ltd., Unit F1, Market Overton Industrial Estate, Market Overton, Rutland, LE15 7PP. Tel. 01572 768311.Website: http://www.redlineoil.co.uk
Superblend
Superblend Zero Lead 2000 relies on potassium to prevent valve seat recession. The dilution rate of the latest version (in terms of the ratio of Superblend to petrol) is lower than its predecessor, meaning that less of the product is required for a given volume of fuel; in other words, it is now cheaper to use! Superblend Lubricants Ltd., Unit 2, Feldspare Close, The Warrens Industrial Park, Enderby, Leicester, LE9 5SD. Tel. 0116 286 1001.Website: http://www.superblend.co.uk In addition to the products tested and approved by the FBVHC, there are many other products available which claim to reduce/eliminate valve seat recession. Just one is the manganese-based Redex Lead Replacement Octane Booster. Check out STP products too
Tesco Tops the Lot

Tesco has recently introduced a new, higher octane (99 RON) Super Unleaded fuel, typically two octane numbers higher than the usual ‘Super Unleaded’ petrol (97 Ron), and higher than Shell’s Optimax (98 Ron). It is important to appreciate that this is NOT a lead substitute petrol, and is not intended to tackle the issue of valve seat recession. Rather, it may be more suitable for cars (including classics) with engines running with relatively high compression ratios, which can struggle on standard (95 RON) unleaded petrol; ‘pinking’/detonation and possible piston damage can be a worry with such motors running on standard 95 RON unleaded. Initial assessment by enthusiasts has indicated good results with the new Tesco fuel it is claimed (There is an interesting review of the fuel and a forum relating to it on http://www.pistonheads.com).

 

Lead was used in gasoline to control the rate of burning, to raise the octane level _ it was a cheap way of doing it.
Lead in gasoline was never good for any engine, it builds up in the oil and eventually plugs things up _ it's called sludge.
It was more important to change your oil in the old days even more so because of the leaded poor quality fuels. Oils weren't that great back then either.

When I rebuilt the engine in my 51 Bentley, there were massive amounts of sludge, I scooped it out and collected it in an ice cream bucket, I notice that the bucket became quite heavy because it was full of lead. You could see it, this shiny sliver goo, it was everywhere.

The Bentley and my Jag are quite happy running on unleaded fuels and the Bentley gets driven a fair amount and driven hard _ no valve problems.

The only reason why they stopped using lead in fuel because it was plugging up the catalytic converters.
Even then, with todays environmental concerns, it probably would have been discontinued any way, even of it didn't affect the converters.

 

You're now muddying the waters with cleaning additives, lead substitutes and ethanol content.

None of these factors has anything to do directly or indirectly with octane ratings.

 

Just got back from a weekend away with one of the local car clubs. I ran 95 RON going and 98 RON on the way home. It seemed to run a bit quieter using the 98 RON (could be my imagination) so I'll continue to use the 98 RON for now. Thanks for all of the replies.

 

Here's more on the subject, it mentions the advantages of leaded fuel to prevent pre-ignition, _ which in turn prevents premature failure of valve seats, not that the lead itself some how magically lubricates the seats and valves to prevent wear.

Why Lead Used to Be Added To Gasoline

 

No it doesn't. It prevents 'detonation'- a very different process unrelated to pre-ignition.

Today's fuels contain different compounds that control detonation far more effectively than TEL.

 

OK, I always put pre-ignition and detonation under the same roof.
Pre-ignition caused by carbon deposits in the combustion chamber that get hot and cause the fuel to ignite in places where it isn't supposed to _ and when. Pinging if you like.

Where as detonation is caused from the fuel simply burning too fast either before it gets to the combustion chamber and or after "spark", once it gets to the combustion chamber.

The two terms are pretty close, both can cause damage to the engine.

At any rate, that's the way I see it.

 

Not really. Pre-ignition is premature (ie. prior to the actual spark) but otherwise normal burning (deflagration) of the fuel. The reasons why are numerous, carbon spots being just one.


False, sorry, that's a common myth.

Detonation is spontaneous explosion (detonation) of the fuel inside the combustion chamber subsequent to normal burning. It has nothing to do with the speed of the fuel burning.

One is burning the, other is an explosion- Camp fire vs sticks of dynamite.

A higher Octane rating reduces a fuel's tendency to detonate but has no effect on pre-ignition.

 

Doesn't it do both ! Higher Octane fuel helps with both pre-ignition AND detonation.

Higher Octane fuels can withstand higher pressure/temperature without pre-igniting, so anything that is acting as a glow plug for pre-ignition will have less effect on a higher octane fuel than a lower octane fuel.

Higher Octane fuels help eliminate detonation, they burn slower reducing the chance of detonation especially in engines where greater spark advance is used.

There is quite a lot of research regarding additives used to increase the Octane rating can have an adverse effect on detonation, and it is both RON and MON that should be looked at the difference between the two is the sensitivity of the fuel, this issue is less prevalent in the US than Europe, but again that's a whole other subject

 

No.

No, high octane and low octane fuel ignite and burn in exactly the same manner. Once again pre-ignition is still 'burning', while detonation is 'exploding'.

Octane rating has nothing to do with flame speed /rate of burn. All gas burns at the same speed. The goal is to eliminate any explosion.

 

Interesting discussion Mikey, I've watched some videos on it since my last post.
My B3000 truck is a perfect example of pre-ignition, it was pinging, and that engine has a tendency to do that due to it's high compression, but still designed to run on 89.

Everything else remained the same, even the wires and plugs after the rebuild, the only exception is that all the carbon was removed from the engine _ and no more pinging.
All was checked before the engine rebuild, EGR circuit (cleaned as well), correct heat range and gap of plugs, cooling system was in order etc...
The only thing left was carbon deposits, and they were numerous, it was owned by an old gentlemen in the city who did a lot of short runs and never allowed it to really get to temperature.

 

Well Mikey, there is a hell of a lot of information out there that doesn't agree with these statements, Fuel is a mixture of Octane and Hectane, both burn in different ways, so how a higher Octane fuel can burn exactly the same as a Low Octane fuel does not make sense.
I will bow out of this discussion, as it is going nowhere.

 

I'm sorry for opening Pandora's Box. I just wanted to know what everyone else was using.


Stu

 

LOL We just had this chat with Mikey in one of the other forums

https://www.jaguarforums.com/forum/x...-95ron-187591/

Just don't mention the war.

Next topic is nitrogen in tyres followed by direct injection.

Cheers,

Nigel

 

Nothing to apologize for as it was a perfectly reasonable question with a relatively simple answer.

The subject comes up quite frequently on this board, it's just unfortunate that also it brings out all the very old myths and misconceptions.

If the concept of detonation (explosion) is properly understood then it can be seen that the 'burn' rate of a given fuel would have no effect in eliminating the event. The fuel would still explode. Mixing the terms pre-ignition and detonation and their nicknames of pinging and knocking confuses even further.

Gasoline/petrol is not made up of just or even several compounds plus a bunch of additives. It's a blend of dozen of petroleum products taken throughout the refining process each contributing to a carefully controlled end product meeting dozens of specs. Octane rating is just one of them. Other specifics are of little interest to the consumer (other than Reid Vapour Pressure for those who drive hot running carbureted cars) so are not usually published at the pump. All pump gas is blended to have a very tightly controlled burn speed. I've seen examples of low octane fuel having a burn speed at the low end of the range with high octane at the opposite end.

Here's an interesting summary for those who are still not convinced.

http://www.rockettbrand.com/.../Tech...0&%20Power.pdf

 

Last bit of info Re-

Tim Wusz

VP of Engineering
Rockett Brand Racing Fuels
Tim Wusz worked for Union 76 doing fuel development work for street applications and racing applications for 39 years. Currently, Tim is working for Rockett Brand Racing Gasoline.


Quote from Tim Wutz :-
Myth: The higher the octane, the slower the burn.
Fact:
In many cases, high octane gasoline has faster burning characteristics than low octane gasoline. It is rarely slower.