Unleaded or LRP

[grover]

A friend has just purchased a '97 Vauxhall engined seven and the guy he bought it off told him to use 4-star or LRP. Is this correct?

[StewartG]

It's doubly correct at the moment being as you can get LRP PRACTICALLY WITHOUT QUEING down here in London I suppose that's where many of those K series engines fall down or should that be run out

[captain chaos]

I've got a tuned vauxhall and i was told to try and use SUL obviously because of the octane. If I use LRP or 4-star should i use an octane booster?

[Alex Wong1697456877]

 

 

I think a '97 Vx in standard tune should run on UL without trouble. With a tuned one, it all depends what the engine is mapped to. If it's mapped to use SUL, use SUL. If it's mapped to use UL then either LRP, UL or SUL should be fine as long as you don't have a catalyst or a lambda sensor. I'd still use SUL for track driving as it gives a bigger safety net before pinking occurs. I've run my car on 4* (the real stuff), UL, SUL and LRP and I can't say I've ever really noticed a difference. Mine was mapped for UL.

 

Does anybody know whether there is a disadvantage to running LRP instead of UL? (apart from cost). I wondered whether the extra anti knock ingredients would be beneficial. I know they're not as good as lead but seeing as my car runs on UL normally, I wondered if there would be any benefit/detriment to using LRP.

[simonray]

I'm getting very confused about LRP. I thought it was 97 RON but now I'm told it's only 95. I've got hardened valve seats so I only used LRP in my Roger King x-flow on the assumption that it had a higher octane rating (the ignition hasn't been retarded). Some people on the net are now saying that the additives in LRP are as damaging to valves as running UL, if not more. Now I don't know whether to a) carry on using LRP b) use SUL whenever I can get it c) change the timing and use UL. I seem to remember that Roger told me someone had come over from the continent for a rolling road session and had used Premium UL mistaking it for SUL, but that the car had run well with good power. So is using UL without adjustment an option. Is there any problem with mixing SUL/UL and LRP? I'm even more confused thatn when I started writing this! Does anybody know the answer?

 

[Rob Morris]

I run 97 Std Vauxhall on any petrol UL, SUL, LRP, 4* one advantage with no Cat and bloddy big carbs it will burn anything including small birds if they get too close to the inlets.

[mark.hall]

My Vx is mapped for UL, but I would use SUL for track days, and it is currently filled with LRP, 'cos thats all I can get. The only thing I have heard about LRP is that, because the different oil companies use different additives, they should not be mixed. Ie if you use Texaco LRP, it may not be compatible with BP LRP, and so may cause problems. I don't know what problems they may be, but it doesn't sound good sad.gif

[Jason Plato]

The base feul for Super unleaded and LRP is rated at 97 Ron ( Octane ) the LRP then has a few extras thrown . Hence LRP could be used in place of Super unleaded , providing the car has not got a cat . The extras in LRP damage the Lambda probe and the surface of the cat .

Logic would say that the anti - knock additives in LRP would benifit a car such as Alex's when used in anger as an extra saftey margin .

Here in Wales I have no choice in the feul I use as there is nowt about .... yet . I was however sold 20 L at the club night " on the black market " by the Holligan .... with this I enjoyed the best drive I have ever had up to Buith Wells and back yesterday afternoon . Not a car in sight !! .

Dave :-)

[Roger King]

Dave J. and Alex Wong have both got it right.

 

There are two separate issues with fuel. Octane and valve seat protection.

 

Octane is a measure of a fuels resistance to 'knock', variously known as detonation, pinking, etc, although people sometimes use these names to mean different things.

 

Knock is a situation where the fuel no longer burns smoothly, but suddenly explodes violently at the flame front. This explosion can be enough to (seriously) damage the engine (pistons, head, etc). The higher the octane number, the more resistant the fuel is to knock. The two major factors that affect an engine's tendency to suffer from knock (leaving aside fundamentals like combustion chamber design) are compression ratio and ignition advance - the higher the ratio and the greater the timing figure, the more likely you are to have a problem. In practical terms, this means that you must run a fuel with a high enough octane to prevent this happening.

 

At present, premium UL is 95 octane, whereas SUL, 4* and LRP are 97. It therefore follows that the last three are interchangeable from the point of view of knock. It is also true to say that if your engine is set up to run on 95 octane, there is no advantage (despite the stories people sometimes tell) in running a higher octane; equally, there is no disadvantage apart from in the wallet. What you must not do is run a 97 octane engine on 95 octane fuel. I do however, agree with the advice given by others here that it is a good idea to run the higher octane fuel on track simply because it gives some extra safety margin under arduous conditions.

 

PLEASE NOTE THAT IF YOU HAVE A CATALYTIC CONVERTER ON YOUR CAR THIS WILL BE DAMAGED BY LEADED 4* OR LRP FUEL. IN THIS CASE YOU MUST RUN ONLY UNLEADED FUEL (OF WHICHEVER OCTANE IS SUITABLE).

 

There is also the issue of valve seat wear. Older engine need lead to prevent valve seat recession; without the lead the engine will suffer long term damage to the exhaust valves and seats. This generally means Crossflows and some of the other engines used prior to the Vauxhall and K-series (these engines do not need lead, but won't be damaged by it unless there is also a catalytic converter fitted). LRP is generally reckoned to be a very poor substitute for proper leaded 4* and on a hard driven Caterham is likely merely to postpone the damage.

 

The solution here is to fit proper hardened exhaust seats (usually possible), or, at a pinch, to run unleaded fuel with one of the aftermarket additives (beware, some are useless).

 

A completely standard Vauxhall will probably be OK on premium (95 octane) unleaded, but check with Caterham first. SUL will do no harm, but once again, IF YOU HAVE A CATALYTIC CONVERTER, LEADED OR LRP ARE A DEFINITE NO NO. If you haven't got one then you can probably chuck in anything except diesel or paraffin!

 

In response to Simon Ray; yes a customer did come over with an engine that I had built for him to run on 97 octane fuel and yes, he had put 95 octane in by mistake. The engine was a Crossflow with unleaded exhaust valve seats fitted and a compression ratio of around 11.2:1. Amazingly, it ran without any detonation problems whatsoever on the 95 octane fuel and with ignition timing at around 34 degrees full advance! I was amazed, but have since found that many Crossflows will run on the lower octane fuel without problem. Please note that THIS IS NO WAY IS A GUARANTEE THAT ANY PARTICULAR ENGINE WILL BE ABLE TO DO THIS UNLESS IT HAS BEEN CHECKED ON AN ENGINE DYNO OR ROLLING ROAD - sorry, but just covering myself there.

[Alex Wong1697456877]

Roger,

 

Would it be logical to conclude that in a car like mine (Vx mapped for UL with no cat) that LRP would be the safest petrol available, followed by SUL then UL? In other words, do these anti valve recession ingredients do anything good for modern engines with no cats?

 

 

 

Alex Wong

alex.wong@lotus7club.co.uk

www.alexwong.net

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[Roger King]

Alex,

 

There doesn't really seem to be any advantage in running LRP in an engine that is compatible with unleaded fuel, but in your case, without the Catalytic Converter, it should do no harm either (usual disclaimers apply here).

 

I can't claim to have done a proper scientific test over, say, 150 000 miles, to prove that there is no benefit, but I can say that in general use an unleaded engine on unleaded fuel will suffer less valve seat wear than leaded engines used to do on leaded fuel.

 

Of course, LRP is generally easier to get than SUL, so this may be the deciding factor.

[Roger King]

Alex,

 

There doesn't really seem to be any advantage in running LRP in an engine that is compatible with unleaded fuel, but in your case, without the Catalytic Converter, it should do no harm either (usual disclaimers apply here).

 

I can't claim to have done a proper scientific test over, say, 150 000 miles, to prove that there is no benefit, but I can say that in general use an unleaded engine on unleaded fuel will suffer less valve seat wear than leaded engines used to do on leaded fuel.

 

Of course, LRP is generally easier to get than SUL, so this may be the deciding factor.

[Roger King]

Alex,

 

There doesn't really seem to be any advantage in running LRP in an engine that is compatible with unleaded fuel, but in your case, without the Catalytic Converter, it should do no harm either (usual disclaimers apply here).

 

I can't claim to have done a proper scientific test over, say, 150 000 miles, to prove that there is no benefit, but I can say that in general use an unleaded engine on unleaded fuel will suffer less valve seat wear than leaded engines used to do on leaded fuel.

 

Of course, LRP is generally easier to get than SUL, so this may be the deciding factor.

[Roger King]

Looks like I've got Multiple Entry Disease now. Not sure how that happened, but what does it say about a person's ego when they read their own entries (which is how I found out what I'd done)?

[Alex Wong1697456877]

Admit it Roger, you#re starting to reach high like the rest of us. cool.gif

 

Thanks for the replies.

 

Alex