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Ernest

Best fuel

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Hi all

In the last two years of TR6 ownership I have been using 'top-grade' petrol. But this week I have been told by a very respected classic car garage

that  should only be using the ordinary petrol as the higher octane has a very adverse effect of the P.I. system. - I think is was on 'deteriorating' seals.

What are the views of you guys?

Best Wishes

Ernest

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There was a preriod 20 or more years ago when petrols contained oxygenates such as MTBE to raise the octane. But it is nasty, persistent, toxic stuff so is no longer used https://en.wikipedia.org/wiki/MTBE_controversy    At that time the PI suppliers changed to MTBE-resistant seals and that is what your socurce may have recalled.

Today the problem is ethanol. It picks up water, but anti-corrsion additves in fuel should help with rusting. However  ethanol can slowly oxidise to acetaldehyde and maybe formaldehyde which can crosslink and stiffen rubber seals and diaphragms in the MU.  eg over winter. Only cure I know would be to run the engines every month to flush out the stale fuel.

Peter

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Another concern is fuels with enhanced detergents eg BP Ultimate. They are useful for keeping modern engines free from deposits:

https://en.wikipedia.org/wiki/MTBE_controversy

That might be good for the PI, I dont know. But if those detergents strip the glassy film of ZDDP off rubbing surfaces (eg rings) then we have a problem. Modern engines do not rely upon ZDDP anti-scuff, and levels in modern oils are very low. I doubt high detergent fuels have been tested in classic engines and with our ZDDP oils.  In a world where both fuel and oil formualtions are changineg we are left with uncertainty.

A 6-pot racer described on here all six exhaust valves having a white deposit after 2000 miles running on BP Ultimate and a high-ZDDP Valvolene racing oil. If that deposit was zinc oxide then this could be a sign of problems with these new fuels.

There is a tech talk on classic oils at IWE...they might have answers.

Peter

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Hi Ernest,

if you use the lower grade of fuel then you may encounter 'pinking'. This is not good for the pistons etc.

I would stick with the higher grade from decent suppliers - Shell, Texaco, Esso etc,  Although good reports have cme back on the Tesco's 99RON offering.

 

Roger

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Triumph used to recommend 97 octane, 4-star. Modern fuels with this octane rating will destroy the original fuel system elastomers. I had to replace mine with Viton.

Running a PI engine on lower octane fuels will cause detonation-pinking- which will quickly destroy the pistons if it happens under load. Pinking can be reduced somewhat buy retarding the timing- but this will also greatly reduce power as well as load up the cooling system.

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If abroad, you can get some lovely stuff, "Shell V Power Racing" at 100 Octane....yes the Tr's on the LBL loved it!

Iain

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The pinking ( detonation) in PI TRs only happens transiently upon flooring the throttle. The cuase is octane fractionation in the inlet manifold dut to the lack of transient enrichmenr.Its a design fault, a quirk.  More here:    https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

Because the pinking is brief and at low rpm it's harmless. It is the only reason the PI engines need high octane, a carburettor engine will run happpily on 95RON and a comp rat of 9.5:1.   The cure for PI pinking is to check the fuel psi is correct, tune the MU to run richer, retard the spark, add heat to the manifold...in combination. This mix explains why some PIs pink more than others.

But the best cure that no-one has implemented that would allow running pinkless on 95RON would be to retard the spark for a second ot two after flooring the throttle. The benefit also comes in then being able to weaken the cruise mixture, optimise the cruise sparks and achieve higher mpg, and abolish the tick-over exhaust stink.

Peter

 

Edited by Peter Cobbold

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7 hours ago, RogerH said:

Hi Ernest,

if you use the lower grade of fuel then you may encounter 'pinking'. This is not good for the pistons etc.

I would stick with the higher grade from decent suppliers - Shell, Texaco, Esso etc,  Although good reports have cme back on the Tesco's 99RON offering.

 

Roger

Always run mine on Tesco Momentum, never a problem, and it contains less Ethanol then others. So I am told

 

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+1 for Tesco Momentum I've run a lot of motors on this with no issues along with Shell V Power.

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6 hours ago, Peter Cobbold said:

The pinking ( detonation) in PI TRs only happens transiently upon flooring the throttle. The cuase is octane fractionation in the inlet manifold dut to the lack of transient enrichmenr.Its a design fault, a quirk.  More here:    https://supertrarged.wordpress.com/2013/06/12/the-lucas-pi-lean-spike/

Because the pinking is brief and at low rpm it's harmless. It is the only reason the PI engines need high octane, a carburettor engine will run happpily on 95RON and a comp rat of 9.5:1.   The cure for PI pinking is to check the fuel psi is correct, tune the MU to run richer, retard the spark, add heat to the manifold...in combination. This mix explains why some PIs pink more than others.

But the best cure that no-one has implemented that would allow running pinkless on 95RON would be to retard the spark for a second ot two after flooring the throttle. The benefit also comes in then being able to weaken the cruise mixture, optimise the cruise sparks and achieve higher mpg, and abolish the tick-over exhaust stink.

Peter

 

I would suggest the exhaust stink of the CP engine is due to the valve timing ( lots of overlap ) and would require an afterburner to eliminate. Compared to the U.S. market low duration cam engines they are indeed stinky, and the exhaust is visible in bright sunlight when idling. More extreme cams than the CP don't need bright light!

Dog slow as they are, the U.S. market TR250/6 get much better fuel economy and don't stink - that's got to be worth something.

 

Tom

 

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I dont know if Shell V power here in the US is the same as what you get in Europe but my (more or less PI spec engine) loves it. Using the US octane system is is rated at 93 which I think equates to 98 RON in the UK.

 

Stan

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2 minutes ago, Tom Fremont said:

I would suggest the exhaust stink of the CP engine is due to the valve timing ( lots of overlap ) and would require an afterburner to eliminate. Compared to the U.S. market low duration cam engines they are indeed stinky, and the exhaust is visible in bright sunlight when idling. More extreme cams than the CP don't need bright light!

Dog slow as they are, the U.S. market TR250/6 get much better fuel economy and don't stink - that's got to be worth something.

 

Tom

 

And lots of overlap lowers the effective comp rat at lower rpm, another trick to kill the dreaded PInking ?

Dunno why Triumph stuck with the PI, other than a sales gimmick. It must have been obvious very early in development the PI was not the gift to CA emissions they sought.   

Maybe a 250 on triple webers would be a match for an early PO, without a stinking rich tickover... 

Peter

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31 minutes ago, Peter Cobbold said:

   

Maybe a 250 on triple webers would be a match for an early PO, without a stinking rich tickover... 

Peter

I've got a couple of those, the one with the CP cam has done 93K miles with it so far but it does stink compared to the stock engine with 10/50/50/10 valve timing. It's simple to lean out the idle until it won't run, and go back to where it just will and prove the point. As for the P.I., wonderful as it is I have long contended that TRIUMPH fitting triple DCOEs would have made them worth 2-3X what they fetch today. Here's a look at a CP cam on Webers idling:

Tom

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  • I run my TR6 and other classics on Tesco Momentum most of the time, or Shell V-Power if I can't get the cheaper Momentum from Tesco.

At 99 octane, these fuels perform well, with no pinking, and no need to retard the ignition timing. I've been using these fuels for 10 years plus and can't see any evidence of harm to my classics, including my PI equipped CP series TR6.

Nigel

Edited by Nigel Triumph
Typo

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Getting back to your original question, most modern, high octane fuels will probably destroy  any original  elastomers in the PI system. The reason for using PI is power. To get the maximum power you need high octane with the correct timing. 

If you're garage believes your elastomers  are incompatible with modern high octane  fuels you need to have them changed if you want to enjoy the advantages of PI. 

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22 hours ago, Peter Cobbold said:

There was a preriod 20 or more years ago when petrols contained oxygenates such as MTBE to raise the octane. But it is nasty, persistent, toxic stuff so is no longer used https://en.wikipedia.org/wiki/MTBE_controversy    At that time the PI suppliers changed to MTBE-resistant seals and that is what your socurce may have recalled.

Today the problem is ethanol. It picks up water, but anti-corrsion additves in fuel should help with rusting. However  ethanol can slowly oxidise to acetaldehyde and maybe formaldehyde which can crosslink and stiffen rubber seals and diaphragms in the MU.  eg over winter. Only cure I know would be to run the engines every month to flush out the stale fuel.

Peter

Hi Peter,

Last year I did the EC500 around Scotland ( 1925 miles door to door ) where I travelled to the never regions of Britain. The further north you go the less petrol stations there are, I used petrol brands that I had never heard of, but always their super grade. My timing is set up as the brown book and I did not have any pinking. The key issue for me is to make sure that the rubber seal parts in the PI system, are made from Viton B  and not the A grade which does not with stand ethanol as per a MOD test report that I have read.

Bruce. 

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1 hour ago, astontr6 said:

Hi Peter,

Last year I did the EC500 around Scotland ( 1925 miles door to door ) where I travelled to the never regions of Britain. The further north you go the less petrol stations there are, I used petrol brands that I had never heard of, but always their super grade. My timing is set up as the brown book and I did not have any pinking. The key issue for me is to make sure that the rubber seal parts in the PI system, are made from Viton B  and not the A grade which does not with stand ethanol as per a MOD test report that I have read.

Bruce. 

Bruce, Some pink, some dont. Detonation is a subtle combustion phenomenon, a mere 50C increase in flame temperaturue can induce it. That measn anything affecting combustion temperature can induce or avoid pinking: cam. mixture, timing, water jacket, waterless coolant, atmosphere, comp ratio/skimmed head. Your set up must have a favourable combination. 

Detonation a key limitation to running boost. But I can run on 95 RON with 5 psi boost and an 8.5:1 head with no pinking, thats equivalent to atmopsheric 10.5:1 comp rat. So PI engines were it not for the design flaw in lacking acceleration charge should also be able to run 95RON and be free of pinking.  I've thought a lot about how to overcoem the problem and adding more fuel upon flooring the throttle is too complicated. So I envisage retarding the spark about 5 to 10 deg crank by pulling the disy moving plate about 2-3 mm anticlockwise ( measured at the srping pin). A pull solenoid replacing the knurled adjuster will do. A microswith actauted by the butterly opening from closed and a 2 second timer relay would complete the circuit. As I have swapped PI for one SU the mod wont be trialled unless an adventurous PInking TR owner rises to the challenge !  Given a pink-defeater the MU can then be retuned to run lean at cruise and the vacuum advance pressed inot service to  advance the spark at cruise. That would improve fuel consumption too.  

To me, having to run rich on 97-99 RON and with no vac advcance for cruise mpg is inelegant. The PI is an indication of an engineering compromise too far; Triumph didnt complete the job.

Peter

Edited by Peter Cobbold

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Wow 

What a high level of expertise in evidence here - It is so good for non-experts such as myself to be able to take advantage

of this resource. On balance,  I am thinking that I will stick with the higher octane - so thanks all for your input.

Best Wishes

Ernest 

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