qim Posted August 23, 2017 Report Share Posted August 23, 2017 BP has an Ultimate fuel that claims to have a minimum of 98 octane but also advertise as 100 octane. What would I have to do if I switched to this fuel from the current 98? Is it just the ignition timing that needs adjusting? Thanks Camilo Quote Link to post Share on other sites
BrianC Posted August 23, 2017 Report Share Posted August 23, 2017 What is so special that your engine even needs 98 octane? Quote Link to post Share on other sites
peejay4A Posted August 23, 2017 Report Share Posted August 23, 2017 (edited) ...and you don't need to adjust anything as long as you're running OK on 98. If you're tempted to advance the ignition a bit on 100 and you're travelling and can only get 98 or less you could have a problem. Leave it alone. Edited August 23, 2017 by peejay4A Quote Link to post Share on other sites
qim Posted August 23, 2017 Author Report Share Posted August 23, 2017 (edited) Hi Brian Well. after my attempt, last week, at tuning the carbs I am happy to say that all plugs look nice and brown; and there is no black smoke coming out of the exhaust. However, having taken the car for a longish drive I find it that it is not as lively as it was in the late 70s, early 80s. Mind you, nor am I... and I wonder whether this is due to 95 octane petrol that I use at present (no longer 4 star, which if I remember was 102 octane) Camilo Edited August 23, 2017 by qim Quote Link to post Share on other sites
john.r.davies Posted August 23, 2017 Report Share Posted August 23, 2017 (edited) The octane number of a fuel is a measure of its "antiknock" property. It has absolutely no bearing on the power available from that fuel, only on how efficiently your engine can burn it. The fuel under test is run in a special one-cylinder engine with adjustable compression ratio (CR) which is adjusted until it JUST doesn't "knock", by undergoing compression igniton. Octane, or more strictly one of its isomers, 2,4, trimethyl pentane, is a hydrocarbon liquid that is knock-resistance and is mixed with 'n-heptane' a very knock-prone fuel. The octane number is the proportion of octane to heptane that runs the same in the test engine as the test fuel. So, 100 octane fuel resists knock as well as 100% octane. The point is that increasing the CR allows combustion to proceed more efficiently, hence the fuel economy of diesels. Giving your engine a fuel with a higher octane that it requires achieves nothing except lightening your wallet. If you have no knock - aka preignition, pinking - no need to go 100 octane. John Edited August 23, 2017 by john.r.davies Quote Link to post Share on other sites
qim Posted August 23, 2017 Author Report Share Posted August 23, 2017 (edited) If you have no knock - aka preignition, pinking - no need to go 100 octane. No pre-ignition. I have occasional, slight pinking, which I try to counteract by retarding the vernier wheel. Mind you, it only happens If I choose to climb a hill in 4th O/D when I should be in 3rd..., and if again I go into a bend or roundabout in a higher gear than recommended.It also seems to happen after I fill up the tank, possibly due to different fuels from different stations Other than that, surprisingly..., the car is doing fine and the consumption is getting closer to what it should be. Edited August 23, 2017 by qim Quote Link to post Share on other sites
john.r.davies Posted August 23, 2017 Report Share Posted August 23, 2017 Modern, lead-less fuels have other, more volatile anti-knock agents, that can be lacking by the time the station's bunkers are getting empty, or if they don't sell their contants quickly So try for well used, popular pumps. I'd say your engine is getting the right fuel even if, occasionaly, not the right gear! JOhn Quote Link to post Share on other sites
qim Posted August 23, 2017 Author Report Share Posted August 23, 2017 I'd say your engine is getting the right fuel even if, occasionaly, not the right gear! Yes, I agree. It's all down to the fact that I have short legs and have some difficulty depressing fully the clutch pedal; so I become lazy and try to manoeuvre with minimum gear change... Quote Link to post Share on other sites
rhino_mac Posted August 23, 2017 Report Share Posted August 23, 2017 You should speak to Ben and Vicky about high octane fuel. They filled up their TR3 on high octane by mistake on Paris-Prague in hot temperatures and the ethanol played havoc with evaporation issues. Cured with the aid of frozen spinach under the bonnet according to Vicky last night until they could dilute it with regular fuel. I would stay well clear and stick to regular fuel if your car is running OK. In terms of remembering how fast cars are, I think that gets distorted over time. I test drove a TVR Chimer a while ago (which was a bucket list car for me) and it seemed quite slow compared to its fearsome reputation. A friend drove it and said it felt considerably slower than his old Chimera of 15 years previous. However, his current car was a 500hp V12 Bentley and I had a 450hp Audi RS5. When we pointed out the lack of apparent power the garage owner asked what we expected on the basis of our regular road cars, which were 200hp+ over the Chimera. Modern cars are actually quite quick making older cars feel especially slow. Quote Link to post Share on other sites
ianc Posted August 23, 2017 Report Share Posted August 23, 2017 qim - the remedy for short legs (I have the same problem) is to fit an adjustable push rod to the clutch master cylinder. I bought one from Revington for my TR4 and it made a very real difference, so that now I can disengage the clutch fully - no more gear crunches! Ian Cornish Quote Link to post Share on other sites
Ben Freer Posted August 23, 2017 Report Share Posted August 23, 2017 You should speak to Ben and Vicky about high octane fuel. They filled up their TR3 on high octane by mistake on Paris-Prague in hot temperatures and the ethanol played havoc with evaporation issues. Cured with the aid of frozen spinach under the bonnet according to Vicky last night until they could dilute it with regular fuel. Just to clarify it was high ethanol fuel not high octane that scuppered us! Geoffrey has a higher CR than standard and really hates standard 95 octane. We use 98 octane (BP Ultimate or Shell V-power) only (particularly since the "spinach incident"). The frozen spinach was used to cool down the carbs as we were suffering from vaporisation brought about by the higher ethanol content in plus 30 degree temperatures and hard driving at altitude. We decided not to eat the spinach after it had defrosted however . I have since installed an in-line fan and ducting aimed at the carburettors to use in queuing traffic in hot weather to reduce the vaporisation. (I'll report back after the 10CR as to its effectiveness! Sods law it will be cool and wet!!) Quote Link to post Share on other sites
rhino_mac Posted August 23, 2017 Report Share Posted August 23, 2017 Personally I loved the spinach story. Inventiveness at it's very best. Quote Link to post Share on other sites
qim Posted August 23, 2017 Author Report Share Posted August 23, 2017 qim - the remedy for short legs (I have the same problem) is to fit an adjustable push rod to the clutch master cylinder. I bought one from Revington for my TR4 and it made a very real difference, so that now I can disengage the clutch fully - no more gear crunches! Ian Cornish Hi Ian Yes, I recall an earlier post when you mentioned that. I contacted Revington to enquire about that but got a neagtive reply. Dp you have the invoice with the part number? Thanks Camilo Quote Link to post Share on other sites
Don H. Posted August 23, 2017 Report Share Posted August 23, 2017 qim - the remedy for short legs (I have the same problem) is to fit an adjustable push rod to the clutch master cylinder. I bought one from Revington for my TR4 and it made a very real difference, so that now I can disengage the clutch fully - no more gear crunches! Ian Cornish Aren't all master cylinder push rods adjustable, Ian? At least to some degree... You're talking about making the push rod longer, yes, so the pedal at rest point is higher and actuates the clutch before the pedal gets too far way from you? I guess Revington have a longer rod? Camilo, don't you have a similar problem with the brakes? That would concern me more than the clutch... Quote Link to post Share on other sites
qim Posted August 23, 2017 Author Report Share Posted August 23, 2017 Camilo, don't you have a similar problem with the brakes? That would concern me more than the clutch... My right leg is longer... I find that the brake pedal actuates near the top, while for the clutch it has to be depressed quite a lot more. Of course, I can (and did) bring the seat forward but it is not a very comfortable driving position. Camilo Quote Link to post Share on other sites
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