Petrol Is super worth it ?

[Gargamel]

Evening,

I recently bought an S-type for £1700. It's a perfect example, 3.0 of wafty loveliness. It is in great nick and I bought it with 104'000 miles on it, and a six month warranty. A decent deal I thought, given the condition.

Any way. I average 24.5 mpg on the digital display, I am pretty conservative, but commuting in it means inevitably traffic and the gauge can be seen visibly draining in the traffic.

Would I get better numbers on super unleaded? Is it worth it ?

[NormanD]

Gargamel said:

Would I get better numbers on super unleaded? Is it worth it ?

No and No

Also at that age with wear in the engine even less need

[supermono]

Yes and yes

Once you run a couple of tanks through, reset the ECU and see if you begin to notice the difference. I believe I always have done on my cars. Engine wear shouldn't be an issue at your mileage assuming it's not been abused with too much fannying about and poor oil quality/change schedule.

Various car magazines have seen gains in power fairly soon and even before ECU has really had time to adapt.

It could all be in my mind of course

[iamAlegend]

You shouldn't see much of a difference, marginal MPG increase and no more power/torque due to the ECU picking up on the fuel mixture.

Older jags like the xj40/xjs would be slightly better as they were tuned for 97 octane.

[supermono]

iamAlegend said:

You shouldn't see much of a difference, marginal MPG increase and no more power/torque due to the ECU picking up on the fuel mixture.

i don't know what that means 'picking up on the fuel mixture'

My understanding is that ignition timing can be optimised for more power with a better octane fuel and therefore give a bit more power before knocking occurs.

The trick is to get a tankful through preferably two, then reset the ECU and drive it for a bit. I've always found this gives better performance though mpg is harder to quantify. Could be in the mind of course I don't know for certain but I definitely think I get better speed from super.

SM

[Gargamel]

Thanks all, doesn't seem to be much consistency in the answers.

Given the extra cost for Super, It needs to pay for itself in greater MPG, doesn't sound like it will.

What prompted this was I filled up a couple of times from Supermarkets and just have a suspicion that I get lower mpg from those tanks than from my regular petrol.

Could just be a coincidence

[fatjon]

I'm a tight wad when driving my daily driver on the road (MX5 Turbo) and always try to get good MPG so I blind tested these fuels by covering the trip meter. After driving through several tanks full over a month I found it made absolutely zero difference using them, not a jot. BUT Optimax did give me a significant power hike and smoother running in the Cerbera, even though it made bugger all difference to the MPG.

[supermono]

fatjon said:

I'm a tight wad when driving my daily driver on the road (MX5 Turbo) and always try to get good MPG so I blind tested these fuels by covering the trip meter. After driving through several tanks full over a month I found it made absolutely zero difference using them, not a jot. BUT Optimax did give me a significant power hike and smoother running in the Cerbera, even though it made bugger all difference to the MPG.

I think you have to drive hard to get the difference, concerted full throttle high revs work all the time to get used to the car and then you start to notice. If you just blast away from the lights now and again you tend not to get used to the nuance.

SM

[fatjon]

Maybe so but if you are using "concerted high revs full throttle work all the time" on the road you either own your own road or will soon enough be off the public ones and will not be missed. I would suspect that a poster asking about if these fuels will improve his MPG is probably not interested in driving concertedly with full throttle at high revs all the time.

[supermono]

fatjon said:

Maybe so but if you are using "concerted high revs full throttle work all the time" on the road you either own your own road or will soon enough be off the public ones and will not be missed. I would suspect that a poster asking about if these fuels will improve his MPG is probably not interested in driving concertedly with full throttle at high revs all the time.

You're absolutely right, I didn't read the OP properly. In that case, I really don't know one way or the other. Apologies I only know about the performance aspect as above.

SM

[iamAlegend]

supermono said:

i don't know what that means 'picking up on the fuel mixture'

My understanding is that ignition timing can be optimised for more power with a better octane fuel and therefore give a bit more power before knocking occurs.

The trick is to get a tankful through preferably two, then reset the ECU and drive it for a bit. I've always found this gives better performance though mpg is harder to quantify. Could be in the mind of course I don't know for certain but I definitely think I get better speed from super.

SM

Ignition timing and amount of fuel injected is something different. Air Fuel mixture is what is monitored by the ECU (oxygen left in the exhaust), the engine can only ingest so much air so the amount of fuel injected is the thing which is changed. Charged engines are different.

But you are correct, the ECU will correct it's timing after so long with a different fuel to prevent knocking.

[Jon1967x]

I've never noticed any difference with fuel, I do notice a difference with changes in the air e.g cold dry days v warm humid ones. Shame you can't buy air :-)

Have you tried any of the fuel additives that remove deposits in the engine? I saw a review on tv (fifth gear) that was very promising, tried it on a friends shogun that was a bit lumpy and difficult to start and it made a noticeable difference.

[a8hex]

Jon1967x said:

I've never noticed any difference with fuel, I do notice a difference with changes in the air e.g cold dry days v warm humid ones. Shame you can't buy air :-)

Pity you can't get cold humid days, they'd help even more.

[awooga]

I notice a huge difference in my 3 litre x type when using V power. I get > 26 mpg driving it enthusiastically on super and about 22 on normal unleaded. I'll need to get the calculator out to work out if that's economically sound vs the price of the fuel, but still building up the profile. Is that about a gallon a tankful? Is that worth the extra per litre? I cannot feel any difference in ooomph under the right foot of one vs the other though.

[supermono]

awooga said:

I notice a huge difference in my 3 litre x type when using V power. I get > 26 mpg driving it enthusiastically on super and about 22 on normal unleaded. I'll need to get the calculator out to work out if that's economically sound vs the price of the fuel, but still building up the profile. Is that about a gallon a tankful? Is that worth the extra per litre? I cannot feel any difference in ooomph under the right foot of one vs the other though.

I'm not sure what the price differential is these days but if you're really getting 20% increase in MPG it's definitely paying for what I estimate is a 5% price difference. Can you be sure that's right? Even as a super unleaded convert I'm still surprised you get that sort of improvement, particularly driving it enthusiastically. The car should I'd have thought be pouring in just as much fuel at full throttle no matter what octane it is, and the car is making better use of that by producing more power (arguably).

MPG improvements should theoretically come at part throttle cruising when it can inject a little less of it to make the same required power.

SM

[8bit]

I've got a 4.2 XKR, I've switched to Super for a few tanks then back again. Absolutely no difference either way from what I can make out, either in terms of performance of economy. Each model is different though so my experience may not be shared by others.

[supermono]

8bit said:

I've got a 4.2 XKR, I've switched to Super for a few tanks then back again. Absolutely no difference either way from what I can make out, either in terms of performance of economy. Each model is different though so my experience may not be shared by others.

Did you run two tanks, reset the ECU and then continue for a few hundred miles? I think the adaption takes a long time (if ever) otherwise.

SM

[Hooli]

Jon1967x said:

Have you tried any of the fuel additives that remove deposits in the engine? I saw a review on tv (fifth gear) that was very promising, tried it on a friends shogun that was a bit lumpy and difficult to start and it made a noticeable difference.

I've known a few older/high mileage engines improve after using injector cleaner. The biggest improvements I've seen are on older engines with a low annual mileage, I guess lots of regular use keeps the deposits washed out before they can gum up.

[Benbay001]

As far as i am aware high octane fuel is only necessary in engines with high compression ratios.
Its so it doesnt detonate before its meant to. Right?

[supermono]

Benbay001 said:

As far as i am aware high octane fuel is only necessary in engines with high compression ratios.
Its so it doesnt detonate before its meant to. Right?

it certainly helps with detonation but that isn't caused only by compression ratio it's also ignition timing. the car can vary its ignition timing by software but cr is a constant. getting the ignition earlier is helpful for power but if the fuel octane is low, before ignition advance is optimal auto ignition will happen ahead of the flame front and cause engine damage. knock sensors will detect this and retard ignition meaning power isn't maximised.

rubbish petrol will detonate earlier and perhaps the ecu will retard ignition quite a lot so be resetting it after good fuel is properly established in the system, the safe settings will be erased allowing the engine to more quickly optimise for better fuel.

SM