Which is the best juice...

[Back2a7in0xfordshire]

So, to resurrect a favourite old topic... what fuel should we use in our beloved 7s?

 

I've done a quick hunt and there are numerous threads about how supermarket fuel is cr*p, and you want to go for the busiest place (so the fuel isn't sitting around for long), etc, but no specific chat on what fuel is recommended for 7s.

 

I drive a 2002 Superlight R, with 1.8 190bhp VHPD engine (K-series). And the guy I bought it off a couple of months ago said that he only used standard unleaded - can someone enlighten me if these engines have been built to run on standard unleaded (hence we shouldn't use 'super') or whether its better to use super?

 

I'm aware that 'super' has cleaning agents and is a higher octane, etc, but not sure if this suits certain engines more or less than others. So, what would be the best juice for my VHPD?

 

Ta

 

[Stationary M25 Traveller]

If it is set for standard 95 octane, that will be fine.

 

Shell and Texaco were always reckoned to be the best.

 

As you say, the V-Power or Momentum type premium fuel costs more for some detergents and additives. I use Shell 95, but treat it to the occasional tank of V-Power.

[MADMALC]

On my SLR No27 with standard engine I used 'ordinary' fuel for the road and 'super' for sprinting or sustained 'brisk' road use.

The main differences I noted was that 'popping and banging' on the over run was considerably reduced with 'super'. The throttle pick up was also crisper with 'super'.

I never noticed any decernable difference in actual performance.

Hope this helps.

[MikeMolloy]

I have no quantitative evidence for this, but when I did the Academy we were told by Caterham to consider using super unleaded (boggo 1.6 K-Series engines) as it would lower the engine temperature on track.

 

Anybody got their coolant and oil temps accurately instrumented and can confirm?

[Surreptitious]

Always use the Shell Super.

Went on the Tafia run and car ran well on the way to Aberdovey, had to fill up with local plonk and car popped and banged all the way home.

[Stationary M25 Traveller]

They save the rough stuff for the cross-border invaders

[outnabout]

When I took delivery of my 1600K supersport in 97, the then Len Unwin at Caterham Dartford recommended ''super unleaded'' and this is what I've used except when caught out. For the amount of miles I've covered in that time 20K, the cost difference is minimal.

 

Hope that help

 

ChrisL

[Jonathan Kay]

RatRace recommend Super Unleaded 98 RON for K series.

 

Jonathan

[glasgow]

super unleaded is also gentler on tank and hoses

 

Ahmed

[Graham D]

super unleaded is also gentler on tank and hoses

 

That's interesting - why?

 

[Jonathan Kay]

*arrowup* *arrowup*I guess it's because of lower ethanol content, but I don't know of any objective data on the effect on hoses.

 

Jonathan

 

Edited by - Jonathan Kay on 29 May 2013 22:24:16

[Roadsport06]

Quoting Graham D: 

super unleaded is also gentler on tank and hoses

 

That's interesting - why?

I assume Ahmed is referring to ethanol, although I understand that this is now in Super unleaded such as momentum 99 and V power.

[Back2a7in0xfordshire]

Just filled up with V-Power and agree with MADMALC - definitely less popping/banging on overrun and faster pick-up. Perhaps psychological...?!

 

And yes, price differential is so small on the mileage that if it is better for the engine/car/performance then probably will stick with super. Just wanted to check cos wasn't sure if some engines were better to not have super.

 

Thanks team.

[revilla]

I had the Z & F mapping done to my K Series VVC. Mark Stacey recommended the super unleaded if I was planning to drive it enthusiastically with that mapping to reduce the chances of detonation issues.

[john milner]

I experimented with Super for a few weeks last year in a standard VVC.

Acceleration and responsiveness was a bit down, the exhaust note was flatter. MPG was the thing I was trying to test and it is possibly a bit better on motorway runs but about the same on my usual roads. Hard to tell for certain but I think it took a couple of hundred more RPM to cruise at the same speed as standard unleaded which doesn't make much sense as I thought more RPM = less MPG. All in all inconclusive if there is any benefit but costs more so was not worthwhile.

[Jonathan Kay]

Quoting John Milner: 

Hard to tell for certain but I think it took a couple of hundred more RPM to cruise at the same speed as standard unleaded which doesn't make much sense...

That's some powerful fuel... were you putting it in the gearbox or the diff?

 

:-)

 

Jonathan

[Stationary M25 Traveller]

No doubt inducing some huge losses in the gearbox or diff !!

[john milner]

Did I write something funny? The diff/gearbox comments have gone over my head.

I think super is supposed to create less energy than standard not more.With the right configuration super allows for higher compression before going bang which gives more power than lower compression. With the wrong configuration it is harder to burn so reduces power. At least that is my understanding which may be total blx.

[Jonathan Kay]

It was the comment about the fuel changing the relation between engine RPM and road speed. That's fixed by the gearbox and final drive ratio (and tyres).

 

Jonathan

 

Edited by - Jonathan Kay on 30 May 2013 20:09:46

[john milner]

OK I see what you mean. If speed was solely down to gearing it wouldn't matter what engine you had as 3,000 RPM would produce the same speed with the same gearing. Therefore a KA would be as fast as a Ferrari with the same gearing at 3,000 and it isn't.

[Roadsport06]

John, are you getting mixed up with speed and acceleration? Any engine with identical gearing will travel at the same speed. A 120bhp Caterham will travel at the same speed as a 260bhp one IF the gearing is identical and the rpm too. The 260bhp one will have better acceleration at the same rpm though.

[Mostro]

Quoting Jonathan Kay: 

It was the comment about the fuel changing the relation between engine RPM and road speed. That's fixed by the gearbox and final drive ratio (and tyres).

 

Jonathan

 

Agreed, but what about air resistance? Would a full-on headwind require more RPM to do the same speed (say 70mph) than without, or does it just require more right foot to do the same RPM?

 

/Just interested

 

Edited by - Mostro on 31 May 2013 12:13:54

[Roadsport06]

More right foot. Rpm dictates the speed, think of it as cogs needing to spin at a given speed to make wheels spin at a given speed.

[revilla]

Only if your clutch was totally knackered!

 

Otherwise each revolution of the engine causes a fixed amount of revolution of the wheel determined entirely by gearing ratio. Therefore the number of revolutions of the engine per second and the gear ratio completely determine the amount by which the wheel rotates each second, and therefore your road speed.

 

In fact there may be a tiny variation caused by slippage of the tyres on the road, but not enough to make any noticeable difference (i.e. when pulling a big wheel spin your RPM goes up but your road speed doesn't, but in normal driving they are locked together).

 

You can calculate the number of times your wheel must go round to cover one mile by dividing one mile (e.g. in meters) by the circumference of the tyre (in the same units), then in simple terms divide this by the gear ratios to determine how many times your engine revolves in one mile. This will be the same up hill, down hill, into wind, with the wind, running on unleaded, leaded, super unleaded or even diesel etc. as it doesn't depend on any of these factors, it is just fixed by the design of the mechanicals of your car.

 

The only thing would change it would be things that affected the physical gear ratios, for example changing the wheel or tyre size, gearbox or differential.

[sjmmarsh]

Mostro

 

It is the latter - you may need more right foot (and fuel consumption) to achieve the same speed (and hence RPM).

 

98 or 99 RON fuel should allow you to achieve the same speed with slightly less throttle and hence better mpg. In practice it depends on how the ECU is set up - some expect 95 RON and don't adjust if you put 98 RON fuel in it. The mpg in this situation is unchanged, but the additives in 98 RON may help the engine and it can run slightly cooler (on trackdays).

 

Steve