Shell Optimax

[danhay]

I know the benefits of this fuel are recognised widely within the PH circle.

I always understood that the higher RON rating meant that it enabled cars with anti knock to run more ignition advance, and therefore a bit more power.

However, I've have felt immediate improvements even in vehicles with carbs and no engine management..so not just down to cleaning of the inlet system?

I'm beginning to suspect that Optimax might have a slightly higher calorific value than normal petrol?

How else could it make non FI vehicles feel faster?

[Fatboy]

as you say, cleaning out the inlet tracts etc would help, and you might have been running a bit too much advance for regular unleaded, hence a power increase on going to the higher octane optimax?

[danhay]

When the car went in for a service, which included a tune up (carbs and distributor) it had ordinary 95 ron unleaded in it. Also, if it was set up for higher octane petrol would it not pink with lower octane stuff in?

[Fatboy]

I would have thought it would pink as well, but I'm just guessing - perhaps it was far enough advanced to be below max efficiency on 95 RON, but not far enough to pink? Don't know if that's possible though...

There must be some better reason, but I can't think of it

[thepeoplespal]

danhay said:

I know the benefits of this fuel are recognised widely within the PH circle. I always understood that the higher RON rating meant that it enabled cars with anti knock to run more ignition advance, and therefore a bit more power. However, I've have felt immediate improvements even in vehicles with carbs and no engine management..so not just down to cleaning of the inlet system? I'm beginning to suspect that Optimax might have a slightly higher calorific value than normal petrol? How else could it make non FI vehicles feel faster?

RON95(ordinary unleaded) and RON98 (Optimax) refer directly to the calorific values of the fuel you are using. So yes your vehicle may feel a bit faster or your MPG might be a bit better with the higher RON fuel.

I tend to fill up with Optimax when going on a trackday, just to get a bit more performance out of the engine, even if it is normally set up of RON95.

[VYT]

thepeoplespal said:

RON95(ordinary unleaded) and RON98 (Optimax) refer directly to the calorific values of the fuel you are using. So yes your vehicle may feel a bit faster or your MPG might be a bit better with the higher RON fuel. I tend to fill up with Optimax when going on a trackday, just to get a bit more performance out of the engine, even if it is normally set up of RON95.

You sure RON refers directly to the calorific value of the fuel? RON (Research Octain Number) is a measure of the fuels tolerance to detonation, (pinking), in a "Standard" research engine. I am pretty sure you can have High RON values with Low calorific value and Vice Versa.

In fact, when Optimax first came out there was some comment that it had a lower calorific value than the 95 RON fuel. Certainly my Cerbera would return better MPG on UL than on Optimax, that might be the driver though. Not knocking Optimax, it's good stuff but I have never seen any benefit other than smoother running with any of my TVR's, 4.0 Chim, 4.2 Cerb or the T350T.

[danhay]

VYT said:

In fact, when Optimax first came out there was some comment that it had a lower calorific value than the 95 RON fuel.

That would explain smoother running? I had an Dual fuel car, and that felt smoother, though less quick, when running on LPG which has only about 80% of the calories of petrol.

[Pigeon]

I remember driving an almost-new VW Jetta in 1991 which was supposed to run on "ordinary" unleaded, but achieved better MPG on the higher-octane version because you no longer had to thrash it like a dog to get anywhere.

[Roop]

Optimax helped my Golf GTI no end. After a coupl eof tanks I noticed it picked up cleaner, pulled harder with little or no hesitation and when the warm weather came no more pinking...! The Golf ran a dizzy so no electronic ignition or anti-knock.

I have always used it in the Type_R so can't comment on what running on crap does for a more advanced engine.

Having spoken to some of the guys at TVR that have done engine rebuilds, they always comment on the fact that those engines that have been run on Optimax are immaculate inside and noticeably better than the rest. Perhaps they have much higher quality / more effetive detergents in Optimax.

On a slight tangent, has anybody used Shell V-Power 100 octane whilst abroad...?

[Fatboy]

danhay said:

VYT said: In fact, when Optimax first came out there was some comment that it had a lower calorific value than the 95 RON fuel. That would explain smoother running? I had an Dual fuel car, and that felt smoother, though less quick, when running on LPG which has only about 80% of the calories of petrol.

IIRC LPG has much better anti-knock properties than UL, not neccessarily to do with the calorific value...

[dinkel]

Roop said:

Optimax ( . . . ) Optimax. On a slight tangent, has anybody used Shell V-Power 100 octane whilst abroad...?

I guess Optimax is V-Power. Check the Shell-site . . .

[roop]

Optimax is only 98 Octane whereas V-Power is 100 Octane. Only available on the continent AFAIK (maybe only in Germany)

Roop