DavidM

OK, it seems that that the 'power' of the engine in different parts of the world seems to be directly related to what kind of fuel you can feed it. It is somewhere between 237hp and 250hp (176kW - 184kW). If I take the 100 octane fuel (Japan) and say it gives me 250hp, then the weakest possible fuel (95 octane) gives us 5% less - this is 237hp on the dot. I don't think the head gasket (or whatever it is that is different) makes the difference. The numbers seem to relate it directly to fuel.

The (unleaded) fuel here is Aust is sold in 3 different types:
- Regular = 92 octane
- Premium = 96 octane (Minimum requirement for the S2000 here)
- Optimax = 98 octane

The specs here claim 176kW (237hp) with this fuel, though, I'm assuming that feeding the car Optimax (98 octane) will give the car 180kW (243hp). Also, the car here weights 1259kg - not sure how it compares to the models in UK/US/Japan. Anyone knows?

Also, my car is 'just' run-in (getting its 1st service tomorrow) so I'll line it up against my fathers HSV R8 (5.7L V8 beast with 250kW) - fastest one clocked here has been 6.0secs ... this compares well with BoxterS (this one is auto so 6.0 is the best I expect from it). We'll see how the S2000 fairs.

2kturkey

Hmmm, the mystery deepens further - can any one tell me what the workshop manual states in terms of differences between C1 and C2 motors. If Europe has the F20C2 am I correct in interpreting your comments Paul as saying that you guys don't have the higher compression motor with thinner head gasket?

As to the other points, yes, the OZ Stook weighs 1274Kg - 14 more than the Euro version. I don't know why this is but could it be the fact that we have the CD changer as standard (weighs a good 5 kilo). The manual also states not all markets get a/c as standard - this could account for the remainder (although I think all euro vehicles have a/c).
As for length, well I don't want to go into Aussie bragging rights but yes our Stook appears to be 10mm longer. I put this down to the standard front number plate mounting frame - can't think of anything else.

djohnston

I can only speak for the US market, as that's all I know, but there is a huge misconception here about octane numbers and what they mean, as far as the United States of America is concerned.

Here in the US we can buy gasoline at the pump from 87 or 86 to as high as 93 or 94, and as someone else correctly pointed out, this octane number may not be the same one as used in the UK or Australia. But getting back to the US, gasoline manufacturers here used to advertise their "premium" fuel (highest octane number and price) as having "more power". They never actually explained what they were comparing it to, but these companies were taken to court in the last decade and all forced to change their advertising so that it correctly stated the facts, which are that 93 octane is not more powerful than 87, it simply is more resistant to premature ignition (detonation or pinging as it's known). This is a fact.

That being said, certain high-performance cars are designed to use only the higher octane fuel, as these cars have a higher compression level and require that higher octane to properly make use of the capabilities of the engine. These cars will accept the lower octane fuel, but as the owners' manuals state "performance will be diminished" as the anti-knock sensor changes the ignition timing to account for the less-than-optimum fuel being used.

So the upshot is to use the fuel for which your car is designed; if your car doesn't require premium, using it will not improve it's performance. If your car does require premium, not using it will hurt performance.

Clear as mud indeed...

Luis

There are 3 octane ratings that I am aware of:

RON (Research Octane Number: used everywhere except the USA)
MON (Motor Octane Number)
(RON+MON)/2 (Pump Octane Number: used in the USA)

MON and RON both measure the gasoline resistance to auto ignition, albeit under different conditions. From this perspective the method used in the USA is the more complete. There is a rough equivalence between systems, with the stress on "rough". This is not a question of units but measurement methods!

I think there is a misconception in this thread that somehow Octane ratings relate to fuel stored energy. This is not so. What happens is that modern engines have detonation sensors that can detect that the gasoline is pre-igniting, adjusting timing as a result to prevent damage. As timing is advanced, power is lost and thus the lore about lower octane = less power.

Note that for auto-ignition to occur a lot of things must happen simultaeously. If it's cold enough, if the engine is not under severe load, you most likely can use a lower octane fuel with no detonation.

And you certainly cannot expect to get more power just because you're using a higher octane fuel.

As for engine versions there are 3 that I am aware of:

F20C (JDM, higher CR, 250PS=247HP, Reco: 100RON)
F20C1 (OZ, USA, ??, 240PS=237HP, Reco: 95/96 RON)
F20C2 (most if not all of Europe, 240PS=237HP, Reco: 98RON)

No one could determine for sure what the differences are between F20C1 and C2.

DavidM

Just looked up the weight in the owner's manual - it sais Aust S2000 = 1272kg. The US version weights 2kg more (not sure why). Though, the 13kg 'extra' that the Aust models carry over the Jap models is probably the airconditioning - that weights about that.

btw, I don't think the weight difference makes any real difference to the performance. There's more discreprtancy between the weight of the drivers that the cars :-)

Regarding the 'more octane in a fuel increases power'. I'm not sure why some of you say that is not so. In car's that are not designed for 'different' fuels (no knock sensors) I agree, but on cars that have knock-sensors - it cartainly should make difference. Knock-sensors work both ways ... if the fuel is 'weak' then the ingintion point is retarded while if the fuel is 'strong' then the ignition point is advanced. If you can compress the fuel+oxygen more then of course it gives you more power (more bang). Better fuel means more compression on the fuel (advanced ignition) and therefore more power. Even my previus car ('93 MR2) had more power with 'better' fuel even though it run fine on the standard unleaded (92 octane). I could feel the difference between the fuels in that car. Also, the manufacturer that makes my father's R8 (HSV) claims that the 'better' fuel gives you more power in that car. Stands to reason that S2000 (being even more performance oriented) would not be any different here.

UK Paul

Luis,

Thats more crystal, thanks for looking things up!!

Jap. version 11.7:1 Compression ratio to allow highest octane rating fuel. Thinner head gasket to give higher C/R.

Europe version F20C2. C/R of 11:1 I think, still high. Recommended 98 Ron min. Will work with 95 Ron but engine management will adjust timing to avoid 'knocking', thus losing power!

UK spec S2000 has A/C as std, but not cruise control, could this weird device on a 6 speed manual weigh the 13 kgs?.

Australia: We have the front no. plate frames also, maybe you just have a fatter arse

p.s. Get mine back tomorrow.

Luis

David, the reason why we say so is that using less than 98RON will not lead invariably to detonation. It depends on a lot of other things (WOT, temperature, etc...).

up to a point! If you fire the mixture at TDC you WILL be loosing power although cylinder pressure is at its max. That's because combustion will not be complete before the piston is in it's retracting stroke. The best ignition time is variable, but always before max cylinder pressure (TDC).

[Edited by Luis on 01-16-2001 at 08:28 AM]

The Reverend

This is absolutely not the case. A knock sensor works as follows: it uses a microphone to tap into the block and listen for abnormal noises caused by pinging and/or detonation. If it hears such noises, it retards the timing rather severely to eliminate the pinging and save the motor from being damaged. It listens for early signs of pinging so that the damage is not fully in progress before it reacts. Aftermarket knock sensors like the J&S safeguard do not react as drastically as stock knock sensors. They listen for knock and react in smaller increments and to the needs of each individual cylinder. This keeps power loss down while still preserving the motor.

Anyway, in NO CASE WHATSOEVER does a knock sensor ever advance timing beyond the stock level!!! Furthermore, at WOT, fuel and ignition maps are based on set pre-programmed curves. Provided knock is not detected, no changes are made.

Anyway, I'm getting tired of this thread - higher octane does not make more power, it only allows your to run a higher performance motor more safely (higher compression, higher boost, whatever). If anything, using an unnecessarily high octane gas will cause you to loose power as it will be less willing to burn.

DavidM

Of course 'better' fuel can't give you anymore power than the engine is designed for. In this case that being 250hp. Though, for all the people who are getting 240hp, the 'better' fuel will give them better performance. As it is, to get 240hp - you have to be feeding it the 'weak' fuel ... we agree on that, right?

So if feeding it the 'weak' fuel gives you 'only' 240hp then feeding it the 'better' fuel will 'advance' the timing of the ignition and hence produce more power. Maximum being 250hp with the 100 octance fuel.

S2000 was designed to run on 100 octane fuel and giving it anything less just 'retards' the performace (ie. gives you less power). Do we agree here?

Luis

David,

The only engine rated at 250PS (247HP) is the one sold in japan. The CR of this engine is higher than on the Rest of the World (ROW) cars.

Because the compression is higher, there is a higher probablility of fuel auto-ignition (higher pressure=higher temperature=easier to ignite the fuel), thus Honda in Japan recommends 100RON minimum.

Feeding 100RON to a ROW car, will do nothing! You are still locked at the 240PS (237PS) max rated power. If anything, it may even reduce performance as the additives put in to raise the octane level may negatively affect the combustion process. This is what the reverend was saying...