naishou

Correct. There are two different methods for measuring octane. In the US they use the average of both numbers and we use the RON number only. Supposedly their system is a more reliable indicator of the fuel's resistance to detonation in a real world environment. Japan uses RON like us.

DavidM, the Japan cars have 250ps, not 250bhp. 1ps (metric horsepower or some such rot) is less than 1bhp so their cars do not have that much more power than ours.

The extra power of the Japanese car does not come from leaner mixtures or more timing advance. It comes from higher compression. I would be extremely surprised if their ECU is programmed any differently from ours.

Higher octane fuel in itself does not give more power. Rather, engine characteristics that lead to more power generally require higher octane fuel to avoid engine damage. There are two ways I can think of that you can get more power out of a car by using 98RON fuel instead of 95 or 96.

Firstly, some cars might be operating near detonation and the ECU is retarding timing. Adding better fuel allows the ECU to advance the timing again. This is a common theory but flawed, mainly because if the car is detonating at all it's on the boundaries of safety and that's probably because it's hot, in which case it won't be developing maximum power anyway. It is also commonly believed that ECUs "learn" to adjust their timing maps over days of driving but I've recently seen evidence that this is not the case (APS website). It seems that people are confusing the closed loop operation that maintains stoichiometric fuel ratios at cruise with some other kind of learning facility. At WOT or any other non-cruise conditions the ECU reverts to pre-determined maps and only adjusts the timing if it detects detonation (pinging).

The second mechanism is that our higher octane fuels are also higher quality in general, which means that they burn faster once ignited and burn more completely. This is where the extra power comes from. It's not as sexy, but this is the mechanism that I think is mainly responsible. One way or the other, on 98RON here in Aus we are probably getting the same 179kW as the US. Our cars are not tuned differently.

Bernie

Naishou

you engineers...I don't know!!

DavidM

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... the Japan cars have 250ps, not 250bhp. 1ps (metric horsepower or some such rot) is less than 1bhp so their cars do not have that much more power than ours. ...
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Yep. sorry my mistake ... though I typed "hp" instead of ps. I think 237ps is what they claim in Europe ... which is 240hp.

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Higher octane fuel in itself does not give more power. Rather, engine characteristics that lead to more power generally require higher octane fuel to avoid engine damage. There are two ways I can think of that you can get more power out of a car by using 98RON fuel instead of 95 or 96.
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I 'm not 100% sure how it works (lots of theories around), but I do know that the local WRX club put one car on a dyno with 95RON fuel and then again with 98RON fuel and they menasuer a gain of a few kW ... it was 2.5% gain I think.

Also, I do know that HSV as well as CSV both claim more power from HSV cars when 98RON fuel is used.

Also, manufactures like Porschew and BMW often claim their 'peak' power with 98RON fuel while the car can still run fine on the 95RON fuel.

In the S2000 I have not tried running 95RON fuel so I'm not the one to say if you can feel the difference. Though, in my MR2 I swapped between 95RON and 98RON regularly and you could definaletty feel the difference.

2kturkey

Other way round David, 240PS = 236HP.

Wilch, in Japan there are 4 different grades of fuel (at least there were last time I was over there). The octane rating for their normal fuel is significantly lower than Aust std. premium and is around the same as our standard unleaded.

DavidM

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Other way round David, 240PS = 236HP.
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I'm just looking at a "SportsAuto" (German magazine) review of S2000. Under engine this is what is written: "240PS (176kW)" . Another magaziner "Auto-Illustrate" has it as "240PS (177kW)". At the same time all the US and UK publications list the S2000 as 240hp.

So ... I'm no conversion expert but 240PS seems to be the correct equivalent to 176kW ... so now all we need to know is whether 176kW = 240hp. According to my unit converter - 176kW = 239.3hp(metric) = 236hp(Electic). I'm not 100% sure which unit type they use in the States, but I'd pressume that it's not the 'metric' one. If they use the 'electic' unit then 240ps = 236hp = 176kW.

ps. This would lead me to believethat the hp(metric) unit is actually PS.

pps. This makes me wonder it they actually do have extra 4hp claimed in US (and UK) over us and Europe? Or am I just having problem matching up the units. Or does everyone use the 'metric' hp units?

2kturkey

Not 100% sure but I think you're probably right there David.

naishou

Yes, that is correct. I don't know anything about metric horsepower except that they are smaller than brake horsepower (bhp). 1bhp is 746Watts = 0.746kW, so I guess 1ps is about 735W or so. Strange number but there you go.

I think various quotes of 240bhp and 240ps are just an indication that Honda rounds it to the nearest sensible value for various markets before quoting (except ours ). In Japan outputs are always quoted in ps because it sounds more impressive than kW. The numbers are more often than not nice and round like 200, 220, 250 etc. This makes sense because it's ridiculous to quote power outputs like "176.5kW". There's no way the same car makes the same power within a few kW on different days or even different dyno runs, never mind different cars. The tolerance for power outputs is probably a few percent even in controlled conditions.

Col

If someone is really keen I have the full workshop manual which has the details of both engines and you can sit and read the tiny differences. But the only obvious one is compression. The ECUs are a different part number but not sure where the real differences are.

With regard HSVs, I had two Senators the first was the 205KW and it liked premium although the knock sensor protected with standard. My second was the 220KW 5.7 bored motor and it really liked premium to the point that it felt flat with standard mainly because the ECU retarded it a lot for protection. Apparently if you got one of the aftermarket PROM changes the output went to 235KW on premium and 225 on standard as they weren't as conservative in retarding on detecting pinging.

On my last long trip in the S2000 the first part of the journey was on standard (servo had run out of premium...) while the second part was on premium. The difference was very obvious particularly mid revs where the car was a lot "smoother".

2kturkey

Bernie, there are two factors at play here. First, it always feels faster in the passenger seat compared with the driver's seat. Second, up in Queensland with all your humidity any vehicle will not provide the same performance that it otherwise could on a cool dry day. I know that CA is not cool but it has very dry air and this really helps.

naishou

OK, why does dry air help? I think humidity being a handicap is a myth. Hot air yes, humidity no. When humid air is used in combustion the water that is in suspension as small droplets expands into steam which adds to the expansion of the charge and makes more power. This was explained in "The Last Word" in New Scientist about a year ago. I know that my WRX, which has much more dramatic performance swings than the S2000, goes best on a rainy day and even faster on a rainy night when it is both cold and humid.