3 March 2006: Octane

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n Japan, drivers have access to higher octane rated fuel compared to the United Kingdom. Like 101 RON. In the UK we manage with 95 RON (standard unleaded), 97 RON (super unleaded) and 98 RON (Shell’s Optimax). Although the European specification Accord was never sold in Japan, the engine has probably been used over there and given Honda, I figured it ought to be able to cope with higher octane fuel.

I’m now running Hoshi on Optimax. Now admittedly, I was always planning to run her on the higher octane petrol since I understood that the ECU adjusts ignition timing to compensate with the higher grade. Although I wasn’t really expecting quite the difference I’ve experienced. Honda state that the engine will run on 95 RON quite happily, it’ll probably cope with 92 RON, but providing it with more octane has been good.

She has expensive taste. Going on how she drives, the hesitancy at low engine speed / low load conditions has materially reduced. Sure, she is still occasionally jerky during the warm up period but less so. There’s also superior acceleration under 2,500 rpm, making for significantly improved flexibility. There is no longer the surge of torque at 2,500 rpm, it’s available from 2,000 rpm.

She may pull better at higher engine speeds but I can’t tell at the moment. And whilst Optimax is 98 RON, Tesco are now selling 99 RON fuel. I may have cause to investigate this stuff in due course.

However, although the improvement in performance is welcome the most significant difference is when it’s time to fill up. I’d managed to squeeze thirty five to the gallon on a couple of occasions by driving like she was on eggshells. That Honda engine is just begging to be taken to the redline; on Optimax, I drove Hoshi normally over my commute and recorded just under thirty seven miles per gallon. Even taking into account the higher price of Optimax it’s marginally cheaper to use it compared with ordinary unleaded. Yes, of my thirty mile commute over twenty five miles is on dual carriageway or motorway, but I’m certainly encouraged by this figure.

What is less encouraging is the way the Accord behaves on favourite back roads. The car handles well enough, there’s more body roll compared to the Ka and less feel through the steering. It’s impossible to demonstrate cornering speeds because in almost all cases it’s the visibility limit that curtails speed and not available mechanical grip. The Accord understeers much sooner than the Ka did but when lifting off the front end drops back into line rather than the tail steps out. It may be possible to unstick the rear of the Accord (and I will find out *cough*) but at the moment, the front tyres are materially less grippy than the rear, even despite the rear tyres being Michelin Energy tyres.

If I’m prepared to use the gears and revs, then the Accord is a whole lot quicker than the Ka on the straight bits. But in the twisty stuff I genuinely don’t think the Accord would leave the Ka. Actually I suspect the Ka was gradually walk away on a couple of my favourite roads... This is no poor reflection on the Accord, merely that the Ka is nimble, pointy fun on the right kind of road. One of the first lessons one is taught at racing school is that to make something quicker, adding more power is at the bottom of the list of to dos. Giving it higher levels of grip, chassis poise, feel, improving the brakes, reducing the weight and then finally increasing power. It’s easy to see why.