Higher Octane

[David Regan]

Hi All.

At my MOT/Service, tthe mechanic suggested that I use higer octane petrol (95/8) as I have a Jap import and they are manufacture to produce lower emissions (or something along those lines).

Has anyone ever heard of this before?

[Ian Linden]

This only applies to certain engines on expensive "high-performance "cars, such as some Mazdas, Hondas and Toyotas, e.g. the famous Mazda KLZE. The higher octane models are particularly high compression and high revving, to provide more power, and, if anything, give worse emissions, not better.

I feel sure your engine (which is not, from the photos I've seen of it, turbo'd) is the normal 16 valve Suzuki 1600cc which runs on 91 RON unleaded, so our 95 RON is overkill

[David Regan]

Mmmmm???????

Ian. It looks as though it is a bog-standard 1600 engine! (Although somebody has whacked turbo all over the top of it )

How can these engines be modified to make them turbo? Or at least to give a little more omph...

I have heard that many people think the manual X-90 is slow and sluggish, yet I find my automatic to be really nippy and that it accelerates fantastically. What's your opinion?

[Ian Linden]

Well, I think my manual X-90 is fairly nippy for its weight, but it's no sports car. It does respond to high rpm, but runs out of steam at about 65 (partially due to me having Vitara size tires and not having changed the final drives for a lower ratio).

I think that, at lower speeds, the auto box may well give better response, because the torque converter can give the effect of a lower drive ratio. The real test is something like the time taken from 60 to 70 mph.

As for improving the power, there is nothing cheap. Adding a turbo is a bespoke job for an expert, and would cost thousands. A better route would be to fit a 2.5 litre V6 out of a GV, complete with gearbox. But doing it to an auto would be a real headache, because of the electrics.

[David Regan]

Eeek.Thanks Ian. It would also prove costly to run!!!!!!

[Ian Linden]

Here's another way - mind you, he doesn't say how much power, and you'd have to reverse the swap for the MoT, or you'd certainly fail on emissions:

http://www.samuraiguy.com/WildBoreCarbs.htm

I don't advocate this, but it's interesting to get an idea of the possibilities.

I think there more to it than said there, as that conversion is to use the engine in a Samurai (carburettor model). To do your X, you'd have to fit a lower pressure fuel pump, and change the distributor to one with vacuum advance.

Also, I'm not sure how easy it is to sychronise four carburettors!