Andrew Posted May 22, 2003 Share Posted May 22, 2003 ESSO 95ron 1.11 Bar Optimax 1.04 Bar BP 98ron 1.03 Bar Run these different fuels over a month and 95 Ron keeps giving the same result. Ambient temperatures can account for small differences, but on 3 occasions I have tried Optimax and 95 ron within an hour or so of changing the fuel. Optimax has been taken from 3 different garages too, so can't be a dodgey batch. Doesn't make sense to me, wondered if anyone can find what I'm not taking into account? I was lead to believe more boost equals more power, and that the higher the octane value the more boost you would produce? Quote Link to comment Share on other sites More sharing options...
Adam W Posted May 22, 2003 Share Posted May 22, 2003 Octane is a measure of fuels resistance to detonation, ie how hard you can compress it before it will spontaneously explode. The more boost you run, the more air/fuel mixture you are trying to cram into the combustion chamber each time, so you can see that the fuel mixture will be subjected to higher compression at high boost (cos there is more of it in a fixed space). So, you need high octane fuel in order to run high boost safely. Changing fuels should not affect the boost pressure produeced by the turbos, this is regulated mechanically by a variety of linked systems. Quote Link to comment Share on other sites More sharing options...
Andrew Posted May 22, 2003 Author Share Posted May 22, 2003 Thanks for explaining that Adam. Need to find out what's giving me these variable boost readings. I always run on Optimax, until I got caught short and had to fill up with regular, then noticed this small boost hike. Naturally related it to the fuel. Resently swapped over to colder plugs (copper) maybe that has something to do with it? Quote Link to comment Share on other sites More sharing options...
Wolf Posted May 23, 2003 Share Posted May 23, 2003 Surely the fact that the car compensates for fuel means that using the two so close together, unless you pulled the ECU fuse to reset the ECU, the car would be working on the lower settings anyway?? HAve I misunderstood this? Quote Link to comment Share on other sites More sharing options...
Andrew Posted May 23, 2003 Author Share Posted May 23, 2003 Did it both ways Peter, resets and non resets. Question is, are boost pressure figures a good performance measure? Obviously not as the high grade fuels should make the car run better. Quote Link to comment Share on other sites More sharing options...
Thor Posted May 23, 2003 Share Posted May 23, 2003 Just because you are running more boost doesn't always follow that you are making more power. If you run a lower grade fuel there is a good chance the knock sensor will pick up detonation and back the timing off to compensate, hence more boost but less power. I can't explain why you are making more boost on lower grade fuel, except for ambient difference when testing, or possible taking readings in different gears. Quote Link to comment Share on other sites More sharing options...
Andrew Posted May 23, 2003 Author Share Posted May 23, 2003 Thanks Thor, I'm starting to understand now. As I say I was always led to believe more boost = more power, obviously that's not the case. And as I've posted before when running on Optimax and millers, I can feel a slight power increase. The peak boost readings were all done in 3rd gear, as that seems to be where all the power comes in before I hit my 112mph limiter. Quote Link to comment Share on other sites More sharing options...
Thor Posted May 23, 2003 Share Posted May 23, 2003 Andrew, more boost would mean more power if all variables stayed the same, but by pulling timing to compensate for knock the ecu effectively reduces power. Quote Link to comment Share on other sites More sharing options...
Andrew Posted May 23, 2003 Author Share Posted May 23, 2003 I'll continue running Optimax then. Naively I thought I'd be able to run cheaper fuels and pump out more power That's the good thing about this BBS, I'm on a constant learning curve Thanks for all the replies. Quote Link to comment Share on other sites More sharing options...
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