Compression Ratio / Racing Fuel

[slickshoot]

I have a classic mini that I race in which I use either a 1293cc or a 1380cc depending on which is feeling the most healthy at any given time. Both of the engines were recently rebuilt & the was dropped into the car, put on the rollers but then first time out the engine failed. We dropped the other engine in for the next event which also then failed. Upon closer inspection the head gasket had gone on both engines, blowing a hole in exactly the same place on both engines between cylinders 1 & 2, fatally damaging the block on the 1380 in that same spot. I have ran these engines without any similar issues for the past 5 years or so. I have since had the 1293cc engine rebuilt (by an alternative engine builder) who pointed the finger of the problem at the fuel we used (Shell V-Power Nitro+). Now we have used this fuel for 5 years or so with these engines & for many years previous to that with other performance A series engines with no bother. Our engine builder is adamant this was the cause but I feel it's strange that this problem seems to have just emerged out of the blue so I'm still eager to consider other causes. The 1293cc that we've just had rebuilt following this issue was running a compression ratio of 12.4:1 before the blowup & 12.6:1 now (following a head skim) so I realise the compression is at the higher end of the scale. The only other areas I feel could be relevant are cam timing & the electronic timing (running a Polestar ECU).

The fuel I would ideally use (Sunoco R6SR) is designed for engines with compression ratios up to 13:1 but is not allowed in the MSA Blue Book meaning I would be running ilegal if I use it so any thoughts & comments would be appreciated as I really need to get to the bottom of this.

Many thanks!

[randy]

Fuel is a possibility. V-Power is the best commercially available fuel but its possible to get a bad batch. Is there any reason the ignition advance has changed, maybe the crank pickup re-positioned or similar? Also, are you running very close to knock the whole time as you may want to back it off a little?

[slickshoot]

Well when the first engine went it was fresh back from the rolling road so I'm assuming anything unusual would/should have been picked up then? But as far as I'm aware nothing fundamental had changed & the timing wasn't pushing any boundaries as far as as being too advanced is concerned.

I think I need to get the laptop plugged back into the ECU to see whether there is anything unusual going on.

Do you think I can rule out cam timing for this particular problem then? The pistons didn't seem to have suffered any damage at all.

[stevieturbo]

Presumably it was on the dyno to be tuned ?

If you are suspecting CR is too high for the fuel, was the tuner not listening for detonation whilst tuning ?

And if this is the suspected cause of the failure, when rebuilding, it would have been worth lowering the CR surely ?

For fuel, are you allowed any additives ? Whether octane boosters, methanol etc etc