Cylinder pressure to determine fuel octane

[2TFool]

So to recap, this Engine has an extreme porting job and a rather unusual squish band? It probably won't make any power until 6000 or so and I will quickly tire of it on the street and I'll be looking for another top end suitable for the street? I can lower the cylinder pressure with new heads, but that still doesn't deal with the aggressive porting.

But I do have the bike with the engine that it has for now. I didn't build it as it is, it just came to me and I couldn't say no, always regretted having sold my RD 400 a few years ago. I've been working hard, cleaning it up and changing a few details, it had been sitting for about 10 years collecting dust and light oxidation and I am going to ride it as it is even if it's just once or twice. I'd rather not buy a 5 gallon pail of race gas, but I will if I have to. I guess I feel a little nervous putting 93 octane in it, if I were to then would the only way to tell if it was OK was the audible sound of pre ignition, right around without my helmet on with my good ear turned towards the bike, or is there a better way?

How about some 100 octane low lead Av gas. I can get it locally and it wouldn't be a permanent solution to the aggressive tune of the bike, that would be a new top end which would be a project for the coming winter.

Thanks for your replies, I appreciate your help and admire your accumulated knowledge

[m in sc]

if it were me, I'd drop some pump 93 in it and try it. ive heard people claim high octane requirement a lot, where its absolutely not needed.

listen for detonation. it'll probably be fine. if it pings back the timing off.

[1976RD400C]

Check timing, B9 spark plugs, AV gas if you are worried, ride it, come back and say "holy crap!"

[JKV45]

if it were me, I'd drop some pump 93 in it and try it. ive heard people claim high octane requirement a lot, where its absolutely not needed.

listen for detonation. it'll probably be fine. if it pings back the timing off.

Many engines will run better and make more power with just enough octane to prevent detonation - and no more.

[m in sc]

exactly. 

[2TFool]

Ok, that's what I'll do, 93 and keep an ear out,
Thanks