lotus 9xx engine Compression on 91 octane

[creepingfur]

Does anyone know the max-compression you can run on 91 octane (California Premium) in a 907/912 engine?

10.9/11:1 is know to work, but I would like to go higher (12 or 12.5:1).

Will this Ping?

Any recommendations?

cheers,
-bp

 

[DrEntropy]

ummm... my first reaction is that anything past 10:1 is gonna detonate on every fuel in a commercial pump ANYWHERE in CONUS.

I'm running 9.5:1 in an Alfa 1750 and it pings with "plus". You'll need to find what's called "Racing Fuel" for anything past 9.5:1... at over $8.00/gal and restrictions.

Hateful circumstance, but the way of it. Lower comp and a turbo may be an answer.

 

[creepingfur]

Hmmm... Interesting take...

The Lotus 907/910/912 was designed from day one to use unleaded fuel and I know the stock compression was 9.5:1 for most 907/912 motors and they can run on "plus" out here (89 octane) without pinging.

10.9:1 and 11:1 are a common upgrade with Esprit (S1/S2/S3) and Jensen Healey cars and know a few people out here that run 907s with 11:1 with no problem on our premium (91 octane). So to 11:1, I'm not to worried.

Even a R16 Europa high compression (11:1) will run on 91...

 

[LotusPosition]

At the time of my TC build, I was told by numerous, well known experts that 10.25:1 would be as far as you should go on pump gas (93).

I have been running that for 15 years now, no issues.