Gen 3 Ls optimum fuel

Hi Team

I'm new here. I'll try to keep this to the point.

I'm working on tuning a gen3 ls1 that has a mafless otr, ls6 intake, stock heads, kalfords C-12 cam, long tube headers into 3" cat delete pipes then into a dual 2.5" cat back system.

I am based in New Zealand where we have 91,95 and 100+ octane fuel available at the pump.

In an ideal world I would test for myself but dyno access is limited.

So my question is, which of the fuel options is going to be best to tune and run on?

I'm sure 91 is out but is there any advantage, or disadvantage between, the other two on this setup?

Also while I'm here, do you know if the 2.5" exhaust will be limiting, in regards to power potential?

Thanks in advance.

Jeremy

Don't forget 98* at BP and Mobil, and E10 at Gull - I use the latter because it's around 10% cheaper and the car's manufacturer says to use 98 octane, and being NZ new it's fine with the ethanol (the import version isn't). Depending where you are, there are still 2 or 3 GULL outlets with E85.

If you're not sure what you need, I'd suggest starting with the highest available to you and tuning to best torque or knock, if the former then try the next octane down and check again, if the latter you're going to need better fuel or carry some octane booster with you, for when you do a fill.

For the folks in the North Americas, we use RON, your PON is around 4 numbers lower for the 'same' fuel.

Hi Gord

Thanks for your reply.

I'm down in invercargill. We don't have gull and BP, mobil only sell 91,95.

Assuming there isn't any knock limitation, is there likely to be any performance difference between 95 and 100 octane?

I don't have my own dyno, so not easy to do a lot of testing.

Cheers Jeremy

If you can use the optimum timing, and fuelling, for MBT - best torque throughout the operating range, on 95 there will be no benefit in using a higher octane.

If you can't then it may be worth while, but you may be trading off a very small gain for the convenience of readily available pump fuel.

If the 100 octane is Avgas, it is probably leaded, and will kill the lambda(s) in short order, so bear that in mind.

If the car is a 'play car', 'track car', or similar with low fuel usage, if you have safe storage and need the octane, you may wish to consider buying bulk in 20 or 209 litre drums?

For the dyno', the SI has a very active motorsport tradition, and Teretonga is actually in your home town, that suggests there should be some places local to you that can do the final tuning, such as

https://www.autocentreparts.co.nz and maybe http://www.dynotech.co.nz - no doubt there are more.