100% true Chip kinda makes me laugh at some of the stories tho....as far as tune up it should be close if your running race gas already like c12 or ?? my jetting stays the same. if its pump gas probably need to be little richer when switching to AV.the only time I need to change anything on my setup and Ill run 3/4 different types of fuel depending on my resources is when I use Q16 which is a lot richer than AV.as a matter of fact this year and from now on I will be using AV gas 95% of the time or Q16 if I
want alittle more performance its the only fuel thats ever outperformed the AV gas everything else runs the same.

I've run AvGas in my collector cars that sit through the winters, no issues at all. The cars run great on that stuff. All of the cars have modified engines with higher compression, so pump gas is borderline anyway, after sitting for a few months I couldn't hardly get the cars to run. Using AvGas there is no issue for storage, and I can drive them hard without worry.

My current mixture is 2 gal of 110 with 3 gal of 93 pump gas. Trying to get away from pump gas, but don't need straight race fuel for my engines as I'm at 10.9:1 compression.

110, That's probably 'Standard.'
https://www.sunocoracefuels.com/fuels/compare-fuels
https://www.sunocoracefuels.com/fuel/standard

Its going to be tough to calculate the change unless you measure the SG yourself. The pump gas specs will vary depending on where you live, time of year, and batch. Most of Md, the first two variables will apply. Chart from Exxonmobile reposted here:
https://www.tapatalk.com/groups/racingfu...s10.html#p16730

Its a little different than what we get up here, but both are Complex Model Refomulated Gas (RFG). For SE Penns'ia, if I understand correctly, it should meet 8.5 RVP in summer and is allowed 11.5 RVP Winter. Also that refiners need to supply Summer blend by May 1, but retailers have until June 1 to be switched over. Southern RFG may be a little different, along with the mandated summer/winter switch over dates. Winter blends are a b*tch in warm weather.

Anyway I think you just going to have to test at the track

What does specific gravity have to do with the tune/jet/heat range of spark plugs?

Can't answer the last part. Assuming the fuel is similar, I would think no effect on heat range.

re Jetting. If the density is signficantly different, the amount of fuel (mass) going through the restrictions will be different. The volume passed will be the same but the mass change changes.

I don't know if that's more important than the Stoich ratio, which also varies. If you look at the Sunoco's or Vp's specs, you can see the stoich varies as well as the specific gravities. On average, we can pretty much assume our street fuels with eth have stoic AFR rations less than 14.7 to 1.

For the guys (gals) looking for the last drop of power or consistancy an advantage of racing fuel that all the properties are published and consistant.

I look at that as the way to measure how thick the gasoline molicules (SP?)are, the higher S.G. the closer the molicules are to each other(thicker ) so I have needed to lean the fuel mixture to get the spark plugs and time slips the best I can get them, 100 L.L. aviation fuel with .690 S.G. I bought and used needed bigger jets than on race gas to get close to what I liked to see on race gas with .740 S.G.
Always jet up until the 1/4 MPH slows down, no matter what type of gas

We've used AVGAS and a Super unleaded 50/50 mix for years and on many different engines with no issues, race gas is just so expensive over here in the UK. The 100LL is about a 1/2 of the price of real race gas.
I once had to get some race gas at the track as I progressed through the rounds and ran out of my normal avgas/super mix. FWIW we didn't notice any difference in performance or any change in the AFR's just a lighter wallet