73 S - engine photo and octane question

[mac73s]

I am planning to install the freshly rebuilt 2.4 S engine in a few days (it was rebuilt to stock specs) and would like to hear fuel recommendations. I know the 2.4 was a lower compression engine that the 2.2...just curious what today's octane rating would be best for this engine. Thank you.

[72targa]

If you rebuilt it to the stock 8.5:1 compression ration, you can run all day on 87 octane regular unleaded...

Looks very nice, by the way...

[304065]

Your motor was designed to use regular gas back in the day of tertraethyl lead, before MTBE, before the additives we use today. Before the inclusion of 10% ethanol, which changes the Stochiometric ratio to 14.1:1 and reduces your miles per gallon accordingly.

Given the amount of mileage you expect, I wouldn't use anything less than the highest octane pump fuel you can buy.

The reformulated Panther Pee that is sold to consumers today as gasoline needs all the help it can get.

Remember: octane rating is a measurement of how slow the fuel burns. . . it does not alone produce power on its own.

[Chuck Miller]

Lovely engine mac,

I used 91 in the 2.4S, and now as well for the 2.7 / 9.5 rebuild..........

And I also add about a cup of Marvel Mystery Oil to the gas and one to the oil about every 3 months..........

My .02

[Flieger]

Your motor was designed to use regular gas back in the day of tertraethyl lead, before MTBE, before the additives we use today. Before the inclusion of 10% ethanol, which changes the Stochiometric ratio to 14.1:1 and reduces your miles per gallon accordingly.

Given the amount of mileage you expect, I wouldn't use anything less than the highest octane pump fuel you can buy.

The reformulated Panther Pee that is sold to consumers today as gasoline needs all the help it can get.

Remember: octane rating is a measurement of how slow the fuel burns. . . it does not alone produce power on its own.

If he's got 8.5:1 compression ratio then 87 octane E10 is fine. Octane rating is octane rating. The ethanol will just help lower the intake charge temp a smidge because of the greater heat of vaporization. But maybe you are looking at it as the gasoline fraction being too low an octane rating, since the ethanol will bump the octane rating up.

I run 91 but I don't know what compression ratio I have.

[RSTarga]

Premium, my mechanic says it's really hard to adjust the mixture on regular. MFI is pretty sensitive.

[72targa]

If it ain't knocking with 87, anything higher just goes out the tailpipe as unburnt fuel...

[Cliff]

I am planning to install the freshly rebuilt 2.4 S engine in a few days (it was rebuilt to stock specs) and would like to hear fuel recommendations. I know the 2.4 was a lower compression engine that the 2.2...just curious what today's octane rating would be best for this engine. Thank you.

Mac, your engine looks very sanitary......nice work

[mac73s]

Thank you to everything offering their thoughts on fuel and compliments on the engine...I've attached a 'before' photo and detail of the rebuilt MFI. The fuel question pertained to the several gallons I want to add to the tank for the initial start...can always adjust what I use later, but wanted the optimum choice to begin with.

[ESully]

If it ain't knocking with 87, anything higher just goes out the tailpipe as unburnt fuel...

Higher octane means slower burn. Using too high an octane will reduce performance. Unless you are operating under extreme conditions, stay with the original recommended octane.