Should I be running premium or regular?

[RECHRGD]

The thread on compression ratio got me thinking.  I always thought that my engine had sixpac pistons, but wasn't sure.  It used to have issues with pinging back when I was running the stock 346 heads, so I always ran premium fuel.  When upgrading to aluminum heads, I discovered that I did not have sixpac pistons and that, in fact, my CR was only about 9.4 with the new heads.  Should I be running 87 or 89 octane?  Could I actually be loosing power running more octane than needed?  Heaven forbid!!  Bob

[Ghoste]

You wouldn't lose power by running a higher octane than needed just a little money.

[RECHRGD]

You wouldn't lose power by running a higher octane than needed just a little money.

Well, considering I put about 5,000 miles a year on the car, it will add up to more than a "little money".

[Ghoste]

It's all relative I guess.  You won't lose power and in your case you may not gain much either.  Then again, I can tell you for sure that my car doesn't need leaded 110 but when I treat it to a tankful, you actually hear the exhaust note change before you can smell the racing fuel.  The car runs smoother, cooler,  starts easier and just has an overall better "feel" to driving it.  I don't run racing fuel in mine all the time because of the expense but I do always run as much octane as I can afford.
Now my more modern daily drivers, that's a different story.

[PocketThunder]

I was just thinking the same thing, thats why i looked for an answer in the compression ratio thread. 

My question is.... i'm going to pull the 440 in my 69 RT and i want to put 3000 miles a year on that car.  What compression ratio do i go with to be able to drive the car on 87 octane?  How about 91 octane?

Or is it more complicated than that depending on cam and intake?

thanks
Paul

[RECHRGD]

It's all relative I guess.  You won't lose power and in your case you may not gain much either.  Then again, I can tell you for sure that my car doesn't need leaded 110 but when I treat it to a tankful, you actually hear the exhaust note change before you can smell the racing fuel.  The cars runs smoother, cooler,  starts easier and just has an overall better "feel" to driving it.  I don't run racin gfuel in mine all the time because of the expense but I do always run as much octane as I can afford.
Now my more modern daily drivers, that's a different story.

Well, if higher octane will make it run smoother and cooler, then that's a good thing.  I guess I'll just stick to what I've been doing.  Thanks,  Bob

[Ghoste]

That's my personal experience though, it could be that my combo likes that better for some reason even though it doesn't ping (the normal test for insufficient octane) on the 94 unleaded I typically use. 
Do you find a difference in the way it runs from 87 to 89?

[RECHRGD]

That's my personal experience though, it could be that my combo likes that better for some reason even though it doesn't ping (the normal test for insufficient octane) on the 94 unleaded I typically use. 
Do you find a difference in the way it runs from 87 to 89?

I have never run anything but premium.  Maybe I'll try a tankful of regular and see what happens.  Thanks, Bob

[Ghoste]

And Paul, yes the cam can have a significant effect on it.  It isn't just the compression ratio that affects the tendency for an engine to detonate or preignite, effective cylinder pressure comes into play as well.

[b5blue]

My 440 (.060 over) running 346 heads and a resto Mopar cam and a six pack, I'm happy to report, is running mid grade 89 Oct. fine. (Speed Pro 9.5 to one pistons) I'm trying 87 Oct. next.......

[1969chargerrtse]

Mine is a stock rebuilt 440/375 906 heads.  I cruise a lot so I normally use regular piss water gas with no issues, unless I stomp on it.  If I hear a ping I back off.  I also do timing by ear like in the ole days.  I ran my 454/365 vette on regular also with no issues, but again mostly for a gentle cruise.

[mally69]