What kind of fuel are you running?

[Kingfish 11]

I run Chevron Supreme which I believe is around 93 octane. The 351W I have has been bored slightly when I overhauled it around 50K. I believe the compression ratio is still 10.7 to 1. So the other day I was cruising by my local Union 76 and saw racing fuel selling for around 8 bucks a gallon (I think). I entertained the idea of putting some in the tank but didn't. Because not to long ago someone told me than unless you need really high octane gas by using it when you don't need you actually make less horsepower. I think the 76 racing fuel is up around 100 octane. Back in the good old days when I first bought the car (I bought it new) I put Chevron Custom gas in it which I believe was around 100 octane and I swear I could feel it in the gas pedal. Maybe it was all psychological! Probably so! What I'm wondering is what would be the optimum octane for my 351W at 10.7 to 1. The engine now has 73K on it. Do any of you run octane booster additives?

 

Thanks for any feedback! Steve.

[rwcstang 201]

well i have a 351w (392w stroker) with almost the same compression so I was told to only fill up with 91 no less.

[RPM 1,190]

I'm no engineer, but fwiw I believe I read that higher octane burns at a lower temperature.

 

Bob

[Alan_Mac 48]

unbranded ethanol free 92 octane. My car run much better w/o ethanol.

[Chris'69Mach 23]

Funny thing that you brought this up .... back in the 80's when I was stationed a little north of San Diego, I put "California Gold" (that is what the pump called it) in my Datsun pickup ... it was 104 octane and it did seem to me that I got a little more pep with the pedal and got an extra 120 miles to that tank on the way back home for some time off.

 

I don't know but back then, I would have always used that higher octane if I could have found it anywhere else.

[Rsanter 152]

You get the maximum HP from the lowest octane fuel that you can use without getting preignition.

What octane you need is based on several factors.

 

First is your mechanical compression ration

 

Second is how much initial advance you have dial in and more important how much total advance you have

 

Next is the cam you have. Some cams are compression building and other are compression loosing cams. Remember that guy you knew that had 12 cr and that fat loopy cam and bough he was a hot shot. Well that fat loopy cam with lots of overlap bled off a bunch of compression

 

From there it gets more complicated. Piston dome shape, combustion chamber shapes, open verses closed chamber heads, port volume, port geometry, valve angles ( canted verses incanted as well as base valve angles),........etc

These factors effect the fuel mixing, flame front travel and efficiency, charmer distribution, tumble, dictribution from cylinder to cylinder......and a whole bunch of other things

All of these can effect the octNe required to avoid preignition.

 

And by the way, if you are listening for the pinging sound as a way to tell if you have it of not. It's already too late. By the time you can hear it you've got it really bad.

Modern cars have a knock senson on the block that detects the vibration or harmonic of preignition and then will automatically reduce the overall advance to avoid the condition

 

Bob

[sportsroof69 13]

^^^ what he said. You won't see any horsepower or fuel economy gains from running higher octane, if you don't need it. I run 91. I do run 110 when I spray more than a 150 shot, for some insurance. Nitrous and detonation is bad.

[Kingfish 11]

I put marine fuel in my boat thats at a marina here in Sacto. It's suppose to be Ethanol free and I believe it. It's a Honda 150 hp outboard and with that fuel it runs so much better. I think if I could put that fuel in my Mach I would! Leaded high octane fuel in the old days burned slower because of the lead. I don't know how many brain cells I lost filling up but I really don't think it was all that much of an issue all thing considered!

 

Steve

[1969vert 55]

You get the maximum HP from the lowest octane fuel that you can use without getting preignition.

What octane you need is based on several factors.

 

First is your mechanical compression ration

 

Second is how much initial advance you have dial in and more important how much total advance you have

 

Next is the cam you have. Some cams are compression building and other are compression loosing cams. Remember that guy you knew that had 12 cr and that fat loopy cam and bough he was a hot shot. Well that fat loopy cam with lots of overlap bled off a bunch of compression

 

From there it gets more complicated. Piston dome shape, combustion chamber shapes, open verses closed chamber heads, port volume, port geometry, valve angles ( canted verses incanted as well as base valve angles),........etc

These factors effect the fuel mixing, flame front travel and efficiency, charmer distribution, tumble, dictribution from cylinder to cylinder......and a whole bunch of other things

All of these can effect the octNe required to avoid preignition.

 

And by the way, if you are listening for the pinging sound as a way to tell if you have it of not. It's already too late. By the time you can hear it you've got it really bad.

Modern cars have a knock senson on the block that detects the vibration or harmonic of preignition and then will automatically reduce the overall advance to avoid the condition

 

Bob

 

 

Yep...what he said....

I run 93 in my black car and 87 in the rest...

[sportsroof69 13]

All lead was used for was lubrication. It has no effect on the fuels ability to resist detonation.

[Kingfish 11]

Sportsroof69: PLEASE READ THIS. It plainly states that lead helped reduce knocking (detonation) along with lubricating the valve seats.

 

http://www.todayifoundout.com/index.php/2011/11/why-lead-used-to-be-added-to-gasoline/

[Rip Rock 13]

Depends on the tune I run. Mostly 91.

[sportsroof69 13]

Sportsroof69: PLEASE READ THIS. It plainly states that lead helped reduce knocking (detonation) along with lubricating the valve seats.

 

http://www.todayifoundout.com/index.php/2011/11/why-lead-used-to-be-added-to-gasoline/

 

Okay

[tony 63C 14]

Chevron Supreme, but only because it is ethanol free up here in Canada. Ethanol supposedly reacts with and corrodes the metal alloy that carburetors are cast from which eventually messes up the fuel metering.

[Brian Conway 264]

91 Octane is what is available here. A station near me has VP Racing fuels 100 and 110 octane. I run the 91 in my 428 with timing set at 14 degrees/34 degrees actual and no problems. That picture with prices is from 4-2-14. Brian

[Alan_Mac 48]

Brian is the 100 octane price $4.13 or 8.98 / gal?

[Brian Conway 264]

$8.98 and that was two weeks ago. The 91 octane is now $4.28. Brian

[j69302 11]

The different grades of fuel, from 87 octane, on up to racing fuel, and even 100 octane Low lead aviation gasoline(Which if you convert to the same octane scale as advertised for gasoline, it actually is equivalent to about 104-108 octane), contain the same amount of energy. About 115,000 to 120,000 BTUs.

 

Octane does not affect energy content. Using a higher octane fuel in an engine with lower octane requirements will not result in a loss of power -- Only loss of money.

 

However, using a lower octane fuel in a engine with higher octane requirements can lose some power to do knocking.

 

Lead was added to increase the octane. The fact that it lubricated and kept the valves cooler was just icing on the cake.

[sportsroof69 13]

Using a higher octane can absolutely cause a loss of power. Higher octane burns slower, and is harder to ignite (ie....resists pre ignition), so if you don't compress it as hard, it doesn't create the same energy, as a higher compression engine......an engine that needs higher octane.

 

 

 

Regardless of any lead added, 91 octane is 91 octane. 91 octane with lead will not resist detonation any better than 91 unleaded. If it did, then it would have a higher octane rating.

[fvike 173]

Shell V-Power 98 octane RON which translates to 93-94 on the US AKI(R+M)/2 octane rating