Octane Options

[Bulldog9]

Lets talk Octane..... What is the consensus on grade of fuel? I'm running 96 x 71 bore & stroke with .060" deck height 58.8cc chambers in the heads, and flat top pistons with no valve reliefs, and figure my CR is around 8.6:1. I'm thinking I can run regular, but no idea.

I've been running Chevron 92 so far, but dont want to wast $ and leave unburnt fuel residue. The higher the octane, the more resistant the fuel is to combustion, so unnecessary use of 'hitest' is dirtier combustion wise than regular.

I haven't done any experimenting yet, but wanted to get some experience before I do. I plan to run the current tank down to close to empty, then put in 5 gallons of regular and see how that goes, but just wondering.

[Mikey914]

With that compression you should be able to run reg.

[stugray]

Altitude also matters.
The higher the alt. the lower octane you can run with a given setup.

I am closer to 10:1 and I run 92 at 1 mile high.
I run the same gas in my BRZ which is 12.5:1 but has knock sensing tech with timing compensation.

[Tom_T]

Steve -

My 88 Westy WBX-4 with Digifont is a development of our 914 engines & at about 8.6:1 IIRC & factory specs it at 87 (85-87), & it's run fine since 88 at all altitudes & long XC trips for 28 years.

Also, I always ran 87/85-87 in my `73 914-2.0 with D-jet & stock CA/USA CR (7.6:1) & know folks with the Euro P&C at 8:1 who also used regular with no problems.

So I think you'd be okay, as the others above have said.

Cheers! (IMG:style_emoticons/default/beerchug.gif)
Tom
///////

[Bulldog9]

Great, thanks guys. Now I just need to find the co-ops that sell non ethanol fuel.

[80cap]

I think the better thing to consider is that ethanol fuel sucks. I am lucky that a gas station near to me sells straight 92 octane gas. I use it in all my lawn equipment and two stroke motors. The gas doesn't go bad in 30 days and destroy all the carbs and fuel lines. The extra cost is worth it in no repairs.
Brian

[Ansbacher]

My '74 2.0 L with dual Dellorto carbs loves 90 Octane Non-Ethanol. The difference between using it and the ethanol crap is like night and day. I have had tankfulls of ethanol blends that caused the car to run so poorly I was forced to siphon it out. Put non-ethanol back in and everything was back to normal.

Ansbacher

[914_teener]

Lets talk Octane..... What is the consensus on grade of fuel? I'm running 96 x 71 bore & stroke with .060" deck height 58.8cc chambers in the heads, and flat top pistons with no valve reliefs, and figure my CR is around 8.6:1. I'm thinking I can run regular, but no idea.

I've been running Chevron 92 so far, but dont want to wast $ and leave unburnt fuel residue. The higher the octane, the more resistant the fuel is to combustion, so unnecessary use of 'hitest' is dirtier combustion wise than regular.

I haven't done any experimenting yet, but wanted to get some experience before I do. I plan to run the current tank down to close to empty, then put in 5 gallons of regular and see how that goes, but just wondering.

Octane is a rating referring to the tendency to detonate. So the rating refers to a ratio of mix of octane and heptane. That is the standard. Octane and heptane are two different carbon chain molecules fuels. Buying a higher rated octane fuel doesn't mean it is a dirtier fuel.

I think when you posted combustion you meant detonation?

The propensity for detonation is caused by many factors but mostly by the combustion chamber and how the engine breathes and the fuel, so several things besides that octane rating.

Jake Raby has wrote untold threads on this.....he mostly says this in a few words as "its all in the combo" on how to create optimum power, not just in the CR ratio or the octane rating of the fuel.

[jim_hoyland]

Speaking of Ethanol; manufactures of AFR gauges and sensors warn against fuel with additives or contaminants; the sensors self destruct in their presence.

Any thoughts whether the ethanol could affect AFR sensors ?

[Bulldog9]

Lets talk Octane..... What is the consensus on grade of fuel? I'm running 96 x 71 bore & stroke with .060" deck height 58.8cc chambers in the heads, and flat top pistons with no valve reliefs, and figure my CR is around 8.6:1. I'm thinking I can run regular, but no idea.

I've been running Chevron 92 so far, but dont want to wast $ and leave unburnt fuel residue. The higher the octane, the more resistant the fuel is to combustion, so unnecessary use of 'hitest' is dirtier combustion wise than regular.

I haven't done any experimenting yet, but wanted to get some experience before I do. I plan to run the current tank down to close to empty, then put in 5 gallons of regular and see how that goes, but just wondering.

Octane is a rating referring to the tendency to detonate. So the rating refers to a ratio of mix of octane and heptane. That is the standard. Octane and heptane are two different carbon chain molecules fuels. Buying a higher rated octane fuel doesn't mean it is a dirtier fuel.

I think when you posted combustion you meant detonation?

The propensity for detonation is caused by many factors but mostly by the combustion chamber and how the engine breathes and the fuel, so several things besides that octane rating.

Jake Raby has wrote untold threads on this.....he mostly says this in a few words as "its all in the combo" on how to create optimum power, not just in the CR ratio or the octane rating of the fuel.

Yes, brain fart, detonation. Due to its 'resistance' to detonation, it burns slower and sometimes not as completely, hence 'dirtier'

Jake said something in a few words? (IMG:style_emoticons/default/chair.gif) (IMG:style_emoticons/default/poke.gif) Bur he is spot on with that comment, hence all the relevant data in my original post.

[carr914]

E-Free! (IMG:style_emoticons/default/aktion035.gif)

http://www.pure-gas.org/

[Bulldog9]

E-Free! (IMG:style_emoticons/default/aktion035.gif)

http://www.pure-gas.org/

You sir are a god...... (IMG:style_emoticons/default/beer.gif)

[Mark Henry]

Anything above stock CR you likely should move up to premo, but seeing the age of our cars I use pure gas and so that is premo here by default.

Speaking of Ethanol; manufactures of AFR gauges and sensors warn against fuel with additives or contaminants; the sensors self destruct in their presence.

Any thoughts whether the ethanol could affect AFR sensors ?

I do have a hard time believing that ethanol would harm a Bosch O2 sensor, they're in millions of modern cars. They must be talking about "fuel treatments."

I know that dragsters running on methanol the AFR readings double.
So it stands to reason that ethanol is affecting the readings, but by how much I don't know, I would imagine not a whole lot.

[somd914]

Ethanol-free... Only a dream here in Maryland. Oh how I wish (IMG:style_emoticons/default/headbang.gif)

[Mark Henry]

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

[Dave_Darling]

If you're running a stock mild, mild, mild cam I would suggest sticking with premium. Porsche specified 87 octane for the US-spec 2.0 with 7.6:1 compression, and the equivalent of 91-92 octane for the Euro-spec 2.0 with 8.0:1 compression. They do try to err on the conservative side, so you can probably run higher compression on ~92 by just giving up some of the safety margin.

If you have an aggressive cam, you will effectively "leak out" some of the compression. How much depends on more factors than I can calculate--it's usually best to talk to the people who designed your cam grind to find out what they think you should run.

--DD

[r_towle]

I run cheap gas in everything I own.
Audi, 914s, 911, truck, everything

I don't see the point of premium if the car is tuned properly, just a good tune up.

Ethanol has reduced the power by 15% already.

[914_teener]

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

Wow....great question.

Any Petrochem Engineers out there?

[Mark Henry]

The one thing I've wondered about is if you remove the ethanol from the gas what would the octane rating be on the end result?

It's easy to remove, just add a bit of water and it will separate the ethanol from the gas.

Wow....great question.

Any Petrochem Engineers out there?

Ethanol is basicly a octane booster, so I would think it would go down. What I'd like to know is if you were to remove the ethanol from 91 will you get at least 87 octane?

[gfg3]

Ethanol-free... Only a dream here in Maryland. Oh how I wish (IMG:style_emoticons/default/headbang.gif)

Just FYI. Pure-gas.org lists 42 ethanol free stations in Maryland. Might not be near you, but you might want to check it out.