Thank you Bill for deepening our insight. 10.25:1 comression ratio, can run on pump gas.

 

Norm,
Absolutely. Race fuel isn't really necessary until You go above 11-1 on then a blend of pump gas and race fuel will work fine.

 

The term octane was coined a long time ago in order to provide producers and consumers with a way to determine the knock resistance knock quality of a fuel. A standard fuel consisting of 100% isooctane was used as a standard, and it was burned in a "standard" engine built to SAE specs. I doubt that much isooctane is used in todays fuels, but the term remains. To confuse things further, there are 3 ways to represent the octane value in pump fuels, such as MOTOR, RESERARCH, and by government decree M + R / 2, which is the average of the first two. As Uncle Bill explained, you need the right fuel for each particular engine.

 

Pump gasoline is an interesting subject and doesnt closely compair with race gasoline in formula or consistancy which is what I think bill kind of said. Some companies do add oxygenates to increase octane example from a gasoline producers website... Oxygenates may be used in areas of the U.S. where they are not required as long as EPA's concentration limits are observed. Because all oxygenates are more expensive than the conven-tional gasoline they displace, ethanol's tax incentives make it the only one likely to be used near its concentration limit. The other oxygenates will be used at lower concentrations (1–7 vol %) only when the octane of the gasoline needs enhancement and when adding oxygenates is the most economical solution....

some fuel loads require the addition for the octane requirement some do not, why would they not use ethynol to meet the limit for octane. I do find it iteresting that they are allowed to use up to 10% ethanol(same as the old gasohol if anyone rembers) or 15% mtbe(methyl tertiary butyl either)to meet vapor pressure requirments in any of the grades. Different areas are required to have different formulations for air quality so thermal values and consistancy can vary from area to area .


My other comment was that high octane fuel is a waste of money in a engine that was not designed for it ie low compression not all our engines have computers to adjust timing to attempt to compensate and some cannot adjust enough anyhow . Exerpt below is from GM fleet documents.

Use the Recommended Grade (Octane) Fuel . Purchasing higher than
required octane fuel is a waste of money. Using higher octane fuels in a
vehicle that only required regular unleaded fuel will neither increase
performance nor improve gas mileage. In all cases refer to your owners
manual and ONLY use the octane rated fuel recommended for your vehicle.
Previous Technical Tip, available on www.GMFLEET.com

There is also supporting evidense that using premium fuel in a engine not designed for it can foul cats because of unburned fuel but I dont have time to go through it now.... I should be wiring a Camaro up now.

I think the question originally was will a 10.2:1 compression engine run on 89 octane which I think the answer should be no will it run on 93 ? steel heads/aluminum heads make a difference??

 

I think you mean iron or aluminum Griff. If it does make a difference, which is better to use with lower octane gas?
THX for all your imput.

 

The material that it is made of doesn't reflect the necessary octane usage. It is the compression ratio that you would be looking at. Aluminum pistons are better due to less rotating mass.

 

While I can't vouch for this absolutely in the engine building world, damn near everything but cookware that claims to be iron is ussualy steel anymore, anyway.

 

I should have said iron lol. Today was the first day of deer season in Pa as I sat in my treestand wondering why I do this every year I started to think of this conversation I sort of went off on a tangent about the fuel stuff and I apologize for that(at my job I remediate gas station spills so I have a some knowledge of the reformulated fuels ) Bill had a very good explaination of octane and as far as the head material I was sort of hoping he would respond because it can be a very deep issue, and I am not that deep but I will try.

Iron heads have a higher heat retention than aluminum which all things being equal will cause an iron headed engine to achieve detonation at a lower compression than an aluminum headed engine. The rule of thumb is 10 to 10.5:1 compression for 92 to 93 octane for aluminum and 9 to 9.5:1 for iron 92/93 octane. There are alot of factors that play into the equation to change those numbers ie quench area, chamber design, piston design, thermal coatings, dynamic compression, timing even to some extent rod length. The flip side of the equation is that iron heads can make more power due to the heat retention issue which could make the compression/detonation issue a wash iron verses aluminum(a 9:1 iron head could make as much hp as a 10:1 aluminum) which leaves the issue of weight and cost. The aftermarket iron heads are heavy I would guess 40lbs heavyer than aluminum but are prob $300 to $400 cheaper. The iron eagle platinums perform very well for the $. There are some repairability issues but they also go both ways so I guess it is either a weight or cost or personnal preferance issue.

 

Norm, As far as I know, all modern pistons are aluminum but the process is different ( Cast or Forged ).

 

Yeah they are, but you never no with a stock rebuild. Just a hone job with larger piston rings.