What Octane

[Heyblue]

1984 crossfire fuel injection (sort of) I assume the proper gas for this year is 87 Octane. Don't have the owners manual and the service manual does not seem to address this issue. Comments please

 

[DonB]

I wouldn't assume anything. My '90 requires premium, as stated by fuel filler, "Premium Fuel Recommended."

I skimped once and used regular 87 octane and she didn't like it at all. NOT AT ALL!

When in doubt, use the good stuff. She will appreciate it(and so will you.)

 

[hcbph]

Owners manuals can be found on EBay, that's how I found one for my 86. The 86 runs fine on 87 octane but it's a cruiser so it's not being pushed hard. No racing, no pinging, just hits the road and runs just fine.

 

[Vettehead Mikey]

87 octane is what it was designed for. Higher octane was not required until 1987 I think.

 

[Wegone]

Just me its a Corvette it gets the best!! Just part of owning a sports car.

 

[Vettehead Mikey]

It might make you feel good but the car couldn't care less.

 

[LLC5]

Just me its a Corvette it gets the best!! Just part of owning a sports car.

FWIW higher octane fuel in not a better fuel, it just has a higher octane rating number, and it does accellerate carbon build up.

 

[kpic]

It is a double edged sword; too high or too low is bad. The best answer is use what the engine manufacturer says to use.

IMO, this article is very informative on the subject.

Obviously, PCM cold enrichment strategy is required even in the case of a brand-new engine because sufficient vaporization of atomized fuel on the backs of cold inlet valves is impossible to achieve. But the inevitability of carbon buildup accumulating on the valves will eventually result in cold (and sometimes even warm) engine performance issues such as stumble, sag, stalling, etc. Injectors spray their fuel volume very close to the beginning of an intake stroke; it’s only later in the stroke that the inlet valve actually opens in order to draw air and fuel into the cylinder. Small portions of the atomized hydrocarbons sprayed by injectors onto the backs of the closed inlet valves will invariably be absorbed and transformed by heat into additional activated carbon residue.

MOTOR Magazine Article | MOTOR Information Systems

Personally, I buy Top Tier gasoline because it has more detergents than bargain gasoline.

 

[Vettehead Mikey]

Personally, I buy Top Tier gasoline because it has more detergents than bargain gasoline.

But additives has nothing to do with octane rating- the OP's sole question.

We just need somebody to mention ethanol and we'll have the gasoline trifecta. :ugh

 

[Wegone]

It might make you feel good but the car couldn't care less.

FWIW higher octane fuel in not a better fuel, it just has a higher octane rating number, and it does accellerate carbon build up.

OK my car does not run good on low octane with an 11.5 compression ratio. I'll step out now!!

 

[Vettehead Mikey]

OK my car does not run good on low octane with an 11.5 compression ratio. I'll step out now!!

The OP's car is 9:1, like all '84s. That's the difference.

 

[Wegone]

The OP's car is 9:1, like all '84s. That's the difference.

Original post

1984 crossfire fuel injection (sort of) I assume the proper gas for this year is 87 Octane. Don't have the owners manual and the service manual does not seem to address this issue. Comments please

My response

Just me its a Corvette it gets the best!! Just part of owning a sports car.

I also have an L83 & LT1 they also get Hi Test. BP 93 octane. Did not mean to start a disagreement.

 

[LLC5]

OK my car does not run good on low octane with an 11.5 compression ratio. I'll step out now!!

Agreed, with high compression engines designed to run on high octane you definitely want to use it. Engine power and fuel mileage will be decreased (sometimes dramatically) with the usage of a lower octane fuel rating in and engine designed for high octane usage. Ignition timing will be pulled and fuel maps can be altered by the PCM to account for the detonation that will occur with low octane fuel in any engine designed to run on high octane. Basically use the octane rated fuel that the engine builder or manufacturer (OEM engines) require. Using higher octane fuel than is needed will only get you slightly faster carbon build up and a lighter wallet.

 

[Vettehead Mikey]

Did mean to start a disagreement.

I'm sure you meant 'didn't' mean to start..........

Using higher octane fuel than is needed will only get you slightly faster carbon build up.

Never heard that one before. Why would this happen? We know that millions of drivers use higher octane fuel than required thinking 'it's better' but I've never heard about it causing carbon deposits.

 

[Wegone]

FWIW higher octane fuel in not a better fuel, it just has a higher octane rating number, and it does accellerate carbon build up.

Interesting... I was always under the impression that carbon build up was a direct result of improper tune, air fuel mixture, oil consumption.

 

[LLC5]

I'm sure you meant 'didn't' mean to start..........



Never heard that one before. Why would this happen? We know that millions of drivers use higher octane fuel than required thinking 'it's better' but I've never heard about it causing carbon deposits.

When we have a runability (sp?) issue with a vehicle under warranty we are sometimes required to call our tech line. The first question they will ask if the vehicle is an 87 octane engine is: what brand of fuel is the customer using (preferably Top Tier and at a high volume dealer) AND what octane fuel. If the customer is using 92 octane in an 87 octane engine, their response is to get the customer off the higher octane fuel immediately because of carbon build up issues that affect valve coking and injector contamination. Apparently the chemicals used to get the octane rating higher promote faster carbon build up. 87 octane fueled vehicle still have carbon build up issues, but at a slower rate.

 

[Heyblue]

Thanks to all that replied. Since my car is designed for 87 Octane that is what I will run in it once I get it back to road worthy status (bought a project car). I am basing my decision on technical facts that the compression, timing etc for MY car is designed for the 87. As an interesting side story (hope that is allowed in this forum). I also own/ride a Harley and am a member of a ridding group. This particular vehicle is designed to run on 91+ Octane. There are members of my group that believe they should keep there ride topped off with "the Good stuff". Funny thing, most pumps around here have only one hose, so the first gas coming out is what the last person used, almost always regular (87). Being "topping off" a fuel tank that is only a few gallons total is probably 50% or more regular fuel.

 

[DonB]

Mine is 10.5 to 1 and she needs the premium.

Sent from my SAMSUNG-SGH-I577 using Tapatalk

 

[Vettehead Mikey]

Funny thing, most pumps around here have only one hose, so the first gas coming out is what the last person used, almost always regular (87). Being "topping off" a fuel tank that is only a few gallons total is probably 50% or more regular fuel.

Ssssssh! Not supposed to tell! Let the other guy go ahead of you so that he gets the 'slug' of 87.

 

[kpic]

But additives has nothing to do with octane rating- the OP's sole question.

We just need somebody to mention ethanol and we'll have the gasoline trifecta. :ugh

Additives clean the carbon deposits. Cutting to the quick, as LLC5 mentioned is the root cause of the problems.

It is rather simple, gasoline meeting a cold inlet valve creates deposits and deposits create problems. Sorta common sense, n'est-ce paz?

Ethanol blend gasoline is a subject unto itself especially in older or aluminum alloy engines. Designers do not compensate or accommodate what they were unaware of at the moment of the design.