Turbochargers and Octane Ratings

[Mod10]

Anybody here have much experience with turbocharged engines? All the new cars with turbos have a warning that only 93 octane is safe to use in the engine, anything less can cause damage.

Is this true? I don't see how using regular gas will damage an engine.

 

[Evil One]

Regular gas can cause the engine to detonate, if the computer doesnt catch it quick enough it can damage pistons, valves, and/or rods... it can also cause them to pop a headgasket.
93 octane is cheap insurance, and helps you get the most out of your boosted vehicle.
I have been building and racing turbo engines for about 20 years now and have had all of the above happen.


Jim

 

[Mod10]

Thanks for the info.

 

[Evil One]

Now, I am not suggesting for you to do it... however...
Newer cars have some pretty dang smart computers and I have seen many people drive their turbo cars on regular gas when the prices shot up over $5 a gallon with no problems.
The computer backs off timing and some also limit boost when they sample the fuel and tell its a lower octane... and if/when they detect minor detonation.
If you do this, I wouldnt run it hard or make prolonged pulls under boost.
But, the way I see it... you get a turbo car to exercise your right foot, so toss the good gas in it and take her for a run


Jim

 

[whitecoyote]

Anybody here have much experience with turbocharged engines? All the new cars with turbos have a warning that only 93 octane is safe to use in the engine, anything less can cause damage.

Is this true? I don't see how using regular gas will damage an engine.

I would say it depends on the manufacture/engine. I have this 2010 Taurus SHO. 93 octane is recommended, but Ford says you can run 87 octane, but beware of "knocking", which will cause damage.
I have tried both octanes in the SHO, and they work, but with lower octane your gas milage goes down. With 93 octane your gas milage is at its best.
So, lower octane may be cheaper, but you burn more. 93 octane cost more, but you burn less. With that said, I now always burn 93 octane.

 

[caseydog]

Aye,

Jim speaks the truth , engines today are designed to run in certain parameters , ignition timing curve and injection profile and many other parameters are controlled by the computer, now if the knock sensor signals the computer that knock (detonation) is present the computer then has to modify all the other parameters it can to try and eliminate the knock before damage occurs.
Now the computer may be able to compensate enough to prevent engine damage , but chances are that the engine will be out of it's optimum range for fuel economy , power or emissions or all three. If high octane fuel is recommended it's probably best to use it.

Ray

 

[GregG]

Turbo engines have a lower compression ratio than non-turbo engines.

So....in a non-boost situation....you can get away with 87 octane, such as in a daily commute situation. But there is NO WAY I'd run it wide open throttle unless it had premium in the tank.

Your engine should have knock sensors installed, which will pull timing out when it senses detonation, but..........I would hate to trust them.


What make and model, and how much boost does it have?

 

[cussedemgun]

Mod10,

The octane number is a way of rating the burn rate of your fuel. The higher the number, the slower the burn rate.

Each car engine is engeneered for a cruise speed at XXX RPM's. The stroke length, compression ratio, amount of fuel delivered (injected or carburated), spark timing, & valve over-lap all have an effect on the burn rate required.

To compare to the shooting sport:

A gun designed for IMR 4350 powder (high octane slow burning) will not last long if Bullseye or Unique ( low octane fast burning) is substituted.

By comparing the combustion chamber of your engine to the chamber pressure of your gun, the need for pressure control becomes somewhat clearer.

Hope this helps, Jim

 

[Mod10]

What make and model, and how much boost does it have?

I was looking at the new Volkswagens. I think I will stick with a naturally aspirated engine.

Thanks for all the input.

 

[rburg]

There is a stopgap measure you can take. I'm cheap, so I buy at Wally World on Fathers day! You just find some octane booster on sale, and buy a case. Fathers Day is the best time because auto junk is on sale.

If you're running mid range fuel (I'd never stoop to trash 87 octane) and the engine starts pinging, just dump in a bottle or two. It does boost the octane, as measured by you either hearing audible pinging or feeling a loss of power.

In my situation, I don't have a turbo engine. But if I run cheapo fuel in my daily driver Jeep, the ride home is interesting. It will downshift on the interstate 10 or 15 times. Just driving on a minor upgrade will require the engine to shift out of OD. Running premium fuel seems to allow it to run under load and still make enough power to keep going at highway speed.

Remember, all fuel you buy probably isn't as listed. You can have cheating by the station operator, or mistakes at the depot or by the truck driver doing the delivery. When I think I've purchased quality high octane fuel and it starts it pinging routine, I just dump in a bottle of octane boost. If I get some knocking the next day, I dump in another. So far, its always solved the problem.

And higher octane fuel, at least for me, results in better fuel economy. If I fill the tank with cheap stuff, and spend a week or so putting up with downshifts, I often only get 12 mpg out of the tank. Premium almost always results in 15 mpg. Its a 25% improvement, for only paying an extra $.20 a gallon. With fuel at $3.00 a gallon, I pay maybe 7% more but get 25% more miles. And its only true for Ohio gas. The crap the EPA foists on us in KY is a waste of money. It doesn't ping, but it never gets decent fuel economy. So I work and fill up in Ohio.

 

[BubbaBlades]

One more thing to consider when feeding turbo engines is that 93 octane may not be enough. I blew up my (lightly modified) GMC Syclone turbo engine when the turbo overpressurized (more than the 15 psi limit) and bent several rods. My highly modified Buick Grand National would run fine on 93 octane up to 15 psi of boost however it needed 100 octane to run 20 psi of boost and 116 octane to operate properly at 24 psi of boost. Money saved on lower octane gas than needed will probably not pay for a $8,000+ engine rebuild/replacement.
Mark

 

[venomballistics]

Anybody here have much experience with turbocharged engines? All the new cars with turbos have a warning that only 93 octane is safe to use in the engine, anything less can cause damage.

Is this true? I don't see how using regular gas will damage an engine.

yes there is truth to this.
Having built turbocharged as well as super charged engines in my lifetime, I can tell you that the equation gets mighty complex as to where the octane cut off ends up.

this can also apply to non turbo engines with extraordinarily high compression as well.

 

[KyWstJoe]

My ZO6 isn't turbocharged but GM suggests 93 octane. They also say you can use 89 or 87 but will lose performance. I had to put a few gallons of 87 in one time and it ran just fine. I always use 93 but I am tempted to try a tankfull. Cheap, cheap!

 

[perrazi]

where i live they have ethanol blended gas at 89 octane and is cheaper than 87 octane. i drive a pontiac g-8 and it works out fine for me. i get 22.5-24 mpg on the highway. we only have 91 octane as our best and only difference i can tell is that acceleration is a little snappier with the 91. top speed seems to be the same with either fuel.

 

[parts]

Speaking of octane. Last Saturday I attended the trials for the Gran Prix of Alabama, held at Barber Motorsports outside of B'ham. Really a world class facility and it was something to see the Indy cars. Sun oil had a tanker dispencing gas for the cars. The smaller cars would drive down to the pump and fill up. The Indy teams had very elaborate, motorized portable fuel tanks; they'd fill these up and take them back to the pit area and fuel their car from them. What surprised me the most was it was pay at the pump with credit cards! 112 Octane, $9 a gallon!

David

 

[BrianE]

run fine on 93 octane up to 15 psi of boost however it needed 100 octane to run 20 psi of boost and 116 octane to operate properly at 24 psi of boost. Money saved on lower octane gas than needed will probably not pay for a $8,000+ engine rebuild/replacement.
Mark

I raced highly modified Turbo DSMs for several years and Mark is correct. Dont use anything less then recommended or it will do damage... Not worth it for a few pennies.