Jase

Has anyone been on the gmcanada.com website and looked at the specifications for the two models?

It shows that the 2.2 and the 2.0 S/C both use 87 octane

http://www.gmcanada.com/english/vehi...coba_opti.html

so my question is: will we get better performance out of the S/C if we use 91-94 octance?

im surprised that the S/C would be tuned for 87 octane

MrCleanY0

when I bought my ION the dealer told me to use 93 octane or it wouldn't run right. But, I never really noticed a label anywhere near the guage or the filler that specified. Maybe I'll just have to look harder.

CoolCobalt_NY

I think............ If you look on Chevy.com under specs. for the Cobalt, it tell you to use 87 oct....

There is a thread on here about all that.. Dont know where it is or went... If you use anything different, you'll cause the engine not to run right..!

Look around for the thread.. It's all there...

aka_Matt

it says to use 91 octane, with a footnote:

Cobalt SS Supercharged will operate with 87 octane unleaded fuel. However, a power loss will be noticeably felt by the driver.

Nocturn

I posted about this on another site, but the engine can run on 87, but as with the new GTO and most new GM cars, the engine will retard the timming causing the engine to lower its performance in order to avoid detonation in the cylinders.

Jase

i figured as much

not that i would consider running 87 with FI

EvenStar

Well most likely Ill be running 91-93 anyway, but most engines these days will RUN on 87 octane, but certain engines (mainly performance) won't run as WELL lol

White97Jimmy

Why would the GTO's need higher octane fuel? They don't use forced induction, just LS1/LS2 engines.

b-spot

High compression

Archplsm

^^^^ yes, fuel type is not determined by forced induction but by compression rating on the cylinders. Pretty much anything over 10:1 needs the good stuff. It needs a bigger boom to get over the negative pressure in the cylinder because it is sooooooo tight (compression)

b-spot

It doesn't actually have a more powerful explosion, it just prevents early detonation that occurs when a flamable gas is compressed.

White97Jimmy

I know the compression ratio & higher octane fuel deal, I just didn't know that the LS2 engines were higher compression. I guess thats how GM is adding power inexpensively.

Archplsm

Cobalt SS/sc has a 10:1 compression ratio.

Oh and a little side word. I don't want to get anyone's feathers in a ruffle, but I think this whole detonation deal is getting to be the new catch word. Yes the fuel selection will help control detonation, BUT I really think we need to revisit the basics of fuel combustion in an engine. The differences in the different octanes is different percentages of octane levels in the fuel. i.e. 91 has 91% octane in the fuel. The high the octane level the high amount of fuel is combusted in the chamber. The more fuel used in each combustion produces more power and economy of fuel. This is why race cars use turbo blue (really high octane levels). On my Cav I saw the 89 gave me the best price per mile, and that car was rated at the cheap stuff.

b-spot

WRONG.

Octane just prevents detonation. Thats what it does. Its not a catch word, more octane, higher compression required for pre-detonation.

It doesn't make more fuel combust. Race cars use it because their turbos are running at 20+ PSI which is very high COMPRESSION which would lead to pre-DETONATION of any lower octane fuel, this means your piston is still on its way up when the gas explodes, very bad for your internals.

Good try though

Archplsm

UMMMmmmm then why do all the NA racers use it, i.e. ARCA, NASCAR, and all the other stock car racer, no turbos there

b-spot

LOOK UP AND READ.

HIGH COMPRESSION NA CARS ALSO NEED HIGH OCTANE. COMPRESSION = EARLY DETONATION.

Jase

uh... doesnt the 2.2 have 10:1 and the SS/SC have 9.5:1?

if not, damn GMCANADA website

PenguinPIE

iTrader: (5)

does anyone know how much power would loose if 87 were used in the SS S/C?

Nocturn

Have to agrree with B-spot on that one, Octane is just the amount of octane in the fuel, Octane resist combustion. Using lower octane at higher compressions causes detonation (ingiting before the spark for those who dont know). The reason race cars use it be it turboed or non is the same reason, higher comrpession ratios.

Turbos for example may only run say 12PSI on 91 octane, but often with a tank of 101 or 105 octane they can run up to say 15PSI without damaging the engine.

NA cars often need higher octane for the same reason, higher compression ratios, race cars can use 11.5:1 and I have even seen a 13:1 on something but don't remember.

Top fuel dragster have to use alchohol/methane fuel because their compression ratios are in the region of 45:1 or so....Something like 1/2 down the track the sparkplugs blow out from it and the car runs on the compression of the engine alone I have herd.

b-spot

Hooray! Someone else who understands!

Thats true about the dragsters too, and fricken crazy, I don't get how they control it so that compression causes detonation at the right moment.. very finely tuned cars.

Nocturn

There also rebuilt after every run, so when you do it for a living I guess you make it your business to see it runs 100%.

Voodoosoup

Here arw some interesting top fuel dragster stats.

7500 peak HP
500ci
Max boost at full throttle 45.5psi
Supercharger spins at 12,654Rpm at max engine speed and it takes 900HP just to turn the supercharger at 8500Rpm
16 Spark plugs per Engine. The twin MSD magnetos produce 88amps. you need just 12 more to power your mig welder.
The fuel system can pump 77 Gallons per minute wide-open. 22.75 Gallons of fuel are used during warmup, burnout, staging and the quarter mile run!!!!!!
New ready to run top fuel motor $58,700
29 minutes, it takes to tear down and rebuild a top fuel motor between rounds.
Each engine is rebuilt 184 times a year, if the driver goes to the final round at every race.
Power to weight ratio of 3.37 HP per pound, about 20 times better than the new Z06 covettes.
.84 seconds 0-100MPH
Top speed 333.08MPH Peak deceleration of 6G's
12,000lbs. of downforce are produced by the rear wing at 325MPH
the downward thrust made by the exhaust gases escapingthe headers alone generates 800 pounds of downforce.
World record ET 4.441sec
18 seconds of racing completed if you nake the final.
If you make the final in every race, your total racing time for the season would be less than seven minutes!!


This was taken from a recent Motor Trend article..

Nocturn

I disagree, using 89 in the SS/SC will hurt performance as the engine retards the timming to compensate.

MikeSS

Uhh that isn't right at all. Racing fuels are 105-120 Octane usually. So unless fuel makers have defeated mathematical theories, I am pretty sure it refers to the octane content, not percentage. Like Proof in alcohol.

MikeSS

Yup, higher octane fuel won't help an engine designed to use regualr 87 Octane fuel, but an engine designed for 91+ will be hurt with 87 Octane fuel.