Topic: Why 91 Octane in the 2.4?

[CarolinaSolstice]

Does anyone know why Pontiac recommended 91 Octane in the N/A 2.4?
It's not a Hi performance motor and it's not a Turbo?

I know GM has used this 2.4 in other vehicles and I believe 87 was recommended so I was wondering what the difference was in the Solstice?

[Sol Asylum]

Are you sure?  I know the manual said the 2.0 is recommended to run 91 but can run 87 (if you have the GMPP tune you get a 91 label to put on the fuel door).  I thought the 2.4 was 87 per the owners manual.

[CarolinaSolstice]

Are you sure?  I know the manual said the 2.0 is recommended to run 91 but can run 87 (if you have the GMPP tune you get a 91 label to put on the fuel door).  I thought the 2.4 was 87 per the owners manual.

Yes I'm sure...I looked at the manual yesterday.
You can run 87...but there will be a slight loss of power and 91 is recommended.
So again my question is why is 91 recommended?

[Uranium-238]

Yes I'm sure...I looked at the manual yesterday.
You can run 87...but there will be a slight loss of power and 91 is recommended.
So again my question is why is 91 recommended?

Plenty of reason why GM would setup the 2.4 to run higher octane...it is a sports car after all. Probably to get a better timing curve.

Even in my LM7 pickup 93 sees a performance increase, it uses the high vs. low octane timing table...which means more power...

[Sol Asylum]

Make sure you were looking in the section for the 2.4 engine I am pretty sure the manual has both the 2.4 and a 2.0 section.  What year is your car?  It's possible there was a manual rev between my 07 and your year manual and there could also be an error.

[RedOne07]

Please delete.

[DaveOC]

Make sure you were looking in the section for the 2.4 engine I am pretty sure the manual has both the 2.4 and a 2.0 section.  What year is your car?  It's possible there was a manual rev between my 07 and your year manual and there could also be an error.

I have copies of the manuals for each of the model years, all of them have the same language regarding octane, and none of them have a separate section for the 2.4 and/or 2.0.

In other words, one manual applicable to each year, for both the 2.0 and 2.4 engined cars.

:dunno:

.

[DaveOC]

Owner manuals I have seen do not even mention the engine type in the "octane section"

I agree.



.

[CarolinaSolstice]

Make sure you were looking in the section for the 2.4 engine I am pretty sure the manual has both the 2.4 and a 2.0 section.  What year is your car?  It's possible there was a manual rev between my 07 and your year manual and there could also be an error.

I'm looking at the right section is says 91 "recommended" for the 2.4. for maximum performance or something like that...I'm paraphrasing as I don't have the manual in fron tof me but 91 is recommended.

[CarolinaSolstice]

Owner manuals I have seen do not even mention the engine type in the "octane section"

The ones I've owned do.
For instance for the Dodge Challenger they talk of the different octane requirements for the 6 or the 8 and then the larger 8 like a 392 VS the 345

[Uranium-238]

FWIW, 91 octane is also only "recommended" for the Camaro...I can tell you the low octane table has a noticeable lack of power, and I won't put less than 93 in it. Back when the car was stock but for an intake and exhaust, it'd still knock on occasion even with 93. Hell, even my LM7 knocks on the "recommended" 87 octane.

Will a 2.4 see a similar difference? Doubtful. But if the book says do it, do it. 87 might work, but is it worth cheaping out on? If it knocks, use higher octane fuel. If it doesn't, and/or you don't mind the lack of power, then 87 won't hurt anything.

As an OBTW, use something like HP Tuners to verify knock, not just your ears...

[Critterman]

Simple answer, compression ratio

[Sol Asylum]

I have copies of the manuals for each of the model years, all of them have the same language regarding octane, and none of them have a separate section for the 2.4 and/or 2.0.

In other words, one manual applicable to each year, for both the 2.0 and 2.4 engined cars.

:dunno:

.

My bad, I got the solstice manual confused with my other Pontiac's manual.

You guys are right it doesn't specify any engine where it specs out the octane.

I agree with Critter compression ratio.

[CarolinaSolstice]

On another site they mentioned the Variable Valve Timing is why 91 is recommended...makes sense.

[Sol Asylum]

Doubt it, my other Pontiac has a V6 with variable valve timing and that runs 87.