944togo

I know this has been on the board before, but was mostly regarding turbos. What would be the best octane for autox and DE events for my 944 N/A. I've gotten different answers, so just trying to see what others are using - I've tried low and high octane, but tough to say if it affected my times since courses have always been different, though I'm leaning towards the 94 octane though some say it's not what is recommended for my engine and may decrease performance.

Thanks
944to-go

Antonio951

i dont know but i have a similar question, i put premium BP fuel in my car and i just drive it about 300 miles a month, is it alright to put premium in? 87 n/a with 80K

FormulaOne10

Amoco Ultimate used to be the best for clean burning and performance, however I know that the formula has changed some since their merger with BP. I have heard it is still a good premium gasoline, though possibly no longer tops. Your octane requirement on the street or track really shouldn't change. In our cars if you are not getting any knock you are likely running the proper octane for your application. Turbo guys have to be more careful with this.

What you can be concerned about, and is the only reason I use premium in vehicles whose octane rating does not require it, are the additives and detergents put in fuel to clean your fuel system and maintain the integrity of the fuel for a nice clean burn. For example, many of the additives that are put in Chevron's Techron are put in many brands of gasoline. Many of those additives aren't even made by Chevron, they are purchased from other petroleum producers who put those same things in their gas. In other words, most premiums are a pretty good mix with some being better than others. But I digress...

Bottom line - premium is a waste if you are looking for more octane than you need. Premium is a good thing if you need the octane or want to keep your engine as clean as possible. Just remember to consider how the additional costs of premium will factor in the long run vs any prevention they may have helped.

DerSchlechtSpecht

Yes you can put premium in but my question is why? Why spend the money on something that makes no difference other than being more expensive, having a higher octane ratine and being called premium in a car that requires 87 octane?

Christian

DerSchlechtSpecht

wow, figure out how to post pix and im going crazy!


sorry
Christian

ERAU-944

87 is all the car needs for anything.

i'd also replace that TPS... didn't sound like your car wanted to start too much.

-Michael-

M758

In my 944 spec car I run 91 oct premium. I would also run this on the track for a DE car. These applications spend alot more time at full load and high RPM. The extra octane is insurance vs detonation in these conditions.

In my street 944 NA I use 87.

Z-man

IMHO, 93 octane premium is most like the best choice. 91 octane works fine too. 94 or race gas (100 octane) is overkill and won't help improve the engine's performance.

Save your $$ and stick with 91/93. Anything lower than that, and your engine management system will detect engine knock and retard the timing and ultimately decrease your performance.

Of course, YMMV, (pun intended)
-Z.

Bryan

The conventional wisdom that I've heard on this is to use the lowest octane your car will tolerate without detonation/knock sensor intervention.

The reason, besides saving money, is that the higher the octane, the less burnable hydrocarbons there are in the gasoline. The octane additive doesn't burn. So it essentially displaces burnable material and you get less enery out of a given volume of fuel. Lower octane means more burnable fuel and hence more energy released on combustion.

I'm trying my S2 engined 944 on Sunoco 89 octane right now and it seems to run great on it.

Bryan

M758

Remember the rules are different for 944S and 944S2 since they have a higher stock compression ratio.

8V na cars had 9.5:1 CR so 87 is fine
88 Model with 10.2 CR
16V cars had 10.9:1 CR (I think) so they need higher octane
Turbo cars of course need higher octane as well.

Also remember the 8v engine did not have knock sensors so the engine will not be retared to prevent detonation. On the track due to the high heat, speed and loading I'd use the best pump gas I could find to minimize issues. Race gas is waste at 2x the cost of pump gas, but a $0.20 per gal increase in cost for 91 vs 87 (note 91 is best out here in Az) is worth it. No it won't increase performance, but insurance vs detonation is worth it on the track.

On the street where my 944 rarely sees over 4000 RPM and rarely full throttle is a waste of money.

Bryan

Detonation is most likey to occur and high engine loads and low rpms. Like when you "lug" the engine. This is because there is a much larger time window for detonation to occur when the engine is turning slowly. At high rpms, the compression stroke happens so fast that even if the mixture starts to ignite early, by the time the explosion has propagated throughout the cylinder the engine is past TDC anyway. The engine will attempt to advance the ignition timing under load, also making detonation more likely. So if high load, low rpm driving doesn't cause detonation, you're probably not going to have it at any other time.

Racing conditions excepted, of course. The heat and stress and continuous high output being demanded of the engine can cause detonation and all kinds of stuff to go wrong.

I'm definitely using the knock sensors on my S2 motor as a safety net for this fuel experiment. But a friend of mine runs a Sentra SE-R and the 160K mile SR20DE motor in that thing lives on a constant diet of 87 octane and runs like a top. And it's a high compression motor, I think. Plus, it's a "lean burn" engine which you'd think would be more prone to detonation - lean mixture will detonate easily, a rich mixture is less likely to detonate for some reason.

Bryan