Will that be Regular or Unleaded?
 

All the talk, such as http://www.pelicanparts.com/914/914QA/914Q_engine_fuel_octane.htm, about what fuel to run in our beloved 914’s seems to revolve around what grade of UNLEADED to use. Supposedly there is a gas station across town that sells REGULAR gas, lead and all (at about 25% more than unleaded). Since REGULAR is [supposedly, I still have too see for myself] available should I use it?

Tim
'73 914 F.I. 2.0L

[This message has been edited by TimW (edited 07-17-2001).]

No reason not to, unless your car is one of the 75-76es that are equipped with a catalytic converter. (Not all were, and not all that were originally equipped with them still have them.)

But the car should run fine on either, as long as you're not putting fuel in that has a lower octane rating than recommended.

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

Leaded fuel is of a lower quality that unleaded, but the lead helps make up for it. That is part of the reason why unleaded costed more when it first came out.
My suggestion is, mix two gallons of leaded with 8 gallons of premium unleaded.
Suppose you have 92 octane unleaded, and oyu mix 87 octane leaded, you will end up with somewhere in the 93 octane range.
Tetra-ethyl lead had a dramatic effect on the octane level in small concentations, then has much less influence as the concentration increases, sort of a diminishing returns example. A little lead raises the octane a bunch, but as you ad more it makes less difference, until it finally has no influence at all.
Sooooo, it is possible to make unleaded premium a higher octane by mixing a smaller portion of lower octane leaded fuel.
Sorry if i didn't explain it very well, you will have to take my word for it.

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Gerald Gore II (Sam)
73 914 350 small block

Well, yes, it sounds like you could make some 93 octane fuel.

But why??

Most of the four-cylinder cars are rated for regular-grade (87 AKI) gasoline. Most of the 1.7s are rated for standard premium (91-92 AKI). So why should we bother buying or making even higher-octane fuel?

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

Q. So why should we bother buying or making even higher-octane fuel?

A. From the link above "...because the car will run cooler."

[This message has been edited by TimW (edited 07-18-2001).]

I don't think it will. Or rather, I think that it will, but in the same proportion as the amount of power you lose by running high-octane fuel: Way too little for anyone to notice.

This is one place where Wayne and I disagree. I'm not sure either one of us holds his opinion on the subject very strongly, and could easily be convinced otherwise if we saw some actual results.

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

Thanks!

[This message has been edited by TimW (edited 07-18-2001).]

Pardon me for interjecting, but I've heard it explained this way:

Higher octane fuel slows the flame propagation during combustion; it does NOT intrinsically add any more energy to it. It is the air/fuel mixture exploding too fast that is the leading cause of pre-ignition, and higher octane fuels are designed to "explode slower", if you will, so as to not pre-ignite. The tendency toward pre-ignition occurs mainly in higher compression engines, engines with timing too far advanced or with too many carbon deposits in the combustion chamber (or a combination of the above).

Thus, if your 914 runs fine on 87, without pre-ignition (pinging), you will realize virtually no benefit from running it on a higher octane grade (except perhaps psychological). I have run my 914 2.0 on 87 almost exclusively since I've owned it, and the car absolutely runs great! The couple of times I've run it on 91/92 octane (due to no regular being available), I couldn't tell the difference. These are relatively low-compression engines we have.
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Disclaimer: I could be wrong about all of the above, but that's my understanding of octane and engines.

You're quite correct, djs. One little-known fact is that a higher-octane gasoline actually contains less total energy than a low-octane gasoline! The difference is, from what I hear, very very miniscule--too small for any driver to ever tell the difference. Probably too small for a dyno to reliably tell either, but I'm just guessing here.

The thing is that some engines can take advantage of the slower-burning high-octane fuel's detonation resistance to get more work out of the energy that is there. Those are engines with higher compression, more advanced timing, etc. But if you don't have an engine that is set up that way, using higher-octane fuel is simply a waste of money.

Unless it gives you a sense of security--in which case you should go for it!

--DD

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Pelican Parts 914 Tech Support

A few pics of my car: http://www.pelicanparts.com/gallery/Dave_Darling

Though this is not an issue with stock 914 engines, some of the newer engines use knock sensors, which will retard timing if knock is detected. Therefore, if the octane is too low, knock is detected and the timing is adjusted. Though you will not hear knocking, power will be down due to the timing change. So when experimenting with fuel, if your engine will benefit from a higher octane, you should feel the difference in the "seat of your pants" while driving.