Drewster67

So, is it safe to say.....if my fuel doors displays.

(everything is in German including the instrument panel)

Oktan min 98 ROZ/RON -

My shark will need 98 Octane to run effectively?.

What is ROZ?.

Is it related to the wizard of ????? HA HA HA Ha .. Not funny I know :-(

D67 <img src="graemlins/r.gif" border="0" alt="[king]" />

Mike Schmidt

[quote]Originally posted by chris928:
<strong>There's no "may" about it. Higher octane = lower power. I'm amazed that more people don't know this. You should only use enough octane to eliminate detonation and NO MORE. Anything beyond that and you WILL lose power.</strong><hr></blockquote>

Correct. I'm not sure why people with low compression engines think that they'll gain anything using the same gas as race cars with 13:1 or more compression. It's the same sort of thinking that makes people put two big Holley Dominator carburators on their otherwise stock 1972 small block Chevy.

Dozman

Mike,
Making a comment on here like you did, what are you trying to achieve? To make yourself feel surperior to others? Maybe you are the total guru of Sharks. Maybe we can all just call on you for help?

This may be true you do not understand why people would think this. But I also I wonder why people want to switch to R-134a. I wonder why people say their a/c does not work well, and try all the quick fixes. But refuse to clean the evaporator.

But I appreciate someone asking a question because he/she does not know. Amazing things happen when people ask questions... THEY LEARN!

Maybe stop knocking people for asking questions on subjects that they have limited knowledge on. One day when you post a question here, maybe one or two or more people will respond to you like this. I hope they won't, because this site has been an excellent source of shared knowledge. Well, one of the points of having Rennlist exist is dedicated to keeping more Porsche's on the road without taking their cars to the P-Wrenches.

John D.

KBlair

I've had people tell me that if you've run higher octane, say 91, for a long time then you should not go back to lower octane. Any truth to that? I think it's bunk, so I readily filled up my shark with 89 for the 700 miles trip (well, 2 fill ups really). I was told by the PO that he only ran 93 for the 2 years he owned the car and that the friend he bought it from only ran 93 for the 5 years he had it. 7 yrs total. It ran great on 89, no detonation. I'm going to try 87 in a few weeks to see how it goes, after some fuel system cleaner is run through the system.

Mike Schmidt

Dozman,

I'm sorry if I offended you or anyone else in some way. That was definitely not the intent of my post, and I did not intend to knock anyone. Sometimes things don't come across in text the same way as they are intended, or as they do when speaking directly to someone. I think that may be what happened to some extent.

I'm all for people asking questions, and becoming better informed. You're absolutely right about having Rennlist as an excellent resource of information, especially for a car that had as limited of a production as the 928.

Mike Schmidt

[quote]Originally posted by KBlair:
<strong>I've had people tell me that if you've run higher octane, say 91, for a long time then you should not go back to lower octane. Any truth to that? </strong><hr></blockquote>

Higher octane gas burns more slowly than lower octane gas does. If gas with a higher octane than the engine really needs is used over long periods of time, that slower burning gas may increase carbon deposits in the combustion chamber. If there's enough carbon buildup in there, it takes up space and decreases the volume of the combustion chamber, increasing the compression ratio to some extent. In addition to that, the carbon buildup insulates the combustion chamber, and can cause hot spots. The hot spots will increase the chances of detonation. These two factors can cause the need for higher octane to avoid that detonation.

That's the reasoning, and the basis of why some people say that you shouldn't switch back to lower octane. I really don't think this occurs very often, if at all anymore. I'd suspect that it was more common with cars years ago, the recommendations are just a throwback to then.

KBlair

Thanks Mike, that's the first time I've heard "Why" you shouldn't.

Dozman

Mike,

I appreciate your response here on rennlist. I was not offended that much. I have thick skin. In the short period of time that I have been on Rennlist, I have seen a few others make some similiar posts. The outcome was a few people that were offended not sharing the wealth they had with others. I hope that everyone keeps sharing, and everyone ask the questions they do not know. Even if the questions have been asked previously. This way others will learn.

Thank you for your apology, time, and understanding.

I am sorry if I have upset you or aggravated you with my response previously.

John D.

Jims928s4

I found a short document Produced by BP Australia
that seems to sum up this topic:

<a href="http://www.bp.com.au/fuelnews/PET0605.pdf" target="_blank">http://www.bp.com.au/fuelnews/PET0605.pdf</a>

Mongo

if running such high octane like 104 in a 928S, S4, GT or GTS I'd think you'd have to advance the ignition timing 1-2 degrees to compensate for the later combustion. If there is no adjustments in timing needed to run 104, I would like to run it, that or 100 octane even. WHichever works for the car better <img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

<img src="graemlins/burnout.gif" border="0" alt="[burnout]" />

WallyP

Porsche says what is best for the '87 is 95 RON unleaded. That will usually be 92 or 93 (R+M/2) on the pump.

If the 104 is "leaded" (which does NOT mean that it contains lead!) using it will ruin your cat - which means that you won't pass emissions inspection.

Fuel labled "unleaded" does not contain compounds of lead - nor of boron and other substances that will poision the cat. If it isn't labled "unleaded" at the point of sale, it will probably ruin the cat.

One more time:
Higher octane fuel is NOT better - it is only more resistant to detonation. If you don't have detonation, you do NOT need higher octane fuel.

Eran Sharon

Hi,
Does anyone know which of the following is best or running my 1980 Euro 928S (Engine M28.11)?
the sticker on the car says 98 RON (Leaded, I Assume)
Locally available fuel rates are:
(91 Unleaded, 95 Unleaded - not suitable, right ?)
96 Leaded
98 unleaded
99 unleaded

WallyP

Eran,

You are missing a vital part of the info - what measurement system is being used for the octane ratings?

If all of the fuel ratings are RON, then your car can run on 98 or 99 unleaded.

Octane has nothing to do with leaded or unleaded.

A very few older vehicles can be damaged by using unleaded fuel in heavy-duty operation. Virtually no auto will be damaged by using unleaded fuel in normal operation.

Rob M Budd

I miss Ethyl too. And Lucy, Ricky and Fred. And Uncle Milty, those "Men from Texaco",,,,

John.

Fow what is is worth, I used to run the Bastard on 87 octane while running 8 psig of boost, never had a problem. 93 octane is a smart move for me, since detonation could become very expensive.

I have a NA 944, it gets 87 octane and I don't notice any difference if I run 93 octane in it.

I think if you have low enough compression (i.e. 9:1 or lower), ou can probably run the 87 octane and have no issues at all.