Re: [DML] Re: catalytic converter question

["Tom" <tomcio@xxxxxxxxxxx>]

Hello David and the list!

What you said makes perfect sense! There might be a situation when a car
that was designed to use lower octane fuel actually runs better on higher
octane fuel. This happens if you raise the compression in the cylinders.
That can be either intensional (more power, but requires premium gas) or by
carbon deposits inside the cylinders. What happens is that when carbon
buildup is large enough (usually carbon deposits are indication of mixture
being too rich OR that the owner is using higher octane gas than he should)
it causes the compression to go up. That's why you might need to switch to
89 gas and it will run better. After a while you will need to go up again
until there are no more grades and you will have to fix the problem that
caused it.
If your car runs better and you get better gas milage with higher octane gas
it means that  the carbon buildup is large enough to raise the compression
so it needs that slower burning fuel. That can be caused by mixture being
too rich. Maybe its time to check the CO (upstream from the catalytic
converter) and to check the cylinders for carbon deposits. If left untreated
it will lead to blown head gasket.

The difference between grades of gas is in octane rating. Octane rating is a
system created to indicate how fast the fuel burns. 87, 89 and 93 have the
SAME amount of additives. The only difference is that the higher the number
the slower it burns. 93 is not better in ANY way than 87. It is not cleaner,
it does not have more additives, it does not burn cleaner. It burns slower
and it is meant to be used in high compression engines that are designed to
use it. 87 will burn faster and it's meant to be used in lower compression
engines.
The DeLorean was designed to use 87.
If you use higher rating fuel that your car was designed for you are
actually doing more bad than good. Higher octane gas burns slower, so it
will not have enough time to burn completly in an engine designed to run on
87. That in turn will cause the unburned gas to enter the exhaust. It will
be not enough as to be the cause for failed emissions if you use it once.
BUT if you keep using that slower burning gas all the time you end up with
carbon deposits and higher readings on the emissions test.


Tom Niemczewski
tomcio@xxxxxxxxxxx
VIN 6149
Save the dream so you can live the dream...


----- Original Message ----- 
From: "David Teitelbaum" <jtrealty@xxxxxxxxxxx>
To: <dmcnews@xxxxxxxxxxxxxxx>
Sent: Wednesday, April 21, 2004 1:52 AM
Subject: [DML] Re: catalytic converter question


> I understand exactly what you are saying about the way the octane
> rating is calculated. It has been my experience that going up with the
> octane helps pass emissions testing. It also seems to help with fuel
> efficiency but not enough to justify the increase in price. I cannot
> give you a scientific reason for it. My guess is that the additives
> used to increase the octane make the fuel burn more completly. I
> notice I get better gas mileage on a tank of higher octane than lower
> octane. I do not say you need to use 91 octane on a regular basis but
> it has been my observation that it does lower HC if you go with the
> higher octane. These are my observations and opinions and everyone is
> allowed to agree or disagree. I say try it, it can't hurt. If you
> don't notice any diffference than at least you know you are not
> missing anything. Generally if you do fail emmisions testing changing
> the octane of the gas you use won't cut it. At least it should be
> fresh. If you still fail then you HAVE to find and fix the problem.
> David Teitelbaum
> vin 10757
>




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