...P

Here is an article that is seemingly un-related to the title.
But what is said about the 944 motors may also apply to certain 928
models too.

On my turbo volvo when I use the lowest grade of fuel available here
in Tennessee with 10% ethanol (87 octane) I get EXACTLY the same
fuel mileage as the higher 93 octane. I have kept records in my console
over 20 tank fills to see, and the octane just does nothing for fuel mileage.

However, with some cars (and now the article has some relevance)
that have the built in knock sensor like the 5-cylinder 4-valve DOHC
turbo with the Porsche designed heads, lol, octane does make a difference
in performance due to the ignition advance being adjusted.



So I just found this article in my archives and thought it would help set
off a good discussion about octane and the experiences of others with
the various model years, etc. With my 1983 I honestly don't know if it
has an octane sensor or not. From time to time I fill with 93 octane from
the local YC because it has no ethanol, and all I can say is the car likes it
(a lot). I don't know if it provides any real power advantage over the
other octanes for the 1983 16v, but it sure does with the turbo volvo
which runs MUCH stronger with the higher octane.


regards,

P

j.kenzie@sbcglobal.net

I don't think the 83 L-jet, like mine will perform better with just a change of fuel octane. BUT, with higher octane, you can advance the timing by adjusting the distributor, due to higher detonation threshold with higher octane, and you should safely get better performance and even mileage for the same driving patterns. I think there is and octane safety plug for below spec gasoline, but not for sensing higher octane gas. A knock sensor does this all for you electronically if all is working properly.
Dave

...P

Thanks Dave,

I learn something every day and appreciate the info. I am planning on advancing the ignition a bit now that I no longer have to worry about the emissions testing, due to permanent antique plates. Will be interesting to see how that works.

Got a suggestion for advance on a stock 83 model in this context?

Regards,

P

andy-gts

your right , with knock sensors pulling at most 9 degrees of timing this protects the engine with side effect of down on power….makes sense….

the tuner has a program for on the lynx computer with switch for 95 octane gas which made a little more power for the texas mile but I tootle around on premium .

here is an interesting article on how to make your own high octane fuel for , ahem…….enhanced performance….


duh…. computer says invalid file but I can print it off and scan and post I guess...

dr bob

Folks have been dumping things like toluene into the tank to enhance the octane rating, but to really be effective you need to be concious of the total energy available from all the components of the base fuel when you build the injection and ignition maps. Ethanol, for instance, raises the octane rating but has significantly lower specific energy. To take advantage, you get to run much higher combustion pressures via higher mechanical compression ratio, or denser intake charge via turbocharging or, ahem, supercharging. The mass of fuel needed is significant enough that you start to depend on the fuel evaporation into the chamber for some charge cooling. I suspect that a turbocharged ethanol GDI system would be ideal.

Meanwhile, without knock sensors and some more continuous adaptation of both fuel and ignition maps, pre-S4 928's will have a tough time reliably extracting extra performance unless the fuel composition is very carefully managed.

In my wayback history, I drove a Saab 900 Turbo with some user enhancements. It had a KE-jet fuel system, with a dr bob digital controller replacing the original analog box. The system would make buckets of power with alcohol injection added. But every tank of pump gas needed about 4 gallons of alcohol in the aux tank. Run out of alcohol and risk the engine unless the maps were adjusted significantly. Mechanical overpressure valve with manifol pressure asist wasn't exactly a tune-on-the-fly piece, so it needed a lot of driver participation in the engine protection department when the alcohol tank was dry. Fast-forward to today, with much better controllers commercially available, and for sure much better instrumentation. If I were trying to get the most out of a pre-S4 car for the street, one of the better digital engine management systems with knock sensing would be at the top of the upgrade list, after Cayenne GTS brakes and before the turbochargers.

andy-gts

for information only






Tuesday September 28, 110 *

The information contained here is courtesy of www.gnttype.org -- it's really a kick *** website for car fans
Good explanation of "Why use toluene?"
How to calculate final Octane:

(Initial gallons * gasoline octane) + (Added gallons * additive octane)
------------------------------------------------------------------------ = Final Octane
Initial gallons + Added gallons
Fast facts: Automotive gasoline is ~6.2 lbs/gal, Aviation gasoline is ~5.9 lbs/gal
Don't use it unless you have no other choice -- because the PCM doesn't know the density is lower, you'll run lean, maybe TOO lean
**USE AT YOUR OWN RISK!!!!
Richard Lassiter's "How to Mix Your Own Brew"

FORMULA 1
Toulene
R+M/2...114
Cost...$2.50/gal
Mixtures with 92 Octane Premium
10%...94.2 Octane
20%...96.4 Octane
30%...98.6 Octane
Notes: Common ingredient in Octane Boosters in a can.
12-16 ounces will only raise octane 2-3 *points*,
I.e. from 92 to 92.3. Often costs $3-5 for 12-16 ounces,
when it can be purchased for less than $3/gal at
chemical supply houses or paint stores.

FORMULA 2
Xylene
R+M/2...117
Cost...$2.75/gal
Mixtures with 92 Octane Premium
10%...94.5 Octane
20%...97.0 Octane
30%...99.5 Octane
Notes: Similar to Toulene. 12-16 ounces will only raise
octane 2-3 *points*, I.e. from 92 to 92.3. Usually mixed
with Toulene and advertised as *race formula*.

FORMULA 3
Methyl-tertiary-butyl-ether (MTBE)
R+M/2...118
Cost...$3.50/gal
Mixtures with 92 Octane Premium
10%...94.6 Octane
20%...97.2 Octane
30%...99.8 Octane
Notes: Oxygenate. Very common in octane booster products.
Has lower BTU content than toulene or xylene, but oxygenate
effect makes the gasoline burn better and produce more energy.

FORMULA 4
Methanol or Ethanol
R+M/2...101
Cost...$0.60 - $1.75/gal
Mixtures with 92 Octane Premium
10%...94.3 Octane (Methanol)
10%...94.7 Octane (Ethanol)
20%...Not Recommended
Notes: Methanol is wood alcohol. Ethanol is grain alcohol and found
in Gasohol in 10% ratios. Both alcohols are mildly corrosive
and will eat gas tank linings, rubber and aluminum if used in
excessive ratios. Main ingredient in "Gas Dryers", combines
with water.

FORMULA 5
Isopropyl Alcohol and Tertiary Butyl Alcohol
R+M/2...101
Cost...$0.60-$1.50/gal
Mixtures with 92 Octane Premium
10%...94.5 Octane
20%...Not Recommended
30%...Not Recommended
Notes: Similar to Methanol/Ethanol. Isopropyl Alcohol is simply
rubbing alcohol.


MAKE YOUR OWN OCTANE BOOST
How to make your own octane booster (this is the basic formula of
one of the popular octane booster products). To make eight 16 ounce
bottles (128 oz = 1 gal):
100 oz of toulene for octane boost
25 oz of mineral spirits (cleaning agent)
3 oz of transmission fluid (lubricating agent)

This product is advertised as "octane booster with cleaning agent
*and* lubricating agent!". Diesel fuel or kerosene can be substituted
for mineral spirits and light turbine oil can be substituted for
transmission fluid. Color can be added with petroleum dyes.



cool to think about

James Bailey

...p , high octane fuel basically burns slower that is it ! You do get slightly more magic cleaner juice but hardly makes it Premium in any way but COST...and no more power or gas mileage or happy faces on the front of the car. It is all marketing to get people who "love their cars " to be nice to them and feed them fuel that is largely a waste of money but good for the gasoline companies ! If your car is designed to run on high octane it is best to use it or as the article mentions if it has knock sensors it will retard timing no knock sensors and you can bust all the piston rings blow the ends off the spark plugs and punch holes in the pistons. Which you can also do by twisting your distributor too far....how much is too far ?? Depends on your engine how much carbon is in the combustion chamber ?

andy-gts

I TOTAlly AGREE with MR Bailey !!! I posted the formula FYI only…. if the engine is not made to be high octane user …total waste of money

just like the octane boost you buy in a bottle total waste !!

upstate bob

If anyone here has dyno'd an early engine, what is the best total advance, full throttle, at 3K and over?

Regarding ethanol vs methanol: ethanol has a much greater ability to dissolve plastics than does methanol,
-yet I continue to drink it.

Hold On

Bump it up 3 dgrees

928wolf

So, should I be wasting my money on 93 octane premium for my '85 EURO? I have been assuming the answer was yes, now I'm not so sure.

The Forgotten On

For the high compression Euros, S3's and S4's you should be running premium as that is what they require. The same goes for K-jet cars too otherwise either your timing will retard in LH cars or you will get less power and some possible knocking in K-Jet cars.

The U.S L-Jet cars only require 87, but I have gotten 3 MPG better when I run premium 91 VS 87 regular in my 81, others results may vary.

j.kenzie@sbcglobal.net

Other way to look at it is maybe you have carbon deposits in your combustion chambers, and thus higher effective compression. If you thought that was true then you should run higher octane gas, or fix the carbon problem so you have predictable performance and safety. BTW I remember Greg Brown saying he runs premium in all his Porsches, as a safety measure, I believe.
Dave

WallyP

Anytime that you are reading older info on octane ratings (or RoW info), always remember the difference between the Research Octane that everyone used back in the day (and the rest of the world still does) versus the (R+M)/2 that we use now.
And, also always remember that one "octane point" is 0.1 "octane number".

hacker-pschorr

Relying on the knock sensor to save money on gas is a good way to damage the engine. Same as using cheap oil and / or going 20,000 miles between oil changes.

There is no such thing as "a little knock".
Running 87 octane in one of these engines, under load it will start to detonate, yes the knock sensors will sense this and retard timing to eliminate the detonation. After a few moments the engine will raise the timing to try and bring the performance back up to nominal, detonates again, timing retarded again.... over and over and over you are detonating that engine.

If your car is boosted in any way and / or has compression higher than 9.5:1 - you should be running premium regardless what the manual says. That is unless you only buy (or lease) new cars and will be rid of it before the warranty expires.

Direct injection helps things greatly by allowing higher performance engines with lower octane gas, but I don't see anyone building a direction injection engine any time soon.