Iván

Hello,

In Colombia the best fuel we can get is 88 Octane. Porsche recommends 91 octane for turbo cars. Can this affect the boost or make
the car to start knocking?

If the wategate´s spring is altered to produce less boost, would this help the knocking?

Thanks,

special tool

Well, you would be better off adjusting the FQS wheel (on the DME)to retard timing and enrichen the mixture slightly.
Can you buy tolene or xylene for octane boosting?

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

smkn951

tolene, xylene? just add it straight to the tank? how much for a full tank? do local parts store carry these? do i need special license to purchase?how does it affect emissions? does it have any other benifits ie clean inj and or valves?

Iván

Thanks for your input. I am not having this problem right now, but I am trying to raise the boost in my car, the factory gauge reads only 1.2 bar. Someone told me today that if we open up a little bit the spring in the wastegate we can reach 1.75 bar of boost, but we may have some problems with knocking due to low octane fuel !!! ????
Iván

special tool

If you have 1.2 bar, you are not going to get more boost by shimming the wastegate. You most likely have either an intake leak in the plumbing, or a fault code in the DME causing a limp home mode.

Tolene and xylene are in fact - gasoline - long chain hydrocarbons and are already present in most gasolines that you buy. I have EXTENSIVELY experimented with these and the 951 and found that around 10-12% tolene is good. Xylene has a higher RON number, but it really slows down ignition and destroys throttle response - so, although it it very resistant to detonate, the effect is killed by a dead pedal.

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Iván

"You most likely have either an intake leak in the plumbing, or a fault code in the DME causing a limp home mode."

Thanks Special tool,
Ok that agrees with the majority of the information that I have gathered about this problem.

I have read that for the DME I should take the Car to a Bosch shop and get it checked.

What specifically should I look for in case of a leak in the plumbing?

User 41221

Or the cycling valve may be faulty, its a pretty common failure, too.

Regards,

toddk911

Special tool,

So you have seen a difference in running Tolene vs. Xylene????

special tool

Todd - yes, seriously. It will even go as far as slowing down boost threshold about 200 rpm (all things equal - fuel pressure, chips, mix percentages, etc., etc., etc.) The ron + mon / 2 number of xylene is only 3 higher than tolene - so I really don't know if the ignition modifications necessary to extract the power from xylene would be justifiable.
Tolene actually has a BTU/Lb. energy content only SLIGHTLY less than diesel fuel (huge).

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Mike B

That is good info special tool...Thanks!

Danno

"tolene, xylene? just add it straight to the tank? how much for a full tank? do local parts store carry these? do i need special license to purchase?how does it affect emissions? does it have any other benifits ie clean inj and or valves?"

Check out the Fuel-FAQ section on my <a href="http://members.rennlist.com/951_racerx" target="_blank">951 RacerX website</a>.

"So you have seen a difference in running Tolene vs. Xylene????"

"The ron + mon / 2 number of xylene is only 3 higher than tolene - so I really don't know if the ignition modifications necessary to extract the power from xylene would be justifiable."

Both of these are the primary octane-boosting components in unleaded race-gas (compare their smells). The only difference in your own home-brew mix will be the quantities added. You'll need less to make a tank of 100-octane gas with xylene than toluene. You actually do not want to increase ignition advance in order to take advantage of the higher-octane because you're already close to the point of diminishing returns on ignition where the earlier combustion will just end up compression the pistons and rods, rather than spinning the crank.

What the higher octane lets you do is increase the boost!!! With 100-octane, you can run about 21psi safely on a 2.5L provided you have an upgraded turbo that can provide the required air flow and matched chips to deliver the matching fuel. Using 110-octane, 25psi is possible. In both cases, you want to retard the ignition about 3-5 degrees since the higher-pressure, denser mixture will burn faster.