What Fuel to Use in 2002 Turbo?

[frached]

Hello,

Just checking with the Turbo owners here to see what fuel to use in my Turbo. Which fuel do you guys use in your Turbos? High octane? Lead additive? 

Thanks 

[Einspritz]

That depends on where you are, what is available and what you want to afford.

 

The engine was developed to use 100 Octane gas with no ethanol, and the tuning procedures are geared for that. You shouldn't need added lead.

 

You can tune to other gasolines, e.g. 91 Octane with 15% Ethanol "consumer" gas as is here in California. The caveat is that you tune to the gas which you use, which changes depending on the fuel. A tedious process. Here is where either an exhaust gas analyzer or Lambda sensor along with a knock sensor helps greatly.

 

Be aware that with the lower Octane and Ethanol containing fuels there is more likelihood for detonation as well as too much distributor advance.

 

The Kugelfischer system, both Tii and Turbo work on fuel density, so a change in that specification will have a material effect on performance.

 

In the case of (unleaded) race gas e.g. 100 Octane, 105 Octane, there is not too much benefit of the more expensive (105) fuel. But you need to look at the chemistry of the race gas, see the fractional distillation curves and fuel composition to tune to the best power. Race gas chemistry generally allows for a slower more complete combustion and sometimes necessitates a change in spark plugs.

 

Many owners don't want to afford Race gas but it has the best chemistry in my opinion. At the very least you know what you are using in your engine.

[wkohler]

So are you saying that when they change from summer to winter blends of the "consumer" fuels in California (and where I'm at in AZ, we get the lovely CA fuel), you'd need to re-tune?  The complexity of this system and my lack of experience with it has made me concerned.

 

Edited August 20, 2018 by wkohler

[Einspritz]

Yes, most definitely.

 

The problem then becomes knowing what the "blends" really are, as the percentage of Ethanol can change, though as I understand it the "base stock" is the same for all brands.

 

As to the complexity, yes it is two orders of magnitude more complex than a Tii. The best advise I can give you is to take copious notes with diagrams of your settings e.g. the location of the white mark on the aneroid in the altitude compensator; which sets the idle mixture.

 

In addition and just like a Tii, make sure that your pivots, bearings, and linkages are all up to snuff and that there is NO slop in any of that path. Otherwise you will be chasing a %CO that will change every time you rev the engine. The same goes for the distributor.

[frached]

Einspritz, thank you for sharing your vast knowledge. Not to make the issue even more complex, but I live in Florida and the car will not be driven that often. How do I, or do I even need to, adjust for fuel stabilizer, which I would probably use in the car? 

 

90 octane non-ethanol is readily available. I was told 93 octane non-ethanol is also available but I haven't found any yet. In lieu of the 100 octane race fuel type product, would you recommend a 90 or 93 ethanol free with an octane booster additive? 

 

Do you know of any source for an exhaust gas analyzer? About a year ago I tried to find one to work on another car and could not find one anywhere.

 

Thanks again for you input. Fares

[Einspritz]

Hi Fares;

 

90 Octane is OK, you just have to tune for it. That said, most of the "old" style octane boosters are mostly Toluene; look up the MSDS for each product you are considering and it will tell you in general the composition of the product. A newer product on the market is this:

 

http://race-gas.com/

 

But I have no experience with it, nor have I constantly used octane boosters in general.

 

As far as analyzers go, I started using a Heathkit in 1985 which was put in the tailpipe and ran a wire to the cab of the car. You will be hard pressed to find one of those today and there are better. Another analog tester is the Gunson's Gastester MK2, made in England. I was given one of these but have never used it.

 

The next thing I did was weld a bung in the primary muffler and install a wideband Lambda Sensor, then making a volt meter for the readout in mV and converting to %CO.

 

Today you can get a professional meter from Innovate:

https://www.innovatemotorsports.com/products/lm2.php

Nifty things include data logging for more than one channel and the ability to play back the test sessions.

I will probably get one of these.

 

Purchasing the accessory fitment to the tail pipe, you can remove the unit after you are done, or weld in a bung in either the front part of the front muffler or in the down pipe if you don't care about originality. Either way, make sure that the sensor does not hit the body with the rocking of the engine under load and that the wire is routed such that it is not melted by the exhaust pipe. Also, make sure the engine is warmed up and the exhaust is free of moisture so it does not affect the readings.

 

I have installed a J&S ignition system with a knock sensor which serves to retard the spark of the detonating cylinder and provide a soft rev limiter among other things. That unit has a simple LED bar graph readout for the mixture and knock. These units have been installed in my Tii as well and have had no problems in over 250,000 miles. Precision Automotive Research is a distributor.

 

If you do not have the service advisements from BMW, let me know and I can PM to you. What they do not say is that you really must set the %CO at full throttle / full load / full boost WITH the fuel that you have chosen, avoiding detonation. In addition, you need to set the %CO RICHER than the advisements.

 

This is all with the understanding that the injection pump is calibrated properly. If you have had it rebuilt, you need to have obtained the output curves to verify that it was done correctly. All too many "rebuilders" say they can to this, but I am not convinced unless I see the data. If not, you can be chasing tuning problems when the problem is with the pump. See the attached to show my first pump rebuild from a known rebuilder; I couldn't get the engine to run. The second graph shows a properly calibrated pump. I can't tell you how many Tii owners I have coached tuning their engines to find that the pump calibration was to blame.

 

Many who I have talked to have experienced cracked exhaust manifolds and certainly cracked exhaust housings on the turbo itself. I have the records for my car going back to the original owner; the manifold and turbo have been replaced four times each due to cracks. I believe that improper tuning, running lean, and not letting the engine cool before turning off all contribute to that. In addition, make sure that you have the ducting from the front spoiler directed to the center of the turbocharger to aid in cooling while underway.

 

Hope this provides some additional understanding.

 

Best,

 

Ted

 

 

[Einspritz]

You might find this helpful:

 

https://www.pure-gas.org/index.jsp?stateprov=FL