DFI, Batch Fire, and other myths

[Greg Hermann]

>Greg Hermann wrote:
>>
><snip>
>> >According to a service bulletin, the 3.8l engine suffers from carbon
>> >accumulation on the back of the intake valve which significantly
>> >reduces performance.  I've seen the effects. It's very similar to
>> >losing the accelerator pump on a carb'ed engine, and the exhaust is
>> >excessively rich.  My thought was the carbon is insulating the valve,
>> >preventing vaporization.
>> >Shannen
>>
>> The carbon (more accurately coke, the black kind)  is residue from the
>> gasoline. Run av gas and it won't happen :-) !! It can also restrict
>> breathing pretty drastically.
>>
>> Greg
>Lessee... Av gas was missing something, maybe detergents or the added
>lubricants that are in auto gas?  Can't remember.  Is there any truth
>to the story that unleaded av-gas is more correctly called low lead?
>Shannen

I was just making a funny--but for a race only motor av gas is a good deal.
Have a motorcycle racer buddy who has used nothing else for a LONG time. He
swears by it, and claims never at it. Says no need to drain the fuel system
(completely) when the bikes are parked for the winter. No gummy deposits
such as constantly screw up the operation of CD carbs, either. His favorite
demo is to pour splashes of av gas and car gas side by side on the concrete
driveway--the av gas spot is completely gone and totally dry pretty
quickly, the car gas leaves a little bit of sticky, gummy residue. With it
being that clean, mebbe the av gas does not NEED as much (or any)
detergent. I shall inquire as to the lead---

Obviously, the av gas has less high boiling components--but I SUSPECT that
the big difference as to intake valve coking is a function more of ash
content of the fuel--The coke is basically glazed on ash. I have also seen
it happen on intake valves with (IR) Weber carbs, incredibly thick. Since
the worst case I ever encountered was on a 2.0 liter 911 motor that never
ran anything but the old (very good) Amoco UL Super Premium, I strongly
suspected the ash level in the motor oil that was always used in the
engine. The oil came in a green can , and I promise it was NOT Wolf's Head,
although it implied ties to that same eastern state!! :-)

Regards, Greg