Injector Sizing: REALLY dumb question -Reply

[Tom Sharpe]

Just a couple of observations. I have seen 400 SBCs with alcohol Holleys and more
cam than I have idle like a John Deere garden tractor without stand-off, that's
why I picked a 109 DEG center cam. It has a very broad torque curve, cruses at 15"
vacuum and gets 25+ MPG. It just won't idle....

2. BSFC is a measure of combustion efficiency and is affected by intake/exhaust
tuning and anything that affects the combustion process, including particle
(droplet) size (atomization?), turbochargers, EFI, Carb boosters(Webber), C/R, and
temperature (density?). Smokey U. had a twin turbo, carburated 2.5L Fiero with
heated fuel that ran 400 deg. intake temps to increase fuel vaporization. The
Turbo was required to force the hot mixture into the combustion chamber. No Knock,
great power, & teriffic BSFC numbers. I don't remember all the details, but it ate
exhaust valves every 10K miles. Detroit was looking at his prototype.

3. The heat loss problem can be improved with ceramic coatings. More on those
later.
I swear by them. Everything Tech Line says is true.

Greg Hermann wrote:

> >10-4 but it all depends upon RPM. Each duration (overlap) value has a
> >different scavenge RPM and when you are under it (or turbocharged) all kjinds
> >of unpleasant things happen. I have seen fuel haze "standing" on top of a
> >carburator from this..  Tom.
> >
> Tom-- I suspect you of a plot to keep me up late. I've tuned many Webers
> from scratch. seen fuel standoff too. It's why Weber will sell you extended
> boosters for IDA's and DCOE's. But the headers are still wrapped around the
> cam grinder's neck. Fuel standoff is primarily due to standing (sound)
> waves in the intake ports, which happen when the i valves are closed, not
> to self egr. When it happens, you can put the extended boosters in, and, by
> keeping the fuel that's way out there from falling onto the floor, you
> bring the BSFC right back into line. Too bad Passini's books are out of
> print, and somebody thought they need mine more than I did!
>
> I will admit that if you are trying to run a cam that has no business
> turning slower than 4 K on the street, you can get some burble,
> particularly on a single plane manifolded V-8, but I thought that modern
> valve spring materials and cam ramp rates had pretty much cured that crap.
> The other side of that is that I can and have set up 1649 cc , 4 cyl.
> (naturally aspirated) Alfas (80x82, 2mm over 1600) with cams that wouldn't
> make any power below about 5000, with 11.5 compression and two 45 DCOE's
> with 36mm chokes so they would make about 185-190 HP, and yet idle smoothly
> at 700 RPM, and pull smoothly (if only about as hard as a clapped out 1300)
> if you floored them at 1500 rpm in 5th gear. (P.S. Still only a single plug
> head, but made best power with only 33 degrees total advance--go ahead,
> ask!) Yeah, there was some fuel standoff, but I don't think much self egr.
>
> Regards, Greg