More conversations with Jim Steck regarding Superchargers, EFI, & Twin Spark engines
(Non quoted portions are Jim Stecks comments)
There are two basic types of mechanically driven superchargers...positive displacement and centrifugal. The centrifugal is not well suited to street-driven cars with small engines. As Greg Hermann stated in digest #1036, 'their boost, after all, varies with the square of their rpm.' This means max boost at the redline only...if you want 8 psi maximum boost and consider 6500 RPM your redline, you would have only 2 psi boost at 3250 RPM...an increase in power of only 14%.
Several companies have designed systems to improve this condition. Studebaker used a mechanical variable speed drive on their Paxton supercharged engines, but the drives were very high maintenance...some would say "unreliable". In the Alfa GTA SA, the centrifugal superchargers were driven by hydraulic motors, powered by a variable displacement pump...probably more reliable, but more complicated and certainly more expensive. It's also less efficient...converting mechanical power to hydraulic power and back to mechanical power.
Boost control is generally not used on mechanically-driven superchargers. The output cannot be throttled without damaging the supercharger from over pressure or over temperature...it must be bypassed or recirculated. This is not something that can be done with a wet system...fuel added before the supercharger...and pressurized carburetors have their own problems...collapsed floats, regulating fuel pressure, hot fuel, etc. So, port fuel injection is the only reasonable approach.
Positive displacement superchargers are a much better match to the air requirements of a piston engine and can usually be matched in size and drive ratio to provide a very nice power curve without any auxiliary boost control. The usual method is to tune the basic engine for maximum torque at low RPM. Then at higher RPM's, the torque curve is pulled up by the increasing boost...producing a torque curve similar in shape to a normally aspirated engine, but higher all the way across.
"How sophisticated do the electronics need to be? Stock 'black boxes' make me very uncomfortable. Custom, one-off, insides known only to one person in the known universe scare the pee-pee out of me. How simple (as in it works really well and is still bullet-proof) can the EFI and if Really required, programmable ignition system be made?"
I only have personal experience with the Electromotive system. The TEC (Total Engine Control) integrates fuel and ignition and has been nearly bullet proof. I had a crank sensor fail because I didn't know how much the nose of the crank moved around...and the trigger wheel hit it ...and I've had one throttle position sensor (a General Motors part) that needed replaced after about 60,000 miles...internal diagnostics told me I had a failure. I've heard similar Testimonials for Haltech, Motec (expensive) and Autronic.
(from Greg Hermann)
My experience here is different and may not be typical. The engines I've built with aftermarket EFI have been 'high RPM engines' with fairly large valve overlap. I've tried several different knock sensors, mounted them in several different locations and always have to ignore the signal above 5000 RPM...where the really destructive detonation occurs.The Alfa engine is noisey and fools the sensor at higher engine speeds. Since I've never detected any knock at low speeds, I have never been able to use this feature. My ignition curves are worked out on the dyno and have an appropriate safety factor.
As fas as 'closed loop' operation goes, I consider it essential, and have developed a tuning strategy that produces excellent power, good throttle response and good mixture control during part-throttle operation...this applies to unleaded fuel engines only. The fuel map is developed for maximum power...plus a small safety factor...and then the output from an O2 sensor is used to lean the mixture out during part-throttle operation. The Electromotive is designed to operate in 'closed loop' this way. Its 'auto tune' function is intended only for setup. It sounds like the Autronic 'auto tune' is also intended for setup only and not continuous closed loop operation.
Tuning these systems
is not difficult. It may look overwhelming at first...the Electromotive
system has over 400 variables...but the 'Tuning Wizard' will
get you a basic calibration that will get you running...better
than a lot of Weber conversions I've seen. Then you can then
start fine tuning by pressing a few computer keys. You don't
need a box of jets, or springs and weights, just a laptop...sorry
Biba, you'll have to use a Windows machine.
On supercharged engines...I'm working on the design of a bolt-on supercharger kit using an Eaton M62 supercharger. If someone wants to deliver their car to me tomorrow, I'm ready to start installation.
The multiple engine maps are completely unnecessary...as the Electromotive system will adjust the fuel delivery to driving conditions based on feedback from an O2 sensor. I would develop a calibration that is optimised for performance in open loop, but would operate in closed loop until past half-throttle or high RPM. This strategy works very well for performance and drivability. Since we don't have annual emission testing in my county, I don't have numbers to fall back on, but believe I could make the system pass on almost any vintage Alfa...certainly on any Spica-equipped car. A limp-home mode is also part of the system.
A new stock clutch is capable 200+ Hp on a spider and 250+ on a Milano. A Milano transaxle would be advisable in an Alfetta. I've already produced similar cars, but with turbo superchargers instead of mechanical. The intake on the Eaton blower would not be difficult to design and build, and the power level would be easy to manage. The turbos produced a minimum of 275 Hp and were daily drivers...with occasional track use. After 60,000 miles, the end gap of the rings in my engine had only grown 0.002 inches. Brian's Alfetta hasn't been torn down, and my improved engine only has a couple thousand miles on it...the increased Hp was too much for the spider transmission.
An engine can always make more flywheel Hp with a turbo because of the mechanical losses in driving a blower, but an engine with a 50-60 Hp increase would be easy to build. The real problem with turbos is the exhaust syste...even stainless steel has to be considered temporary. You can expect some rebuilding every couple years. And the exhaust note doesn't sound as good...it's not crisp. To me, the sound of a supercharged small-bore engine is the best! And I like the whine of the blower.
(The following has
been removed at Jim Steck's request - see following).
The brake kit is fully
developed, and costs & performance known, but the details
of building brackets, and intake for the building of a supercharged
engine are still not fully worked out...I'm not ready to publish
a cost estimate for a system. There are a lot of variations that
could be made that would really affect costs.
Since the rotor diameter and caliper piston diameter are not changed, the brake bias does not change. The only thing the vented rotor does is keep the rotor temperature in it's designed operating temperature...stops it from overheating. There have been other discussions on the Digest about cooling the rear brakes on these cars...some suggesting that ducting more air to the rears should do the job. I've even seen a track car with squirrel-cage blowers mounted in the rear seat area blowing cockpit air directly on the calipers...it was an improvement, but not a complete solution.
The vented rotor is
the air pump, and with roughly 3 times the surface area and more
than twice the mass, it absorbs the brake energy better and gets
rid of it much faster.They will easily keep up with the vented
front rotors of the V-6 cars.
Here is where the choices have to me made. Compression ratios from 8.5 to 7.0 would be used, depending on the boost/power desired. At the lower end of boost pressures and RPM, the stock Borgo pistons could be cut down...I think a 180 Hp engine could be built with stock rods and modified stock pistons. A good intercooler would help keep piston temperature down.
"How loud would you say the whine is? Ahmet emailed me and said before they installed a 'muffler' on his GTV's supercharger, it sounded like a 747 taking off. Afterwards, it was somewhat more bearable but still very loud. Doubt if that would thrill any potential clients I might have. Can one hear the engine over the supercharger whine, or does the whine pretty much become the 'engine' sound? Most of the cars I restore are for couples."
More horsepower will make more exhaust noise, but should be able to be muffled...another one of those 'unknowns' in building a supercharged car. The intake noise is another problem. I've driven a supercharged T'bird, and the noise was almost undetectable...but I don't know how extensive the work on the air cleaner / silencer is. Personally, I love the sound of the old superchaged Alfas, with all the gear and supercharge whine. The noise question can only be addressed after the first system is built...another reason I'm reluctant to quote any prices yet.
I'll be happy to discuss options with anyone interested in building one.
"All I ask is don't say in your subject headings, " Was, etc." Then talk about turbos for V6's. Just talk amongst yourselves and leave us little guys who admit we have little guys and aren't afraid to admit it - though we would like to achieve a bit more potentiality from our undersized units. (I can hear the echos now, "Speak for yourself, Biba!)."
I think Mark Donohue had it about right when asked about the horsepower of the Turbo 917's...how much horsepower would be enough? Without looking up his exact words, he said something like ("When I have enough power to spin the tires all the way down the longest straight").
is going to put a TS head on his engine - I'm assuming pre-TS
block. Please tell me if I'm wrong but heard the water passages
don't line up all that well - perhaps other things. The only
TS head I was up close and personal to was some years ago at
Alfa Ricambi. The head seemed taller. A fair amount taller. Should
this be the case, what happens if a Spider goes over a large
pebble which hits the pan guard which pushes the engine up into
"Wes Ingram shows
the Electromotive ignition system set up for a 4-cylinder alfa
engine on his website. He cleverly uses a Spica cover on which
to mount the pick-up. Would be nice to have an ignition which
is a really mount it and forget it type. Jim did have a problem
with oneignition setup because he belatedly found that the front
pulley had avery slight wobble. This surprises me after looking
at Wes's as the pickup appears to be some distance away - but
then, I don't know the complete story."
but thought you might enjoy them.
The Besic's Series 4 Alfa Spider next to the Bank's record breaking streamliner.
Bonnie at the salt flats in 2001.
Bonnie's engine bay BEFORE (taken in 2001)
Bonnie's head AFTER (see below - taken in 2002)
At least we're in
good company...Al Teague, in the Banks Engineering streamliner...retired
today. His last run had a terminal speed of 410 mph.
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