Re: Scott Fisher/ Velocity stacks

[Scott Fisher <sefisher@domain.elided>]

Tom Lesko wrote: 
> 
> Scott, I enjoyed your post on velocity stacks.
Thanks!
> As I read it I was wondering what it all meant in 
> terms of application to a "daily driver". 
That's part of what makes this so tricky. Much of the application's 
effectiveness depends on how much fabrication you're willing to do, 
whether you're willing to modify your car, and other concerns. And the 
truth is, the difference may only be on the order of single-digit power 
enhancements, if that. 
We'll start with the well-worn truth that Alfa did a stellar job, on the 
whole, in balancing the compromises inherent in any automobile. Unlike 
tweaks to, say, a Sixties-era domestic sedan (where it *is* possible to 
bolt on a $50 air filter and get an additional 20 bhp -- been there, 
done that, finally had the tickets drop off my driving record :-), 
tweaks to an Alfa fall into one of the following two categories:
1. Easy and/or cheap, and ineffective 
2. Difficult and/or expensive, and effective
Basically, in tuning any car, there are two things to do -- correct 
weaknesses, and enhance strengths. There are very, very few weaknesses 
in an Alfa, which is a shame as correcting weaknesses is usually a lot 
cheaper and easier than enhancing strengths.
> To be more specific, could I add velocity stacks to my 1600 Veloce 
> and reasonably expect to clean the air prior to it entering the 
> stacks and still enjoy the benefits of the stacks? 
There are a couple of possible answers here. One is to use the readily 
available directionally adjustable velocity stacks (IAP and Ricambi sell 
them, and probably other sources too) on the front of your Webers, then 
mount sock-style air filters over them. One trick that road-racers and 
autocrossers have started using: "prefilters" from sprint-car 
suppliers. These are finely built synthetic-fabric bags that go *over* 
the foam unit on a sprinter's Hilborn injection tube. Think of the 
typical dirt-track sprint car environment and you'll see why a prefilter 
might be a good thing: they stop flying mud from entering and plugging 
the foam filters, but they're easily removed and tossed into a washer. 
Kaeding Performance in Campbell, California used to have these on the 
wall when I was in there regularly in 1990-92 for the EP MGB I was 
building; I haven't used 'em myself, but I've teched cars that had them 
in place.
The main gotcha with this is the underhood air problem we've been 
discussing; the lower density of heated air means you're getting less 
oxygen per unit volume than if you were getting cooler air from outside 
the engine compartment. This is why so many race cars used to have hood 
scoops, holes cut in the hood with the air intakes sticking out, or 
other ways of getting cool air into the motor.
I don't think you'd really be happy cutting holes in the Veloce's hood 
for the ram tubes to stick out, so that leaves ducting. What a 
road-racer would do is get some large ducting (looks like dryer ducting, 
more or less), run it from in front of the radiator (just inside one of 
the "mustache" openings in the Alfa's grille -- or actually, they'd 
probably run it from the headlamp nacelle, unless those ducts were used 
for brake cooling) to just in front of the ram tubes, and then either 
prop the trailing edge of the bonnet up an inch or so to let the 
displaced hot air out, or maybe punch some louvers in the hood, 
depending on the rules. Since you're probably not expecting to have the 
kind of underhood air flow on the street that, say, Al Leake gets coming 
down the back section of Sears Point at something over 100 mph, this may 
not be a problem for you. Added benefits would be the induction roar 
that's been mentioned, plus a WAY serious coolness factor when you 
raised the bonnet at club meets and car shows. An aluminum heat shield 
between the carbs and the manifold would not only keep away some of the 
heated air from the stacks, it would also provide a good mounting point 
for the trailing edge of the duct.
But let's look at your last question, because something like this is 
what I'm thinking of for my 1300 GT Junior when I get the "good" motor 
for it in the next 12 months or so:
> Also, would enclosing them in an air box similar to a GTa box, have 
> detrimental effects on the efficiency of the stacks? 
In that you can't typically fit 5-inch stacks inside the GTA air box 
(which I've seen), yes, these two solutions are pretty much mutually 
exclusive, especially with the limited underhood space in a 
Giulietta/Giulia.
Here's what my reading/practice are leading me toward (and note that 
this is all still gedankenhochleistung -- er, "theoretical high 
performance" :-):
Ricambi/Shankle sell a carb plate designed to bolt onto the front of the 
dual Weber/Dellorto carbs on our cars. This plate has what some folks 
call "stub stacks" built into them. 
A "stub stack" looks like you took a sharp knife and sliced the top inch 
or so off a bagel (assuming you could find aluminum bagels, that is), 
then riveted that to the carb plate.
Why they work: In my overview of velocity-stack technology yesterday, 
recall my mention of the pinching-off effect that the 90-degree bend at 
the carb's intake has on incoming airflow. As it turns out -- and 
again, I'm away from the book that has the actual figures in it -- a 
stub stack of this variety was the most effective shape at increasing 
airflow into a carburetor. I think the tests Vizard ran indicated that 
you had to get to something like 11 inches of ram tubing (*with* the 
right shape at the ends) to improve on the airflow enhancement provided 
by a stub stack mounted on the carb face. (This does not include the 
advantages of inertial ram, but it addresses one of the only remaining 
weaknesses in the Alfa: the 90-degree carb throat entry.)
Now, here's the best part: Once you've mounted this carb plate to the 
fronts of your Webers/Dellortos, you then (with, again, a little 
fabrication) can fit a GTA-style air box over the carb plate, and run 
the inlet hose forward till it's in front of the radiator. What *I* 
have thought of doing then is mounting one of those Bosch cone-style K & 
N filters at the inlet of the airbox tube. Matching the tube dimensions 
and the cone filter's outlet will require some research and measurement.
Now for the bad news...
The worst part about this is that the actual enhancement to airflow is 
likely to be on the order of 10 to 15 percent, and unless you then 
compensate for the additional airflow by adjusting your Webers (that is, 
replacing mains, air correctors, and maybe accelerator pump jets, plus 
possibly chokes), your car still won't make any more power. I think the 
relationship between airflow and horsepower is something like 0.3 to 1 
- -- that is, a 10% improvement in airflow will give you a 3% improvement 
in horsepower. So at approximately 100 bhp in a stock 1600, you may 
spend several hundred dollars to get 3 to 5 bhp. Big whoop. Of course, 
if you've got a 1600 race car that puts out maybe 150 bhp, the 
percentages are the same but the base is higher. You may then realize, 
oh, let's be generous and call it 7 bhp -- and that may be enough to 
keep your grille ahead of the next guy's when they drop the checker. 
Remember, in a 20-lap race, a 5/100 of a second advantage per lap is a 
1-second margin of victory.
I think it's important -- because I've written so much how-to and 
been-there-done-that prose about modifying cars in the past few days -- 
that I mention something that tempers all these go-fast observations:
The first rule of modifying any car should be lifted directly from the 
Hippocratic Oath: "First, do no harm." The second rule is that, barring 
turbosystems and other massive changes, tuning a car that's as 
well-designed as an Alfa is typically a matter of single-digit 
percentages here and there, and often making only one change to a system 
violates the first rule. Many people have complained to magazines that 
they put on a header (to pick one example) and the car got slower. 
People who don't *really* understand what's going on will then say 
something about needing "backpressure" in the exhaust to make it work, 
but that's not only incomplete and somewhat inaccurate, it misses the 
point; the point is that the header changed the engine's air/exhaust 
flow characteristics in only one dimension, and that unless you also 
change your cam timing and fuel delivery curve (and maybe more) to take 
advantage of the new scavenging characteristics, you will have spent 
whatever you did on that header to make your car slower.
It's also worth closing with this: One of the first cars that I started 
modifying to get less power (not my intention, but nevertheless the 
result), not quite 20 years ago, was an early US-model VW GTI. I would 
read all the magazines every month, and they'd talk about the cool 
things available for the car. The ultimate performance piece for the 
GTI at one point was the Oettinger cylinder head; I used to sigh over 
its performance specs and over the glowing (if not always well-formed) 
prose in "VW & Porsche" magazine (the predecessor to today's "european 
car" -- la plus ca change...)
What was so ultimate about it?
It was an aluminum head with dual overhead cams and a cross-flow setup, 
so that the air/fuel came in one side and the exhaust went out the 
other. Cost something like $4500 in 1983 dollars, but it was the 
trickest of the trick back then.
I note with some amusement that I spent less than that in 1995 dollars 
to purchase an almost identical cylinder head design from Italy, and as 
an added bonus it came with one of the most beautiful cars in the world 
to drive around under it. :-)
So Alfas aren't *impossible* to tune for added performance, but the 
factory really did all the easy stuff already. There are very few weak 
links in most Alfas, at least in the high-performance versions for a 
given era. Just means you have to think a little harder before doing 
anything, and adjust your expectations accordingly.
All the best,
- --Scott Fisher

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End of alfa-digest V7 #872
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