On Mon, 2 Feb 2004, Jim Jones wrote:
> Robert:
Hello.
> I was interested in your explanation of what Webers
> can do for a stock motor. While that somewhat flies in
> the face of other opinions I've heard ("you need to
> increase compression, change cams, etc. before moving
> up to Webers), it sounds like you speak from
> experience. I guess what a lot of us less-enlightened
> folks want to know is this:
The folks that pooh-pooh Webers on street cars completely mis-understand
the principle of carburation. For example, it is somewhat easy to make a
Z.S. 175 run rich on a TR6. Is this car over carburetted? NO. It's tuned
incorrectly. Period. The Weber DCOE 40 has a lot of adjustments. Add to
that the chaotic nature of how a carb works, and it is possible to go down
paths which do not solve the tuning issue. Folks throw up their hands and
concede.
> On a BONE STOCK motor, would triple sidedraft Webers
> give the best bang for the buck in terms of
> performance improvement for the dollar? Or should one
> pursue the other mods first? (Compression, cam,
> exhaust, headers, ignition, etc.)
Would a set of DCOE 40's give the best bang for the buck. I will say with
100% certainty NO. But, this is a qualified "No". If you do other stuff,
and then throw in a set of DCOE 40's, you will get the absolute best
power.
Let me frame the answer thus.
If you yank your crank-driven fan, you'll get several ponies. Some say up
to eight dyno provem HP gain. The cost is free. This is excellent bang for
the buck. BUT, if your goal is to make a stock motor run better at higher
RPMs, the stock induction system will let you down after about 4500 RPM's.
Sure the motor will pull that high, but you'll be on the downside of the
curve.
Another part of the equation that is missing from many discussions is "how
do you intend to use the car?". The answer to this is crucial to making
the right decision... but we all know there is no "right" decision. At any
rate, if your goal is boulevard cruising, then absolute HP gains is the
least of your concerns, even if you think otherwise. Chances are for the
cruiser that the oohh-aah factor of a set of triple Webers is the real
benefit. How do you put a value on the oooo-aah thing?? BUT the Webers can
be made to perform in the role.
Now, back to the issue of the intent of the car. In certain venues, adding
Webers is allowed by the rules. Given the addition of the Webers and other
performance mods, you can really tune your TR6. 160 HP plus is doable once
you start getting into the engine. But your query was about not going into
the engine.
To make any motor go better, you make it breathe better first. On a TR6,
the intake is a restriction. The early cars have a fairly tight intake
path, and with some hogging out can be made to breathe a lot better. Also
working against early "federal spec" TR6's is the cylinder head, as we
(the colonies) got a special head that in stock form flows like crap). A
late head with a late-style intake will flow a lot better in stock form.
So too, the exhaust on the stock cars is fairly restrictive. If you go to
a good free-flow exhaust, dump the fan, make the ignition system more
robust and add some low-restriction air filters, there are documented
cases of achieving 130 flywheel HP on a TR6 motor. Note: parasitic losses
become critical at high RPM, so balancing is not only suggested, it is
required if you are going to this level of development on a TR6 motor.
That 130 HP number is roughly 25% HP increase over stock. A third of that
comes for "free" when you dump the fan. Balancing will set you back $250
or $300, a good header another $450, custom exhaust - $300, a set of K&N's
$60 and a Crane ignition another $100 or so. Once you get all this stuff
in there, you're pretty close to the big number, but you are not there
yet. The last 5 or 6 HP is going to cost a lot of $$$. Webers cost $1.5k
and then you need to spend another $200 - $500 tuning. Then you can see
the upper HP numbers.
Now, many folks see this net gain as silly because if you look at the
Kastner dyno pulls (get the book!!!), you'll see that going to 10:1 and
adding a header and a mild cam (like an S2) will get you 140 HP with stock
induction. The net cost is lower than the DCOE 40's, so most folks
conclude that it's cheaper to just crank up the compression and stick a
cam in there. Well, it is cheaper, but it might not be the right solution.
For example, in SCCA the addition of the cam puts you square into "real
race car" territory. So building a 140 HP motor is nothing considering
that to be competitive you need to shed 600 pounds of weight from your
car. You want to talk expensive... this is a slippery slope. So SCCA has
classes where the internal motor mods are not allowed, but external mods
are. In Solo II, this is the so-called "street prepared" class. TR6 lives
in FSP with some really eclectic cars. But a well sorted TR6 with 130 HP
and stock weight (figure 2300 pounds in 100% legal rules form) is a nice
match for the lighter Hondas and old A1 VW's (1500 cc Scirrocos are fairly
light but only have 1700 or 1800 pounds, ditto for the CRX (not Si)).
So, as always, the answer "depends".
> Perhaps there is no RIGHT ANSWER, but I'd like your opinion.
I'll be honest, there is no right answer. However if you came to me as a
tuner and said "Bob, I want to turn 13.5 second quarter mile times in my
TR6", I would give you one answer. If you told me that you use your TR6 on
Sundays to drive on country roads, I'd give you a totally different
answer. What we all arrive at, no matter how we use our TR6's is a series
of compromises. My race car is fairly quick because I made decisions that
made the car totally unsuitable for street driving. Ironically, the motor
is probably the closest system on the car to stock because my goal was
reliability. So yes, there is no "right answer".
But that's part of the fun of this whole car hobby thing. Searching...
> Thanks, Jim Jones
Ta-ta,
rml
|