Reply to "4 x Weber 48 IDF (not IDA) conversion"

> Talking of high HP and as this is still a topic on Weber stacks,
> can you educate me a little. I recall reading Webers on an IR manifold
> can support up to maybe 500 HP and then they drop off as the Independent
> Runner manifold is restricted in per cyclinder flow rates in comparison
> to an open plenum type design. Is that true, valid to a point or urban
> myth?

That statement is based upon David Vizard's testing on a 350 SBC.
Vizard found that 48mm Webers on a down draft IR intake will make
more peak HP up to around 480 HP, compared to a plenum intake and
4 barrel carb. Beyond that, a larger 4 barrel carb can make more
peak power but will usually be down on power in the lower rev ranges.
BTW, Vizard ran 48mm Webers on his pickup truck due to the better
power curve.

Another guy recently tested Webers against a Victor Jr single plane
on his 331 Windsor. The engine had a 3.25" stroke, 4.030" bore,
5.4" rod, 11:1 compression ratio, Victor Jrheads that flowed 301.5
CFM intake and 200.5 CFM @ 0.6" valve lift, custom solid flat tappet
cam 262/264 degrees duration @ 0.050", 0.592"/0.544" lift. Results
were:

.....Holley..Weber
RPM..Tq..Hp..Tq..Hp
4000 338 257 382 291
4400 371 311 400 335
4800 398 364 449 411
5200 411 407 441 436
5600 413 440 438 467
6000 412 470 434 496
6400 400 488 422 515
6800 401 519 399 517
7000 390 534 386 514

The Webers make better power until 6800 RPM. While the peak
is lower, the average between shift points is higher so the
car will accelerate faster with the Webers.

> The carbs become restrictive, not necessarily the manifold.

Correct. Larger Webers will increase the point at which
the carbs becime restrictive. When Ford was testing IR
set-ups for Pro Stock (using the Autolite in-lines), they
maxxed out the flow of the larger inlines and resorted to a
mini-plenum between the IR carbs and intake.

> 48ida's are used because of the torque trade off.
>
> 427 Fords had a set of 58mm carbs made for them for racing.

Yup. Shelby ran the 48's on 289's and Ford had a batch of 58's
for 427's. The 58's were rare but there are guys like Gene Berg
that make similar big bore Webers today.

> Also, I personally never found the Webers feeling restrictive.

I doubt it's the sort of thing you'd feel in the seat of your pants.
It's only by comparison testing you'd notice. I recently drove a 408W
with a set of 48mm Webers in an aluminum bodied Kirkham Cobra replica.
It supposedly had 550 HP and I believe all horses were present and
accounted for. I've driven a Superfromance Cobra replica that had a
dyno-verified 556 HP 418W that had a Victor Jr single plane and Race
Demon 4 barrel carb. The Weber-equipped Kirkham felt much stronger,
due in no small part to 400 lbs less weight, I'm sure, but the Webers
performed flawlessly. No flat spots anywhere in the powerband, pulling
strongly from 2000 RPM to my 6000 RPM shift point. Power was not
dropping off at that point. I was impressed.

> Power under that was ok. It just didn't pull like a 427 does.
> Actually I think a 428cj is the king down low anyway. I think
> it is noticably more powerful down low then the 7 is.

None of that is due to the bore and stroke differences. Torque
follows displacement, the product of bore and stroke. Shorter
stroke and bigger bore is easier on the components at high RPM
and permits better breathing (larger valves or less unshrouding
for the same valve area). In the case of 427 and 428, it's the
tuning that makes the difference, particularly the 428CJ cam.

> I think everyone is too dyno crazzy.

The dyno is a tool. Used correctly (calibrated and corrected for
the same day), you can learn a lot.

> They can't explain why a car with an engine with 100hp less on the
> dyno kicks the crap out of the other car.

It is torque at the rear wheels that accelerates a vehicle. If an
engine averages 100 HP more betweeen shift points than another
engine (on the same dyno under the same conditions), it will out
accelerate the other when installed in the same vehicle.

> Incidently. Why put a 427 small block in front of a ZF that has
> notariaty for not being able to handle a 427FE torque? Torque is
> torque.

On a street car, the tires are the fuse. If you break traction at
400 ft-lbs, it doesn't really matter if your engine makes 600 ft-lbs.
The transaxle won't see it. That said, there are people who can
break an anvil in a sandbox and lose all the pieces.

Dan Jones