>I realize this is not a cheap or easy solution,
>though its probably one reason youre motor seems sluggish down low.
I'm coming in to this late so allow me to respond to a bunch of different
posts all at once. Is low end performance the problem? With as mild a cam
as you have, you shouldn't have any problem with low end unless there's some
sort of tuning or mechanical problems.
>I have a 351C with 2 primaries. And this is a big problem. I am preparing to
>build a new set of headers (I dropped the engine and moved it back, so an off
>the shelf set from my manufacturer wont fit) that are 1-3/4 to improve port
>velocity. 1-3/4 diameter primaries should be fine for 450 hp, which is my goal
>in the end.
4V exhaust ports are sized for 1 7/8" diameter primaries, that is 1 7/8"
is the smallest diameter that will cover the exhaust port. 1 3/4" pipe
can be used but you'll need to transition to a larger diameter at the port.
2" is excessively large for a street application but common on Panteras which
have truely odd exhausts. The Pantera GTS exhaust consists of tri-y headers
with 2" diamenter primaries feedding into a very short 2 1/4" collector,
leading back to a kid's lunchbox-sized mufflers (they sound good though).
Tri-y's are not as sensitive to primary diameter as bank separated 4-into-1
headers, but necking such large primaries into such a small collector can't
be good.
>As far as the 4V heads especially the open chamber ones you dont really have a
>big enough cam, displacement or compression to use them. The ports and valves,
>as others have said, are simply too big. They work well with strokers, 10+:1
>compression and high rpms.
Agreed. The 4V heads like displacement, compression, and/or RPM. However,
it is possible to build a 4V headed motor that makes good low end power.
A friend built a 351C with CJ cam, 4V closed chamber heads, Offy Dual Port
intake and Holley 780 that didn't lack for torque. In a 4000 lb Torino with
26" tall tires, highway gears and a C6, it would spin tires any time you
wanted but that's not the kind of motor you want in a 4 speed Cobra.
>the large ports give low vacuum signals at low rpms, so its difficult to get
>low end driveability.
With a mild cam like you have, the vacuum signal should be fairly high,
particularly considering the dual plane intake and carb. The cam lobe
centers are important with big port heads like a 4V Cleveland. You
want something on a 108 lobe center, maybe 110. They will help with
keeping the intake velocity up. Also, do not block the heat risers
on a dual plane Cleveland intake. The heat helps vaporise any fuel that
drops out out of suspension.
>Jeff gets away with it because he's running an awesome independent runner
>induction system,
Yup, independent runner intakes can make a big cam much more streetable.
One of the guys in the Pantera club ran a 260ish deg @ 0.050 cam with
well over 0.600" lift with Webers and then IR EFI. He said it was fine
in traffic. Another guy I know recently switched from a 4 barrel to
PPC's IR EFI on his 372 Cleveland stroker and he wondered where his
nasty 105 degree lobe separation angle cam went.
>Tim was able to improve his low speed tractability by having his carb tuned
>to so its booster venturis are more sensitive.
Annular boosters are a particularly good modification if you are running a
single plane intake manifold. I've also found multi-strike ignitions (e.g.
MSD-6AL) helpful.
>The port plates will help, but they arent the answer, but rather (in my
>opinion) a band-aid.
The only intake port plates I care for are the Roush port stuffers,
preferably with an intake manifold welded up to match. TFC and Parker
both make 4V race intakes that are meant to be used with their port
stuffers.
>Or better yet, buy a pair of 2V Aussie heads which have ports slightly larger
>than the US 2V heads, but have a quench combustion chamber that raises the
>compression 1 point without any problems with detonation.
All of my Aussie heads have the same size ports as all of my 351C-2V heads.
I'm not sure where that myth started but it pops up in magazines from time
to time. You are absolutely correct on the quench chamber. It raises
compression (by more than 1 point) without detonation problems.
4V heads should work fine in this application be closed chamber are better
all around.
>Edelbrock, Weiand and Holley all make nice 2V dual plane intakes that will
>work well with these heads and you can pick them up for between $100 and $150
>used.
Edelbrock is the only company making a dual plane 4 barrel intake for 2V
heads. It's a fairly low rise unit, about the same as a stock Ford 4V
intake. Weiand makes the single plane Weiand Xcelerator 2V which is a
pretty decent piece for 2V heads. I'm running one on the temporary engine
in my Pantera and it will pull just fine from 1000 RPM in fifth gear.
Holley no longer makes a 2V intake but when they did it was a single plane
(the Street Dominator) as well. I'd avoid the Street Dominator, as it's
ports are substantially smaller than a 2V intake ports. It was really a
low RPM piece. Of the commonly available 2V intakes, the Weiand Xcelerator
is probably the best choice. There are also several 2V intakes available
from Australia (Redline, TFC, Parker, etc.). The TFC and Parker are very
tall single plane, air gap, race intakes, along the lines of a Roush high
port intake.
For 4V heads, the intake choices are completely different. The best intakes
are the single plane Holley Strip Dominator and the Blue Thunder dual plane
high rise. That also brings up a good point, never assume that something that
works well on a 2V Cleveland will work well on a 4V. Treat them as completely
different animals when picking components. A Weiand Xcelerator 4V (on 4V
heads) is a dog down low but a Weiand Xcelerator 2V (on 2V heads) does just
fine down low.
>Finally, I would go with more cam, something similar to what Tim is running
>or maybe something along the lines of the Crane H-290 (formerly Fireball II
>290) cam:
http://www.cranecams.com/master/apps/ford37.htm
That's a little smaller than the cam I'm running in my Aussie 2V headed 351C.
With a 735 CFM Holley, a Weiand Xcelerator 2V single plane intake, and
1 3/4" diameter headers, it'll pull 5th gear in my Pantera from just off
idle. I spec'd the cam for my '56 F100 truck project (engine's temporarily
in my Pantera while I build a 408C stroker) and I think it will be a great
truck cam. I'd want more in a lightweight Cobra.
continued on next post - original reply too large...
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