(here's a really long post that has a lot of information about 2V and 4V builds. I hope it's useful to someone.)
Keith, I would like to give you some more input. The aussie 2V heads that Mike mentioned will help low end torque with increased port velocity but there not going to improve HP numbers. Also, if you consider the swap to closed chamber heads be aware that depending on your pistons and the chamber volume of both heads you could increase your compression as much as 2 points. The following web address is for Keith Black piston info.
http://www.kb-silvolite.com/page45.htm#SECT2 You don't need torque in a 2500lb straight shift car you need horse power.
You asked about the exhaust port plates and would they help? I think they will because the exhuast port on a cleveland 2V or 4V is a bad design. The exhaust exits the chamber going up into the port and then has to turn down to exit the head. The plate will actually even the port out and make it a more uniformed size. The aftermarket world has figured this out and raised the exhaust ports dramaticly to improve exhaust flow. Just for you information the exhaust ports on 2V & 4V heads are almost the same size at there smallest point were they turn 90 degrees in the head. The 4V head exhaust port is a little wider but is the sams hieght. (see atached photo).
As for carburetors, any custom carb shop will tell you vacuum secondaries are for automatics and mechanical secondaries are for straight shift transmissions. Edelbrock carbs are good for daily drivers but they are not for high HP applications. They don't respond well to the low vaccum signals that big cams tend to produce. I would stay with your Holley for now and just try to tune it a little more. By the way my carb specs are as follows:
Flow(cfm) 880
Main jets: pri. 73 sec. 83
Power valve: pri. 6.5
Nozzle size: pri. .028 sec. .031
You also said that you were a bit perplexed with your Desktop Dyno. I'll tell you what I have found to work with mine. Input head flow information instead of using there generic selections. If you do a search on the web you will find sites that have head flow information for a cleveland. It may not be exactly what you have but it will make a diference in the end results. You can also get all the information you need from Cranes web site to input diferent cams.
http://www.cranecams.com/CraneCams.htm I have built a library of head and cam information in my Desktop dyno and it helps when I want to experament with different ideas. You will probably find that your cam is on the smaller side and that changing it will yeild the biggest results but use your Desktop Dyno to compare different cams. It really does work.
I figure you will need to perform a compression check just to make sure all 8 cylinders are good. Then I would start working with the carburetor and the distributor. A vacuum gauge is also a very useful tool when fine tuning. I would like to know what kind of advance curve your distributor has been set to, and do you have a vacuum advance or is it just mechanical?
Bottom line is don't be afraid of those 4V heads. They will make horse power and lots of it even on the street. You just need to optimize everything around them to get the best performance. Thats what your Desktop Dyno is for.
>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...
>I did have a question on the cam you recommended. Maybe I am reading the
>specs wrong (or maybe reading the wrong specs), but it looks like the H-290
>actually has less duration at .050 than what I am currently running, 216 vs
>220, although it does have more lift, .524 vs .505. So, is it really that
>much more aggressive of a cam? In addition to the lift increase, I was
>thinking I would need duration figures in the low 230's.
With 4V quench heads and flat top pistons (10.5:1 compression will run fine
on 92-93 octane), I'd want at least 230 degrees duration, 0.550" lift,
108 lobe centers. Tim Tullio had a well sorted, very streetable combo in
his Pantera. His engine consisted of an Erson hydraulic flat tappet cam
(232 deg duration @ 0.050", 108 LSA, 0.545" lift), Rhoads lifters, 4V quench
heads, flat tops pistons, 735 Holley, coatings, C&A rings, MSD ignition,
wrapped headers, and MPG Stinger exaust port plates. He tested a bunch of
4V intake manifolds, including an Edelbrock Torker, Weiand Xcelerator 4V,
Offy Port-o-Sonic 4V, Holley Strip Dominator, along with a couple dual planes.
Tim spent a lot of time optimizing the carb for each intake. In the end, the
Holley was 4 tenths quicker in the 1/4 mile than the Torker and had, by far,
the best driveability (smooth with no flat spots) of all of the single planes.
He said it rivaled the dual planes down low, as far as driveability was
concerned, and by 3000 RPM was pulling away. He could never get the Torker
to smooth out at lower RPM, despite a lot of tuning time. He never got to
try a Blue Thunder high rise dual plane which is generally regarded as the
best dual plane for 351C's.
>While I'm asking about cams, do roller cams really generate 30-40 additional
>HP over non-roller cams?
Not warranted in this case. You might want to consier a solid lifter flat
tappet cam though.
>If you want an engine with low end torque and moderate HP at the top end,
>4V heads probably arent the best choice.
True. Aussie 2V heads would be the choice in that case. To make big
horsepower they will need porting work though.
>If you are willing to sacrifice a little torque down low in exchange for
>some more HP up top, you can do it with the 4V heads, but you really need
>more compression and cam to make best use of them.
Absolutely. 4V heads like lift (2V's peak early but 4V's keep climbing)
and compression. The best streetable 4V combos are built around flat top
pistons and closed chamber heads.
>But as others have shown, you can more than likely reach your target of
>350 with a cam swap and some tuning.
Yup, 2V heads are fine to 400 HP with a little attention. A good all
around 2V build is one I spec'd out for a club member's Pantera. Charlie
had a Pantera with a basically stock open chamber 2V engine with Holley
Street Dominator intake and Pantera GTS headers and he was not happy with
its performance. He wanted something that would pull from 2000 to 6000 RPM
with some idle lope. I talked him into:
ported Aussie 2V heads
Weiand Xcelerator 2V intake
Holley 700DP
1.73:1 roller rockers
flat top pistons
Comp 282S solid lifter flat tappet cam (part # 32-238-4)
236/236 @ 0.050" lift, 0.570"/0.570" lift (minus 0.022 lash), LSA 110
windage tray
MSD 6AL ignition
He absolutely loves the new engine. With proper tuning, it should be
over 400 HP and still be street friendly.
>I think youll be giving up a noticeable amount of torque with the huge
>headers though. So my opinion would be to try installing the exhaust
>port plates,
One of the guys in the Pantera club did quite a bit of testing of exhaust
port plates. The only ones he found that worked were the MPG Stingers
exhaust plates (the 1/4" thick brass ones, not the stainless steel ones).
As a rule, the Mustang drag racers don't care for exhaust port plates
because the headers have to make a tight turn down at the exhaust port
to clear the shock towers. With those sort of headers, the 4V dropping
port floor helps the flow make the tight turn and blocking it off with
a port plate just introduces a constriction. Pantera headers may respond
better to exhaust port plates because the header goes straight out from
the port. I'd expect your Cobra headers are similar so the Stingers would
be worth a test.
>borrow a 600 or 650 cfm vacuum secondary carb and play with your timing.
His 700DP isn't overly large for a 351C, assuming it has been properly
tuned. Double Pumper carbs will be set up overly rich out of the box,
so they will need some tuning. I should be able to dig up the jets were
ran in Charlie's 700 DP.
I run a Holley 735 (off a 428CJ) and it works just fine and will even pull
down 20 MPG on the highway (Panteras don't have much aero drag). If you've
got the hood clearance, a Predator would be ideal for a big port 4V, due to
it's variable venturi area and CFM. A friend runs one on his 372 Cleveland
stroker and loves it. Says it doesn't lack for torque, even on the the big
port Holley Strip Dominator.
>Keith, I would like to give you some more input. The aussie 2V heads that
>Mike mentioned will help low end torque with increased port velocity but
>there not going to improve HP numbers.
Stock 4V heads will outflow a set of stock 2V's, Aussie or U.S., by a fairly
wide margin. To get realy good horsepower out of a set of 2V's, I recommend
bowl porting and installation of a somewhat larger intake valve (4V is too
large for 2V ports, 2.1" seems to be the best). Retain the 1.65" exhaust.
Use valves with neck-down stems, back cut the heads of the valves, and tear
drop the guides. Worked over Aussie 2V's will perform quite well. The
beauty of 4V heads is you can just bolt them on and make big power. A guy
I know just sent me his dyno sheets of a very simple 351C with 0.597" lift
Ultradyne solid lifter cam, Holley Strip Dominator, flat top pistons, and
bone stock quench heads... 500 HP at 6800 RPM.
>Also, if you consider the swap to closed chamber heads be aware that
>depending on your pistons and the chamber volume of both heads you could
>increase your compression as much as 2 points.
True. For pump gas, you want flat top pistons and closed chamber heads.
>You don't need torque in a 2500lb straight shift car you need horse power.
Agreed. My approach is to not worry about the amount of power that a
4V headed motor makes below say 3000 RPM. All that really matters is
that it is tractable down low and then let the RPM build power. In a
drag or road race, your RPM's will be up anyway.
>You asked about the exhaust port plates and would they help? I think they
>will because the exhuast port on a cleveland 2V or 4V is a bad design. The
>exhaust exits the chamber going up into the port and then has to turn down
>to exit the head.
2V exhausts don't need the port plates. They don't turn as far as the 4V
ports (actually they don't have the floor drop away like the 4V does).
2V heads flow nearly as much as 2V (at least at lower lifts) and have higher
average flow velocity (important for scavenging).
>The aftermarket world has figured this out and raised the exhaust ports
>dramaticly to improve exhaust flow.
Just like Ford did way back in the early '80's on the Motorsport high port
heads.
>Just for you information the exhaust ports on 2V & 4V heads are almost
>the same size at there smallest point were they turn 90 degrees in the head.
>The 4V head exhaust port is a little wider but is the sams hieght. (see
>atached photo).
A very good point most people don't realize. The big problem with the 4V
head is the exaggerated area change of the exhaust. The minimum areas of
the 2V and 4V exhaust ports are fairly similar but the 4V exit area is huge,
much of it wasted dead space. There are some tuning tricks that are important
with The narrow lobe center cams that work so well on 4V motors (helps keep
the intake velocity up). An important one is an efficient exhaust (free
flowing mufflers and pipes...otherwise you can have a reversion problem).
For the same reason, I've moved away from recommending dual pattern cams
with lots of extra lift and duration. Given the sort of cams a performance
Cleveland runs, the extra duration just causes reversion problems.
>As for carburetors, any custom carb shop will tell you vacuum secondaries
>are for automatics and mechanical secondaries are for straight shift
>transmissions.
True but if you have a vacuum seconadaries carb and a manual tranny, all
is not lost. Holley makes a quick cahnge spring kit which makes it easy
to tailor the opening point.
>Bottom line is don't be afraid of those 4V heads. They will make horse
>power and lots of it
Yup. If ther ever was a vehicle built for 4V heads, it would be a nice light weight Cobra.
Dan Jones
(this one came from this forum)
http://fordforums.com/forumdisplay.php?f=497&page=2&sort=title&order=asc&pp=25&daysprune=-1
It wouldn't be the first time one of those books were wrong.
