Manifold Question - Performer vs A331 Torker

I believe you are confused about the Torker part number. The A331 version of the Torker is a special manifold manufactured by Edelbrock for Ford SVO, it has modified runners to work in conjunction with the SVO A3 cylinder heads and only SVO A3 cylinder heads. A331 is actually the last part of the Ford part number, which is M-9424-A331. If you are utilizing iron 4V heads you'll just want the run of the mill Edelbrock Torker, Edelbrock part number 2760.

The RPM Air Gap intake manifold, part number 7564, is a 2V intake manifold that can be bolted to 4V heads. Its a good street manifold, and I believe that's what you want if you are driving your car on city streets and open highways, obeying the posted speed signs, etc. Don't worry about leaving horses on the table unless you are racing in a series for trophies, money or a championship. As a generalization, two plane intake manifolds will make more torque (and therefore horsepower) below 5000 rpm compared to a single plane intake manifold. The Torker will make more torque and horsepower above 5000 rpm.

A carburetor can be tuned to provide smooth operation at low rpm with a single plane intake manifold, but that's not the point. The RPM Air Gap manifold is rated by Edelbrock for powerbands that fall within 1500 to 6500 rpm, the Torker is rated for powerbands that fall within 3500 to 7500 rpm. Which manifold sounds like it fits within the engine speeds where you operate your motor? Which intake manifold is designed to compliment the powerband of your camshaft? For spirited acceleration onto an on-ramp, or a possible stop-light race, the Air Gap manifold will do the job better. I would guess you operate your motor below 5000 rpm at least 95% of the time. So optimize the motor for operating in the engine speeds where it is used the predominant amount of the time. You will not miss the high rpm torque and horsepower you are leaving on the table.

Make sure you are using a 750 Holley or a 650 BG Demon with your intake.

-G

Thanks George - Exactly what I needed to know. I'm assuming the air gap manifold has a "built-in" spacer (hence the "air gap" designation) for lack of a better description and an additional spacer would not be needed - correct? Sounds like the Air Gap version is what I will be going with - its also what my engine guy recommended based on what I've told him.

Good follow-up on the carb. Probably going with the Holley 750. Any particular model you would recommend with the setup already mentioned?

quote:

Need to make a decision pretty quick.

Are you planning on keeping your engine screen?

That will change your choices quite a bit.

Larry

quote:

Originally posted by inhotwatter:
... Probably going with the Holley 750. Any particular model you would recommend with the setup already mentioned ...

I recommend the Holley 750 CFM HP series carburetor #0-82751 (street calibration) for most builds. This carb doesn't have a choke, but that shouldn't be much of an issue in Nashville. Since it lacks a choke, you can acquire a deeply dropped air cleaner base, designed for a big block Chevy in a Corvette, and by juggling air filter height, you can give yourself some head room for fitting the air cleaner assembly under the engine screen, if that's even a consideration.

-G

Just my probably unpopular $0.02: If you keep that engine below 6000 rpm, you should go with a 600cfm carb.

Engine size x Engine rpm x Engine VE / 3456 = 351 x 6000 x 0.9 / 3456 = 548 cfm

Staying conservative on cfm gives you excellent throttle response, and I've never felt lack of power at high rpm.

I'd recommend Summit's 600 cfm vacuum secondary carb, it's the carb Holley never built but should have. My Pantera really woke up and became fun to drive when I installed one of these

quote:

Staying conservative on cfm gives you excellent throttle response

I had that same thought. But not quite sure about the 600 cfm. Perhaps a bit on the low side.

After selecting a manifold for low end response, the addition of a 750cfm carb seems counter productive.

And as for running no choke, Nashville is not exactly Southern California. With Winter average lows in the 20's and 30's, it would make for a rather troublesome first few minutes after start-up if you plan on Winter driving.

I run a Holley Street Performer 670, w/choke, vac. secondary, and the Performer. A Moroso dropped-base air cleaner lets it all fit (just barely) beneath the stock flat screen, Works for me.

Larry

Don't do a whole lot of cold weather driving; however, it does happen occasionally so choke would be nice, but not mandatory.

Interesting the different takes on the carb choice. I would have thought that more air was better and that a 600 or even a 680 would have starved the motor for air - especially with an upgraded cam and heads.

Gotta agree with Mikael. The Holley 6619 vac-secondary 600 cfm carb was at one time the most popular bolt-on carb for Panteras that were actually driven any distance. Good power up to maybe 5500 rpms, terrific throttle response and 21-22 mpg. It will run out of breath above 5500 no matter what intake you use but was the carb of choice for autocrossing for Mustangs, Panteras and 'Vettes.
With a 750 Holley vac-sec, figure on gaining 20 horsepower, losing some throttle response and dropping mileage to 17 with no other changes. A 750 double-pump is a race carb and will usually drop your engine into the 12-13 mpg range with little extra power. They desperately need tuning on your engine to run right. Double pump carbs are calibrated rich out-of-the-box.
The carb size and type you need depends on how you drive, where you drive and how much you can afford. On most really hard-driven Panteras, a tuner-modified Holley 700 double-pump will be ideal up to around 650 bhp, and will cost around $750- nearly double the out-of-the-box price. My 700 Holley from CC in Reno gives great power AND 20 mpg. It has lots of stuff inside it that Holley never saw. There may be other combinations of a similar size but I'm satisfied for right now.

I've just re-read your original post and noticed you are using Edelbrock heads, that hadn't registered in my mind previously.

My carb recommendation had been based upon the assumption your motor was built with 4V heads. The 2V heads throw a wrinkle into the equation. They are not the same heads as a small block Chevy or Windsor Ford, where a 600 CFM carb works well on the street. On the other hand, they work at higher velocities than the 351C with 4V heads. They kinda work in an area between those two extremes. The 750 carb will work, but I might be inclined to recommend something a little smaller, like a 700 CFM Holley.

The old 750 double pumper had a list number of 4779, it was jetted too rich for any street application. It was jetted for a big camshaft and low intake manifold vacuum. So when you used it in an application with substantially more intake manifold vacuum, the low rpm circuits flowed too much fuel. Its not smart to base the suitability of the 750 Holley on the experience of someone who bolted on a list 4779 out of the box.

HP series Holleys are not jetted anything like that. They are tuned very well out of the box. They are Holley's answer to the popularity of tuner carburetors. List #0-82751 has a street calibration (high intake manifold vacuum, leaner jetting) out of the box. Its has been used successfully by a lot of people. I'm sure it would work in your application. But if you could find a 700 CFM Holley that's been tuned by one of the carb tuning shops, that would be cool too.

Use a double pumper for best acceleration; the Pantera has a manual transmission, low gearing and light weight to justify the double pumper. I agree however that if fuel economy is important to you, a vacuum secondary would be a better choice.

-G

Fuel economy is of zero importance to me on this car. Not that I don't care about mileage, but I have a miata in the garage that runs great and still gets 29 mpg when I feel the need to conserve. I'm really more concerned about driveability and not having to have it tuned every 6-months. Bottom line - when I punch the gas in 2nd gear I want this car to come alive and roar to life. The stock setup that I had was, well - disappointing. After spending several thousand dollars on the rebuild, cam, heads, etc - I don't want the carb to be the weak point.

I'm not an engine guy which makes this a little tough as everyone seems to have a different direction and point of view. Sounds like something between a 650 and 750 is where I need to be based on general comments so far. Is there a reason you don't recommend the 850? Is it just overkill in this application or could it actually reduce performance?

I don't have the cam specs with me - its aggressive, but not radical. I'm also told the compression will be around the 10:1 if this helps. The car has big bore headers if that matters. Again - appreciate the feedback.

Allow me to quote from my homepage, then I'll shut up

"We all know size matters. But as opposed to many things in life, here bigger is definitely not better. The most common error we've seen on street cars and a few race cars is too big a carburetor. But if the engine is an air pump, why not get the biggest carburetor, to avoid having a restriction there? Without getting too technical, big bores mean less velocity and less acceleration of air/fuel mixture. That may be a little difficult to accept, one would think that the less restriction, the more velocity and acceleration. Though it’s not exactly the same principle, think of garden hose where the water is flowing at a certain rate. If you then squeeze the end of the hose, then you can get it to spray much further. At the top end of the rpm band, too small a carburetor will be a restriction and limit power. Small but adequate and non-restrictive passages builds air/fuel speed and thereby throttle response. Too small a carburetor may lose some power in the high rpm band, but will work excellent in the 0-5000 rpm band. But while too big a carburetor will work well in the 5-7000 rpm range, it’ll be sluggish everywhere else, and especially the throttle response will suffer. Do you want a car like that?

So what‘s the ideal size? Fortunately there is a simple formula. But with such a formula available and accepted by everybody, how come so many people still buy the wrong size carburetor? Unfortunately the result of the formula is usually much lower than what people tell you. So if your friends or competition runs 750 or 850 cfm carburetors, do you dare buying a 600 cfm? More must be better, right? No. This, like camshaft duration, is an area where you’ll be thankful that you trusted the formula and not the hype. The formula works. If the thermometer shows 30 degrees and your friend tells you it feels more like 40 degrees to him, which do you trust?

The formula is:

Engine size x Engine rpm x Engine VE / 3456

-Engine size is in cubic inches (cid). This is the easy one.

-Engine rpm is the max rpm that the carburetor should be able so support. Don’t go overboard on this one. You may wish to run a 7500 rpm screamer, but unless you strengthen the engine internals like crank, rods and pistons to be able to withstand it, you’ll only try it once. And honestly, when we accelerate full throttle, do we wait until max rpm to shift into next gear? Rarely, because it doesn’t make the car faster (see How to win, "4"), and most of us have so much money and time invested in that engine we want to keep it alive. So if you add up the total amount of time your engine has been above 5500 rpm, it’ll be a few seconds only.

-Engine VE is Volumetric Efficiency, a number telling how effective an air pump the engine is. It takes a dyno to measure your engine’s Volumetric Efficiency, but here are some ground rules. For stock smog engines VE would be around 0.8, for a well built performance engine it would be around 0.9. An engine with forced induction could be just above 1.0.

Example: A well tuned 351 cid engine that will see max 6000 rpm would need the following size carburetor:

351 x 6000 x 0.9 / 3456

equal to 548 cfm(!) So a 600 would be a great and fully adequate choice. Still many engines have 750 cfm or 850 cfm carburetors on them, enabling them to theoretically go into rpms that they never do. So it’s a waste of money buying the big carburetor. But even worse, the oversized carburetor makes the car less fun to drive below 5000 rpm because the carburetor is ruining drivability and throttle response."

Sorry...

That carb sizing formula is practically useless. It is simply a volumetric
relationship. As with any equation, you need to understand how it was derived
to understand it's limitations and how to properly interpret the results. The
formula is quite easy to derive since it's only a displacement relationship
(see attached derivation and commentary below). One needs to understand that
a carb's flow rating is defined at a specific test pressure drop. The industry
standard for four barrel carbs is a pressure differential equal to 1.5 inches
of mercury (Hg). What this means is a 4 barrel carb rated at 600 CFM will
flow 600 CFM of air, at wide open throttle, when a pressure differential of
1.5 In Hg is applied across it. This is just one point on a curve. When
installed on an engine, this same carb may flow more or less. If the pressure
drop is larger, the carb will flow more. If the pressure drop is smaller, the
carb will flow less. The 1.5 inches of mercury test pressure standard has
little to do with the pressure drop at which a carb will function reasonably.
A good carb will function well on quite a bit less than 1 inch of Hg drop, a
bad one may need two or three inches. 1.5" Hg pressure drop is too much for
a highly tuned engine. 0.7" is considered non-restrictive, though racers may
shoot for 0.5" Hg. Two barrel carbs are usually rated at a different pressure
differential (3.0 In Hg). The reason for the 1.5 In Hg pressure drop is mostly
historical. When 4 barrel carbs first came into popular use, the vacuum pumps
used to rate 2 barrel carbs were unable to pull the same pressure differential
across a 4 barrel carb, so 4 barrels were rated at a lower pressure drop.

There's no such thing as a carb that flows too much, just carbs that don't
atomize well or have a poor air-fuel curve. What's really important is the
atomization the carb provides to the fuel-air mixture and the restriction
(pressure drop) it imparts to the incoming airflow and how well the carb
controls the air-fuel ratio across the rev range. By paying attention to the
aerodynamics of a carb, you can increase it's flow without decreasing the
atomization. Such a carb will increase power (assuming the engine can utilize
the extra flow) without hurting throttle response or fuel economy. Simple
things like a dyno stack or a K&N stub stack can increase carb flow too.
Atomization is a strong function of the booster design and the venturi diameter.
The larger the diameter, the slower the flow and the poorer the mixture.
If you can increase the flow without increasing the minimum area, you get
a higher flowing carb without the down-sides. That's what the tuner carbs
do. For carbs like that, the standard carb sizing formulas just do not apply.
We run a Holley HP950 on the dyno that works better across the rev range on
a 351C than a standard vacuum secondary Holley 4150. Another thing to keep
in mind is that it's important to route cool air to the carb. 1.5 inches of
Hg pressure drop across a carb represents a 5% loss in air density (and
therefore horsepower) at sea level. That's equivalent to going from 80° F
inlet air up to 107° F inlet air.

Be aware that some carb manufacturers and tuners may refer to a carb as a
750 if it started with a 750 main body. After streamlining (by milling the
choke tower off, smoothing the main casting, narrowing the booster legs,
replacing the straight-leg boosters with dog legs, thinning the throttle
shafts, countersinking any screw heads, fitting a different baseplate, etc.),
that 750 body may flow 830 or more CFM, when tested at 1.5" Hg pressure drop.

Here's the carb sizing relationship and a brief discussion I wrote a while
back to try to illustrate the pitfalls of the sizing equation. The forum
software will likely remove my spaces and screw up the formatting but here
goes:

DISP RPM
CFM = ---- * ---- * VE
2 1728
where:

DISP = engine displacement in cubic inches
CFM = required carb flow in cubic feet per minute
RPM = maximum engine speed in revolutions per minute
VE = volumetric efficiency (dimensionless, 1.0 = 100%)
1728 = conversion factor between cubic inches and cubic feet
= 12*12*12
2 = conversion factor for four stroke engine

This equation can be simplified to:

DISP * RPM * VE
CFM = ---------------
3456

Note this sizing formula is simply a relationship between cylinder volume and
the flow required to fill that volume at a given engine speed. Also note, for
a four stroke engine, displacement is divided by two because an intake stroke
occurs every other revolution. While, it's easy to determine displacement and
maximum rpm, you'll probably have to guess at the third variable, volumetric
efficiency (VE), unless you have access to a dyno. Volumetric efficiency is
simply a measure of how efficiently an engine fills its cylinders. A stock,
low performance, street engine may have a VE between 0.7 and 0.8. High
performance street engines may fall between 0.8 and 1.0, while highly tuned
race engines can have VE's exceeding 1.0, perhaps as high as 1.25.

One other thing to understand when using the formula above is that a carb
will only flow in the presence of a pressure differential. On one side of
the carb there is atmospheric pressure and on the other side is manifold
pressure (usually referred to as manifold vacuum since it is typically lower
than atmospheric pressure). Since engines vary in their manifold vacuum
characteristics, a standardized pressure differential was established to
provide a meaningful comparison for different carbs. Before this standard,
venturi size was used for comparison. The standard for four barrel carbs is
a pressure differential equal to 1.5 inches of mercury (Hg). What this means
is a 4 barrel carb rated at 500 CFM will flow 500 CFM of air, at wide open
throttle, when a pressure differential of 1.5 In Hg is applied across it.
When installed on an engine, this same carb may flow more or less. Two barrel
carbs are usually rated at a different pressure differential (3.0 In Hg).
The reason for this is primarily historical. When 4 barrel carbs first came
into popular use, the vacuum pumps used to rate 2 barrel carbs were unable to
pull the same pressure differential across a 4 barrel carb, so 4 barrels were
rated at a lower pressure drop.

Flow ratings from one standard can be related to flow ratings from another
standard. For 2 and 4 barrel carbs:

Flow @ 1.5 In Hg = (CFM Rating @ 3.0 In Hg)/SQRT(3.0/1.5)

Which is approximately:

Flow @ 1.5 In Hg = (CFM Rating @ 3.0 In Hg)/1.414

This relationship is derived from the fact that, for incompressible flow
(assuming subsonic flow... flow will choke at Mach one), the volumetric flow
rate through a venturi is proportional to the square root of the pressure
differential:

Q = K1*A2*SQRT(2*Gc/Rho)*SQRT(P1-P2)

or more simply:

Q = K2*SQRT(P1-P2)

where:

Q = volumetric flow rate
K1 = flow coefficient
A2 = downstream area of the venturi
Gc = gravitational constant
Rho = density
P1 = inlet pressure
P2 = pressure at venturi minimum area
K2 = K1*A2*SQRT(2*Gc/Rho)

Computing the relationship for volumetric flow rate at the two flow
differentials and equating yields the conversion formula.

As an example of using the sizing formula, let's say we have a modified 4.1
liter (252 cubic inches) Buick V6 with a VE of 0.9 and we plan to turn no
more than 6400 rpm. Plugging our numbers into the formula yields a
theoretical estimate of:

252 * 6400 * 0.9
CFM = ----------------
3456

= 420 CFM

In practice, Joe Murawski of the Wedge list runs a 4.1L Buick in his Triumph
TR7 and has tried a variety of carbs, in sizes ranging from a Holley 390 to a
785 CFM Quadrajet, settling on a 500 CFM Edelbrock/Carter AFB as providing the
best power and driveability. His carb choice is somewhat larger than that
predicted. For reasons discussed below, we'll see this is not unusual.

While the formula above may yield useful estimates, it is not necessarily the
ideal it is often portrayed to be. If you have a carb that can flow 500 CFM
in the same application and still properly atomize the fuel, it should make
more power than the 400 CFM carb. From this perspective, larger is better.
Ideally, a carb would present zero restriction to the intake stroke. Such a
carb would have an infinite flow rating. Unfortunately, carbs require a
pressure differential to properly mix fuel with air, which is why carb sizing
is important (and why the above formula is useful, if used in a modified
form). Keep increasing the size of a carb and, at some point, the booster
venturis will not properly atomize the fuel/air mixture and droplets of liquid
fuel will be pulled into the cylinders. Not only is this bad for performance,
it's also hard on the engine. The liquid fuel tends to wash oil off the
cylinder walls, increasing ring and bore wear. This is a particular problem
with engines using large overlap cams, since they provide lower vacuum levels.
When using a larger carb and cam, proper tuning (carb and ignition) becomes
more important.

It's important to understand the basic sizing formula is just a guideline.
It ignores a number of important factors such as manifold design, cam timing,
vehicle weight, gearing, transmission type, intended usage, etc. Furthermore,
it ignores important differences in carb design like venturi efficiency, bore
layout, and secondary style and method of actuation. In practice, I have found
that the above formula applies mainly to square bore carbs with non-air valve
secondaries (Holleys, Autolites), and even then it can be conservative for a
performance application. It typically yields a compromise of fuel efficiency
and power.

Using a dual plane, divided plenum, intake usually allows the use of a carb
with a larger CFM rating than with a single plane, open plenum, intake. This
is because the divider cuts the effective plenum volume in half, increasing the
signal to the boosters. Because of this fact, Edelbrock suggests multiplying
the CFM predicted by the basic sizing formula by 1.1 to 1.3 for single plane
manifolds and by 1.2 to 1.5 for dual planes.

As another example, consider the engine I used to run in my Detomaso Pantera.
It's a 351C Ford with Aussie 2V quench heads, 1 3/4" headers, and a single
plane, open plenum, Weiand Xcelerator intake manifold. Since I retained the
stock cast pistons, I chose a cam with a shift point of 6000 rpm. As a guess,
pick 0.9 for the VE. Since the Pantera is relatively light with short gearing,
pick the high side of the range for K (the intake factor):

K*DISP * RPM * VE 1.3*351*6000*0.9
CFM = ----------------- = ----------------
3456 3456

= 713 CFM

This agrees with my real world experience with Holleys on street modified 351C's.
600 CFM carbs provide good throttle response and fuel economy but can up 20+ peak
horsepower to 750 carbs. On the downside, the usual vacuum seconday Holley 750
with it's lame straight leg boosters hurts fuel economy and has poor throttle
response. The 735 Holley I ran was a happy medium with good throttle response,
power and 20+ MPG on the highway. The big difference with the 735 Holley is it
uses the excellent Ford-designed skirted truck boosters. Note we're referring
to stock Holley carbs here, not custom models with milled choke horns, thinned
booster legs and cross shafts, knife-edged butterflies, streamlined main bodies
and improved booster designs. Those modified carbs can flow more mixture, while
providing adequate atomization. Examples are the various tuner carbs, Holley's
HP series, Quick Fuel technologies, the Demon series etc. For those carbs, the
sizing formulas don't apply very well.

I chose a Holley 735 from a 428CJ application which seems to work well. This
carb, while flowing nearly as much as a 750, has a venturi cluster design that
provides a stronger signal. Throttle response and fuel economy are relatively
good (20+ mpg on the highway), without incurring a noticeable power penalty.

Two other important considerations are bore layout and method of secondary
actuation. Carbs with air valve secondaries (Rochester Quadrajets and
Carters), especially those with spread bore layouts (Thermo Quads, Quadrajets),
can usually be sized larger than square bore Holleys and Autolites. This is
because the smaller primaries increase the flow speed through the boosters,
providing better atomization, while the air valve secondaries passively
restrict air flow until the engine can handle it. Taking these two factors
into consideration, Vizard suggests the following two rules of thumb for
street performance engines where power is more important than fuel economy.
For air valve secondary carbs with an upper rpm limit of 6000 rpm, use:

CFM = 2.3 * DISP

For square bore non-air valve secondary carbs use:

CFM = 2.0 * DISP

For engine speeds above 6000 rpm, multiply by the ratio of maximum rpm to 6000
rpm. Note the second formula yields 702 CFM for my 351C example, which is
close to the basic sizing formula with the intake manifold correction factor
applied. Note that the stock 4300D Motorcraft spreadbore used on 1972 to 1974
351C-4V's was rated at 715 CFM (or 750 CFM, depending upon who you believe).

As an extreme example, I've successfully used a 750 CFM Quadrajet on a
relatively stock 231 cubic inch Buick V6. With the Qjet, it got slightly
better fuel economy than the previous 2 barrel carb (due to the small
primaries) and had noticeably more power (due to the huge secondaries). The
driveability of the carb was fine with no bogs or flat spots. On the V6, I'm
sure it never pulled anywhere near the 750 CFM rating but it did pull what it
required. You could never put a Holley 750 on a little low compression V6 and
expect to make it work. The air valve secondaries allow the use of much larger
CFM ratings without incurring driveability problems. There is a price to be
paid however. Even when wide open, air valve secondaries are slightly more
restrictive to airflow than non-air valve secondaries.

While these formulas should help you choose a carb flow rating, nothing beats
trial and error. Also, once you have a carb installed, you can determine how
restrictive it is by using a vacuum gauge to measure the difference between
atmospheric pressure and the pressure under the carb. With the air cleaner
removed, the air above the carb will be essentially atmospheric. If there's
any difference between it and the pressure sensed under the carb, it's due
to the carb. The higher the difference, the greater the restriction.
Measurements should be made at wide open throttle and 0.7 inches of mercury
is considered non-restrictive.

An alternative to the carb sizing formulas is to realize 100 HP requires 140
CFM based upon a reasonable assumption for Brake Specific Fuel Consumption
(BSFC). The BFSC assumption keeps us from having to guess at volumetric
efficiency. A 550 hp engine uses an actual 770 CFM but you need to convert
the pressure drops. 4 barrel carbs are rated at 1.5" but that is too
restricitive. 0.7" is more reasonable for a tuned engine to keep the carb
from being overly restrictive.

Flow @ 0.7 In Hg = (CFM Rating @ 1.5 In Hg)/SQRT(1.5/0.7)
770 = X / 1.46385
X = 1127 CFM flow rating required

A 350 hp engine uses an actual 490 CFM but that doesn't mean a 490 CFM rated
4 barrel carb will provide the required flow. It takes 717 CFM at 1.5" Hg to
equal that 490 CFM at 0.7" Hg pressure drop:

Flow @ 0.7 In Hg = (CFM Rating @ 1.5 In Hg)/SQRT(1.5/0.7)
490 = X / 1.46385
X = 717 CFM flow rating required

Note the sizing formulas are derived with an implicit assumption of a plenum
manifold and do not apply to independent runner manifolds. Completely
different duty cycle. A plenum manifold allows multiple cylinders to share
the total flow of the carb. On a plenum intake, each cylinder gets to draw
from each barrel (if single plane) or half the barrels (if dual plane) but,
on an independent runner intake, it's one barrel to one cylinder. Independent
runner applications require much larger total CFM because of this. Also, 4
barrel carbs are sequential in that only the front 2 barrels operate at low
demand so 4 barrel carbs can be sized larger without much adverse effect on
low RPM torque.

Dan Jones

> I'm right in the middle of an engine rebuild and am using Edelbrock Performer
> RPM aluminum heads.

As others have noted, the Edelbrock heads have 2V ports while the Torker
is for 4V ports and the A331 is for Ford Motorsport high ports. The A331
ports are no where near the 2V port locations. You have several choices
for 2V intake manifolds. With the Edelbrock heads, 10:1 compression and
a stout cam, you have the potential to make over 400 HP. The best intake
for you depends upon several factors. If you need to fit under a stock
engine screen and need carb heat for cold start up, then I suggest the
Weiand Xcelerator single plane for 2V heads (not the 4V version). If
manifold height and carb height are not issues, then the Edelbrock RPM
Air Gap will work better. The low profile Performer 2V will need some
work in the plenum area to not be a major restriction.

> Also, if I go with either intake, should I use a carb spacer as well for
> better performance?

Yes. We typically see 10 HP with the right spacer.


> The car has big bore headers if that matters.

The collectors on the Hall Big Bores are too small. Exhaust is very important,
particularly the mufflers. The stock and Euro GTS mufflers cost 50+ HP on a
400 HP 351C on the dyno compared to a good muffler like a straight through
Magnaflow. With too small a carb, bad mufflers and the wrong intake manifold,
you can make a sweet running 400+ HP 351C into a lame one that makes less than
300 HP and gets worse fuel economy. I've got the dyno data to prove it.

Dan Jones

Ok - Sorry for the delayed response, but I've been trying to process all the information from Mikael and Dan. First let me say thank you to everyone who has replied and given advice.

I'm not sure which direction I will go just yet on the carb, but will likely wind up with one in the 650 to 750 range. As I mentioned, I'm not an "engine guy" so a lot of this is admittedly going over my head. The thought though that bigger is not necessarily better is not wasted on me.

Right now, I'm probably leaning towards a 700 double pumper. Worst case, I can get another one and bolt it on for comparison if I'm not satisfied. I will likely put on a carb spacer and either a drop air cleaner or a dog bone style air cleaner(just like the look). If I go the dog bone route, I will either go screenless or buy an extra screen and cut it up so the dogbone can go through.

My engine builder tells me that I should have a big grin on my face as my car leaves the shop once its back together. I know at this point, I'm ready to have it back!

Forgot to ask - If I want an engine screen to fit a dog bone, what would I expect to pay? I can buy one uncut, but I would rather not ruin a perfectly good screen if someone has one lying around that has already been modified.

quote:

I can buy one uncut, but I would rather not ruin a perfectly good screen if someone has one lying around that has already been modified.

Watch this board, Ebay, the DeTomaso mail list, and your POCA newsletters for anyone selling a modified engine screen.

Or, just order some stainless wire mesh and make your own:
http://www.twpinc.com/twpinc/c...ategory_id=TWPCAT_12

Ok - I feel like an idiot at this point. The intake that is sitting in the shop is an Edelbrock Performer - Not an Edelbrock Performer RPM Air Gap. My question is this - should I send it back and get the RPM Air Gap or stick with just the standard Performer? The cost difference is only about $120. Any clue as to the HP difference between these two?

I know one of the comments from previous posts was asking about the air screen. If I decide to leave the screen in place, will the RPM Air Gap version fit with a dropped air cleaner?

I believe Dan mentioned that if I went with the standard Performer that it would need some work in the plenum area. How much would this help if I decide to go with the standard Performer and what exactly needs to be done?

quote:

If I decide to leave the screen in place, will the RPM Air Gap version fit with a dropped air cleaner?

No chance.

Larry

Larry - so yours is a standard Performer? I believe you mentioned that it would fit below the screen.

quote:

so yours is a standard Performer

Yes, with a dropped base and a 3" tall filter element, it just clears the early all mesh screen.

I'll check how much of a dropped base and get back to you.

Larry

> Ok - I feel like an idiot at this point. The intake that is sitting in the
> shop is an Edelbrock Performer - Not an Edelbrock Performer RPM Air Gap.
> My question is this - should I send it back and get the RPM Air Gap or stick
> with just the standard Performer?

The RPM Air Gap is a much better intake on a modified engine but is
considerably taller.

> The cost difference is only about $120. Any clue as to the HP difference
> between these two?

See attached dyno results below. If you plot the data, you'll notice the
RPM Air Gap is better across the tested rev range which is more important
than just peak numbers. Also, notice the standard Performer was only tested
with a 1" spacer as the dyno carb fuel log wouldn't clear otherwise. Note
that it really responded to the 1" HVH spacer.

> I know one of the comments from previous posts was asking about the air
> screen. If I decide to leave the screen in place, will the RPM Air Gap
> version fit with a dropped air cleaner?

No.

> I believe Dan mentioned that if I went with the standard Performer that it
> would need some work in the plenum area. How much would this help if I
> decide to go with the standard Performer

On a Ford aluminum dual plane, it helped a bunch on the nearly 500 HP
408C it was tested on. In those tests, the ported Ford aluminum dual
plane made 31 HP and 23 ft-lbs more than an unported Blue Thunder.
The ported Blue Thunder pulled better numbers on the flow bench
(attached to a cylinder head) and would have likely made better power
but was not tested. We did test the ported Blue Thunder this weekend
on Mike McDougal's 393C and it made 411 HP at the rear wheels through
the mufflers and small air cleaner so the porting worked.

> and what exactly needs to be done?

The problem with older dual planes is that half of the runners often
flow much worse than the other half when bolted to a cylinder head.
If you bring up the poor runners to match the good runners, it really
pays off. Note that we really aren't porting the runners. What we do
is cut down the plenum divider and radius the port entry in the plenum
to aid flow into the poorer flowing ports. This needs to be done on a
flow bench with a cylinder head attached and a carb in place. IIRC,
Dave McLain charged Mike McDougal $150 to port his Blue Thunder intake
(correct me if I'm wrong Mike). If you are interested in keeping a
stock engine screen, you may want to consider sending me your intake
and we can port it on the flow bench and dyno it in ported and unported
form. I believe I have a spare Performer here so if you want to hang
on to the intake and drive the car, we can port my spare intake and
exchange them after the testing is completed. If you want to ditch
the engine screen, go with the Air Gap intake. If you look at the
plenum of the RPM Air Gap, you'll see the divider is already cut down
and the runners are reasonably well equalized.

Dan Jones

Performer with 4 Hole 1 Inch Spacer
950 HP dyno carb, Pantera GTS headers and Magnaflow mufflers.
Note: Intake is actually the earlier F-351 4V version but appears identical
to the current Performer. The Perfomrer required a spacer for throttle
clearance so was tested only with 1" spacers. Baseline for Edelbrock
Performer intake was with a 4 hole 1 inch spacer which was needed to allow
clearance for fuel log. Good solid pull and for whatever reason the engine
didn't seem to mind the 1 inch 4 hole on this dual plane. Going to try the
HVH spacer next.

RPM HP Torque (ft-lb)
4100 300.0 384.1
4200 303.2 379.6
4300 312.9 382.0
4400 319.7 381.8
4500 324.6 379.2
4600 331.5 378.5
4700 341.3 380.9
4800 350.0 383.5
4900 354.6 380.0
5000 358.2 375.9
5100 362.0 373.0
5200 367.8 371.2
5300 369.6 366.9
5400 372.6 362.5
5500 377.5 360.3
5600 381.3 357.1
5700 381.4 352.1
5800 374.6 339.3
5900 371.9 330.6
6000 363.0 317.9
6100 370.5 318.4


Performer with HVH Spacer
950 HP dyno carb, Pantera GTS headers and Magnaflow mufflers.
HVH was also better on the Edelbrock Performer but not as drastic as with the
factory iron piece. Performer is better than factory cast iron intake or so
it seems on this engine.

RPM HP Torque (ft-lb)
4100 308.1 391.7
4200 310.7 390.1
4300 322.5 394.8
4400 324.6 387.8
4500 330.6 386.1
4600 339.2 387.3
4700 349.3 390.2
4800 361.1 394.7
4900 371.3 397.5
5000 371.1 390.1
5100 375.3 386.4
5200 378.2 382.4
5300 377.7 374.5
5400 380.6 370.1
5500 385.1 367.5
5600 388.3 363.8
5700 390.4 359.5
5800 390.1 353.3
5900 391.1 348.2
6000 382.4 334.8
6100 384.2 331.1


Performer RPM Air Gap 2V
950 HP dyno carb, Pantera GTS headers and Magnaflow mufflers.
Baseline for Performer RPM airgap intake. Like many of the intakes designed
for 2V heads, the RPM Air Gap will fit either 2V or 4V heads. Running with
no spacer. Going to try the 4 hole 1 inch and HVH spacers next. Good solid
pull with good numbers.

RPM HP Torque (ft-lb)
4000 312.4 405.7
4100 311.9 401.8
4200 320.7 399.9
4300 329.1 402.7
4400 335.8 400.9
4500 344.8 402.2
4600 350.7 400.7
4700 355.8 397.6
4800 362.7 396.7
4900 370.0 396.6
5000 376.2 395.1
5100 381.8 393.1
5200 386.7 390.4
5300 390.3 387.2
5400 392.9 382.1
5500 398.1 380.0
5600 396.7 372.1
5700 394.6 363.6
5800 392.6 355.6
5900 393.2 350.1
6000 396.6 346.9
6100 394.3 339.4


Performer RPM Air Gap with HVH
950 HP dyno carb, Pantera GTS headers and Magnaflow mufflers.
HVH spacer seems to run about in the middle of the bare intake or 4 hole 1
inch. Good all around performance making over 380HP and torque.

RPM HP Torque (ft-lb)
4100 310.1 400.8
4200 314.8 394.1
4300 324.0 395.7
4400 337.1 401.9
4500 349.7 407.9
4600 354.2 404.6
4700 360.2 402.3
4800 367.3 401.8
4900 373.6 400.4
5000 377.2 396.5
5100 381.3 392.6
5200 388.5 392.1
5300 392.9 389.9
5400 395.3 384.4
5500 400.1 381.5
5600 399.1 375.0
5700 390.8 360.2
5800 388.7 351.9
5900 386.0 343.7
6000 384.1 336.2
6100 386.9 332.9


Performer RPM Air Gap with 4 hole 1 Inch
950 HP dyno carb, Pantera GTS headers and Magnaflow mufflers.
Good pull and engine picked up about 5 horsepower and about 10lbs/ft with 4
hole. A good swap and about the best all around combo for these heads etc.

RPM HP Torque (ft-lb)
4000 312.9 409.3
4100 316.6 406.5
4200 324.3 404.7
4300 332.7 407.4
4400 346.3 410.7
4500 349.2 408.1
4600 354.1 404.4
4700 362.8 405.1
4800 371.3 406.4
4900 375.1 402.2
5000 380.3 399.3
5100 387.9 399.1
5200 394.1 398.1
5300 395.3 391.9
5400 398.6 387.7
5500 401.6 383.4
5600 403.3 378.3
5700 400.8 369.4
5800 401.7 363.7
5900 401.1 357.2
6000 403.1 352.5