Need new carb

The 4300D spread bore Autolite carb I've seen rated at 715 cfm & 750 cfm in Ford literature.

Day in and day out, from mild to wild, the 351C likes a 750 cfm Holley (equivalent to a 650 cfm BG Demon). As long as the carb is jetted properly, installing a 750 cfm Holley will not be over-carbureting the Cleveland.

Installing a 600 cfm Holley carb is definitely under-carbureting a Cleveland, it won't rev past 5000 rpm.

cowboy from hell

I run the 670cfm Holly Street Avenger, Ford iron open chamber heads with a little massaging, Ford roller rockers/pedestal mount and a mildly healthy cam. This combo works well for me, I can easily rev to 6200-6400 rpm.

Larry

I run a Holley 670 also .... jetted to 68 /72 and the car runs fine ... 750 ? maybe vac secondaries on a slighlty modifeid engine .. but thats too large for a small block.

Ron

I'm not being argumentative, I want to be a little more thorough and explain my recommendation.

The 351C 4V is not a Weezer (oops, I meant Windsor) and its not a SBC. Comparing the 351C to any other motor of the same displacement doesn't work, the same rules don't apply. The cylinder heads are that different. The best motor to compare a Clevo to is a 396 Rat motor.

The 4300D carb installed by Ford on the 351C was also used on 460 Fords; it is about a 750 CFM carby. It is a little bit bigger carby than the Rochester Quadrajet. Installing a Holley 780 on a Boss 351 netted a gain of only 10 BHP compared to the 4300D, and this was most likely due to the richer jetting of the Holley, not because it was a larger carburetor.

While the Boss 351 in the US had a 4300D carb, the Boss 351 in Australia had a 780 Holley borrowed from the Boss 302. Ford also sold a 780 Holley over the counter in the US for the 351C via their OHO parts program. The recommendation for the 351C has always been 750 CFM ever since its introduction. The guys with really hot Clevelands upped that to 850 Holleys.

The earliest "non-boss" 351C 4V motors (M code) had Autolite 4300A carbs, rated at 630 cfm, they were definitely under-carbed, and struggled to rev to 6 grand. The earliest 4 barrel Clevelands produced in Australia also used the 4300A carby. US Ford switched to the 4300D carb in late 1971. By the time the XC Falcon was under production (1976) Ford Australia had switched to a Carter Thermoquad rated at 750 CFM.

Hall Pantera sold a 600 Holley, along with the Edelbrock Performer intake, DeTomaso valve covers & Pantera air filter as an engine dress up package way back when, and as far as I can recollect Gary's was the only shop anywhere selling a 600 Holley for a 351C.

Outside the Pantera world, in the mainstream where Mustangs, Cougars, Torinos & Montegos roamed, the Ford performance shops all recommended 750 Holleys, and these were heavier vehicles, the majority of which had automatic transmissions.

Keep in mind, the 351C 4V likes headers with 1 7/8" or 2" primaries. 2" primaries on a Weezer or a SBC is an apostasy, but its de rigueur for a 351C 4V. Doesn't it make sense that a motor that likes a "bigger" exhaust system may like more intake capacity as well? This motor likes more of everything compared to those "other" motors of similar displacement. This was a serious high performance motor designed for mass production, those cast iron cylinder heads will support 750 BHP naturally aspirated. Do that with a set of weezer heads, or a SBC double bump head.

Anything under 650 CFM is definitely under-carbing a Cleveland. Sure you can get by with the 670 carbs, and one or two Pantera shops sell 700 CFM Holleys for the Pantera. Since a street motor spends most of its time at lower rpm the difference is not going to be noticeable. But the 750 Holley is not over-carbureting a 351C, not at all, it won't bite you, I guarantee it. The 351C really likes a dialed in 750. The same way a Clevo wakes up when you install a healthy cam, the Clevo wakes up with the 750 too, but can remain docile & drivable when the jetting is dialed in. Even Ford on two continents installed 750 carbs on their hydraulic lifter cammed Cleveland motors.

Long Live the Clevo

Cleveland Symphony Orchestra


cowboy from hell

quote:

Now take that poor oiling system thin wall 351C and use it as a Boat Anchor.

BLASPHEMY!!!

GEEEEZE George... I am glad you weren't being argumentative .....LOL!

Ed....

I can tell you how to do the oiling system too, its really not too involved. Whenever you're ready. However, blasphemers must first leave the room.

Just to add my 1-1/2 sense here (not cents), On a box stock cj type Cleveland, particularly if you are running the low compression version, you will probably be happiest with a 600 or 650 vacum secondary carb.

HOWEVER, I want to remind the old timers here and inform the newbies that the Ford Muscle Parts program highly recommended an 850 Holley double pumper for the 1970-1 351C 4v. Of course this was for the high compression Clevelands since this was 1971 and the compression ratios weren't dropped down to 8.0:1 yet.

Wow, a plethora of great info for a seemingly simple question. It sounds as though I made the right choice when I told the mechanic to order the "better quality" Holley 750. It's been years since I've dealt with carburetors. The last one I seriously fooled with was on my 1970 Javelin 360, so my knowledge is quite rusty.

My goal is to get the car into "dependable" driving condition (already upgraded the cooling, updated to electronic ignition). I'd to have some fun with my Pantera before, sadly, selling. Unexpectedly, my wife is about to pop out twin boys. The Pantera was suppose to be my long term, fun project. Now I have to make some space and eventually move it down the road. You've been great help, so I'm sure I'll have a few more questions coming up in the not-too-distant future. I'm lucky I have a guy working on the car who use to work on Panteras at an L-M dealer when they were first introduced.

One more thought. Since I'm going with the 750, but have the low compression heads, is it better to have the car running a little leaner? Pantera Doug's comments had me thinking.

I'm running a Holley 4150-735cmf from a late
60s early 70s 390-428 Ford. Works for me!

The mixture strength is read as the air/fuel ratio and isn't going to vary much according to the carb size.

What you are going to find is that a carb like 3310 which is a 780 vacuum, an 1850 which is a 600 vaccuum are both "street' carbs and are just about where you want them out of the box.

A carb like any of the double-pumpers have mechanical secondaries and are intended as "race" carbs have very heavy idles. Holley says this is for running with open headers and compensating for the header scavenging.

Those carbs will smart your eyes at idle and can only be leaned out buy enlarging the idle air bleed in the main body.

I haven't used the new Demon carbs yet (I'm playing with FI and multiple carbs like my Webers now) but I believe that some of them have changeable "air jets" on them for this purpose.

If you are serious about getting the mixture strength correct you are going to need to do this all on a dyno or install an oxygen sensor in the exhaust system that you can read the a/f ratio with in real time. That involves a computer with red and green lines on a graph on your computer.

> have installed a 750 double Pumper holley on a stock 351C. Changing jets,
> power valves, etc it ran OK and a little rich. Replace the 750 double
> Pumper holley with a 700 double Pumper holley again changing jets, power
> valves, etc and it ran much better and was not rich at all.

There's more to it than just the carb CFM rating. The size of the PVCR's,
the idle mixture setting (volume) and the float level can have a huge
difference. The booster style can have an effect as well. An example is
the 735 Holley I'm tuning now on a near stock 351C (low compression CJ
with Edelbrock Perfomer intake and Hall big bore headers and exhaust).
I originally set the floats so fuel would drip out the sight hole when
the car was gently rocked and the idle for maximum vacuum. The carb was
rich across the board. By lowering the floats and leaning the idle mixture
(screws at 1/2 turn out), the carb is now lean across the board. Ideally,
I'd like a lean cruise (for fuel economy) in the 15:1 range that goes rich
(12.5:1 to 13:1 range) at WOT when the extra fuel from the PVCR is added in.
With the size of the PVCR's in this particular carb, that appears possible.
On many Holleys, that is not the case. Many Holley's have very large
PVCR's which make them run very rich at WOT. It's possible to re-size
the holes but few do. Luckily, there are Holley style carbs on the market
now with replaceable PVCR's. The magic of a wide band O2 sensor makes
this sort of fine tuning practical.

Be aware when you lean the mixture out, you'll need to increase the timing
to offset the slower burn of the lean mixture. If you don't adjust the
timing, it will run hotter (even at the same water temp, the piston tops
will be hotter). A sronger spark from a capacitive discharge ignition is
a big help when running lean mixtures too.

Dan Jones

For a street car with moderate performance I prefer the Edelbrock carbs. They seem to idle best and start better than holleys. A 600 works great on a 350/351 right out of the box. They also seem to have better part throttle response than the Holleys I have used.

Boy, glad this thread was started! I am having slow throttle response and capped high RPM around 5k. Holly carb and intake were new from previous owner. I can see this weekend that is the first thing I am going to check out, see just what is installed on this engine.

Thanks for the insight guys,

Angelo

> Just to add my 1-1/2 sense here (not cents), On a box stock cj type
> Cleveland, particularly if you are running the low compression version,
> you will probably be happiest with a 600 or 650 vacum secondary carb.

My low compression 351CJ is working great with a 735 Holley.
I would not be happy with 600 CFM on a 351C, even with low
compression. With proper tuning and booster selection, you
can have good throttle response without out choking off the
air flow.

> Since I'm going with the 750, but have the low compression heads, is it
> better to have the car running a little leaner?

Which specific 750 are you talking about? Regardless of carb CFM, you
want to run lean of stoichiometric at cruise for fuel economy and rich
of stoichiometric at wide open throttle (WOT) for fuel economy. 14.7:1
is the stoichiometric ratio. It's the "chemically ideal" ratio where
there is no excess fuel or oxygen left after combustion. Leaner means
there's excess oxygen left after combustion. Richer means there's excess
fuel left. Rich of stoichiometric at wide open throttle will make better
power and lean at cruise will yield better fuel economy. There's no single
ideal ratio that applies to all engines. Some engines make best power at
13:1, others closer to 12.5:1. 12.8:1 is a good WOT ratio to shoot for.
Note that the air fuel ratio is by weight. 13:1 means 13 pounds of air
are mixed with 1 pound of fuel. The usual target values for normally
aspirated 4 stroke engines are about 12.5 to 13 for WOT, 14.0-15.5 at
part-throttle cruise and 13.5-14.0 for part throttle acceleration (or
climbing a long hill, pulling a load, etc.). If you want to lean out the
mixture at cruise for best fuel economy, be aware that you'll also need to
adjust timing. Combustion gets much slower under lean conditions and if
you don't adjust spark timing, the combustion occurs much later and exhaust
temperature climbs. That's bad for the exhaust seats and valves. However,
if you adjust for MBT spark at each A/F ratio, exhaust temperature will
actually decrease relative to stoichimetric (rich will still be somewhat
cooler). For typical gasoline engines, the range or ratios is:

A/F Characteristics
Ratio
5 Rich burn limit. Combustion is weak and/or erratic.
6-9 Extremely rich. Black smoke and low power.
10-11 Very rich. Some supercharged engines run in this range at full power
as a means of controlling detonation.
12-13 Rich. Best power A/F for normally aspirated WOT.
14-15 Chemically ideal. At 14.6 the A/F is at the theoretical ideal ratio
with no excess fuel or oxygen after combustion. Good A/F target for
part throttle cruise and light to moderate acceleration.
16-17 Lean. Best fuel economy A/F ratio. Borderline for part throttle
drivability (worse than borderline if EGR is used).
18-19 Very lean. Usual lean limit (Driveability).
20-25 Lean burn limit. Varies with engine.

> I'm running a Holley 4150-735cmf from a late 60s early 70s 390-428 Ford.
> Works for me!

That's because Ford developed that carb. It has skirted Ford truck
boosters which are superior to the usual down leg and straight leg
Holley boosters and Ford's PVCR's are half the size of the main jets
which means it's possible to get good cruise mixture and good WOT
mixture.

> The mixture strength is read as the air/fuel ratio and isn't going to
> vary much according to the carb size.

The big discriminator is the ratio of the jets to PVCR's. Of course,
you don't know what your jets are going to be a priori but stay away
from carbs with large PVCR's. It's a lot easier to drill out a
too small PVCR than it is to close down one that is to large.
These days, I'd definately get a carb with replaceable PVCR's.

> What you are going to find is that a carb like 3310 which is a 780 vacuum,
> an 1850 which is a 600 vaccuum are both "street' carbs and are just about
> where you want them out of the box.

Not in my experience. Both the 3310 and 1850 are 4160's which means
you can't even change the secondary jets and both have the least
effective straight leg boosters. The PVCR's in the 3310 are likely
too large and the 1850 has side hung floats which aren't good for
cornering. Both of those carbs were designed to be cheap. If you
actually want to do some tuning, stick with a 4150 style carb,
preferably with center hung floats. Replaceable PVCR's would be
nice, too.

> Those carbs will smart your eyes at idle and can only be leaned out by
> enlarging the idle air bleed in the main body.

Carbs like those from QFT have replaceable bleeds and PVCR's which
make fine tuning much easier.

> If you are serious about getting the mixture strength correct you are
> going to need to do this all on a dyno or install an oxygen sensor in
> the exhaust system that you can read the a/f ratio with in real time.
> That involves a computer with red and green lines on a graph on your
> computer.

I'm using an Innovate LM1. You can use a computer for datalogging or
the hand helds built in display for real time data.

> For a street car with moderate performance I prefer the Edelbrock carbs.
> They seem to idle best and start better than holleys. A 600 works great
> on a 350/351 right out of the box. They also seem to have better part
> throttle response than the Holleys I have used.

AFB's definately win on ease of tuning. On the Pantera, what do you do
about the AFB idle mixture screws being up front? A 600 CFM AFB would
definately be too small on a 351C in a Pantera. I run a 500 CFM AFB on
a little Buick 215 (a.k.a. Rover 3.5L) and it works just fine. I've got
a 750 Edelbrock AFB to try on the dyno. A drag racer friend has tested
a 735 Holley from a 428CJ against a 750 AFB, said the Holley was worth
a bunch of power (0.35 seconds in the 1/4 mile on a 428CJ Torino).
Supposedly an 800 CFM AFB is on par with a 750 Holley, air flow wise.

Dan Jones

quote:

Carbs like those from QFT have replaceable bleeds and PVCR's which
make fine tuning much easier.

Hi Dan....Like one of these?? This is a Quick Fuel 670 CFM vacum secondaries, $390 on EBay. It lit my car on fire. Was a 600CFM Holley 4160.

> I would not be happy with 600 CFM on a 351C, even with low compression.

I should have been more precise with this statement. There are
two issues with the Holley 1850 600 CFM carb. First, it's 600 CFM
which may not be a problem. 600 CFM is good to around 300 HP (gross)
before it becomes a limiting factor. 2 CFM per HP is a good rule of
thumb for a square bore Holley. The bigger problem is it is a 4160
model carb with side hung floats. 4160's were made for one reason,
to be cheaper than 4150's. If you plan on doing any tuning (and you
should), then start with a 4150 or convert the 4160 to a 4150.

> This is a Quick Fuel 670 CFM vacum secondaries, $390 on EBay.

That looks like one. The one I was looking at was a Super Street
model but was another $100 or so at Jegs.

> It lit my car on fire. Was a 600CFM Holley 4160.

I hope you mean that figuratively and not that literally :-)

Dan Jones

Is the 4150 also known as the Street Avenger?

I had my choke reset today and my carb completely re-tuned. Man, what a difference! My mechanic mentioned that I should replace my carb the next time a major tuning is required (today's session took him 3 hours) and he highly recommended the Street Avenger.

Good choice? Bad? Better options available?

I am looking for performance first and fuel economy second. A few pix of my current carb and power plant will follow ...

Pic 2 of 3 ...

3 of 3 ...

I'm running a 670 Street Avenger on an Edelbrock Air Gap intake. Stock 351c bottom half with Edelbrock heads, bowl ported with 4v sized valves, and a Comp cams 262H cam. Runs really well on the street, plenty of power but a double pumper mech secondary felt a lot stronger (also used a lot more gas)

quote:

That looks like one. The one I was looking at was a Super Street
model but was another $100 or so at Jegs.

Dan, This was one of QFT's dyno carbs. The guy on EBay has them for the cheaper prices, thus no warranty from QFT. He also has the mechanical versions too!
Jeff