4V carb/intake for 352

1966 M-100 · Post by **1966 M-100** » April 12, 2009, 4:59 am

I came across a 390 4V (from a late 70's truck) for $250. I am considering buying it for the manifold and carb to swap for the 2V on my 1966 "352" as a low budget performance upgrade.

Will this be worth the effort, or do I need to spend some $ on aftermarket carb and manifold?

6166 Junkyard Dog · Post by **6166 Junkyard Dog** » April 12, 2009, 6:28 am

Even though it might look nice with original parts,, that cast iron intake is a real bear trying to lift up over the grill assy,, or even if the motor is out now its easy but look to the future if it has to come off as oppose to a aluminum intake,, + also how easy is it to come across carb gasket sets right now or in the future

DV65CustomCab · Post by **DV65CustomCab** » April 12, 2009, 6:30 am

When I was planning the 4v swap for mine, I researched intakes extensively. Somewhere on the internet I found a site (Mustang?) where a guy actually took the time to dyno every intake on the engine he had built. It was pretty interesting. It turns out that the factory 4v intake is actually one of the best! The only advantage to running an aftermarket one is the weight reduction. You'll want a 'dual plane' (dividied inlet), not a single plane (or open).

As for the carb, a late 1970s carb from the factory is going to be off an emissions era truck and probably loaded with extra fittings for junk you won't want or need. Additionally, it will be tuned for mileage and emissions, not performance. I think you could do much better. The intakes do not typically sell for much as most people believe the Edelbrocks, etc are going to be vastly superior. My point is, I don't see this as being a great buy. I picked up a Edelbrock carb in like-new condition at a swap meet for way under $100 and certainly could find an intake for around the same. Unless the carb he's offering you is something other than oem, I don't feel it has much if any value.

The other thing is that a 4v by itself isn't going to increase performance one iota on a stock engine. The oem 2v is somewhere between 500 and 550 cfm. The primaries on my Edelbrock carb have the same size throttle plates as the 2v! The only additional gain is in the secondaries, which only open when you plant your foot to the floor. So, normal drivability would be no different. Additionally, when you do open the secondaries your stock engine with it's ho-hum cam and ignition timing isn't going to be prepared to deal with all that extra sudden burst of fuel. While it may give a slight gain in passing power, the engine really won't be able to utilize the extra fuel effectively.

Which is why my truck still has the 2v on it.

ICEMAN6166 · Post by **ICEMAN6166** » April 12, 2009, 10:33 am

390 2v and 4v actually have different pistons, with either 2v or 4v cast in them.

no real difference in performance from the cast iron to the aluminum manifold that the normal use would show.
unless you go with an aftermarket cam and lifters, along with headers and a good flowing exhaust you might as well stay with the 2v.

Hawkrod · Post by **Hawkrod** » April 12, 2009, 2:54 pm

DV65CustomCab wrote:When I was planning the 4v swap for mine, I researched intakes extensively. Somewhere on the internet I found a site (Mustang?) where a guy actually took the time to dyno every intake on the engine he had built. It was pretty interesting. It turns out that the factory 4v intake is actually one of the best! The only advantage to running an aftermarket one is the weight reduction. You'll want a 'dual plane' (dividied inlet), not a single plane (or open).

As for the carb, a late 1970s carb from the factory is going to be off an emissions era truck and probably loaded with extra fittings for junk you won't want or need. Additionally, it will be tuned for mileage and emissions, not performance. I think you could do much better. The intakes do not typically sell for much as most people believe the Edelbrocks, etc are going to be vastly superior. My point is, I don't see this as being a great buy. I picked up a Edelbrock carb in like-new condition at a swap meet for way under $100 and certainly could find an intake for around the same. Unless the carb he's offering you is something other than oem, I don't feel it has much if any value.

The other thing is that a 4v by itself isn't going to increase performance one iota on a stock engine. The oem 2v is somewhere between 500 and 550 cfm. The primaries on my Edelbrock carb have the same size throttle plates as the 2v! The only additional gain is in the secondaries, which only open when you plant your foot to the floor. So, normal drivability would be no different. Additionally, when you do open the secondaries your stock engine with it's ho-hum cam and ignition timing isn't going to be prepared to deal with all that extra sudden burst of fuel. While it may give a slight gain in passing power, the engine really won't be able to utilize the extra fuel effectively.

Which is why my truck still has the 2v on it.

I am sorry but unfortunately you misread what was written or the guy was just wrong on the dyno tests. Also you do not understand carb function or ratings either.

First, I think the dyno tests you may be talking about were Jay Browns and the common stock intakes did very poorly compared to all other intakes, it was only the stock 428 CJ iron intake that did so much better than most aftermarket intakes and even better than the Ford PI intake.

Next, a 2V carb does not perform as well as a 4V and you can actually get better performance and economy from the 4V. The 4V definitely will provide better performance because it flows more air and properly tuned it will provide better economy because of more precise metering.

Unfortunately you are both wrong and do not understand CFM ratings. The 2V carb does not flow anywhere near 500 CFM OEM and most were around 250-350 but even that is a useless bit of info because a 2V carb is rated at twice the amount of vacuum as a 4V so a 500 CFM 2V and a 500 CFM 4V do not flow the same amount of air.

If you convert a 2V 500 CFM wet flow rating to 4V standards it would be 353.6 CFM. If you convert a 4V to the 2V wet standard a 500 4V would flow 707 CFM. So you see, you can't say a 2V and a 4V flow anything alike.

You also do not seem to understand carb theory as you say "when you do open the secondaries your stock engine with it's ho-hum cam and ignition timing isn't going to be prepared to deal with all that extra sudden burst of fuel" which indicates a lack of understanding of how a carb works. There is no additional burst of fuel when the secondaries open and the only time secondaries open fully is under full throttle. I am not going to discuss mechanical secondary carbs as those are rarely seem on unmodified "drivers". Secondaries in most street carbs are vacuum operated because they are load sensitive which means they can open at any time off idle while under load. The reality is the primary throttle plates can be barely off the stops and the secondaries can be wide open (there is usually linkage to prevent this though). On a vacuum secondary carb, the secondaries only open when needed not just because you have your foot on the gas. Also, the amount of fuel relative to the amount of air does not change when the secondaries open, it is a relatively constant ratio which is why there is no sudden flood of fuel.

Based on all of this, a correct 4V does give better driveability and economy when set up and tuned properly. The reason is if the 4V is the correct size for the engine and tuned properly the primary throttle plates and venturis are smaller than a 2V and so more accurately meter fuel. Hawkrod

Here is a flow size chart for stock 2V carbs from Ford. The number on the left is the venturi size and you will find it cast onto the outside of the fuelbowl:

.98 = 190 cfm
1.01 = 245 cfm
1.02 = 240 cfm
1.08 = 287 cfm
1.14 = 300 cfm
1.21 = 351 cfm
1.23 = 356 cfm
1.33 = 424 cfm

DV65CustomCab · Post by **DV65CustomCab** » April 12, 2009, 7:19 pm

Hawkrod wrote:First, I think the dyno tests you may be talking about were Jay Browns and the common stock intakes did very poorly compared to all other intakes, it was only the stock 428 CJ iron intake that did so much better than most aftermarket intakes and even better than the Ford PI intake.

I found that one. I searched and searched but could not find the one I referred to. I specifically remember the stock 4v FoMoCo intake flowing as good of numbers as either the Wieand or Edelbrock that was the nearest competitor. It shocked the heck out of the guy doing the testing.

Next, a 2V carb does not perform as well as a 4V and you can actually get better performance and economy from the 4V. The 4V definitely will provide better performance because it flows more air and properly tuned it will provide better economy because of more precise metering.

A little misleading, IMO. The 4v without considering the secondaries may or may not flow better than the 2v. Depends entirely on the venturi size. The two additional venturis of the 4v will, of course, in concert with the two primaries flow more. That's pretty obvious. But, an engine can only draw so much air, so plopping a larger carburator on top will not necessarily result in more flow.

Unfortunately you are both wrong and do not understand CFM ratings. The 2V carb does not flow anywhere near 500 CFM OEM and most were around 250-350 but even that is a useless bit of info because a 2V carb is rated at twice the amount of vacuum as a 4V so a 500 CFM 2V and a 500 CFM 4V do not flow the same amount of air.

.

Can't recall anymore where I saw cfm ratings for the oem 2v but I recall them being around 500. Your listing is interesting and I'll do some further research.
I believe the vacuum/cfm issue is again not really useful because you're only using the secondaries at WOT or higher vacuum needs, depending on type of carb. For everyday drivability I still think we need to more closely compare the primary venturis.

If you convert a 2V 500 CFM wet flow rating to 4V standards it would be 353.6 CFM. If you convert a 4V to the 2V wet standard a 500 4V would flow 707 CFM. So you see, you can't say a 2V and a 4V flow anything alike.

I'll admit this is way over my head.

There is no additional burst of fuel when the secondaries open

Huh?

and the only time secondaries open fully is under full throttle. I am not going to discuss mechanical secondary carbs as those are rarely seem on unmodified "drivers".

If only that were true. I can't count the number of times some hot-rodding genius planted a double-pumper on his street engine. Several years behind the parts counter will reveal many horrors.

On a vacuum secondary carb, the secondaries only open when needed not just because you have your foot on the gas. Also, the amount of fuel relative to the amount of air does not change when the secondaries open, it is a relatively constant ratio which is why there is no sudden flood of fuel.

What you wrote makes sense, but my real-world experience driving a few vacuum operated secondary carbs is that you pretty much need WOT conditions to bring the secondaries into play. They have not, in my experience, been very 'progressive'.

Based on all of this, a correct 4V does give better driveability and economy when set up and tuned properly. The reason is if the 4V is the correct size for the engine and tuned properly the primary throttle plates and venturis are smaller than a 2V and so more accurately meter fuel.

And this I agree with completely.
Unfortunately, very few people select carbs based on anything more than "it was on sale", "oooh, a Holley!", or "it's what Joe Blow told me to use." Back to our original poster, I still think adding the setup in question is probably not a great idea as it very likely won't offer any real improvement over what he has. Beyond that, a stock 2v 352 really isn't going to gain much from going from a 2v to a 4v with no other changes to the engine. Cam, compression ratio, valve size, exhaust all factor into what will determine the best carb choice. Too many people make the mistake of thinking the carb is the 'heart' of the engine. That is simply not the case.

The stock FoMoCo 2v on the FE in our trucks is a simple and reliable unit, provided it doesn't get throttleshaft wear problems. I haven't found the need so far to toss it for a more expensive, complex and likely thirsty solution to a problem that may not exist.

modeleh · Post by **modeleh** » April 12, 2009, 9:39 pm

Good discussion you have here guys.
I have also heard the cast iron "S" code 390 intake which is taller than the regular 390 intake is pretty much the same as an Edelbrock performer, though as stated before you could anchor an aircraft carrier with one.
Another point of consideration when selecting a 4v carb is the design of the fuel discharge boosters. They can make a big difference in the characteristics of the carb. Some carbs will have one type of booster in the primary venturies, and another type in the secondaries. I picked up a 4v Holley off a stock '79 460 and it has the annular discharge boosters in the primaries which give it better low rpm atomization. Another consideration is the strength of the diaphragm spring in the vacuum secondary circuit to tailor it to the load and rpm usage in your truck.
There is some interesting reading about booster differences here if anyone cares.
http://www.carcraft.com/techarticles/11 ... index.html

qwertyd10n · Post by **qwertyd10n** » April 12, 2009, 11:48 pm

ICEMAN6166 wrote:390 2v and 4v actually have different pistons, with either 2v or 4v cast in them.

no real difference in performance from the cast iron to the aluminum manifold that the normal use would show.
unless you go with an aftermarket cam and lifters, along with headers and a good flowing exhaust you might as well stay with the 2v.

ICE... do you think a Comp Cams High Energy 268H cam http://www.compcams.com/information/Products/Camshafts/ would be too much for my truck if I packaged it with a new intake, 4V carb, dizzy, along with the headers that are already on the truck? Maybe a little too lumpy? Maybe the 260H would be a better fit...

Hawkrod · Post by **Hawkrod** » April 13, 2009, 12:00 am

Just a couple of things to add. If a vacuum secondary carb is working properly there is no way to tell if it is working or not you can't feel or hear it. The way to check a Holley is to put a paper clip on the vacuum shaft and see if it moves after a drive. If you can feel or hear the secondaries there is some thing wrong or it is set up wrong. Here are the dyno tests: http://www.network54.com/Forum/74182/se ... sort=match Jay wrote "I had some help over Thanksgiving weekend, including from my pal BradFORD, who brought along his “T” cast iron truck intake to try out on this engine. Having already done the “S” intake, and a C4 cast iron intake, I was curious to see where this one would fit into the mix. After horsing the thing into place, we got the following results, graphed together with the “S” intake and the C4: (graph deleted) The truck intake falls right between the other two cast iron intakes, making it a good, low rpm torque intake, but not much of a stellar high end performer. No real surprises here." ande " The second intake to go on the engine was the S code factory cast iron intake. Shoe was particularly interested in this one, because it is such a common intake and often is removed in favor of an aftermarket unit. How bad was it? We stuck it on the motor to find out.

The results were 355 HP, which was underwhelming of course as compared to the other intakes, but pretty much in line with what we were expecting. Sitting on the floor was the other cast iron intake, a C4 part number which was found as the standard 4 barrel intake on pre-66 FEs. Kurt G said, "Well, as long as we're dating ugly girls, we might as well do this one too." So, off came the S intake and on went the C4.

The C4 intake looked about the same as the S code intake, except the carb was probably about 1/2" lower with this intake as it was with the S code. But, we were about to be treated to the first real surprise of this dyno session. The C4 intake really ran well, making a full 20 HP more than the S intake. The S must stand for Sucks, because the C4 just blew it away. Here's a graph of the corrected Torque and HP for these two intakes: (graph deleted)". Those numbers were down 40-60 HP from most intakes tested except the SP2P (which sucked big ones). Hawkrod

oldtrucks · Post by **oldtrucks** » April 13, 2009, 1:08 am

Hawkrod
Very interesting post. I concur with it 100% all my research and experience follow what you said. I currently run a Edelbrock 460 on my work truck 429 along with a Holly 3310 750CFM carb. I cannot tell you when the secondarys begin to work altho I know they do. The 750 is probably too much carb for what it is used for but it does what I need it to do flawlesly. I did experiment with the power valve, jets and secondary springs until it ran the way I wanted it to.
The only thing I might add is the high rise duel plane manifold will give the carb a stronger signal for better throttle responce but over all a stock 4 barrel manifold won't hold you back on a stock engine.

DV65CustomCab · Post by **DV65CustomCab** » April 13, 2009, 6:00 am

If our discussion gets you to put more thought into such a modification than merely bolting some different parts on your truck, mission accomplished.

I don't pretend to be any expert on performance tuning; I'm a self-taught master of nothing anyway. But, working behind the parts counter for as many years as I did at everything from dealerships to speed shops taught me that the number of people who really think about what they are doing vs those who just DO are vastly different. Don't even get me started on "3/4 race cams".

Carbs are just toilets for fuel anyway. Fuel injection is where it's at.

R Pope · Post by **R Pope** » April 13, 2009, 7:57 am

I have never seen an engine that didn't gain power with a 4V over a 2V, as long as it was jetted anywhere near right. A 352 will probably gain a few MPG too, at least at highway speeds.

Hawkrod · Post by **Hawkrod** » April 13, 2009, 11:15 am

Sorry. last night when I last posted I was having serious keyboard problems (spilled a Monster drink on my keyboard! that stuff is sticky). I took my keyboard apart and cleaned it and will try and add to what I did not respond to.

1. there were definitely a couple of intakes from the aftermarket that barely did better than the stock iron intake. The SP2P actually did worse. the current model Performer (not the Performer RPM or old version with bigger ports) barely outdid the stock C4 intake but did a lot better than the intakes with the S or T on them . The Offy 360 and a similar design Weiand also barely did better. That being said, a stock PI, Blue Thunder, Performer RPM, Sidewinder or an F427 did much better and a stock 428CJ cast iron intake kicked butt as well.

2. Without considering the secondaries you are not considering a 4V and if you did compare them then the 4V should be smaller when not including the secondaries. Part of the reason to have a 4V is to have smaller primaries to allow better fuel/air control. Because the secondaries are load sensitive they only function as needed, that is why it can be so efficient. The idea is not neccesarily to plop a larger carb on, a 2V and a 4V that flow the exact same amount would be the perfect example, the 4V will still outperform the 2V even though the engine would not get more airflow.

3. I think you may have seen airflow ratings for 4V Ford carbs and transposed them. This is easy to do because the numbers to ID them are the same:

2V
.98 = 190 cfm
1.01 = 245 cfm
1.02 = 240 cfm
1.08 = 287 cfm
1.14 = 300 cfm
1.21 = 351 cfm
1.23 = 356 cfm
1.33 = 424 cfm

4V actual as tested
1.08 = 440 cfm
1.12 = 520 cfm
1.19 = 600 cfm

4V as Pony Carbs claims
1.08 = 480
1.12 = 600
1.19 = 670

Please note that it is believed that the Pony carb numbers were something they made up as they have never provided any documentation to support the claims. Unfortunately their claims are commonly accepted but real world flow testing was done and none lived up to Pony Carbs numbers. I personally wonder if Pony Carbs vested interest in larger numbers is why they do not provide any proof of their claims?

I also think you may not completely understand that with a 4V you are usually using the secondaries all the time. It is not a WOT or heavy load only situation. The secondaries open all the time during normal driving and even cruising. That is not to say they are constantly open but they do open as needed. As I noted last night, if you have a Holley, you can put a paperclip on the shaft and take a drive and see if it moves. If the carb is working properly you will find it pushed down the shaft. As long as the carb is set up properly you should never be able to determine if the secondaries are working other than the fact that the car or truck is going. It is a very common misconception that you "can feel the secondaries kick in". Kind of like a 3/4 cam except a 3/4 cam really did exist at one time.

4. Sorry, carb flow ratings are an important and often misunderstood item. The reality is what I was pointing out is that you can't just compare teh numbers from a 2V to a 4V because the specification is different. It is like saying I have a 1000CC engine so it is more powerfull than your 460CI engine because 1000 is bigger than 460. You are using different standards so the comparison only works if you use a conversion factor. It is alos important to note that tehre are several different standards for carb air flow and not all companies use the same standard. You have both wet and dry flow and different number of inches of mercury that the test is done at. It really can be confusing even to somebody who does it regularly.

5. I could discuss mechanical secondary carbs but percentagewise they are rare. You are correct that to many people run them but I did not want to make the discussion even more boring and drawn out for an issue that really is only important to relatively few people.

6. I will bet your experience is not telling you the truth. See the Holley test above. I have had to show dozens if not hundreds of people that their secondaries were working when they came in claiming they did not. In the 30 plus years I have been doing this, this has been one of the biggest issues with people who do not understand carb theory.

7. Yes, there are too many who make bad decisions about carbs but even a stock 4V will make a noticeable change on an otherwise unchanged engine. This si why the factory engine ratings are so different between a 2V and a 4v. Lets just use a 352 car engine for an example. The 2V is rated at 220 HP but the 4V was rated at 250 HP. The engines were identical. The only change is the carb and distributor. They had the same cam and compression heads etc... I use this example often as they were identical so it is a fair comparison. The 4V has more than a 10% increase in power and what is more important is the power is across the spectrum not just top end or bottom end so it is useful power. The reality is a stock 4V is a budget swap and except for better driveability you should see no other differences in wear, economy and function. Having said that though, an aftermarket dual plane intake can produce significant gains on an otherwise stock engine. I would not swap 70's intake but if I was looking at pennies, I would not hesitate to swap an early 60's intake on and go for it. Hawkrod

DV65CustomCab · Post by **DV65CustomCab** » April 13, 2009, 7:17 pm

Good argument. I respect a well stated and researched opinion.

So, why is my 352 rated at 208 hp according to the air cleaner decal but the same engine in a car is 220?

Lastly, the OP said his possible donor carb was from a late 70s truck. Would you bother using it? I wouldn't. I think the aftermarket alternatives would be vastly superior. Plus, oem carbs generally offer limited tuning capabilities.

Fun discussion.

Hawkrod · Post by **Hawkrod** » April 13, 2009, 8:50 pm

DV65CustomCab wrote:Good argument. I respect a well stated and researched opinion.

So, why is my 352 rated at 208 hp according to the air cleaner decal but the same engine in a car is 220?

Lastly, the OP said his possible donor carb was from a late 70s truck. Would you bother using it? I wouldn't. I think the aftermarket alternatives would be vastly superior. Plus, oem carbs generally offer limited tuning capabilities.

Fun discussion.

As far as the truck HP ratings, they had a different cam and distributor curve.

I actually never commented specifically to the original post other than the fact that the 70's T intake is better than the car S intake and the 2V but there are better options.

I also did not mention it but I do run a 70's smog carb on all of my trucks with 460's. They are amazingly good in design and meter very well. They do need to work to use if they are being used outside of the OEM application though. The 4300 is definitely a sound and effective design. Hawkrod

BarnieTrk · Post by **BarnieTrk** » April 14, 2009, 8:12 am

Hawkrod wrote: I actually never commented specifically to the original post other than the fact that the 70's T intake is better than the car S intake and the 2V but there are better options. -- Hawkrod

Hawkrod,

What do you mean by a 'T intake' and a 'S intake'?

I have an intake C6AE9245-G which also has a large 'S' cast on one runner. Is this the same intake you are referring to as an 'S intake'?

I also have a C5AE9425-C 4-V intake, but I don't see any large 'S' or 'T' cast on it.... Any ideas what that intake would have come on, any good/better than the 'S' intake?

Thanks in advance for any & all input!
BarnieTrk

Hawkrod · Post by **Hawkrod** » April 14, 2009, 9:39 am

BarnieTrk wrote:
Hawkrod wrote: I actually never commented specifically to the original post other than the fact that the 70's T intake is better than the car S intake and the 2V but there are better options. -- Hawkrod
Hawkrod,

What do you mean by a 'T intake' and a 'S intake'?

I have an intake C6AE9245-G which also has a large 'S' cast on one runner. Is this the same intake you are referring to as an 'S intake'?

I also have a C5AE9425-C 4-V intake, but I don't see any large 'S' or 'T' cast on it.... Any ideas what that intake would have come on, any good/better than the 'S' intake?

Thanks in advance for any & all input!
BarnieTrk

Yes, that is the S intake, starting in 1966 Ford redesigned the intakes. The T intake will have a big T on it just like your S. Basically any 66 or newer cast iron intake except for a CJ intake is a T or an S even if it does not have one on it. The S intake are used on cars although I think only the 4V is marked with an S but the 2V is also an S design. the T intake is used on cars and trucks. The 69 Mustang 390 intake is a T intake but is unmarked and has a C9ZE casting number. The C5 intake you have is the earlier design and was worth about 20 HP and quite a bit of torque over the S intake on a dyno test. Hawkrod

BarnieTrk · Post by **BarnieTrk** » April 14, 2009, 9:58 am

Hawkrod wrote: Yes, that is the S intake, starting in 1966 Ford redesigned the intakes. The T intake will have a big T on it just like your S. Basically any 66 or newer cast iron intake except for a CJ intake is a T or an S even if it does not have one on it. The S intake are used on cars although I think only the 4V is marked with an S but the 2V is also an S design. the T intake is used on cars and trucks. The 69 Mustang 390 intake is a T intake but is unmarked and has a C9ZE casting number. The C5 intake you have is the earlier design and was worth about 20 HP and quite a bit of torque over the S intake on a dyno test. Hawkrod

Hawkrod,

So if I'm understanding you correctly, the 'S' intake could have been OE on '66 and later FE-equipped cars except the 390 Mustangs and 428CJ cars, correct?

And between the two, the 'C5-" intake was tested to make more HP & torque than the 'S' intake, correct?

Very interesting........ Thanks!
BarnieTrk

Hawkrod · Post by **Hawkrod** » April 14, 2009, 10:03 am

Yes, you got it right but I did make one glaring error (should have reread it! LOL). The 2V's are primarily a T design in a car or a truck but can be the S design especially 66/7. These two designs have a lot to do with emissions so they tend to have choked runners to create velocity and turbulence which makes for lower emissions. Hawkrod

DV65CustomCab · Post by **DV65CustomCab** » April 15, 2009, 6:14 am

...and then there's the T intake I had for mine that wouldn't fit the engine.

Our guess is that it was an FT intake. Won't sit down into the valley between the heads far enough for the bolt holes to line up. That was not a fun weekend.