Trying to understand the diff between 4V & 2V heads

[jaydee]

Pardon my ignorance but I'm trying to get my head around 4V heads and 2V heads.
I know 4V means 4 venturi and 2v, 2 venturi carburettor.

I have an XC 351 that originally had a Carter Thermoquad which I replaced with a Holley.

I have been told I have 2V closed chamber heads, so how can that be if it had a Carter thermoquad (quad meaning 4)?

My next question is I've found some extractors at a good price described as F series (presuming for an F100 or similar). So if I have 2V heads will it be ok to have 4V extractors? I can understand that it wouldn't work the other way, that is 2V extractors on 4V heads.

So can someone please in simple english explain this mystery to me, cheers.

[Paull]

There is no such thing as a 4V nor a 2V head as far as Ford is concerned. This is simply after-market speak.

Have a read of this;
http://www.fordforums.com.au/showthread.php?t=6669462

If you are looking at buying extractors, buy the '2V' ones for a straight port to port match (small port to small port). Or, if you want to go small port (head) to large port (extractor), buy the 4V ones.

[fasty73]

4v has larger ports, 3 fingers fit easily into the inlet port. 2v won't quite fit 3 fingers in, depends on the size of your fingers too lol. Open chamber has more room around the valves and closed chamber only has room for the valves and the rest is flat. Trying to give you lamens terms here. There is such a thing as 2v and 4v according to ford but it had NOTHING to do with venturi's.

[fmc351]

As well as the link above, there is also a wiki on them under the name 335 series engines (dubbed as Cleveland).

http://en.wikipedia.org/wiki/Ford_335_engine

So it appears,
Valve sizes
Port sizes
Open v Closed chamber
Compression
Carb which is where the term 'V' officially comes from?


From the wiki it appears that in the US at least, all 4 barrels were 4V, and all 2 barrels were 2v which is why the association is carb based, but given there appears to be differences in port sizes and chamber sizes that will explain how some say its carb based, and others argue it isnt as there are other differences than simply carb and inlet manifold. But Im not sure how accurate the wiki is, as Im pretty sure there are both open and closed chamber 4V heads. This Im less certain of, but I THINK there are also open and closed chamber 2V heads.

Im sure someone here will have the ins and outs and clear it up.

[mik]

nice pic here
http://i189.photobucket.com/albums/z...difference.jpg

[jaydee]

OK, I'm getting my head around it.
So by looking at those pics, extractors for a 4 v motor shouldn't be a problem for 2V heads?

[Jimmyd]

Originally Posted by jaydee

OK, I'm getting my head around it.
So by looking at those pics, extractors for a 4 v motor shouldn't be a problem for 2V heads?

Originally Posted by Paull

If you are looking at buying extractors, buy the '2V' ones for a straight port to port match (small port to small port). Or, if you want to go small port (head) to large port (extractor), buy the 4V ones.

As Paull said, yes. You get the added bonus that the oversize primary pipes compared to the 2v exhaust ports will act like a crude anti-reversion plate - ie harder to suck the exhaust gasses back in on the cam overlap at higher rpm.

[Bud Bud]

Stop! Before you buy you need to consider these two main points of difference.

1) A 4V header will not seal over a 2V head. There is not enough raised meat on the standard 2V head to stretch past the huge 4V port opening on the 4V flange plate. They will either blow out the gasket or they will just not seal but either way the end result will be the same, they will leak.

2) You say the design of the header is for an F series. If this is the case then it will only fit an F truck and they will not be compatible for a Falcon platform. The engine and tranny are not the only considerations required in the design of a header. The real concerns evolve around steering boxes and drag links etc. because they are simple not in the same place under the bonnet.

It is worth noting that header manufactures do their best to cross reference their designs so they can fit across a whole plethora of vehicles because this helps eliminate fitting problems and also helps to keep inventory levels down but when this cannot be achieved then another design will be required creating a new part number. This is also the case with the whole 2V 4V thing as well. I it could be done, then there would probably only be one part number for both cylinder head types.

Can I ask what headers they are and do they have a part number attached to them? Are they new or second hand? Do you know the history behind them?

Bud Bud

[burnz]

can i ask a dumb question: are the manifolds duell pane or single?? per head setup.

[mik]

i bought some 4v heads years ago second hand from a speed shop, i don`t know if it was an original feature or not but my set had dual valve springs fitted.

[jaydee]

Originally Posted by Bud Bud

Stop! Before you buy you need to consider these two main points of difference.

1) A 4V header will not seal over a 2V head. There is not enough raised meat on the standard 2V head to stretch past the huge 4V port opening on the 4V flange plate. They will either blow out the gasket or they will just not seal but either way the end result will be the same, they will leak.

2) You say the design of the header is for an F series. If this is the case then it will only fit an F truck and they will not be compatible for a Falcon platform. The engine and tranny are not the only considerations required in the design of a header. The real concerns evolve around steering boxes and drag links etc. because they are simple not in the same place under the bonnet.

It is worth noting that header manufactures do their best to cross reference their designs so they can fit across a whole plethora of vehicles because this helps eliminate fitting problems and also helps to keep inventory levels down but when this cannot be achieved then another design will be required creating a new part number. This is also the case with the whole 2V 4V thing as well. I it could be done, then there would probably only be one part number for both cylinder head types.

Can I ask what headers they are and do they have a part number attached to them? Are they new or second hand? Do you know the history behind them?

Bud Bud

Here is a pic, thats all I have to go by at the moment until I see them. They are brand new never fitted.

[jaydee]

Originally Posted by burnz

can i ask a dumb question: are the manifolds duell pane or single?? per head setup.

It's the orignal manifold, what ever that may be.

[fasty73]

Both heads have closed and open chamber options.

[Bud Bud]

Ok they look like either Genie or Genie copy headers (actually I don't think that they are Genies but do look similar) to suit a Bronco so I think that these will not fit anything other than a Bronco imho. Can the seller provide this information? But either way, definitely not a Falcon and probably not an F-100. The passenger side is the key as the two centre collector cones point down. If they were for an earlier model F-100 then they would be more swept back like the drivers side. Also the driver's side needs to be much tighter in shape to clear the tower and steering box for a Falcon as well. If you look at these pics you can see how tight the driver's side needs to be. http://www.bestmufflers.com/bshop/images/PH4050-300.jpg

Also they do look like 4V headers as well. I tried to zoom in but the pic becomes too blurry to tell. What you should see is that the outside of the port should run roughly in line and down and under the top bolt hole. I have seen some headers that have a half moon shape in the corner under the top bolt hole as the port is stretched past this point if you know what I mean.

If they are for a 4V then they will leak along this side of the port on a 2V cylinder head. If you can get a close up pic of a port, then I could tell for sure, but it may be a moot point as I think that they just won't fit your car anyway.

Bud Bud

[wodahs]

these are what you want they are of a 77 fairlane genie extractor (not header)

and like paull said last time i looked yes you can put a large port set of extractors on a small port head but not a small port exterctor on a large port head

[Bud Bud]

Mik, that is the intake side, he needs to see the exhaust side. For those of you who think that you can put 4 V headers on to a 2 V cylinder head, take a look at these two pics.
2V

4V
If you look closely you can see the extra material cast into the face to allow for the bigger port in the 4 V head. The problem with putting a larger 4 V header onto a 2 V cylinder head is the original casting of the 2 V head finishes roughly in the same place (right under the centre of the top bolt) as where the edge of the 4 V port finishes as well.

Bud Bud

[Bud Bud]

Originally Posted by wodahs

these are what you want they are of a 77 fairlane genie extractor (not header)

and like paull said last time i looked yes you can put a large port set of extractors on a small port head but not a small port exterctor on a large port head

Wow, how old are they? They are pressed bent! Genies have been mandrel bending since the mid 80's Do they have a Genie tag?

Ok extractors, headers same thing no matter who makes them. The ones including yours that have featured in this thread so far are tri-Y's.
Yes they are the right headers to suit a Falcon/Fairlane.
Yes the headers will fit but you will still run into sealing issues if you put 4 V headers onto 2 V cylinder head.

Bud Bud

[mik]

sorry my bad , was`nt even thinking inlet or exhaust just trying to show port size comparison.

[wodahs]

Originally Posted by Bud Bud

Wow, how old are they? They are pressed bent! Genies have been mandrel bending since the mid 80's Do they have a Genie tag?

Bud Bud

sorry my bad yes they still have the tag but they are lukeys not genies and they still have the walker exhaust part number in the white marker pen from when i got them from new (thats how little they got used) and yep ive prob had them bout 10 years