single port vs dual port cylinder heads

[monkslayer]

i know that this has probably been discussed before...but can anyone tel me the difference between single port and dual port cylinder heads..and the advantages of one over the other

[jrandy]

Single port heads will always be limited by the way the manifold attaches to the head.
The port(s) cannot be made much larger without removing the mounting flange.
They can be massaged and improved over stock.
SP heads work fine for the engines they were designed for and I am going to go out and hop in my 70 bug and buzz down the freeway in a few minutes and if it doesn't blow up it should get me there.

DP heads are a different deal & lend themselves to modification & performance upgrades.

[Marc]

The smaller inlet tract on SPs gives them higher flow velocity and manifold vacuum off-idle through midrange, so they're a little more responsive in stop-and-go driving; many prefer them for a daily driver even though they give up maybe 3HP at the top end (comparing 1600SP to 1600DP, stock or close to it). In mixed driving you can expect 5-10% better mileage from the SPs
40+ years ago when they were the only thing around quite a bit of effort was taken by some to improve their performance potential, but an out-of-the box DP will flow more than anyone ever got out of a SP so you don't see that done anymore, other than by a few masochists out to make a statement.

[monkslayer]

this might sound rather naive but how do i tell the difference between the sp heads and dp heads by physical appearance..i.e by looking at them

[Bugfuel]

Single port has just one hole for the intake mixture to get in, and it splits into two intake ports inside the head casting to feed two cylinders:




Dual ports have separate intake ports all the way from the outside to the intake valve, requiring a two-hole intake manifold end casting to match it:

[monkslayer]

so,in all my wisdom i bought single port heads as a replacement for my dual port heads,i didnt check.so what modifications will i nèed to make so that i can use the single ports that i purchased.

[harryset]

single port intake manifold, possibly a carb or adapter, not sure about that. Also, cylinder tin won't be correct.

[Bruce2]

.... what modifications will i nèed to make so that i can use the single ports that i purchased.

You sell them and get some dual port heads. You'll spend more money trying to adapt the single ports.

[Marc]

If that's not an option and you must use them, you don't really need to change the entire carb/intake manifold - there are aftermarket endcastings available which will connect the DP manifold center section to SP heads.
http://www2.cip1.com/ProductDetails.asp ... C13%2D3237
...But they aren't free, so even if you take a loss selling the heads you'll probably still be better off.
The two inboard upper cylinder head studs on each side need to be replaced with ones the same length as the outboard ones, and the overcylinder tin has to be changed - anything from `66-`70 will fit (and probably fit better than aftermarket reproduction stuff).
http://www2.cip1.com/ProductDetails.asp ... C10%2D5442

[monkslayer]

actualy from what i can see the only visible diférence is the intake manifold,if i get an sp intake manifold it should be ok...the rest should work..what do you think?i could be wrong..

[Marc]

The 34PICT carb that comes on a DP has a larger base flange than a SP carb, so it won't fit. If you happen to have an H30/31PICT on an adapter flange now, it could be used (without the adapter) but be prepared for possible interference between the accelerator pump linkage and the alternator housing.

[Bruce2]

actualy from what i can see the only visible diférence is the intake manifold,if i get an sp intake manifold it should be ok...the rest should work..what do you think?i could be wrong..

You are attempting to polish a TURD.

Marc told you the top two inner head studs will need to be changed. This is true. So you'll need a set of head studs since they don't sell the studs separately.

Then the next item you will need is a pair of sheet metal cylinder covers. Single port covers are quite different from dual port covers.

On top of a new manifold, you will need a new carburator. Your 34PICT carb has a larger mounting flange than the carb for a single port engine. This means your carb does not fit on the single port manifold.

The next can of worms is your distributor. Depending on what distributor you have, it may not work with the new carb for the single port manifold. If you have a dual vacuum distributor, the single port carb does not have the correct port to run the vacuum retard. And no, you can't just drill a hole in it to make it work.

So far you have spent more money than if you just bought a pair of dual port heads.

Sell your single port heads and buy some dual ports.

[monkslayer]

TURD...really..anyway,forgive the manifold comment,it was made before the other replies was posted,but point noted.,

[Bugfuel]

in other words... it CAN be done, but it is not economically or power wise feasible. You lose at both ends.

If you had a junk SP motor to pull parts off of, you could do it cheaper. I've built bastard engines like this, when the goal was just to have something temporary to keep a car on the road until another engine was finished. I had one or two laying around my shop as loaners for people who didn't want downtime from driving their car, while I was building a real engine for them

[monkslayer]

well..in one way am screwed..in another..i have learnt a lot..lesson 1..look at what you are buying!i think i will stick to the single port..i am actually building a bastard engine..from scratch..getting parts from here and there.the car is going to be my daily driver,so i am not really looking into breaking speed records or racing on the highway but more into economy.am looking into a better mpg,which from what i have heard...single ports offer better in relation to dual ports.the only problem is that the the engine which i got parts was a dual port..so the mainfold is also a dual port one and so is the carb.anyway..thanks all for the info.Over here mechanics do customization all the time(you wouldn't believe),so i might go the adapter way or just do a complete overhaul,new carb,distributor,mainfold,overhead tin...my mechanic pal will help me.