pros and cons of twin plug

[bob joyce]

First of all .... I do not race. Just like driving a well running Porsche.... I am getting parts together and looking to build a 1968 911L aluminum block December 1967.
I have 85mm JE pistons 9.5:1, 2.2 911S aluminum (biral) barrels
I have not taken the motor apart yet, It is rusted and I do not expect to use much.
Weber 40IDAP3C1. with rusted/frozen butterflies.
I am questioning weather to use 1969 911S heads that have been modified for twin plugs.
port size : intake 38mm , exhaust 37.5mm
Valve size : intake 45mm, exhaust 39mm....
So.... what would be the pros and cons of building with these heads.
Thank you for any comments.
Reg.#3596
1961 Roadster.1966 9/12, 1968 911L Targa, 2005 Boxster S
bob joyce

[edmayo]

I believe there will be a head volume /gasket incompatibility using 2.2 cylinders with 2.0 heads. I like the valve size of the 69 S heads, maybe some 2.0 cylinders to go with those heads and pistons. Were the pistons speced for a 2.0 head or a 2.2 head ? I think a twin plug runs so nice, even for street.

[BURN-BROS]

I think you have a typo and have 85mm Biral. If so, source a set of 2.2-2.7 heads. And nothing above 36mm intake port.

First of all .... I do not race. Just like driving a well running Porsche.... I am getting parts together and looking to build a 1968 911L aluminum block December 1967.
I have 95mm JE pistons 9.5:1, 2.2 911S aluminum (biral) barrels
I have not taken the motor apart yet, It is rusted and I do not expect to use much.
Weber 40IDAP3C1. with rusted/frozen butterflies.
I am questioning weather to use 1969 911S heads that have been modified for twin plugs.
port size : intake 38mm , exhaust 37.5mm
Valve size : intake 45mm, exhaust 39mm....
So.... what would be the pros and cons of building with these heads.
Thank you for any comments.
Reg.#3596
1961 Roadster.1966 9/12, 1968 911L Targa, 2005 Boxster S
bob joyce

[bob joyce]

HI Ed... I bought the pistons and 2.2 used S cylinders second hand. I talked to Don at EBS were the pistons came from and he has them registered and knows all of the data. Also I have the box that the pistons came in and there is tec. data listed for the pistons. The box was pretty well beat up so I can only read some of the data.. It reads ... comp height 1.335 , forging 32P,, pin dia. .866, pin length 2.500, JE wire locks, I am pretty sure it says comp 9.5, then it does say top ring 1.5mm 2nd ring 1.5mm oil ring3.0mm and Don said the rings were Japanese... actual weight 468. Above that data was placed a U.P.S. sticker so I do not know what else was on the box.
I would think that Don could answer your question so I will make note of your comment. Thanks Ed.
P.S. ... Yes... I was made aware by John Holleran. ( I knew his father from back in the seventies). When I bought the pistons I talked to him and he gave me a recipe of later heads for these pistons and cylinders.. The twin plug heads I am looking at have a part # 90110400901 ... All that I see is that they are 1969 911S heads but i do not know if they would be 2.0 or 2.2 ( maybe the 1969 S is only 2.2)??

[bob joyce]

Yes... You caught my error ...85mm... So the heads I referred to are to big at the intake port. Your suggestion is 36mm... the heads are 38 mm..

[edmayo]

A 69 head uses a different head gasket than a 70 and up head. It also has a larger combustion chamber, so needs a large piston dome meant for a 2.0 liter head. So you need 2.0 cylinders to go with the head gasket of the 69 heads.

[bob joyce]

ok ... the heads i referred to above are said to have been modified @the combustion area. how they were modified i do not know. but if the intake port is too large 38mm, according to Aaron, then i will have to look at other heads.
now i realize that all 1969 911 are 2.0 litter.
thanks Ed and Aaron.
bob

[bob joyce]

It turns out that the same question (pros/cons) was run down on peli... There they debated 3.0 /3.2 motor configurations, but I can some-what figure the 2.0/2.7 would be similar. So It looks like I will not go twin plug. There is not a compelling reason for a 9.5 :1 - 9.8:1 build to go twin plug. And just from the aesthetic reason, to my eye, most of the set-ups look cluttered and out of place.

[myflat6]

It turns out that the same question (pros/cons) was run down on peli... There they debated 3.0 /3.2 motor configurations, but I can some-what figure the 2.0/2.7 would be similar. So It looks like I will not go twin plug. There is not a compelling reason for a 9.5 :1 - 9.8:1 build to go twin plug. And just from the aesthetic reason, to my eye, most of the set-ups look cluttered and out of place.

I found similar research when I built my motor. I have 9.5:1 CR with my 2.5MFI motor and went single plug. Runs fantastic.