4.6 heads on a 3.5 9.75:1 SD?

General Chat About Exhaust, Cylinder Heads, Fuel Systems And Intake

Moderator: phpBB2 - Administrators

Post Reply
User avatar
Prophead
Helpful or Confused
Helpful or Confused
Posts: 96
Joined: Thu Jun 16, 2016 7:05 am
Location: Falkirk

4.6 heads on a 3.5 9.75:1 SD?

Post by Prophead »

I have seen reference to the above being possible and even potential performance upgrade due to the larger ports, but not found much that is definitive. I'm am looking at this option for two reasons i) Long term I would like to have the new style valve stem guide seals ii) If there is a potential performance gain then better to get the 4.6 heads and refresh those than spending the money working mine

Naturally I don't want to reduce compression so would I need to use the composite gaskets or the older style ones? I understand the 4.6 heads have a smaller chamber due martial being removed from the face at the factory.


Porsche 924 GTv8 Track-day car project
Porsche 944 2.5 Lux gone but not forgotten

User avatar
Darkspeed
Guru
Guru
Posts: 913
Joined: Sun Sep 02, 2007 4:43 pm
Location: Shropshire
Contact:

Re: 4.6 heads on a 3.5 9.75:1 SD?

Post by Darkspeed »

Later 10 bolt heads would increase the compression - probably what you meant to write - composites reduce it back to stock. There can be small gains as the castings are better but not significant.
4.5L V8 Ginetta G27

User avatar
ChrisJC
Top Dog
Top Dog
Posts: 5039
Joined: Mon Nov 20, 2006 1:13 pm
Location: Northants / Cambs
Contact:

Re: 4.6 heads on a 3.5 9.75:1 SD?

Post by ChrisJC »

They'll definitely fit. Use the stretch bolts and composite gaskets.

I am pretty sure that the ancillaries will also fit OK, although you might have spare holes as I think they went to 4 fixings at the ends (or at least at one end!!)

Chris.
--
Series IIA 4.6 V8
R/R P38 4.6 V8
R/R L405 4.4 SDV8

User avatar
Prophead
Helpful or Confused
Helpful or Confused
Posts: 96
Joined: Thu Jun 16, 2016 7:05 am
Location: Falkirk

Re: 4.6 heads on a 3.5 9.75:1 SD?

Post by Prophead »

ChrisJC wrote:
Sun Jul 22, 2018 7:55 pm
They'll definitely fit. Use the stretch bolts and composite gaskets.

I am pretty sure that the ancillaries will also fit OK, although you might have spare holes as I think they went to 4 fixings at the ends (or at least at one end!!)

Chris.
Thanks Chris - ancillaries not a problem as I don't have any bar the alternator
Porsche 924 GTv8 Track-day car project
Porsche 944 2.5 Lux gone but not forgotten

User avatar
Blown v8
Gold Member
Gold Member
Posts: 369
Joined: Sun May 25, 2008 2:20 pm
Location: Kent

Re: 4.6 heads on a 3.5 9.75:1 SD?

Post by Blown v8 »

I had SDi heads on a 4.6 block,so can't see why you can't do it the other way around !

Post Reply

Return to “Exhaust, Cylinder Heads, Fuel And Intake Area”