huskeric

After scouring this forum, as well as many others, I still have a few questions regarding my plan to install 47mm intake valves/new seats on my turbo head to support all the other mods I have done.
The question is whether these valves will physically fit in the stock 100mm chamber. From my reading, I have read both 'yes' they will fit, as well as 'no' they can only be used on a larger bore (i.e. 104 mm)

So... has anyone done this or have knowledge of this swap?

I do plan to have other head work done to ensure proper flow, so that is not a concern. Also, the larger JME cam, stage 3 turbo, intake upgrade, and other mods really would benefit from this additional valve size increase.

thanks
rick

Braymond

Why not just go to the 16v head instead of bigger valves on a 8v head?

huskeric

From my understanding, there is a ton of custom work that needs to be done to install a 16v on a 2.5. Also, trying to locate a 16v head is no easy task, let alone the cost issue.
As such, will just upgrade my current 8v head. Also, lack of performance cams for the 16v.

Braymond

The 87-88 944S 16v head fits the 2.5L block, but you're correct that there's other work to be done besides just mounting the head on the block. I interpreted "the larger JME cam, stage 3 turbo, intake upgrade, and other mods" as "a ton of custom work" too. I guess that does equate to two tons of custom work total ;-)

PaulD_997C4S

1989 944 with 2.7L block has a head that fits on turbo block and has the larger intake valves, although the replacement cost of the Porsche valves, last time I checked, was north of $200 each.
Aftermarket valves are out there for less money.

You want the 1989 944 2.7L head. Not cheap, but good stuff.
I believe the intake valves were 47mm, exhaust is same as 944 Turbo and 2.5L 944's. 944 Turbos were 45mm.

333pg333

Might be of interest. Not sure if you're in the 'Premier 944 & 968 Turbo Community' FB group. Some very nice heads for sale.

huskeric

Thanks... yes, I see the 2.7L head for sale... The head I have has already been d-ported, similar to the 2.7L and I have the valves in hand. I will post a pic of the head tomorrow.
So will probably just have new seats installed...

The head does look quite nice...

Gage

This is not correct. The 2.7 head fits a 2.7 block and a 3.0 block but not the 2.5 block.

Braymond

Yes, Gage is correct. There are essentially two block designs. The 2.5L block (100mm bore) is used on the '84-'88 base, S, and Turbo models. The improved 3.0L block (104mm bore) is used on the '89 base (2.7L), S2 and 968.

Here are images of the two different head designs (Top S2 head, Bottom S head). You can see the coolant jacket outlet is different between them. It's not a huge difference and the head can be adapted, but the work requires some cutting/grinding/welding and maybe a donor head.





Going with your plan to install larger valves in your current head is probably the easiest upgrade option.