The V8 Owners Forum -

The standard inlet port sizes for the rover heads are approx 38mm. 23mm.

My Buick 300 Alloy heads have ports of 44mm x 26mm. as standard and I'm wondering what is done to seal the manifold to heads with the larger ports such as with stage 3/4 heads.

Anyone know the aperture sizes in the standard composite valley gasket, or have one to hand that they could accurately measure?

Kevin

don't have the size but they are the same as the standard tin gasket. If you have them post the external sizes as these are more important, you can always increase the internal size. If they are considerably different on the outside then there wont be enough material left.

Marki,

Sorry i might be being thick, but didn't understand your response. I don't have a gasket to hand at the moment which is why I was looking for the standard aperture sizes to see if they can be made to match the head port sizes and still leave enough material for sealing. Or do the specialists supply gaskets to match their stage 4 heads?

Kevin.

Marki,

I now see what your saying, the external dimension of the gasket is important as it controls what you can open out the internal dimension to.

So I need both dimensions.

Kevin (Thick sometimes)

What I was getting at is I have no knowledge of the 300 heads and as well as having a larger internal port they could also be larger on the outside of the port as in being offset to where standard heads are. If this was the case then you would be unlikely to be able to use a rover gasket or a stage 4 gasket if there is such a thing. I doubt they do by the way as the outside is still the same so even if larger hole wise there wouldn't be any material to seal against. If the external is the same or close to standard then a normal gasket will fit simply by opening out the holes in them.

Marki,

The external dimension of the central pair is 60mm high x 62mm. wide.

Kevin.

Cool I will get back to you after a measure.

I've been messing about with my 3.5 lump and happened to measure the inlets the other day. I've got V8 Development stage III heads and the ports measure 45 by 27mm.

I carefully ground out the valley gasket (tin one) when I fitted the heads. I also matched the edelbrock manifold which was quite a lot of work.

You need to be very careful if the bridge between the ports has been thinned down when you fit the manifold, it is possible to have a large mis-alinement due to the sloppy fit of the manifold.

If you use the tin gasket then put a VERY thin smear of silicone round all the ports (inlet and water) on both sides of the gasket. Let the silicone cure for 1/2-1 hour before fitting the manifold.

HTH.

Pete

Pete,

Thats encouraging, any idea how much gasket there was left at the top of the ports which is the critical area, Bridge area is standard, noreal need to thin it down. The gasket will need work on all the outer dimensions as will whatever manifold I decide to use

My ports are standard at the moment, about 1mm less in height than your stage 3 heads. I suppose if the gasket gets a bit thin at the top and the manifold overlaps I could squeeze in a bit of silicon in for insurance.

Kevin

CastleMGBV8 wrote:Pete,

Thats encouraging, any idea how much gasket there was left at the top of the ports which is the critical area, Bridge area is standard, noreal need to thin it down. The gasket will need work on all the outer dimensions as will whatever manifold I decide to use

My ports are standard at the moment, about 1mm less in height than your stage 3 heads. I suppose if the gasket gets a bit thin at the top and the manifold overlaps I could squeeze in a bit of silicon in for insurance.

Kevin

Hi Kevin,

There was a good 5-6mm of gasket left at the top. At the bottom it goes right round to the other set of ports!

I always use a bit of silicone as the tin valley gaskets are prone to leaking.

HTH,

Pete

Black valley gaskets are much better than the old tin

Sounds like I shouldn't have a problem then if there is 5-6mm. at the top, should only need to trim out about 3mm from the top and bottom and the sides should not be a problem.

Thanks for the info, the engine spec is gradually coming together and I'm just trying to avoid problems with the final build.

Kevin.

stevieturbo wrote:Black valley gaskets are much better than the old tin

I'm sure that your right!

its just that I've "ported" my tin one now and can't be bothered doing the whole thing again with a black one.

The other thing is I did not know whether its possible to trim the composite ones, do they have a "special" edge round the ports?

Pete

Kevin, I am only up the road from you in Bexleyheath and have a brand new composite manifold gasket you can borrow if you want to check the size - send me a PM if you like.


Andy

Andy,

Thanks for your kind offer, it would appear that there's enough meat in the gaskets to handle the bigger ports, at worst may need a little silicon sealer around the top between the head and manifold faces.

I've got to buy a gasket any way so I'll pick a composite one up this week.

Kevin.