4.6 heads or refit my 3.5 heads

[nigelv8]

Hi

I'm fitting a 3.9 block to replace the 3.5 engine in my Capri. I've been offered a set of 4.6 heads which need the valves ground in and the stem seals replaced.

Would these be better to fit or should I get my existing 3.5 heads checked, that they're flat, and refit them? I would probably use the Real Steel typhoon camshaft and RRoads lifters.

Would it be worth matching the inlet manifold ports to the heads?

Any advise welcomed

[sidecar]

Hi

I'm fitting a 3.9 block to replace the 3.5 engine in my Capri. I've been offered a set of 4.6 heads which need the valves ground in and the stem seals replaced.

Would these be better to fit or should I get my existing 3.5 heads checked, that they're flat, and refit them? I would probably use the Real Steel typhoon camshaft and RRoads lifters.

Would it be worth matching the inlet manifold ports to the heads?

Any advise welcomed

The 4.6 heads will fit and will be better. They will have 28cc chambers so you can use composite gaskets without losing any compression.

[mgbv8]

As Pete Say's...
They will be much better than the old heads. I wouldnt bother port matching unless you intend to tune the nuts off it.
The typhoon and rhoades are a pretty good combo for a road car.

[katanaman]

Depends what 3.5 the heads are from? 4.6 heads don't flow any more than SD1 on heads, the only advantage they have is better valve stem seals.

[nigelv8]

Thanks for the comments.

The heads are SDI heads but I thought the 4.6 heads were meant to be a slightly better flow as standard, or have I got this wrong.

[ChrisJC]

Thanks for the comments.

The heads are SDI heads but I thought the 4.6 heads were meant to be a slightly better flow as standard, or have I got this wrong.

I believe that to be a myth.

Chris.

[JSF55]

Tell us more chris? they seem to demand a high price for 4 less holes

[CastleMGBV8]

The later heads have waisted stem valves the sd1 didn't but the Vitesse did.

Kevin.

[katanaman]

4.6 heads have a thicker casting so ultimately the ports can be opened further. This is their only value over SD1 heads which is a good thing but only if your going all out on head work. If you build 4.6 heads with wasted stem valves they will flow marginally more than wasted stems in SD1 heads but it is marginal. They only fetch more money generally because people believe they are a performance upgrade on their own which they aren't.