Fred, the new heads have a chamber that ccs 28-31. Just did mine, 29 to 29.5.
SD1 heads are about 36cc, about 1/2 point compression diff. New heads have a
litle biger ports, but less than 10% diff. Valves are the same size. John
FOSmith@aol.com wrote:
> Franc Buxton <fab@dcs.warwick.ac.uk> writes:
> In general, what are the specification and feature differences
> > between 3.9 s and 4.0 s? Are they the same bore and stroke dimensions?
> > This is one little part of the Rover puzzle I would like to learn more
> > about.
> Hi all, I'm new to this list. I have a TR8 for which I'v just purchased a
>'98 Rover 4.0 short block (with cross bolted mains)to replace my 3.5. I'm now
>pondering what to do about heads, etc. My question is this... Besides the
>deletion of the lower row of holes for the head bolts, what are the
>differences between the 4.0 and 4.6 heads and the earlier (SD1 type) heads.
>Is the combustion chamber size the same? How about the flow characteristics
>and valve sizes? Do the 4.0 and 4.6 engines use the same heads? If the newer
>heads are a significant improvement I want to try to track down a pair. If
>not, I'll just use the heads from my 3.5. Any information would be greatly
>appreciated. Thanks,
>
> Fred Smith
> Orinda, CA
> > T I A.
> >
> > Regards,
> >
> > Dave Kernberger
> >
>
> I have just checked with some local Rover contacts of mine, and
> for general information, the difference between 3.9 and 4.0 engines is
> this:
>
> The 'interim' engine is a 3.9 - actually 3947cc, with some of the
> improvements applied to the 4.6, namely the same 'crossbolter' block, but
> without the crossbolt holes being drilled. It may or may not have main
> bearing caps suitable for crossbolting, some of the earlier ones had old
> pattern caps which did not sit flush with the sides of the housings, so
> nowhere to drill the holes. (I know that bit from experience!) The main
> journals are of the smaller size, despite the common block with the 4.6.
> The 'interim' front cover has the new-design concentric oil pump on the
> crank nose, but has a distributor hole. A worthwhile modification to any
> Rover V8, if you ask me! (see website). This engine came equipped with
> Lucas type 14CUX 'hotwire' fuel injection.
>
> The '4 litre' engine is the fully-evolved version, distributorless
> and with the large-journal crank. Capacity is the same at 3947cc, as are
> bore (94mm) and stroke (71mm). This one uses the Lucas 'GEMS' engine
> management system.
>
> Hope this helps/informs!
>
> Regards,
> Franc.
>
> (Have I ever contributed here before, or just lurked? If the latter,
> Hi, guys, interesting reading - keep 'em coming!) F.
> --
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> W(-(+)^^(+)-)W
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