Idiots guide to swapping RV8 cylinder heads?

Post by **scudderfish** » Fri Sep 09, 2011 1:14 pm

I've never been inside an engine. I've swapped my inlet manifold, but that's about it. I've got a 3.5 RV8 which is now running homebrew EFI/EDIS with an Offy 360 inlet manifold, and at a rolling road session it apparently produced 160bhp. I've been advised that if I swapped the standard heads for P38 ones, I'd see benefits. Not having taken heads off before, how should I approach this. I realise that the P38 heads are 10 bolt vs 14, and I'll need new gaskets, but will it work with my inlet manifold? Will they just drop on, or am I making work for myself setting up pushrods and rocker arms? Help!

Regards,
Dave

ChrisJC · Post by **ChrisJC** » Fri Sep 09, 2011 7:28 pm

The P38 heads aren't any different to the later 3.5 heads in terms of ports & valves.
If you fitted a P38 head and kept the tin gaskets you'd raise your compression ratio a bit, but then you'd have to fettle the rocker preload to compensate for the fact that the pushrods will be a shade too long.

Chris.

mgbv8 · Post by **mgbv8** » Fri Sep 09, 2011 8:15 pm

I guess we need to know exactly what heads you have??

I fitted later 4.6 heads to a very early RV8 that had pre SD1 heads and it made an extra 20hp on the dyno....

Post by **scudderfish** » Fri Sep 09, 2011 8:49 pm

My engine came out of a carbed 1984 SD1 and has whatever heads that car had.

Regards,
Dave

kiwicar · Post by **kiwicar** » Sat Sep 10, 2011 5:38 am

Hi
you have later head castings, as the P38. If you decide to take them off then remember to loosen the bolts in the reverse order of the tightening them and start only slackening by 1 flat at a time . Remove all gasket bits off both faces.
Best regards
Mike

Post by **scudderfish** » Sat Sep 10, 2011 7:26 am

According to the sticky http://www.v8forum.co.uk/forum/viewtopic.php?t=133 the HRC 2479 heads of the P38 have larger ports and a smaller combustion chamber than my ERC 0216 heads (to allow for a thicker head gasket. I assume that they would form a better basis to start any head work in the future.

sidecar · Post by **sidecar** » Sat Sep 10, 2011 8:35 am

The difference will be marginal in my humble, the main difference between Rover heads is that the early ones had smaller valves, if your valves are the larger ones with wasted stems then the heads are near enough the best Rover ones. The chamber size can be sorted out with a head skim, thats all that Rover did anyway. You can then call them 10 bolt heads by just not using the outer bolts.

Really if you want more power then you have to go down the normal route of gas flowing and camshaft changes. (or bigger engine). Some of the standard EFI systems were not really up to being used in tuned engines, you would need to check that out.

160 BHP does seem about right for a standard engine as far as I can remember, you should be able to get 200-220 BHP whilst keeping some low down torque but it will cost some money!

Darkspeed · Post by **Darkspeed** » Sat Sep 10, 2011 12:18 pm

Having had all the Rover heads on the bench I can say that there is negigible difference between the Late 3.9 and the 4.6 heads with regard to flow even though the 4.6 heads are a better quality casting - the restiction is in the valve throat not the port.

A late 4.6 will flow a little better than an early - non waisted stem 3.5 head. However as the work required to get the heads to flow is not that hard you would be better off having the 4.6 heads tweeked before going through the expense and hassle of swapping them.

Andrew

Post by **scudderfish** » Sat Sep 10, 2011 2:16 pm

Thanks all. I'm not confident enough to have a bash at modding my current heads, so I was looking for a more bolt on solution (spanners yes, grinders no). However from what has been said here and on http://www.v8forum.co.uk/forum/viewtopic.php?t=8675 it looks like my idea won't do much except cause me trouble.

Regards,
Dave