The V8 Owners Forum -

Interesting, so if I blueprint it to 10:1 that should make a difference. I then need to choose nice heads as I'm not up for porting them myself. I was looking at some v8developments stage 3 heads as I'm not sure stage 4 would benefit it any further. I've also been researching about merlins but seem to have some fitment issues; exhaust, rockers touching covers etc. Best cam to use in this application? What's everyone running in theirs? I think I'll get some hedman manifolds for it too. How much torque do we think this set up could produce?

If you want a good strong mid range engine - Stage 3 heads and a H218 cam - High static compression ratio's with a high torque cam just creates a requirement for premium fuels 9.8 will be a good figure to aim for.

That's good to know. Is the reason I can't go too high on the compression with a high torque camshaft because there isn't much duration therefore the cylinder pressures will be a lot higher than they would be with a high duration cam? What sort of torque figure do you think I could achieve with that?

Just been researching the 218 Kent and it says that the power band is from 1500-5000 as the disco is an auto and the
Stall point is 2000 rpm this should be good from pull away?

If you have a cam that allows early cylinder filling like a torque oriented camshaft you need a lower compression, if you have a high revving engine you can use a power oriented camshaft with more duration, you are correct in thinking that a torque camshaft will not work with high compression
With high compression you need overlap to run on regular fuel. You should aim for a lower compression and less cam to achieve what you want.

Stating figures is a guessing game as it depends on so many other factors but if you want torque and mid range that's the combination I would suggest. You will of course need to have the intake and exhaust to support it.

Intake I'm thinking of just keeping the banana branch Thor manifold and the exhaust I'm going hedman 4 into 1 they have 1 1/2" primaries and a 2 1/2" collector. After them it will be sport cats and a free flow silencer all in 2 1/2"

Not hell bent on figures I want the disco to have a decent improvement and keep up with modern equivalents.

If left stock the inlet manifold will hurt the numbers as the runners are are too small. They need a lot of porting work to get them to flow enough to keep up with the heads.

That's what i thought and why I mentioned about getting it extrude honed. That way the runners can be enlarged from the plenum all the way down the the intake port.

Is the Thor inlet different between the 4 and 4.6? Seems odd BMW would have gone to those lengths yet restrict the max BHP? I understood it was done for maximum torque. If after BHP, you might do better with the old inlet system?

According to a mate who has one, the Thor is very good indeed at doing what it was designed for - ie a 4x4. So might be the law of diminishing returns trying to improve it?

DaveEFI wrote:Is the Thor inlet different between the 4 and 4.6? Seems odd BMW would have gone to those lengths yet restrict the max BHP? I understood it was done for maximum torque. If after BHP, you might do better with the old inlet system?

According to a mate who has one, the Thor is very good indeed at doing what it was designed for - ie a 4x4. So might be the law of diminishing returns trying to improve it?

The heads and ports are pretty much the same as the 3.5 Vitesse - Why go to all those lengths!! - they didn't go to any lengths at all apart from what they needed to do to get through the legislation on emissions required at the time.

They had no intention of carrying on with that engine so they did the bear minimum they needed to as the manifold only needed to flow the paltry amount of air to feed the ludicrously low power output of the stock 4.6 .

If you want more than just stock performance out of a RV8 every aspect of the induction needs to be modified.

Think I am going to enquire about extrude honing. I think it's the only way to truly open up the Thor manifolds. Who do people recommend when it comes to top hat liners? I have seen that v8 developments do it. Think I'm looking at about a grand to do it but I'm not going this far with out doing it!

I get my top-hats done at Turner Engineering.

This extrude honing sounds interesting - I have a Thor manifold that would benefit from it. Who does it?

Chris.

Deburring services in Cheltenham seem to do it. That isn't too far from me but there seem to be a few places. Search abrasive flow machining or extrude honing and a few come up.