4.2 tuning

[Byff]

I seem to remember that the one tuning advantage that can be gained with a 4.2 is something to do with the induction, throttle bodies or something about the way the engine breathes. Can someone enlighten me? I seem to recall Joolz mentioning a good mod for a 4.2 to get more power - other than dropping a 4.5 in of course.

I'm quite happy with the amount of power my engine gives, but it's always nice to know that the possibility is there.

[trackcar]

it's the small butterflies in teh 4.2 that cause the problem .. you cna get some of the sidavantage back by flow work on the inlets, but typically only 12-15bhp at best. Unless you change the induction the 4.2 is incredibly difficult to get extra hp from..

[Extra 300 Driver]

Doesnt BOSSCERBERA run the 4.2 inlet system?

[trackcar]

If it does I would doubt it's on std butterflies, they just don't flow enough .. the first thing would be to machine the inlet manifold out (fairly straightforward to be honest) and fit the 4.5 butterflies .. that would get you straight up to 4.5 levels with the added benefit of the shorter induction length that's been proved so effective .. that would be a good mod for the 4.2 boys.

[Cooky]

Sounds good,
I'd be up for a bit of that, any idas of cost Joo?
would you loose any of the "smoothness" that a 4.2 enjoys and would it effect the way the revs pour in?

[diycerb]

Last time I had my manifolds off I looked at doing this, but there doesn't seem to be much meat on the castings. For now I've dremelled the sharp lip of casting just behind the butterflies away. When I find a set of dividers that fit i'll measure the thickness of the casting properly.
My thought was that Bosscerbera uses manifolds that look like 4.2 but are in fact unique castings. Can't believe you'd get 500bhp from 4.5 (46mm???) butterflies.

[trackcar]

Hi Richard ..

yeah getting rid of that step is a good move, as is thinning the spindles down and also opening out the narrowed section just as the manifold ends and contacts the heat barrier to the head face .. do all that and up the fuel pressure about 5% and you'll gain 12-15bhp on a good car with no other mods If you have time on your hands it's well worth doing

[diycerb]

Hi Joo's
Wasn't brave enough to grind the spindles but did do the manifold skirts. Have to have a think about upping the fuel pressure, I suppose adjustable would be the way to go.

I'd like to fit 4.5 induction, don't think it would make 4.5 power as I believe the heads aren't as good (inlet valve more shielded???) but hey no doubt I'll take the heads off at some point so could machine them aswell. Red rose 4.2!!!!

The best improvement is making sure the throttle linkage and pots are set correctly. Making sure both both butterfly banks go fully open.
Rich.