Race Engine Forum UK

Guy, firstly thanks for a great forum. I only discovered it a couple of days ago and have been surfing it since.

I sprint/hillclimb a Morgan. I'd love to tell you that it's Lampreda-powered, but these are few and have other problems, in Morgan terms. But it's a 2.0 zetec Dunnell unit that has a very roadable torque curve.

A few adaptations were needed to make it work in the Morgan, and I now need to source a custom-built exhaust manifold that does the unit proper justice. I intend this to be 4-2-1, to maintain low-end torque, but I could not get a big 4-1 collector through the chassis hole anyway.

It seems so obvious to me that 1 and 4, and 2 and 3, should be paired on the primaries so that they are connecting exhaust cycles that are 180 degrees apart.

But have you ever seen anyone experiment with other pairings? Someone told me (were they joking?) that there was a trend in WRC to pair 1 and 2, and 3 and 4? And that Raymond Mays had tried this in the '50s?

I cannot explain this, but intuition tells me that if this were to work the primaries would have the same length as a conventional 4-1?

Thanks for your view, Colin

Hello Colin

thanks for your kind comments and I am very pleased to have non-Fiat here.

Traditionally 4-2-1 are arrayed so that the primaries of two linked cylinders are as far as possible apart in the firing order ie: for firing order 1342, 1 and 4 are 360 crank deg apart and so are 2,3. This ensures that when 1 exhausts 4's ex valve is closed and the pressure wave reflects off it.
There is no reason why 4-2-1 other configurations might not work, but I'd be looking for detailed software analysis to make sure it was OK, because if you get an outgoing pressure wave going back up an adjacent primary pipe to a cylinder that is on an exhaust cycle too (especially if it's near tdc and the overlap phase when inlet and ex are both open) the conflicting pressure waves will cause chronic interference to the induction and firing cycle. This is seen quite commonly on 4-2-1 systems where the primary pipes (or indeed secondary, to a lesser extent) are too short.

I don't know the firing order of the WRC units to which you refer, and even on your motor, you don't have to run 1342, I have known for example of engines set up to fire 1&4, 2&3 simultaneously. I imgaine that with the systems you mention the primaries might be fairly long and perhaps unequal in length.

GC

Guy, I'm assuming that we are still talking 1-4-3-2 firing order, as the discussion was in the context of zetec units.

Why do you say that you would expect the primaries to be unmatched (unequal length)?

And I guess the secondaries would still be matched?

thank you, Colin

well, most in line 4 cylinder petrol engines are 1342, is the Zetec something else?

GC

Guy, sorry. My fingers were not firing in the right order, maybe something to do with the temperature change in Edinburgh at this time of year - I should have said 1342

thank you, Colin

Colin, hi

I would not know what to expect in terms of bores, dimensions if
running a 4-2-1 exhaust at anything other than conventional paired primaries 1&4, 2&3 on an in-line 4!

I wouldn't even guess at it, sorry! And I would not trust anyone reckoned they could do it well enough to make a difference and who did not run software analysis on it! I mean something top-level like Virtual 4T.

Sorry!

GC

Guy, thanks for thinking about this. You have entirely confirmed my worse fears...

This is a complex area, and not one in which to improvise. Without the aid of some complex modelling, there is a reason for that 'traditional' pairing.

thank you, Colin

i'd be happy to make you a bespoke manifold- i would need full engine specifications to allow me dimension the the system first and would also need your moggy to build the manifold on

Just to close this one out for anyone still subscribed.

Guy, thanks for your help on sizing and design. Ended up with a 4 into 1, with waaaaaay-loooong primaries of 32 inches. Simon Hall built this for me, combining his experience of Morgans and his willingness to argue the calculations with me (and weld like a demon too).

Funnily enough, the nasty resonances I had been suffering about 2700 rpm all disappeared, and I need not have been worried about a 4-1 taking away from the smoothness of delivery of this engine.

And we did ceramic coat it. Although the aim was very much about helping to control under-bonnet temperatures rather than look pretty or improve flow. I have to say that it's impact is remarkable.

Now on to tidy up the intake side....

thank you, Colin

Photos please!

GC