V-8 Int. man. design

[Gary Derian]

> > > > > If you have a LOT of money, you can also :
> > > > > 4 - install a different crankshaft, so that it fires like two 4
in
> > > > > lines connected in V Although this seems strange, it is done on
some engines (Ferrari does for example) because the same effects of 
> > (unevenly) timed flow also come into play in the exhaust. An equal
firing 
> > interval for each banks gives best performance because it allows the
use 
> > of tuned exhausts. The disadvantage is that the engine balance is badly

> > influenced (4 cylinder like instead of V8).
> > > BTW, if you use a single plane crankshaft, you also have to change
> > > the exhaust manifolds, as they should be optimised for the uneven
firing interval.
> 
> > 	I was under the impression that with the single plane crank that 
> > the firing pulses are even on each now and therfore make most current 
> > headers perfect for this?
> 
> Basically, when connecting the exhaust pipes of cylinders with 
> evenly spaced firing intervals, the lenght of each of the pipes 
> should be equal (length between exhaust port and the point where they 
> are connected) for optimal results. This way the same conditions 
> apply to all cylinders, especially with respect to the amount of 
> residual gasses trapped in the cylinder after the exhaust valve 
> closes.
> 
> For a standard V8, the uneven firing interval will make a different 
> geometry optimal, and it is probable that this has been taken into 
> account already. Therefore these manifolds are likely to be 
> suboptimal if a flat crankshaft is used.
> 
> Evert

	Normal log type V-8 exhaust manifolds are designed for low cost and
packaging but there is some consideration to firing order.  Chevy small
block ram horn type manifolds which were used for years on Corvettes are
particularly bad in the way cylinders 5 and 7 dump into the same branch. 
Newer Camaro manifolds place the outlet between cylinders 5 and 7 to help
mitigate this.
	An excellent solution for standard 90 degree crank V-8's with a 18436572
firing order is to connect exhaust ports 1 and 5, 3 and 7 on the drivers
side and 2 and 4, 6 and 8 on the passenger side.  This provides consistent
but slightly uneven pulses in each of the four branches and prevents
adjacent firing cylinders from exhausting into the same branch.  Then take
two downpipes from each side eventually merging into dual or single
exhaust.  The old tri-Y type headers use this principle and it is also used
by Mercedes and BMW  V-8 engines.  
		1 8 4 3
		 X    X
		6 5 7 2
	For a flat crank, 1 and 7, 3 and 5 on the driver side and 2 and 8, 4 and 6
on the passenger side will provide the best tuning.  The header for each
side looks like a 4cyl header.
	Chevrolet and several NASCAR teams have done much testing with flat cranks
and 180 degree headers.  I believe that the results are not worth the
effort or vibration.
	The above cylinder numbers and firing orders are based on the small block
Chevy.  Other engines exhaust will look the same but may refer to different
cylinder numbers.

Gary Derian <gderian at cybergate.net>