V-8 Int. man. design

[Gary Derian]

----------
> From: Paul (BRAAP) Ruschman <prusch at ix.netcom.com>
> To: diy_efi at coulomb.eng.ohio-state.edu
> Subject: Re: V-8 Int. man. design
> Date: Wednesday, 28 May, 1997 1:30 AM
> 
> Gary Derian wrote:
> > 
> > ----------
> > > From: Paul (BRAAP) Ruschman <prusch at ix.netcom.com>
> > > To: diy_efi at coulomb.eng.ohio-state.edu
> > > Subject: V-8 Int. man. design
> > > Date: Tuesday, 27 May, 1997 1:44 AM
> > >
> > > I am new to the list and am currently designing my own EFi Intake
> > > manifold for my Chev 350 powered Datsun Z car. I plan on using the
> > > L-jetronic.
> > >       My question.
> > >       My plan is to make a manifold that utilizes two plenums, one
per bank of cylinders. Knowing that the V-8 fires as if it were 4 V-twins
> stacked instead of two banks of four cylinder engines does this effect
> the intake air flow to the individual cylinders? Do I need to design the
> intake like a dual plane 180 degree carb manifold that plenums the two
> outer cylinders of one bank with the inner two cylinders of the other
> bank?
> > >       I feel that this being injected that it shouldn't make much
> > > difference fuel wise, but would one cylinder rob the available air
the next cylinder is supposed to recieve?
> > >
> > >               Thank You,
> > >       Paul (BRAAP) Ruschman
> > >       
> > 
> > Uneven pulsation will affect the intake flow and the averaging that the
air flow sensor sees.  Use two plenums but not for one bank only.  
> Instead, connect cylinders 1, 4, 6 and 7 to one plenum and 8, 3, 5, and 2

> to the other.  This will make each intake stroke at 180 degree intervals 
> and provide balanced flow.  For best performance, the exhaust should also

> be connected this way but the gains are small.
> > Gary Derian <gderian at cybergate.net>
> 
> 
> 
> 	What about doing as I proposed originally with two seperate 
> plenums, one per BANK of cylinders, and adding a balance tube lets say at

> the rear of the plenums or in the middle or at say the runners for 
> cylinders 7 and 8?
> 
> 		Paul (BRAAP) Ruschman
> 		http://www.datsuns.com/paul.htm
> 	        http://www.datsuns.com

	As you pointed out in your original post, a plenum per bank would result
in uneven pulsations.  A balance tube would help but there would still be
very complex sound wave patterns.  I don't know what would happen.  It may
work well enough but if well enough were the goal then why bother?  With
two plenums, evenly balanced, a balance tube between them could be useful
in changing the vibration characteristics of the system.  Porsche used such
a system on the 928 and later on the 911.  At certain engine rpm, the two
plenums were independent creating separate Helmholtz resonators.  I believe
this was mid range.  At high and low rpm, the balance tube was opened
creating a different natural frequency.  I don't know the details but the
theory is interesting.

	Most of the time, these complex intake systems are used to improve the low
speed torque of the engine.  With a 350 in a Z-car you have enough torque
to spin the tires in low gear anyway.  After that, the rpm is kept high. 
So there may not be much point in tuning for optimum low speed torque.  The
Chevy LT1 and LT4 intake systems have a single plenum with very short
runners but their reasons are cost and packaging.

	Just my thoughts.

Gary Derian <gderian at cybergate.net>