> -----Original Message-----
> From: jon@dakota-truck.net
>
> In the August 2008 issue of Mopar Muscle there's an article on a
> '69 Satellite into which the owner transplanted a 318 Magnum from an
> '02 Dak. (http://tinyurl.com/5amxf6) In the article, the owner of
> the vehicle says that the Magnum engines have a "fundamental flaw"
> with the fuel system. He says:
>
> "Chrysler feeds the driver-side bank of injectors from the fuel pump
> in the tank, and then they use a very skinny hose to go between the
> fuel rail on the driver's side to the one on the passenger side. So
> when you fire up the engine, cylinder numbers five and seven fire.
> When they fire, the whole pressure in the rail drops momentarily, and
> then they want to fire cylinder number two, which is as far away as
> you can get from that spot. So the fuel pressure drops over there,
> and that cylinder always ends up lean."
>
> He says used a prototype set of fuel rails from Ross Machine
> Engineering to cure the "number two cylinder starvation problem".
>
>
> Something about the above didn't sound right to me, so I thought
> I'd run it by you folks and see what you thought. (Plus, there
> were a few goofy things about the car that kind've made me question
> the guy in general; for example, his intention with the EFI system was
> to set up the car for the best fuel economy as opposed to power, and
> yet when he installed an aftermarket 5-speed, he chose one with a 1:1
> top gear instead of an overdrive...)
>
>
> I'm certainly no fluid engineer and don't even play one on TV, but
> his explanation doesn't make sense to me. The distance between the
> fuel feed and a particular injector shouldn't matter because the
> entire rail is pressurized and it is the pump which is creating the
> pressure. Its not like the injectors are sucking fuel out of the rail
> and then the pump has to kick on and make it back up or something.
> The injector is just a gate; the only reason fuel comes out when it is
> opened is that the pump is pushing fuel up into the rail from the
> tank, so as long as the crossover tube outflows any individual
> injector, the pressure in the fuel rail should remain the same at all
> times. Also, his claim about having #5 and #7 firing together
> dropping the fuel pressure a bit doesn't seem right either. Its not
> like they are firing at the same time, the firings are spaced out
> equally across all 360 degrees of engine revolution. So, if firing
> two injectors sequentially was enough to drop the fuel pressure in the
> rail slightly, then the next firing would drop it a little more, and
> so on until soon you'd have no pressure at all. It is my contention
> that if even a single firing is big enough to drop the pressure in the
> fuel rail such that it is not back up to its pre-fire pressure by the
> time the next injector opens, then your fuel pump is not big enough or
> you've got some other restriction prior to the fuel rail.
>
>
> Anyway, does the above make any sense, or am I just off my game
> today? :-) For those of you who have torn into a bunch of these
> engines (Bernd?), has it been your experience for the #2 cylinder on
> Magnum engines to be running lean?
>
> -Jon-
Well Jon, not only am I not an engineer, I haven't even stayed at a Holiday
Inn Express. ;-) However, I (and others I will mention) do have real
world experience with these engines under extreme conditions.
First of all, let me say that I agree with your perception of how the fuel
rail is pressurized and what little effect the firing of an injector has on
the system. While I can imagine a situation where someone may have a
large enough engine and large enough injectors to tax a stock system's
capabilities (fuel rail or pump), I can't imagine it being very common or of
any concern to the vast majority of us.
Since you mentioned Mopar Muscle as the source of this story, I will add
that there is a thread on a Mopar forum questioning the validity of another
Mopar Muscle article that proclaims the stock hydraulic roller lifters in
Magnum engines are too heavy and prone to failure at rpms above 5400. For
those interested, look here:
http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=4594789&an=0&p
age=1#Post4594789
Now, for examples of why I agree with you on this fuel rail issue, and
disagree with Mopar Muscle on the lifter issue, let me just say that my Dak
has totally stock fuel rails, injectors and lifters....as does an
acquaintance of mine, Bruce Flodin, a Stock Eliminator, 318 Dakota, racer
from BC. He shifts at 7000 rpm while I shift at 5800-6100....depending
upon conditions. I run 12.90's in the quarter, while Bruce runs high
11's. Here's a qualifying run of his at a NHRA Division race:
(Bruce Flodin, Abbotsford, B.C., CT/SA '95 Dodge, 11.989)
Basically, I don't put a whole lot of stock in much of anything the Mopar
rags write about. When it defies common sense or my experience, I just
call BS on the whole thing and move on. LOL
Ray
http://www.dragtruk.com/ENTRIES/20KM1FD2KWBP.html
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