Don Malling wrote:
> I did not mean to ask about the value of PI vs ZS. My real question is
> the value of triple ZS over stock dual ZS.
>
> Many folks say dual ZS are all that is required -- triple ZS will not
> add much. Yet Kastners manual shows a real difference between the stock
> dual ZS and PI, and he implies that PI vs ZS is the only difference
> between the two engines on the chart. This tells me that there may be
> some possible performance improvements to be made over the stock dual ZS
> carbs.
>
> What does triple ZS accomplish in terms of Kastners dual ZS vs PI chart?
> That is, how much of an improvement is triple ZS over stock dual ZS?
> This is a street engine not a race engine. If I can't feel the
> difference, I'd probably rather spend the $300+ elsewhere.
Don,
Given that this is a street engine that is very rarely driven in anger, I
would spend the $300 elsewhere, unless you want the looks of the triple
carbs and all that shine.
A perennial sin (especially in the hot-rod world) is to over-carb an engine.
The first major step to be made is to simply examine the air requirements of
a motor to figure out how much carb one needs. How often do we see 750 cfm
Holleys on a street-driven small block V8 when they really need only a 600
cfm Holley? One down-side of over-carbing is poor throttle response.
I do not know what a ZS flows; I'm *guessing* it is around 150 cfm (Bob?
Vance? Dick?). If my guess is right, then two of these will flow 300 cfm.
Three of them would be 450cfm, which is more than this motor needs except a
worked motor at really high rpm. For comparison, 40mm DCOEs flow over 200
cfm, so triples would flow 600 cfm, which is WAAAAY more than this motor
could ever use.
However, what more inlet "ports" (i.e. more carbs) do offer is better
atomization. Poor atomization means that the gas particles are larger,
which burns poorly (because they have less surface area than a similar
volume of smaller particles). Poor burning means your motor runs lean yet
consumes more gas! Poor atomization occurs if there is a lot of turbulence
in the flow, causing pockets of low- and high-pressure which in turn leads
to the small particles of gas coalescing/condesning into larger particles.
Turbulence arises from *any* obstruction in the air flow, including corners,
edges, bifurcation points, speed bumps, chicanes, etc. That's why we prefer
to have individual runners for each cylinder, a virtue of multi-port FI,
because they minimize the obstructions in the air path, thereby minimizing
turbulence.
I gotta get back to work! Cheerio,
Shane Ingate in Maryland
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