<VV> Throttle linkage

[Tony Underwood]

At 02:44 hours 11/18/2004 -0600, R. Byers wrote:
>I have just installed 140 engine into my 62 Monza.  The engine, 
>professionally built, with ported heads and an Isky 270 cam,  was 
>originally installed in an automatic 65 Corsa that was never 
>completed.  The engine has a Holley 4412 (500 CFM).  As it has been sitting 
>and will probably be rebuilt, before finishing it, I was thinking of 
>changing to a Holley 1850 (600 CFM) hoping the low speed throttle response 
>would be better.  If anyone has experience with these, I would like to hear 
>about it.


Throttle issues aside for the moment:   


You will NOT care much for the 600 Holley.    Trust me.    It will suck.
Someone else I once knew insisted on trying this, thinking that bigger is
always better.   There was not a happy outcome.   


I've run a variety of 4xbbl carbs on Vair engines.   The bugspray Holley is
a compromise and frankly still not the best carb for a Vair center-mount
intake.   In fact, it's hard to come up with *any* 4xbbl carb that will
work *well*.   

I ran a Holley 390...  it was acceptable as long as the weather was
relatively warm.   In cool damp fall weather typical of what infests this
area the carb and intake runners would actually frost up until the engine
was fully warmed.   Even then it was still a dog to drive.   

I ran a modified Rochester 4-Jet...  it was marginal without a bunch of
fiddling and playing with metering rods and springs.   I had better luck
after I disconnected the secondaries... whereupon the 4-Jet did fairly
decent work which indicated that it was still too large for a Vair engine
if you nailed it.   

I ran several AFBs.   

One was a '66 vintage 580 cfm, not too bad once I did the metering rod
thing like the 4-Jet.   Same problems on cool damp mornings, and it bogged
often.    However, when I disconnected the secondaries ala the 4-Jet it
actually seemed to work reasonably well, *After* much fiddling with
metering rods again.    

One was a '67 vintage 750 cfm, with the secondaries disconnected.   No
point in even trying to run it "unneutered".    It bogged, required a light
touch to get the car moving without hiccups but midrange wasn't too bad and
it did well when nailed, once you got the rpm up.   

One was a '64 vintage 450 cfm originally on a 273 Mopar in a Barracuda.   I
ran this one straight up with some metering rod adjustments.   Best
over-all performance of the bunch.   Still bogged if it wasn't "feathered"
on takeoff, but once the car was rolling and you nailed it, the carb worked
well and it would pull nicely.  Top end was very good, actually made a bit
of "carb racket" whoop when it was pulling hard.    It was also the easiest
starting carb of the batch, hot or cold...  bump the starter and it was
running right there right now.     Over-all, this smallest AFB carb was the
best performing of the whole batch of 4xbbl carbs.  Even at an "advertised"
450 cfm it was still a bit large but it was the closest match and it was
easy to tune and mechanically simple.   

It is my humble opinion that the typical Carter AFB is one of the best
carbs ever to land on any engine to ever mount a 4xbbl.   It's worth
mentioning that the venerable AFB remains in production to this day in
aftermarket licensed variants via rights purchased from Carter, and has
managed to nab the "most popular carb" among the street rod and musclecar
hotrodder crowd.    Unfortunately, there's no longer a 450 cfm variant
available so if you want one of these dinky AFBs you'll need to chase down
an early '60s smallblock Mopar variant or one of the AFBs fitted to the
Lancer-GTs with the aluminum slant-six engine, which also used the 450 AFB.
  Expect trouble turning up one of these little gems.     


A 600 cfm Holley is gonna suck.   Crack the throttle and intake vacuum will
drop and the power valve is gonna pop wide open and mixture ratios will be
all over the map.   


If you want to run a Holley, I'd stick with the 390 cfm.    


Note that I haven't even granted that 4412 2xbbl carb with an honorable
mention.   

That would have to be the WORST carb to put on a Vair 4xbbl intake I could
imagine.  Why anyone would wanna run one of those things on a Vair engine
escapes me.   I have one of those carbs...  it's also the same thing that
the Chrysler 440-6pak engine runs in the center mount position and it's
plenty for most around town driving... that's on a 440 ci hi-perf engine
rated at 390 hp.   In short, it's appx three times too large for a Vair
engine under the best of conditions.  That 650 cfm Holley 1850 would be a
walk in the park compared to that 500 2xbbl.    That alone should tell you
something.      


If you disconnect the secondaries on the 1850 Holley and get a 2.5" power
valve for the primary metering block, you might get away with it.    


Now:   

If you feel like experimenting, you might look around for one of those
small 4xbbl carbs that Mazda was putting on earlier variants of the rotary
engines.   I recall they were in the area of around 400 cfm which is closer
to what a Vair engine would appreciate... providing you could turn one up.
   I fiddled with one while it was on the Mazda rotary engine, didn't seem
too bad once you got around some of the smog gear etc.     

Anything you're likely to put on a Vair engine using one of those intake
manifolds is going to require some tomfoolery with adjustments of
jetting/metering rods and power enrichment circuits.    Gettin g it dialed
in will be a learning experience that will reap rewards if you stick with
it.    

Have fun.   


tony..