Anyone have an original 69 L/78 with THM400 ?

[Hotrodpaul]

Top Pic:



Paul

[nuch_ss396]

Thanks Paul!

Steve

[nuch_ss396]

Follow-up on this topic:

Through my investigation thus far, I have arrived at the
following. If anything is incorrect, please clarify for
me.

1) It appears that the 4346 Holley did not incorporate the
use of a special throttle arm for THM400 applications.
No one can attest to the existence of another part number
for a 4346 throttle arm. So, manual and automatic cars
used the same carb. - correct?

2) It appears that the idle stop solenoid used the bracket
that mounted to the intake manifold with two studs.
Every L/78 & COPO example I can find uses that same
setup. I have looked at Camaro's, Chevelles, and Nova's.
Has any member seen an original setup the differs?

3) The first reply to my initial question includes an
image of a COPO Chevelle restoration. The 4346 throttle
arm clearly shows the existance of a ball stud. My 4346
for my Camaro does not have this stud. So, how can they
both be 4346's? Is there a separate part number for the
Chevelle throttle arm vs. the Camaro & Nova throttle arm?


Questions yet to be resolved:

1) If the ZL-1 used the same idle stop solenoid and kickdown
setup as was used on L/78 & COPO Camaro's, was there any
difference in relation to the 4296 Holley that was
used with the ZL-1? I'm betting that the 4296 had a
very different throttle arm. Does anyone here have a
good, clear image of a ZL-1 w/THM400 carb/solenoid
assembly?

2) Two ZL-1 Corvettes were also produced. I believe they
also used 4296 Holleys, as did the L-88's - correct?
Didn't the Vettes use throttle cables and thus a ball
stud on the carbs throttle arm? As we know, the 69
Camaro used a throttle rod, so no ball stud was needed.
Was the ball stud installed on all 4296 carbs anyway?
If not, wouldn't that indicate a separate part number
for Vette vs. Camaro? How does this fit in with the
4346 throttle arm observation?

3) Most ZL-1's were mid-year productions - right? I have
been told that a few early ZL-1 Camaros were produced in
January. It was also started to me that 4296 Holley's
have not been found with dates that would support a
January build. Can anyone dispute this? Lastly, did
all ZL-1's use the 4296 Holley? Were the early ZL-1's
possibly all manual transmission cars anyway?

This just keeps going, and going, and.....

Steve

[William]

The '69 4346 carb is the same for manual/auto applications. '70 could be different; there are differences between manual/auto carbs for the Z28.

The 1969 Camaro assembly manual shows the bracket/solenoid setup for L78 on page A10 of the M40 section.

Most ZL1s were built with 4346 carbs, possibly because the ducted hood air cleaner vent tube interferes with the rear pump on the 4296. The only known photo of an automatic ZL1 Camaro shows no solenoid.

The first two ZL1 Camaros were automatic, delivered Dec 31, 1968. The remainder of Gibbs 50 were built and delivered during March 1969. 22 0f the 69 were automatic.

We swapped out a 4346 for a 4296 on an automatic ZL1 and no modifications were required. It is a direct bolt-on.

[nuch_ss396]

Bill,

Are you absolutely sure about the 4346 Holleys being used
on the ZL-1's? I've never heard that before. Also, why
would the ZL-1 Camaros get 4346's and the two Corvettes
get the 4296's? I would expect that a 750 cfm single
pumper ( 4346 ) would be severly under jetted for a ZL-1.
I know the L-88's got the 4296's as well. And the ZL-1
nudged a little more power out than the L-88, didn't it?

Your theory on the special ducted hood is interesting.

Just a fast question for you on that topic if you don't
mind. I believe all ZL-1's came standard with the ZL/2
induction system - correct? Back in the day, for serious
racing, wouldn't the second thing done to the car be to
remove the ZL/2 induction setup and put on a monster scoop?
Headers had to be first, then followed my a bigger-bader
Holley.

Why would Chevrolet go through all the trouble to build the
ZL-1's and then put a 750 single pumper Holley on it? It
just doesn't seem to make sense.

I'd like to keep this topic going. This development was
not one I expected.

Lastly, as you have indicated, the lack of use of the idle
stop solenoids on the ZL-1's would make sense from another
perspective. I don't think that Chevrolet expected any
ZL-1's to be cruisers - did they? Idling probably wasn't
too big a concern for these cars - huh?

Steve

[William]

The ZL1/4346 story is documented by two sources. The August 1969 Hi-Perf Cars test of #3 with engine bay photos with the air cleaner removed. When Bill Porterfield was researching the car he obtained the orginal photo and had it englaged such that the carburetor part numbers were legible. This was recounted in John Hoopers 1991 Camaro book. Fred Gibb was interviewed for the story and recalled that the #1 car failed tech at at AHRA meet because it did not have the 850 carb as listed in the AMA specs. Chevrolet sent him correct carbs for the ZL1s he still had in stock.

The OE "flat bottom" ducted hood air cleaner as used on SHP bbs and Z/28s had a 90º vent tube. If mounted on a Holley double-pumper carb the tube will contact the rear pump lever. Chevrolet later redesigned the tube with 2 45º bends to clear the pump. I do not know that this was why the cars were built with 780s.

The ZL2 special ducted hood was included with COPO 9560 and 9561. Racers often removed the valve and did not use a filter.

[ANDY M]

Ed Cunneen's book also includes the story about the AHRA incident, exactly as stated above. The 4296 carb was the one spec'd out for the ZL1.
According to Ed, the first 52 ZL1s and all L-72 cars came with the 780 Carb (p/n 3959164GE). The ZL1 cars got the 780 due to short supply from Holley.
Gibb then got a shipment of the 850s and they were swapped out.