Anyone have an original 69 L/78 with THM400 ?

[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.

[nuch_ss396]

[ QUOTE ]
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.

[/ QUOTE ]

What an amazing topic this has turned out to be. Since the
majority of the ZL-1's came with 4346's, as you both have
clearly pointed out , why do the Holley part books
list the 4296 as the original carburetor? Obviously, if
they were not shipped in time for assembly, how could they
technically be the correct carburetor?

If the vent tube on the lower side of the ZL/2 setup was a
clearance problem, you would think that Chevy engineers
would have Mickey-Moused a clearance tube, wouldn't you?


Steve