The 1969 ZL1 version of the 427 engine was developed primarily for Can-Am racing, where it was very successful in cars like the Chaparral 2F and McLaren M8B. The ZL1 had specifications nearly identical to the production L88 version of the 427, but featured an all-aluminum cylinder block in addition to aluminum cylinder heads, which dropped total engine weight into small block Chevy territory (approx. 575 lb or 261 kg dressed).^{[citation needed]} The engine was also fitted with the new open combustion chamber cylinder heads, a light weight aluminum water pump, a camshaft that was slightly "hotter" than the L88's and a specially tuned aluminum intake manifold. Like the L88, the ZL1 required 103 octane RON (minimum) fuel, used an unshrouded radiator and had poor low speed idle qualities - all of which made the two engines largely unsuitable for street use. [102 octane RON (Sunoco 260) represented the highest octane gasoline sold at common retail stations.]

As impressive as the ZL1 was in its day and despite the "larger than life legends" surrounding it, actual engine dyno tests of a certified production line stock ZL1 revealed 376 SAE net HP, with output swelling to 524 Gross HP with the help of optimal carb. and ignition tuning, open long tube racing headers and with no power sapping engine accessories or air cleaner in place. ZL1 DYNO TEST - COPO CAMARO WEBSITE A second engine dyno test conducted on a second production line stock (but recently rebuilt and partially blueprinted) ZL1 revealed nearly identical figures for the various "Gross" conditions.^[7]

Period magazine tests of the ZL1 were quite rare due to the rarity of the engine itself. "High Performance Cars" tested a production line stock but well tuned example and recorded a 13.1 second/110 MPH quarter mile, which correlates quite well with the previously referenced 376 Net HP figure. "Super Stock and Drag Racing Magazine" recorded an 11.62 second/122.15 MPH quarter mile in a ZL1 Camaro that was professionally tuned and driven by drag racing legend Dick Harrell, although that car was also equipped with open long tube S&S equal length headers, drag slicks and minor suspension modifications. Using Patrick Hale's Power/Speed formula, the 122.15 MPH trap speed indicated low 11 second ET potential (e.g. with larger drag slicks) and suggested something on the order of 495 "as installed" HP in that modified configuration. This large difference in power suggests that the OEM exhaust manifolds and exhaust system were highly restrictive in the ZL1 application, as was also the case with the similar L88..Sal C

 

I have the same engine (1969 L36) and am in the process of reassembling my engine after a stock rebuild. I ordered a Comp Cams Magnum 280H and as I try to decide if the stock springs are going to work with this cam and it's 0.520 valve lift, I am having second thoughts. I have new lifters, pushrods, timing set and the heads were done with new bronze guide inserts, valves, stem seals, etc. The existing cam is OK according to bench measurements of lift but I am tempted to give it a bit of a lopey idle...

 

BTW the carb was originally a Rochester Quadrajet 7029215 EH. They are extremely difficult to find an original because they were a one year carb and only used a few cars including the Corvette L36 with Manual Transmission. There are many carbs that are very similar and it is not too hard to have one rebuilt with the correct metering/calibration to match the 7029215 EH.

 

Photo below is current state of assembly with my son doing all the hard work and me supervising, as it should be.