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RPO ZL1

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l88
2.1K views 4 replies 3 participants last post by  blueduck38  
#1 ·
I have only seen two ZL1's, both were in Novas, and Di$k Harrell built a total four, all crate engines.


ZL1 -

"The 1969 ZL1 version of the 427 engine was developed primarily for Can-Am racing, where it was very successful in cars like the McLaren M8B. The ZL1 specifications were 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 the total engine weight into small-block territory (approx. 575 lb or 261 kg dressed).The first Corvette with the RPO ZL1 engine package was built in early December 1968 and featured aluminum closed chamber heads shared with the L88. Both L88 and ZL1 optioned cars continued to be built with closed chamber heads until approximately March 1969, when the open combustion chamber aluminum heads finally were in production and began being fitted to the L88 and ZL1 engines. The ZL1 engine also featured a lightweight 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, actual engine dyno tests of a certified production line stock ZL1 revealed 376 hp (280 kW) SAE net with output swelling to 524 hp (391 kW) SAE gross 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. 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.

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 (180 km/h) 1⁄4 mile (402 m), which correlates quite well with the previously referenced 376 hp (280 kW) SAE Net figure. Super Stock and Drag Racing Magazine recorded an 11.62 second/122.15 mph (196.58 km/h) 1⁄4 mile (402 m) in a ZL1 Camaro that was professionally tuned and driven by drag racing legend **** 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 (196.58 km/h) trap speed indicated low 11-second ET (elapsed time) potential (e.g. with larger drag slicks) and suggested something on the order of 495 hp (369 kW), "as installed", 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.

The $4,718 cost of the ZL1 option doubled the price of the 1969 Corvette, but resulted in a car with exceptional performance for its day. Just two production Corvettes (factory option at dealer) and 69 Camaros (non-dealer option from factory - COPO 9560) were built with the ZL1.

Chevrolet capitalized on the versatility of the 427 design by producing a wide variety of high-performance, "over-the-counter" engine components as well as ready-to-race "replacement" engines in shipping crates. Some of the components were developed to enhance the engine's reliability during high RPM operation, possibly justifying the use of the description "heavy duty." However, most of these items were racing parts originally designed for Can-Am competition that found their way onto dealers' shelves, and were meant to boost the engine's power output.

Beginning in 1969, the highest performance 427 models were fitted with the new open (vs. closed) chamber cylinder heads, along with design improvements in crankshafts, connecting rods, and pistons, adopted from the Can-Am development program.

Chevrolet gave all 427 engines except the ZL1 a torque rating of 460 lb⋅ft (624 N⋅m)."
 
#2 ·
Yes it goes to show that the factory numbers and cars were not as fast as everybody believes they were. There have been multiple dyno tests of rebuilt engines built to spec and they were pretty much on the ratings. Yes, headers, tuning, slicks and drivers made the cars run, but out of the factory, they were not that fast. Like was said, Dickie Harrell did Chevrolet, Ronnie Sox did Chrysler and that was a big part in seeing better et’s out of them. Also, the camshafts back then were junk. A good aftermarket cam woke them up greatly.
 
#3 · (Edited)
A lot of these drivers shallow staged the cars, to get a run at the tree. There's a video on line, with three or four drivers with a Hemi car and the best et's were Sox, then good amateur racer, then test and tuners and Sox is giving tips to the drivers in between runs. Just found it.
 
#4 · (Edited)
I will say again, I am not a mechanic, engineer, nor a tuner; but the guys I knew with those skills often said, "Given the size limitations of the engine bay, there is only so much you can do with a natural aspirated internal combustion engine. All take fuel and air, so there is just not that much difference in a 335 hp 427 and a L88."

Henry "Smokey" Yunick, once told a group of us arguing which manufacturers had the honest engines, "Boys, you can go buy and bring me a Pontiac from the showroom with a stock 421 ci, give me enough money. Then come back in 30 days and I will have it running with the pole sitter at Daytona. Give me a Ford and I can do the same. The hard part is building one with the reliability to go 506 miles."

He is also famous for saying, "The only way you can cheat is if you are the only one that knows. And if you don't cheat, you can't win." Kind of like, two people can keep a secret, only if one of them is dead.

So it was like BracketChev70 said, it comes down to how they are tuned. I have been quoted as saying, "Drag racing is weight, horsepower, traction, and driver." In that order.

May we please continue this polite conversation?
 
#5 ·
Deaks, Thank you, that film is golden! It is a tutorial on dragging at time. I feel like I just got out of the "Way back machine" and time travel is hard on an old man. I need a nap.

Please preserve it, it is our history.

Neil