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(This first section of information came from Roscoe's Impala Page here)

This is a picture of the first 427 produced by Chevrolet


The Z-11 Impala was based on a standard 1963 Impala 2 door hardtop body with the exception of a few weight saving aluminum body parts. The hood, front fenders, front and rear bumpers including brackets were all aluminum.


The engine was based on a standard 409 block but it was fitted with a stroked crankshaft. The heads were unique in that they had large, oval shaped intake ports that were taller than the hi-po 409 heads. The intake was a two piece design that was all aluminum. The carburetors were the same units that were used on the dual-quad 409s. The air cleaner was totaly unique to the W-motor Z-11 Impalas. It was a form of early "cowl-induction." The "arm" that goes to the fire wall had a rubber boot attatched to the air cleaner housing and the rubber boot fit over an oval shaped duct that drew air from that cowl area. Other differences to the W-motor Z-11 engine was the usage of a deep sump oil pan. The pans had a deeper sump welded to the pan. The pans look homemade but that is how the factory modified them. Also there was a push rod guide plate used on the heads and the valve covers had special corners to clear the guide plate.


On the inside of the car it was standard Impala trim with no radio and no heater. The stock "dog-leg" shifter was standard as was the Delco electric tachometer. No sound deadening was used under the carpet.


The exteriors were very unasuming as there was no identificaton as to the 427 engine. Stock 327 emblems were used and only black wall tires mounted on 15 inch rims with standard hub caps made up the rolling stock.


As mentioned earlier the bodies were stock 1963 Impala 2dr. hardtop bodies. The rear end was the stock unit with 4.11 gears, they had the standard two-piece drive shaft, the transmission was the Borg-Warner T-10, close ratio four-speed, the shifter for the T-10 was the stock "dog-leg" or bench seat shifter, the bellhousing was the 409 style all aluminum "553" casting.


( I would like to thank Rusty Symmes who wrote a book about the Z-11 Impala called Project: Z-11 [ it was never published ] with the help of many friends , Doug Hughes,John Mounts,Mike Martin,and Steve Gunnels to name a few for allowing me to include a few pages from his book on my web site. The rest of this page is all from this book.)


The R.P.O. Z-11 Story


The roots of the famous '63 Z-11 actually began in 1962. Chevrolet, concerned with the poor performance of their 1962 models on the NASCAR tracks, and to improve performance at the dragstrip, decided to raise the high RPM horsepower by a redesign of the 409 cylinder heads and intake manifold. The newly designed head and intakes were to increase volumetric efficiency and improve intake cooling. These raised port cylinder heads and two-piece intakes were released as over-the-counter items before the 1962 NHRA Nationals Drags at Indianapolis. These special parts carried blueprint issue dates of May 4, 1962.


Several racers arrived at Indy with these special parts, and raced in Factory Experimental class. I recognized these parts on Don Nicholson's (FX, Nalley Chevrolet cars). While inspecting his cars, I was intrigued by the height of the intake manifold and carbs, as opposed to the same parts on the '62 409, that I owned at the time. These parts were reported to have come in a kit. Most of these cars also had aluminum fenders, inner fenders and hoods. This was another over-the-counter rush option to improve the weight distribution on drag cars. The '62 Chevys were heavy compared to the early Mopars that utilized uni-body construction. Also Pontiac had already begun to produce 421 CID cars for drag racing, with aluminum front ends. Chevrolet was not about to take this lying down.


There were also a limited number of aluminum '62 Impala Super Sports built at the Flint Plant in late year; some records indicate 18 total. They did not have the new heads. It seems that all were identified by aluminum unpainted cowl plates. There were no other known identifications. The cylinder heads and aluminum parts increased the performance of the '62 cars by 2-5 MPH, when used with a properly prepared chassis and full drag slicks. Dave Strickler was reported to have turned as fast as 11.53 at 123 MPH in match race form in the '62 Bel Air "Old Reliable".


The early '62 Z-11 style cylinder heads had pinned studs and were rough. They were marked CFD (Central Foundry Division) General Motors. The two-piece aluminum intake manifolds were made at Winters Aluminum Foundry, and have the traditional Winters snowflake embossed in the casting. The early aluminum intakes developed a problem with cracking at the bolt bosses and were subsequently redesigned. Some of these early manifolds had different odd part #'s and incorrect firing orders cast on them.


1963 R.P.O. Z-11


As the 1963 models were introduced the Z-11 came into being as an RPO (Regular Production Option) Z-11 engine/chassis option that required zone approval before processing of the order. As far as I can discern, this was done to make sure the cars were put in the hands of racers who would campaign the cars, and further Chevrolets cause at the drag strip.


A note must be made that although the RPO Z-11 is one of the rarest Chevys, it was not the true mystery motor that was introduced for NASCAR and withdrawn from service because of the anti-racing policy of January 1963.


The most important feature of the'63 z-11 engine was a stroked crankshaft bringing the engine up to 427 CID. This displacement figure was arrived at by both NHRA and NASCAR as the legal CID limit for stock car racing. The reasoning behind this decision was that both sanctioning bodies thought the cubic inch race was getting out of hand, and the brakes needed to be applied by limiting displacement size. Ford was already rumored to have plans to field a 483 CID monster motor in 1963, and that was enough to spur both associations into action. A 7-liter (427.2) was decided as the most logical engine size to standardize on.


The Z-11 crankshaft, connecting rods, and pistons differ from the '63 425 HP, 409 CID engine, but the engine blocks were the same. However, the Z-11 blocks were stamped with a QM stamp on original engines. It should be noticed that the "M" is a little deeper impression stamp than the "Q" that was probably beginning to dull from constant use whereas the "M" was unused and sharp. The Q stamp did all the 409 engines. The M stamp did 50 or so engines. The assembly dates appear to around the end of December.


The connecting rods are essentially the length of the soon-to-come big block Chevy Rod (length 6.134 to 6.136), although they were considered a weak point, the heavy Z-11 pistons were the root cause of many failures.


The camshaft that came in original Z-11 cars came from Eonics Cam Co. in Detroit, and actually had the Eonic name stamped on the end of the camshaft. This cam timing of the Z-11 became standard issue in 1964 on regular 409 h.p. engines.


The carburetion of the Z-11 car was the same as the standard 409 425 h.p., and even had a standard choke and heat rizer setup. Also the Z-11 was equipped with P.V.C. system like the 409 425 h.p.


The R.P.O. Z-11 had a unique hollow fuel pump push rod to reduce erratic fuel delivery due to pushrod float. The fuel pump was a special part number until I believe had special valving and spring, etc. with no provision for fuel return to the tank.


Also for the first time on the W block, a canister type fuel filter was used with a 3/8 line into it. This canister had an AC designation with only a small white "star" for a part number.


The Z-11 motor had a new aluminum water pump assembly which had a tendency to fail due to thermal expansion and excesive pressure allowing the front bearing to walk and also the seal to leak. The pump caused more than a few problems on the Z-11 motors.



W's, X's, Y's, & Z's

W - 409 Style Chamber in Block

X - Engine Experimental Engine (small block)

Y - Engine Experimental Engine (small block)

W - 1-307 409 Style

W - 2-327 409 Style

W - 3-348 Production

W - 4-409 Production (?)

Mark I - AFX 62 Style Engine 3833117-425 h.p.

Mark Is - 63 RPO Z11A-3837729

Mark II - 63 427 Mystery Motor (Z33) Never R.P.O.

Mark III - Paper Only Engine

Mark IV - Rat Motor..we all know

Mark V - Redesigned Rat Motor




The most obvious and important common feature was that all Z-11 cars where produced on straight 2 door hardtop Impala bodies.


The aluminum component consisted of the fender, hood, splash pan, grill brackets, front & rear bumper and mounting brackets, and also an aluminum fan shroud. Bodie did have sounds deadner from all that I have seen, and where available with or without a heater. They were all shipped through standard channels by truck or by rail to the dealerships from the only plant producing Z-11s, the Chevy Flint Assembly Plant. All cars had vented backing plates and metallic brake lining. These vented backing plates came equipped with bolt-on rain covers, so if the cars were to see any rain, the brakes would be able to work. These plates are rare and sometimes are mistaken for brake scoops.


Body identification is located on the upper firewall. Some Z-11 cars, probably on the later production run cars, have a Q-11 embossed on the accessory code section of the cowl tag. Some cars that are documented did not have any accessory codes, and some had only the Q to designate the W-style motor.


The high rise nature of the intake manifold made proper air delivery to the carbs a main concern. Each car was equipped with a cowl plenum induction system. Chevrolet had experimented as early as 1961 with a carb fresh air system that utilized the cowl grille high pressure area at base of windshield. This technique was used prior for the flow through ventilation system to the rocker panels to reduce rusting in that area.


The Z-11 did not have "as many believe" an extra link on the upper suspension, although many were added later.


The rear axle assembly probably was the weak part of the entire Z-11 package. Many were replaced with Pontiac rear axle housing, Etc. because of breakage. To the best of my knowledge there was a special set of axles made to reduce axle breakage. This was a help as in 1963 N.H.R.A. began to allow full slicks in A/FX for the first time. Chrysler-type spider gears allowed large fine spline axles.





Did all this "Z" business come from anyway? Well, in 1963 Chevrolet adopted a special alphanumeric coding system to include any car with special equipment such as a high performance option of limited production. Option codes of this nature were given the Z prefix. Thus was born the Z-11 option, the first of the rare desireable Z cars which later gave way to early Z-28's, and also ZL-1's, Z-16's, etc.




Produced only in 1963

The R.P.O. Z-11 option was an additional $1240.00

Shipping weight-3245 lbs.

Curb weight-3405 lbs.

57 Z-11 Impala's were produced

Only 7 are known have survived

Modified 409 engine rated at 430hp@6000 RPM's. (Actual horsepower was 480-525)

Block casting #3830814. Code "QM"

Head #3837731

2 piece Intake manifold #3830623 (top)-#3837733 (bottom)

Cam #3837736 Duration/lift-325/.556

Distributor #1111023

Coil #1115107

Generator #1100628

Starter #1107274

Special cylinder heads

3.65" piston stroke

4.3125" bore (same as 409)

13.5:1 compression ratio

2.20" intake and 1.73" exhaust valves

Special cowl induction air cleaner #6418986, #3839764 (duct)

Tach (redlined at 6200 rpm's)

Borg Warner T-10 4 speed transmission (close ratio)

Special posi rear with 4.11:1 rear gear ratio

Sintered metallic brakes with vented backing plates

15 X 5.5 wheels with 6.70 X 15 bias ply tires

Deleted sound proofing and insulation

Deleted front sway bar