zl1 dream engine - Engine Professional

EPQ414 12-19_Layout 1 10/1/14 8:25 AM Page 12
ZL1
DREAM
ENGINE
A ZL1 appears from the youthful dreams
of a 63-year-old man…
BY HAROLD BETTES
Maybe this is the way it
happened and maybe it isn’t
but it is a story worth
telling. The author presents
the following scenario so
you can appreciate a bit of
history about a young man
and his yearning for a
special engine. The test data
is real. The name of the
dreamer is not given in
order for him to simply
enjoy his dream. Perhaps
you might even know of a
guy like the one described.
The Story of a Dream Engine Begins
Imagine that you are an 18-year-old kid standing at the parts counter of a Chevrolet
dealership buying parts for your 1956 two-door hardtop. You have made fairly good friends
with the parts man from your regular trips to buy parts for your car. You have recently
registered for the draft as required by law and the war in a country in Southeast Asia called
Vietnam is a common discussion point with lots of guys your age. You just graduated high
school and want to go on to college. The year is 1969.
The parts guy at Jack Coyle Chevrolet in San Bernadino, California asks you if you had
heard of the new all-aluminum engine big block rat motor being built and installed in a total
of 69 Camaros under COPO (Central Office Production Order) 9560. The engine
configuration is called the RPO (Regular Production Option) ZL1. The overall concept was
supposedly the brainchild of a drag racer from New Mexico named Dick Harrell that was
working for Fred Gibbs Chevrolet out of Illinois.
The parts guy invites you into the showroom during his coffee break so he can show you
this new optional engine and Camaro package. Your response is only “WOW”. The shiny
Cortez Silver Camaro was priced at an outlandish $7,269 plus destination charges which is
way outside your finances, but the engine is what really draws your attention. You decided
then and there if the day ever comes around where you can afford one you will buy it and
care for it just like you have always cared for the old ’56.
The parts guy explains the new engine in detail and tells you that they are built at the
Tonawanda Assembly Plant in Tonawanda, New York and each one takes over sixteen or
seventeen hours to assemble by selected technicians in a super clean room environment. The
engines are rated at 430 horsepower at only 5200 RPM. The parts guy said with a wink and
a nod that he had heard from insiders that they were really over 500 horsepower and had a
special high performance cam that would allow over 7000 RPM. It made sense because the
12 OCT-DEC 2014 engine professional
Some Engine Build Parts
and Specifications
Bore and Stroke: 4.280” x 3.76”
Block: GM PN1237580
Crankshaft: GM forging number
7115
Harmonic Damper: ATI
Balance Tolerance: +/- 0.5 gram
Connecting Rods: GM parts –
just like the original ZL1 units
with 7/16” boron bolts
Pistons: special order from JE
Rings: 1/16” x 1/16” x 3/16”
Total Seal
Compression Ratio: 11.5:1
(measured)
Cylinder heads: GM
PN12363408, Edelbrock castings
Valve Head Diameter: Intake –
2.190”, Exhaust – 1.880”
Rocker Arms: Stamped Steel
units just like the originals
Camshaft: ground to original ZL1
specs (.560”int lift, .600” ex lift)
by Crane Cams
Valve Springs: Iskenderian
Retainers and Keepers: Comp
Cams
Guide Plates: Comp Cams
Pushrods: Smith Bros.
Timing Chain and Sprockets:
Romac Rollmaster
Intake Manifold: GM PN3947083
Installed with factory valley oil
splash tray
Carburetor: Holley four barrel
4781C double pumper
Distributor: MSD billet 85551- a
specific improvement over the
factory original
Ignition System: MSD dyno
tested with 7AL will be run in car
with MSD 6A either of which is
an improvement over the original
transistorized factory amplifier of
1969.
Oil Pump: Melling M77
Oil Pan: Factory original with
factory windage tray duplication
built into pan
Fasteners: GM and ARP as
required
Bearings: King - rod and main
bearings
Cam Bearings: Coated DuraBond cam bearings
Gaskets: Fel Pro
EPQ414 12-19_Layout 1 10/1/14 8:25 AM Page 13
Massive steel billet main caps are nicely finished like
the rest of the parts used in this build.
The block was bored a small
amount and honed for a final
bore size of 4.280”.
Coated Durabond cam bearings were the first pieces
installed in the block.
Inside the crate was the beginning of fulfillment of
long years of a dream engine.
all aluminum engine was 427 cubic inches
and had a Holley four barrel carburetor and
a special transistorized ignition system. The
parts guy clearly said the ZL1 engines could
be bought independently of any vehicle and
your mind and heart is set to have one
someday even though the engine was priced
at a lofty $4200.
Fast forward through a lot of life’s other
experiences that occurred over the following
45 years and the kid not only survived the
draft and Vietnam where too many of his age
did not. He went to college on the VA
educational assistance program (GI Bill) from
his military service and ended up building a
very successful business but he had not yet
fulfilled his dreams of owning a ZL1 engine.
He has spent most of his adult lifetime
providing for his family and employees and
found very little time for his gearhead
thoughts. The ’56 was sold and replaced with
many more practical cars over the years.
The guy is now 63 years old and still
dreams of owning a ZL1 engine so he finally
started the process toward solution by
contacting Mark Jones of VortecPro Engines
and Machine in Colorado Springs, Colorado.
VortecPro specializes in muscle car engine
packages so the ZL1 build order was a
natural selection. GM Performance Parts
Mark Jones begins to install
the King main bearings in
each position to check for
clearance. The block main
bores were straight and round.
INSET: Checking for main
bearing clearance with dial
bore gage.
www.engineprofessional.com 13
EPQ414 12-19_Layout 1 10/1/14 8:26 AM Page 14
ZL1 DREAM ENGINE
BY HAROLD BETTES
The ZL1 engine is finally on the dyno after 45 years
waiting for the dream to come true. The headers are
connected to 3” in and 3” out Magnaflow mufflers.
started offering the ZL1 engine parts again and
does its part to fill the needs of gearheads that
have bowtie emblems in their thought processes
and of course in their dreams.
The ZL1 Break-in and Test Sessions
on the Dyno
The completed engine was placed on the
dynamometer that is an in-house installation at
VortecPro for cam break-in and for engine test
sessions.
The solid lifter flat tappet camshaft was
broken in using low seat force springs and run
for 30 minutes at above 2500RPM while under a
slight dynamometer load of 30 to 50 lbs-ft of torque. After the
camshaft and lifter break-in cycles, the valve springs were replaced
with the proper springs for high RPM running. After the stronger
springs were installed and the valve lash was reset, the engine was
run for about 45 minutes at various loads and throttle settings
before any test runs were done to check for power output. A
detailed inspection of the valve train was continuous to verify no
problems were lurking there. During these break-in cycles, the
ignition timing was steady at 30 degrees BTDC. The engine was
shut off and when at an appropriate temperature, the heads and
manifold fasteners were checked for torque settings.
After break-in running total ignition timing was set at between
35 and 39 degrees BTDC. Initial dyno test runs were established
between 3500RPM and 6000RPM for timing and jetting
baselines. Best power timing ended up at 39 degrees BTDC.
The data (shown at the left) was taken at a water temperature
of 147°F and an average A/F ratio of 12.5:1. Acceleration rate
was 600RPM/sec. The tests were run with headers and using
mufflers as well. Best power timing was at 39° BTDC. The engine
was not tested past 6700RPM but as is obvious on the graph, a
peak power number was not attained and the engine was still
going strong.
Comparisons to Original Dyno Data
Although original factory dyno sheets are very rare to come across
after 45 years, they actually still do exist if one knows the right
place to look. Certainly, many of the original engineers that
worked on the ZL1 project are no longer available to talk to.
Sufficient for this article and comparison is the following
published data circa for 1968-1969 time frames.
Chevrolet rated the ZL1 engine (427 cubic inches) to be
430Hp at 5200RPM (single Holley 850 four barrel carburetor).
Chevrolet Engineering engines supplied to Chaparral Race Cars in
those days were rated at 525Hp and 540Hp at 6000RPM and
ZL1 Test Data
RPM
4800
4900
5000
5100
5200
5300
5400
5500
5600
5700
5800
5900
6000
6100
6200
6300
6400
6500
6600
6700
STPTrq
528.4
524.2
520.3
517.5
514.9
514.1
513.0
511.3
509.6
508.1
505.4
501.7
497.6
493.2
489.0
485.8
481.2
475.0
471.8
465.9
STPPwr
483.0
489.1
495.3
502.5
509.8
518.8
527.5
535.4
543.4
551.5
558.1
563.5
568.4
572.8
577.2
582.7
586.4
587.9
592.9
594.3
14 OCT-DEC 2014 engine professional
The red line is corrected brake horsepower and the blue line is corrected brake torque. This graph ss a result of an
acceleration test run from 4800RPM to 6700RPM at 600RPM/sec on a dyno. The power has not peaked on this
engine. It will probably never be run to a higher RPM than is shown here after it is installed in its new home.
EPQ414 12-19_Layout 1 10/1/14 8:26 AM Page 16
ZL1 DREAM ENGINE
BY HAROLD BETTES
Quality Controlled
Expansion Plugs
Since 1921
Pistons are special order from JE. Notice the pressure relief channels
also called “Jenkins grooves”. Poetically fitting as Bill Jenkins
originated their use back in the day. First and second rings are 1/16”
and oil ring is 3/16” from Total Seal.
those engines ran with 4 Weber carburetors with a
compression ratio of 11.0:1. As the larger bore aluminum
blocks (4.44”) became available for CanAm racing, those
engines using the same 4 Weber carburetor arrangement
were rated at 560Hp at 6800RPM. However, that engine
configuration (for 430ci) was using a short stroke crankshaft
of 3.47”. Also, there is a lot of conjecture on exactly what
exhaust system that Chevy Engineering used on some of
those reported engine tests but they surely weren’t the
standard cast iron manifolds.
According to the General Motors Automotive Engine
Test Code in place at the time of the building of the initial
ZL1 engines, the engine dyno test data (observed) was
corrected to conditions of a barometric pressure of
29.92”Hg (mercury), inlet air temperature of 60degF, and
dry air. Later on (by 1971 - 1975 or so) the Engine Test
Code Committee changed those values to 29.00”Hg, 85degF,
dry air. That is just to show the reader it makes a difference
for you to know where the numbers come from.
Unfortunately lots of folks just don’t take the extra effort
to do the homework and learn the differences. It makes a
great deal of difference when you mix the emotion of using
horsepower and legendary in the same sentence. Also
worthwhile to note was that data from those early dyno tests
show the friction horsepower (power required internally to
swing around the parts) of the ZL1 (stroke of 3.76”) taking
about 190 horsepower to rotate the internal stuff at
6750RPM. There are guys out there (and even some of them
in the dyno business) that totally disregard the element of
friction horsepower. However the factory engineers do and
always have addressed the frictional element if you look at
the data they have collected. The procedure for measuring
friction torque is also covered in the GM Automotive Engine
Test Code, but some folks ignore facts and create revisionist
history.
Another point to consider about dyno testing is that the
factory dynamometer tests were done in steady state and not
16 OCT-DEC 2014 engine professional
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800-433-6414
1335 W FULLERTON AVE, ADDISON, IL 60101
(630) 953-1000 FAX (630) 953-0174
EMAIL: [email protected]
EPQ414 12-19_Layout 1 10/1/14 8:26 AM Page 17
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Short block assembled. You can see the flat tappet ZL1 cam installed.
The blue anodized aluminum plugs screw into the block and seal with orings.
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Freshly cut heads with 2.19” intake valve perched in chamber. Valve job
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was measured to be 11.5:1. Very moderate intake port bowl work was
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in acceleration mode (also called transient testing) as many
of today’s dynamometers can do. So, how can one relate that
bit of information?
Roughly speaking, the difference between acceleration
testing and steady state is that in steady state the numbers
will be higher values than those taken under an acceleration
test. About how much difference is there? Well, it depends a
great deal on the stroke of the engine so one can use the
following estimate for comparisons. At 300RPM/sec a factor
would be approximately 9 lb-ft of torque per data point and
at 600RPM/sec approximately 18 lb-ft per data point.
Hopefully you will recall that the relationship between
horsepower and torque is stated mathematically as
HP = (T x RPM) / 5252.
In the ZL1 build dyno test data listed, one can add 18 lbft of torque at each data point added in order to equal an
approximation of steady state testing because the testing was
done at 600RPM/sec. Consider that this applies to a stroke
www.engineprofessional.com 17
EPQ414 12-19_Layout 1 10/1/14 8:26 AM Page 18
ZL1 DREAM ENGINE
BY HAROLD BETTES
All prepped and ready for the topside installation.
of 3.76” so don’t go off and try to apply that to just any
dyno test data or you will be mistaken.
Using the approximation listed previously, the
following arithmetic would apply in order to compare
results with factory steady state dyno testing.
• At 5200RPM, 18 + 514.9 = 532.9 and
Hp = (532.9 x 5200) / 5252 = 527.6Hp
• At 6000RPM, 18 + 497.6 = 515.6 and
Hp = (515.6 x 6000) / 5252 = 589.0Hp
• At 6700RPM, 18 + 465.9 = 483.9 and
Hp = (483.9 x 6700) / 5252 = 617.3Hp
It would have been very interesting to see what would
have been the readings at 7200RPM which is where the
camshaft is supposedly good for. However, this particular
guy just wanted to fulfill his dream and only he knows
where that leads. Maybe a place near you. The special
dream engine will not be going into a Camaro, but will
instead be installed in a very nice Chevelle with an
automatic transmission. Sweet dreams and welcome
home.■
Harold Bettes is author of Engine Airflow and co-author of Dyno Testing and
Tuning. He has been a mechanical engineer for over 40 years and has
been involved in motorsports in one fashion or another for more than half a
century. Harold is a recipient of many awards for his contributions in
furthering mechanical engineering in the motorsports industry and
aftermarket. He is an active consultant on test facilities, equipment and
racing engine configurations and designs. He is also writing a novel about
experiences in Southeast Asia, Mexico, and Texas.
18 OCT-DEC 2014 engine professional