Acknowledgments

Without the 350ci engine, would this have been the baseline Camaro Super Sport? Although it lacks the SS hood, you could be easily fooled by the looks and performance of this '68 L30/M20 coupe.

Much of the content of this Research Report was originally released on the Camaro Untold-Secrets web site circa mid-1997 in a slightly different form, and was printed in the former publication of the old United States Camaro Club, the Camaro Enthusiast, in the Nov/Dec 1997 issue (which, unfortunately, contained a large number of printing errors). This CRG Research Report is the most current and correct version, and the only one that is being updated to reflect new information.

Note that the superscript footnotes are linked - click on any superscript numeral to view that footnote.

Background

The RPO L30 327ci-275HP Engine. A real performer when combined with the RPO M20 four-speed transmission. (Shown in 1967 non-smog form.)

The 1967-68² RPO (regular production option) combination of the L30 327ci-275HP V8 engine with the M20 4-speed manual transmission created a true high-performance automobile, in part due to additional components automatically installed by the factory when the 4-speed was paired with the L30 engine. The details of this package were poorly documented and essentially unadvertised; probably only the most discerning people of the era realized the implications. The writers and editors of period car enthusiast magazines rarely delved deeper into available options than the basic promotional literature supplied by Chevrolet, and the Chevrolet marketers preferred to emphasize the SS models, or later, the Z28. Serious racers considered the SS and Z28 to be only starting points, with further modifications required to meet their needs. So it was not well-known (and still isn't³) that the L30/M20 Camaro was the only regular production 1967-68 Camaro outside of the SS/Z28 models to receive the heavy-duty "12-bolt" rear-end, right-side radius rod (in 1967), and multi-leaf rear springs (in 1968), as well as additional performance equipment otherwise exclusive to the SS or Z28 lines. The potential for model confusion is understandable since, without this knowledge, a L30/M20 could easily be mistaken for a SS-350 stripped of ornamentation (if the 327 was mistaken for a 350), or, if the 327ci engine was recognized as such, the L30/M20 could be considered evidence of a factory SS-327.

This Chevrolet ad ran in many major enthusiast magazines. It depicts a 327 coupe with SS-available stripe and calls it a "SS!" Confusing? Yes!

If there is any confusion, some of the blame can be assigned to the manufacturer, since advertising campaigns showed 327-badged Camaros and called them SSs.

And data to correct this confusion is hard to come by. Chevrolet's long-term record-keeping policies do not allow them to verify the options on vehicles they have produced (GM of Canada is the exception, but Canadian Camaros were a relatively small number of the total Camaro population). Add to this that Chevrolet files⁴ have been substantially purged of first generation Camaro engineering data; old drawing numbers are now being reused on new models with old drawing files trashed in the process. And General Motors has even lost the official translation and/or significance of certain of their own production codes.

The 1967 "4P" Fisher Cowl Tag Code; Axle Interaction

Starting mid-year 1967, the 4P cowl tag code, when combined with the 2L code, could indicate either a L30/M20 or a L48 SS-350. A L30/M20 convertible tag is shown here.

A UOIT description has not yet been found for the 4P code. However, UOITs have been found for the even more rare L78 4K and Z28 4L codes, as well as for the L35 4N code and in all three of these cases the UOIT text is identical: "ENGINE REINF ASY". The CRG working theory is that these four codes indicate the body reinforcement and attach holes/nuts required for these different engines at the body location of the radius rod attachment. Even though the body reinforcement itself in all four cases is believed identical, a separate code was created (4K, 4L, 4N) for each additional new engine added after January 1967. (The code progression above does lead to further speculation that perhaps a 4M code was reserved for the 396ci/350HP L34 engine that was considered for introduction in 1967, and appears in the 1967 AIM, but was ultimately withheld until the 1968 model.) The possible need for unique Fisher codes can be explained by additional Fisher trim differences for different models associated with these engines (Z28 striping, BBC rear valence black-out paint, etc). Our working theory further extrapolates that the new codes were reserved as a block, with general knowledge of and in anticipation of the models that were being prepared for release, while conservatively expecting that there might be unique (to Fisher Body) characteristics for each of the models that would require each to be flagged with its own unique tag code. However, in the case of L35 vs. L78 there were no differences in the final Fisher configuration (at least none that CRG has been able to identify at the time of this writing). So the 4N and 4K codes separately identify L35 and L78 even though Fisher built their bodies the same way. Likewise the 4P code does not distinguish between SS-350 and L30/M20.

The "4P" code was, for many years, interpreted in Camaro hobbyist literature as unique to the SS-350. In the mid-1990s a broader interpretation of 4P began to be suspected by the U.S. Camaro Club, and this interpretation was subsequently verified and clarified by the CRG after its inception in 1997. The 4P code is now known to include both the SS-350 and the 12-bolt L30/M20 (the latter includes the additional mandatory "2L" code for the 4-speed.⁵ (A very few of the earliest Z28s in the first urgently-built batch distributed to Trans-Am racing teams acquired the 4P code only because - we speculate - the need for the "ENG REINF ASY" body preceded release of the 4L code that would soon be used for Z28. Likewise, the very first few L78 cars were build from 4P bodies. These were specific exceptions to satisfy immediate needs; the unique "4K" and "4L" codes were used on the remainder of 1967 L78 and Z28 production, respectively.)

The CRG believes that use of the 4P code on L30/M20 is almost certainly tied to the 12-bolt axle/radius rod addition to L30/M20. As a side note, CRG doesn't know if the primary objective was introduction of the 12-bolt (which by then included the radius rod by default), introduction of the radius rod (only available on the 12-bolt at the time of the switch), or if there was recognition that both components were needed. Regardless, just as with the SS version of the 4P code, use of the code on the Fisher bodies led the component switch; in the case of L30/M20 by perhaps seven weeks. Introduction of the 4P code to L30/M20 is believed to have started in the time frame of late December 1966 to early January, while the 12-bolt axles themselves (except for the 1967 optional axle ratio positraction exception, a separate issue) did not appear on the L30/M20 until sometime between late 02B and early 02E (02B 10-bolt cars and 02E 12-bolt cars have been confirmed). Therefore, and confusing as it may be, it is now evident that there are at least seven possible L30/M20 variants for 1967:

1. early L30/M20 cars with neither 4P code nor 12-bolt axle (early non- or standard-ratio posi production),
2. a few L30/M20 cars with 12-bolt optional-ratio posi axle (non-radius rod) but no 4P code (early production),
3. a few L30/M20 cars with 4P code but a 10-bolt non-posi or standard-ratio posi axle (transition period),
4. a few L30/M20 cars with 4P and 12-bolt optional-ratio posi axle without radius rod bracket (transition period, old axles),
5. a few L30/M20 cars with 4P and 12-bolt optional-ratio posi axle equipped for the round radius rod (transition period, new axles); these being physically identical to the next configuration, but with radius rod a side-effect of axle availability,
6. late L30/M20 cars purpose-built with both 4P and round radius-rod equipped 12-bolt (built after the 12-bolt transition).
7. later still L30/M20 cars purpose-built with both 4P and square radius-rod (after introduction of square rod use on 4-speed cars) equipped 12-bolt (built after the 12-bolt transition).

Much more information on the related topic of the 1967 radius rod can be found in the CRG Research Report on 1967 Radius Rods.

The SS-350 Camaro, a.k.a. RPO L48

A better understanding of the significance of the L30/M20 Camaro can be had by first briefly reviewing the specifications of its close cousin, the SS-350.

When Chevrolet introduced the all-new 1967 Camaro on September 29, 1966, the top-of-the-line Camaro Super Sport was powered only by a new high-performance 350ci-295HP small-block V8 that was, in 1967, only available in Camaro. The 350 engine (in its various forms) would prove to be the last⁶ and arguably most famous expansion of the overhead-valve, small-block Chevrolet engine line that began in the 1950's. The previous incarnations, the 327, 283, and 265 (in reverse chronological order) had already developed a formidable reputation for dependable power.

The additional displacement of the 350 was obtained from the 327 engine block via a new crankshaft⁷ that increased the 3.25 inch stroke used on the 327 engine to 3.48 inches while retaining the 4.00 inch bore. This new engine debuted in the 1967 Camaro as part of RPO L48 (named the Super Sport, or SS), and would not be made available to the other Chevrolet lines until the next model year. While the Camaro SS line would soon be bolstered by a series of 396ci big-block engine options that would push advertised power ratings to the 325-375HP range, the 350 engine retains a strong identity as the baseline powerplant of the original Camaro SS, the SS-350.

The RPO L48 350ci-295HP Engine. A "stroked" version of the L30 327 engine. (Shown in 1967 non-smog form.)

During the first two years of the Camaro, RPO L48 was more than just the new 350ci engine; it was a true option package that pulled together a balanced collection of performance components and added a special trim package for visual distinction.⁸ While certain performance components (dual exhaust, for example) were also available to many non-SS models via separate RPOs, other components (like the traction bar, heavy-duty clutch, and 1968-69 multi-leaf springs) were restricted to Camaro models internally designated by Chevrolet as high-performance vehicles and could not be specifically ordered as a separate option.⁹ Not counting non-functional special interior and exterior trim (SS badges, SS hood, SS paint stripe, chrome-plated engine trim, etc.), 1967-68 RPO L48 added seven high-performance component groups to the baseline vehicle:

1. A heavy-duty rear axle suitable for high-torque engines, based on a larger, 8.875-inch diameter, ring gear. This rear-end is commonly called the "12-bolt," after the number of bolts on the ring-gear (as well as on the cover). The standard rear-end of this era was the "10-bolt" rear end with a 8.125-inch diameter ring-gear.¹⁰

2. Significant suspension improvements: stiffer springs (including multi-leaf rear springs in 1968) teamed with heavy-duty shocks and, with 1967 manual transmissions, a rear axle "radius rod" (a.k.a., traction bar).

3. A two-piece rear brake line with rear brake proportioning valve to alter the pressure distribution between front and rear brakes. (1968 only. This came on 1967 SS-350 Camaros only when they were ordered with air conditioning.)

4. A dual-exhaust system with 2.25-inch diameter pipes for reduced engine restriction and improved power.

5. Wider profile 70-series tires: D70x14 in 1967 and F70x14 in 1968, as compared to the standard D78x14 in 1967 and E78x14 in 1968.

6. An upgraded high-torque starter motor, PN 1108338 (used on all 1967-69 SS350s except for 1969 PG and TM350 applications).

7. Heavy-duty, larger diameter (11.0-inch) clutch, suitable for high-torque engines. (Obviously only for use with manual transmissions.)

8. For 4-speed cars, replacement of the base Saginaw transmission used for lighter-duty applications with the more robust Muncie transmission.

Having reviewed the performance features of the SS-350 Camaro, let us look at the L30/M20 Camaro.

The L30/M20 Camaro

While the L48 package got top billing, the less-publicized optional upgrade to the base 327 engine, RPO L30, boosted performance of the base 327ci V8 from 210HP to 275HP. When the L30 engine was combined with the M20 4-speed manual transmission option, and only in this case, Chevrolet considered the L30 engine to have crossed the line into high-performance territory, and added three of the seven SS high-performance components: the rear axle, rear springs (or radius rod in 67), and rear brake proportioning valve. In addition, two of the remaining four SS components could be added via inexpensive option additions, resulting in similar matches to the first five of the seven SS-350 performance component categories.

SS-Equivalent Components That Could Be Factory Added to L30/M20: Dual Exhaust and Wide-Profile Tires

L30/M20 Components That Could NOT Be Factory Upgraded: Transmission, Clutch, Starter

The L30/M20 was outfitted with the same 10.4-inch diameter standard clutch as used on the Z28. The larger 11.0-inch clutch used on the SS could not be separately ordered. However, the standard 10.4-inch clutch in the L30/M20, with its lower pedal force, was arguably preferrable to the SS clutch.

(There were several changes in starter specification, but generally, the L30/M20 received a higher-performance starter than the base LF7 327. However, the L30/M20 starter generally differed from that used on SS350.)

The End Result

The L30/M20 and L48/M20 face off... So close in so many ways!

As noted above, besides the clutch, the other significant difference between the L48 and L30/M20 was the M20 transmission. M20 was not the name of the transmission but rather was the functional designation for any standard ratio 4-speed manually-shifted transmission. Chevrolet yoked the 1967-68 L30 to the less-than-desirable cast-iron-bodied Saginaw 4-speed, heavier by some 14 lbs than the higher-quality aluminum-bodied Muncie 4-speed¹¹ that was placed behind the L48.

As an attempt to compensate for the added power of the L30 application, the L30/M20 Saginaw was beefed-up slightly by substitution of heavier-duty transmission bearings: clutch gear bearing, main drive gear bearing, and mainshaft rear bearing (the first two were same as used in the SS350 three-speed transmission). Unfortunately, history has proven that even with these improvements the Saginaw was not capable of surviving the L30 - very few original Saginaws remain in L30/M20s.

The increased weight of the Saginaw was offset by the lower weight of the standard, and arguably better-looking, standard flat hood used on the L30/M20, as compared to the much heavier SS hood with its non-functional "window-dressing" hump and ornaments. The 1968 L30/M20 with N10 exhaust is documented¹² as being a total of 29 lbs. lighter than that used on the L48/M20, though a few pounds of this advantage would have to be subtracted if the PY5 wide-track tires were added to the 327-powered car. While data that would allow a comparison of vertical Center of Gravity (CG) coordinates are not available at this time, the L30/M20 may have enjoyed a slight advantage from a lowered CG due to the mass shift from the hood to the transmission.

Identifying an L30/M20

For mid-year and later 1967 Camaros, the presence of the 4P cowl tag code in combination with the 2L 4-four speed code can indicate a possible L30/M20. This code is a mandatory requirement for the later 1967 L30/M20 and is described in more detail in the 4P code section.

If either engine or transmission have been replaced, L30/M20 verification requires checking the date-code on the 12-bolt rear end (not applicable to the earlier 1967 10-bolt models); to supplement this one should attempt to locate as many of the other performance components as possible, especially the radius rod (later 1967 models) or multi-leaf rear springs and rear brake proportioning valve (1968 models).

Two views of 1967 12-bolt axles showing the "Mono-Plate" single-leaf, width-tapered, rear spring, with the later rectangular radius rod (traction bar). Also notice the dual exhaust with crossflow muffler and dual resonators; this was standard equipment on the SS and Z/28 and optional for the L30/M20.

Shown below is the two-piece rear brake line with rear brake proportioning valve, located under the driver's side door on the subframe, that was intended to improve pressure distribution between front and rear brakes. (Required for L30/M20 only in 1968. Valve application for 1967 was for factory air-conditioning, as well as Z28 and 396.)

The rear brake proportioning valve, located on the subframe under the driver's door.

Additional information on identifying these cars is shown in the CRG model identification tables for 1967 and 1968.

Without original paperwork, and if most of these components are missing (many are often missing due to modifications or repair made over the years), including more than one of the three key drivetrain items (engine, transmission, rear-end), the claim of a real L30/M20 may be difficult to reliably establish. If you have one of these difficult cases, contact the author for help with additional identifying features.

How Many...?

To supplement the above as-yet untraceable production number, we can make an educated guess of production numbers, based on V8 engine and transmission usage, from the single option production data that is repeated in the table below. While the estimate could be approached from several different ways, the calculation below is made in the following manner: 1) Determine the percentage of L30 engines relative to total V8s engine. 2) Determine the number of M20 transmissions used in V8s (total number of M20s minus an estimate for limited number of M20 transmissions used on L6 cars - 2.7% of M20s, based on a sampling of data available to CRG). 3) Multiply the percentage of L30s by the number of V8 M20s and the result is a rough estimate of the number of L30s mounted to M20 transmissions. This two-year estimate of 11,029 is close to the unconfirmed GM production number of 12,155 L30/M20s. Depending on which number is used, L30/M20s comprised only 2.4 to 2.7% of all Camaros built in these years.

Production quantities this low put the L30/M20 on a par, quantity-wise, with models like the 1967-69 SS with the L78 396ci-375HP engine (9464 built) or the 1968-69 SS with the L34 396ci-350HP engine (4597 built), and significantly more rare than other very desirable production models like the SS-350 or the 1968-69 Z28. Given the relative lack of respect that this poorly appreciated option combination has enjoyed, these thirty years later it is likely that surviving original L30/M20s are counted in the hundreds rather than the thousands.¹⁴

L30/M20 Technical Specifications

The L30 327ci-275HP	The L48 350ci-295HP
Notice how closely parallel are these power curves. (But note the slightly different scales.)

The L30 option¹⁶ began by replacing the standard intake and 2-barrel Rochester down-draft carburetor of the baseline 327ci-210HP engine with a 750 cfm 4-barrel Rochester Quadra-Jet carburetor (four possible carburetors in 1967: 7027203 (early) or 7027213 (late) without A.I.R., or 7037203 (early) 7037213 (late) with A.I.R.; in 1968 there was only one carburetor for this application: 7028213) containing a 0.071-inch main metering jet and mounted to a cast alloy-iron double-deck intake manifold (part numbers 3905393 in 1967 and 3919803 in 1968). To this was added (as shown in the cylinder head table below) higher-performance cylinder heads (retaining the hydraulic lifters) that increased the base compression ratio from 8.75:1 to 10.0:1 and contained larger valves for improved fuel/air flow. A different distributor advance optimized the power curve.

OEM starter applications are still being verified, but at the time of this writing it is believed that the 1967 L30 starter was PN 1107320, which seems to have also initially been applied to the new base LF7 327ci/210HP engine (the starter for the LF7 seems to have been switched to the lower-torque 1107496 starter circa late December). In 1968 the L30 starter is believed to have been PN 1108361, while the base 327 received the PN 1108367.

It is worth noting that the L30 starters, while higher-torque than the base 327 starters, were slightly lower in torque capacity than the nominal standard 1108338 L48 starter. When the 1969 L48 automatic transmission application switched at the start of the model year from the 1108338 to the same 1108361 starter that was used on the 1968 L30, it caused some problems with L48 hot-starting in new "tight" engines. This is noted in Service Bulletin 69-T-9, which specifies replacement of the early 1108361 with 1108420 in the event of a complaint with 1969 L48/automatics. Later production of the 1969 L48/automatics switched back to a higher-torque starter: either the 1108338 (PG) or the 1108420 (TH350).

The Rochester Quadra-Jet carburetor was used on both L30 and L48.

RPO M20. Top: Saginaw 4-speed with 2.54:1 low, available with L30. Bottom: Muncie 4-speed with 2.52:1 low, available with L48.

A 1967 L30 (with 1967 manual transmission smog equipment) engine at home in it's environment.

The L30 engine design is functionally very similar to its progeny, the L48; in most cases they used the same components. In reality the L48 engine is best described as a long-stroke L30! Both engines shared the same block castings (usually), heads, intake manifold, exhaust manifolds, camshaft, and carburetor. The L48 got its 20 extra gross horsepower almost exclusively from the 23 extra cubic inches resulting from the longer stroke, though the fractionally higher compression ratio (10.25:1 as compared to 10.0:1), a byproduct of the change in stroke and piston compression height, was a marginal aid.¹⁷ The L48 crankshaft was obviously different due the longer stroke; less obviously different were the pistons. The pistons from both engines were similar in design; both being flat-head, slipper-skirted, pressed-pin, cast aluminum-alloy pistons with valve relief's on the head. The main difference between the pistons was simply the compression height (changed in the L48 from 1.675 inch to 1.565 inch, to accommodate the change in stroke), which caused other related cascading minor changes in the piston geometry. Rods were 5.7-inch long and of forged steel in both engines.

The 1967 small-journal L30 crankshaft, casting PN 3884577, was forged steel as was the L48 crankshaft. In 1968 the large-journal L30 crankshaft material was switched to nodular cast-iron, casting PN 3941174. L48 used casting PN 3892690 in 1967 and PN 3941182 in 1968),¹⁸ with premium aluminum-alloy steel-backed bearings, upgraded from the copper-lead or Babbitt-metal steel-backed bearings used in the base 327ci-210HP engine. In 1967 Chevrolet began transitioning to a larger main bearing journal in its small-block engines. The new 350 engine was the first to receive the 2.45-inch journal. The remaining small-block engines, including the L30, did not upgrade from the 2.30-inch journal size until the 1968 model year.

Both the L30 and the L48 used the same, relatively mild, camshaft for both years (3896929 machining part number, 3896930 casting) that had a 0.390/0.410-inch intake/exhaust lift and a 310/320 degree intake/exhaust total duration using a 1.50 rocker ratio. Because of the slightly different power curves, different distributor advance settings were selected resulting in different distributor part numbers: L30 used 1111249 and 1111298 in 1967 and 1968, respectively; L48 used 1111168 and 1111264 in 1967 and 1968, respectively.

The exhaust manifolds were unchanged between the three engines, base 327, L30 327, or L48 350. The manifold design was the rear-exiting "log"-type, changed from the center-exiting "ram's horn"-type design that was incompatible with the position of the other engine compartment components in the Camaro. The exhaust casting numbers for 1967 were 3892679/3893608 (LH/RH w/o A.I.R.) or 3892683/3872730 (LH/RH w/ A.I.R.). In 1968 the Air Injection Reactor (A.I.R.) emission control system (a.k.a. "smog") became mandatory for all manual transmission cars; the exhaust manifolds used in 1968 were therefore the same as the 1967 A.I.R. version: 3892683/3872730 (LH/RH).

The 1968 L30 and L48 A.I.R. pumps were identical, installing differently than the smog pump on the base V-8.

The L30 and L48 block and head casting numbers documented by Colvin are shown in the tables below:

Both L30 and L48 engines had the same 4.001-inch nominal bore diameter and 4.4-inch bore spacing. Major engine design differences were mostly in the stroke, piston and deck height/combustion chamber volume, as can be seen from the design parameters summarized in the table of 1968 data below. The result was very similar performance, as seen in the above side-by-side comparison of the advertised gross power/torque curves.

Rear Axle Issues and Front/Rear Springs

In a notable further exception to 10-bolt axle usage for early 1967 L30/M20, CRG research has found that during the 1967 model year (presumably to avoid manufacture and stocking of rarely used ratios of 10-bolt posi design), any and all Camaro models ordered with both G80 positraction and axle ratios of 2.56, 2.73, or 3.55 received 12-bolt axles. CRG has documented a number of examples of 1967 6-cylinder and LF7 cars, as well as a few early L30/M20s (before the later 12-bolt changeover), containing G80 12-bolt axles that were installed by the factory. So, for this separate and distinct reason, there are a relatively few early 1967 L30/M20s with 12-bolt axles, in addition to the later L30/M20s built following the date of 12-bolt changeover.

Relatively late in Camaro development, the higher-performance 1967 models were found to experience severe rear wheel hop under hard acceleration, a dynamic phenomenon of asymmetric spring loading caused by sudden application of high engine torque to the rear axle. The rear suspension must react this torque and the resulting S-shaped deflection of the rear single-leaf springs (called windup by some) actually caused the rear wheels to leave the ground in a disturbing oscillatory manner; this naturally also included a loss of traction. Camaro designers improved the situation with a mid-1967 addition to the higher-performance models of a factory traction bar, called a radius rod, to limit wind-up of the rear single-leaf springs. Much more information on the topic of the 1967 radius rod can be found in the CRG Research Report on 1967 Radius Rods. Since all Camaro high-performance models (except the L30/M20, which was separately slated to be changed to the 12-bolt axle) already had a 12-bolt axle, the radius rod design solution was implemented only on 12-bolt Camaro axles.

As noted above and reported in the Chevrolet Service News, Chevrolet made a mid-year switch from the 10-bolt axle to the 12-bolt axle for the 327ci/275hp engines with a 4-speed transmission (this general axle change applied to all car lines, not just Camaro). As such, the standard L30/M20 10-bolt axle was changed to the 12-bolt design used on SS and Z28, including the radius rod. (The radius rod was not applied to those few lower-performance cars that received the 12-bolt axle due to selection of G80 positraction - they received the earlier axle design without the radius rod bracket.)

Following the 12-bolt changeover the L30/M20 economy/standard/performance rear axle ratios changed from the 10-bolt ratios of 2.73/3.08/3.55 to the 12-bolt ratios of 2.73/3.07/3.55 (these continued through the 1968 model year) while the L48 standard gear ratios remained at 3.07/3.31/3.55 for both years. Just prior to and in preparation for the 1967 axle/radius rod change, the 1967 Fisher Body 4P cowl tag code that had formerly applied only to the SS350 was also applied to the L30/M20. Implementation of the 4P cowl code to L30/M20 by Fisher Body - which implied the addition of the radius rod lower body attachment bracket to the lower right rear body - preceded installation of the 12-bolt axles at Chevrolet Assembly by a few weeks.

Two views of 1967 12-bolt axles showing the "Mono-Plate" single-leaf, width-tapered, rear spring, with the later rectangular radius rod (traction bar). Also notice the dual exhaust with crossflow muffler and dual resonators; this was standard equipment on the SS and Z/28 and optional for the L30/M20.

The traction bar was a temporary fix at best; definitely not very satisfactory. By the 1968 model year Chevrolet was better able to come to grips with the magnitude and extent of the wheel-hop problem. The rear suspension design was modified by angling the previously near-vertical shock-absorbers to better deal with windup related deflections; the right rear shock was angled forward, and the left rear shock was relocated to behind the rear axle and angle rear-wards.

The single leaf spring and radius rod combination of 1967 was replaced in 1968 on performance models with multi-leaf springs (sans the radius rod). Multi-leaf springs, though much heavier, and not necessarily any stiffer under purely vertical loads, provide a much stiffer response than single-leaf springs under wind-up loading, and also provide additional damping in the form of interleaf friction as an aid to the shock absorbers.

The 1967 single-leaf rear spring proved to be incapable of handling the power of the L30 and L48 engines and was changed to a multi-leaf design in 1968.

The assembly plant selected different spring types, stiffness, and load ratings, depending on the major performance-, mass-, and ride-related options to be installed on any given car. Spring selection data extracted from the 1968 Chevrolet assembly manual, reformatted for better comparison, are shown in the following table for the L30/M20 and L48 options. Note that the spring selections for the L48 SS-350 and the L30/M20 were essentially identical, where the option choices overlapped. The two exceptions are: 1) a minor difference between the two models in the rear spring load rating for the F41 handling option, and 2) a special rear spring selection for the L48 when the rear-end axle ratio was optionally selected to be 3.55 or higher.

Spring selection tables provided for the assembly plant considered body style (coupe or convertible), powertrain options (including mass of engine and whether or not usage might be high-performance), ride options (F41 handling package and G31 heavy-duty spring package), and whether or not air conditioning was included. In 1968 there were five possible front coil springs: coupe springs were selected from four designs, while the convertible used either of two different springs (the YZ spring was used for certain combinations on either coupe or convertible). For the rear, there were seven possible rear multi-leaf spring designs: five different springs were used on the coupe (with BI unique to the L48/F41), while the convertible used one of three springs (the OG spring being used on both convertible and coupe). Note that the L48 high-ratio rear axle options, which were made available primarily for drag-racing enthusiasts, RPOs H05 (3.55), G96 (3.73), and certain RPO G80 selections (Positraction, with either 4.10, 4.56, or 4.88 ratio), received specially selected rear springs to further help reduce axle wind-up during hard acceleration. These are not documented as being available to the L30/M20.

Documented Performance

SS350 reviews are available from the November 1966 Car and Driver (with 3.31 gearing) and the May 1967 Motor Trend (3.55 gearing). When adjustments are made for gearing differences, the 1/4-mile abilities of the factory L30/M20 are essentially the same as the factory SS350.

Interestingly enough, at least one L30/M20 is known to have made it into the SCCA Trans Am races. The Heishman racing team had planned from the start to turn their 1967 Z28 race car back to street form for sale at the end of the season. But, to save money, at the end of the 1967 racing season they decided to keep the 1967 Z28 drivetrain and insert it into a new (non-Z28) 1968 Camaro. The team bought a 1968 L30/M20 off the lot because it fit the basics of what they needed. They then swapped the complete drivetrains, putting the 1968 L30/M20 drivetrain into the 1967 Z28 (which was stripped of all racing equipment, repainted, and sold as a "plain jane" street car), while the 1967 Z28 drivetrain went into the 1968 L30/M20 to create their new 1968 model race car. The 1968 race car (a L30/M20 as delivered from the factory, but now part Z28) raced with the factory D91 "bumblebee" stripe as well as the original Z21 exterior trim package.

(Click on photo to expand)

The Heishman No. 24 1968 Trans-Am racer, shown here with Jim Murphy as driver, started life as a 1968 L30/M20; the original 327-based drivetrain was replaced with the 302-based drivetrain from their 1967 Z28 racer. Photo credit: Michael Booth

Conclusions

Footnotes

1. In addition to the 275HP L30, the 327 engine was available (in other Chevrolet models) in variants of 300 to 350HP, more than sufficient to power the small-block version of the Camaro SS. The 350ci engine was developed, according to Camaro engineers of the time, largely as a marketing vehicle to the cubic-inch oriented public, to combat the Ford Mustang 351 engine. Likewise, the 396, offered as a mid-67 Camaro addition, was intended to balance the Ford 390 engine available in the Mustang and stifle criticism of a lack of muscle-car raw power.

2. The L30 engine was eliminated for 1969 and replaced with a slightly lower-performance, detuned 350ci RPO LM1 engine that developed 255HP on regular octane gasoline. The LM1 was sufficiently powerful to be considered "high-performance" when teamed with a manual transmission, but was a noticeable drop in performance below the now 300HP L48. However, the basic concept for the LM1/M20 in 1969 was the same as the L30/M20 in 1967-68; a lower-priced, low-profile, performance Camaro with a significant package of high-performance components. To Chevrolet's credit, the LM1 was given the Muncie 4-speed rather than the Saginaw 4-speed with which the L30 was saddled.

3. Chevrolet, upon request, provides Camaro specification documentation that includes this data.

4. Gib Hufstader, May 1997. Some exceptions remain, but the demise of Chevrolet Central Engineering into the melting pot of GM Engineering, and the retirement and passing of key Camaro engineers now makes this data all that more difficult to trace and find.

5. Camaro Enthusiast, Spring 97.

6. This assumes that one considers the 400ci SBC engine of the early to mid 70’s, with its siamesed bores and externally balanced assembly, to be more of a distant cousin than a direct descendent. Of course there were other subsequent SBC engines with direct lineage to the 265, including the short-lived and specialized 302, the poorly appreciated 307 (developed for low-performance emission-control), and later on, the generally well-respected 305; but none of these were engine expansions in the same sense as the 350.

7. The new 350 crankshaft also introduced a broader change that affected the other small-block V8 engines; the diameter of the main bearing journal was increased in size from 2.30 inch to 2.45 inch. Except for the 1967 350 (which inaugurated the "large-journal" crank), engines from 1967 and earlier used the "small-journal" crank while all engines from 1968 and later used the 2.45-inch diameter "large-journal" crank. Since 1968 was the last year for the high-performance 327, it was also the only year that a forged-steel 327 large-journal crank was produced. The low-end, 2-BBL carburetor, 327 used a money-saving but lower-strength cast-iron crank; by mid-year 1969 the 327 was totally phased out in favor of the lowly 307 engine.

8. In 1969, the RPO code for the Camaro SS package was changed to Z27 and the L48 code became the component code for the default engine of the Z27 code.

9. The "high-performance" designation was, and still is, an arbitrary classification. The difference was often one of interpretation, or a matter of expectation. In the case of the L30, the four-speed model was considered by the public to be a "hotter" car. The dividing line moved somewhat in 1969; the successor to the L30, the 350ci LM1 with 20 less HP, was considered higher performance when mounted to any manual transmission! While these models were not all-out slaves to the horsepower gods, and so probably not worthy of being called true "muscle" cars, they certainly earn the "high-performance" appellation.

10. The 10-bolt rear end has had, at various times during its history, a number of different ring gear diameters. During the first-generation Camaro years, the 10-bolt used a 8.125-inch diameter ring gear. With the 1970 model Camaros the 12-bolt rear axle was phased out and the 10-bolt redesigned to use a more robust, more universally suitable, 8.5-inch diameter ring gear. During the low-power years of the mid 1970s to early 1980s, the 10-bolt ring gear diameter was reduced to as small as 7.5 inches.

11. The Muncie transmission was the only significant SS performance component not available to the L30/M20 as a factory option. This was the only significant shortfall of the L30/M20. While the Saginaw was sufficiently functional, the Muncie was superior and therefore more desirable. The Muncie was not only lighter due to the aluminum case, it was simply a better design, and the gears were constructed from higher quality steels. This didn't necessarily make a Muncie car any faster, but it was certainly less prone to problems in a demanding environment. The Saginaw was disdained more for its low-end origin (the Saginaw 4-speed was developed for the Corvair) than for any inability, real or imagined, to perform. The cast-iron case was a visible sign that the Saginaw was supposedly "lower-tech", but it saved Chevrolet some $75 per unit over the Muncie. Yet Chevrolet charged buyers the same price for an "M20" option, regardless of which unit it actually installed.

12. Deduced from CAC/AMA weight tables for various 1968 Camaros with various option groups.

13. Bob Shonk, private communication, 15 Dec 2000.

14. Please contact the author if you have, or believe you have, an authentic L30/M20.

15. Not offered in domestic Camaros; production of 283 engines ended with the 1967 model year, replaced with the low-power 327 in 1968 and early 1969, which was itself replaced in mid-1969 with the 307.

16. A valid argument can be made that the L30 engine is the historical 327 norm, with the 210HP version a low-end departure from the L30.

17. The standard dual exhausts on the L48 were not a factor in the gross horsepower numbers, since a common dynamometer exhaust system was used in the gross horsepower tests of that day.

18. The 1967 L30 engine used the "small-journal" crank with a 2.30 inch diameter main journal and a 2.00 inch diameter rod journal. In 1968 the switch was completed to the "large-journal" crank with a 2.45-inch diameter main journal and a 2.10-inch diameter rod journal, the same dimensions used on the L48 in both years.

Author Notes

L30/M20 Owner Stories

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