Special guest feature article by Rich Fields

(Please note: Footnotes are bookmarked- click on superscript numerals to view)

L30/M20 Technical Specifications:

Both L48 and L30 engines have nearly identical ci/HP ratios: 1.186 and 1.189, respectively. The common origins and obvious similarities caused Chevrolet to consider the both the 327 and the 350 part of the "Turbo-Fire" V8 family that also included the 283¹⁵.

These charts compare the 327-275 hp and 350-295 hp engines.. Notice how closely the power curves parallel each other. (Note that they are both plotted at the same scale, although the L48 plot has a higher cut-off limit and is therefore on a taller plot.)

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 (part numbers 7027203 or 7027213 in 1967 and 7028213 in 1968) 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. The starter changed; the high compression ratio of the L30 required a low-RPM, high-torque starter (1107388 in 67, 1108361 in 68) that substituted for the typical base V-8 starter (1107496 for most of 67, 1108367 in 68).

Below: An L30/M20 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 aid¹⁷. 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. Crankshafts in both were forged steel rather than the nodular cast-iron used in the 327ci-210HP (the L30 crankshaft was part number 3884577 in 1967 and 3914672 in 1968; L48 used part number 3892690 in 1967 and 3941182 in 1968)aluminum-alloy steel-backed bearings, ¹⁸ with premium upgraded from the copper-lead or Babbitt-metal steel-backed bearings used in the low-end 327-210 engine.

Both the L30 and the L48 used the same, relatively mild, camshaft for both years (3896929 part, 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: 1111249 and 1111298 for L30 in 1967 and 1968, respectively; 1111168 and 1111264 for L48 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.), 3892683/3872730 (LH/RH w/ A.I.R.). For 1968 (all of which had A.I.R. emission control added to manual transmission cars) the manifolds were the same as for 67: 3892683/3872730 (LH/RH). ). The L30 and L48 A.I.R. pump (a.k.a, smog pump) 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:

Engine block castings:

Year	Block Casting Number	(all are 2-bolt mains)	Camaro Usage	Comments
1967	3892657		327-210, 327-275, 302-290, 350-295	Small journal crank
	3903352			un-verified Small journal crank
1968	3914660		327-210, 327-275	Large journal crank
	3914678		327-210, 327-275, 302-290, 350-295	Large journal crank

Cylinder head castings:

Year	Cylinder Head Casting Number*	Camaro Usage	Comments**
1967 (early)	3890462	327/275, 350/295
1967 (late)	3917291	327/275, 350/295	added temperature sending boss, 0.410 valve guide boss diameter
1968	3917291	327/275, 350/295	temperature sending boss tapped for sending unit

*Large valve versions of the same casting were used by higher performance engines like the 302.
**All had a double-hump casting symbol, 63.305 cc chamber, 1.94 in. inlet, and 1.50 in. exhaust.

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.

Engine specification comparator:

	Base 327	L30 327	L48 350
Combustion chamber volume, cc	5.38	4.69	4.79
Crankshaft arm length, in	1.625	1.625	1.74
Overall inlet valve length, in	4.912	4.880	same
Overall inlet valve diameter, in	1.720	1.940	same
Inlet valve seat diameter, in	1.780	2.000	same
Exhaust valve diameter, in	1.500	same	same
Piston type/material	cast Al alloy	same	same
Piston type	flat, notched	same	same
Piston skirt type	slipper	same	same
Top land clearance, in	0.0410	same	0.0230
Skirt clearance, in	0.0008	same	0.0010
Compression ring groove depth, in	0.2247	same	0.2253
Oil ring groove depth, in	0.2071	same	same
Pin bore offset, in	0.060	same	same
Compression height, in	1.675	same	1.565
Piston pin clearance, in	0.0002	same	0.0003
Upper compression ring width, in	0.0778	same	0.0773
Lower compression ring width, in	0.0773	same	0.0778
Lower compression ring gap, in	0.019	0.019	0.018
Connecting rod length, in	5.700	same	same
Rod bearings	alloy-backed steel	premium aluminum	same
Effective rod bearing length, in	0.797	same	0.807
Air cleaner diameter, in	13.00	15.48	same

Rear Axle Data:

For 1967, the L30/M20 "standard" rear axle ratio selection of 3.31 was identical to the L48. In 1968 the standard ratio for the L30/M20 changed to the higher top end 3.07 ratio, which the L48 used for an "economy" ratio instead of the 2.73 ratio used in the L30/M20. Both used 3.55 gearing for the "performance" ratio in both years. The designations of Standard, Economy, and Performance in the following tables apply only to the L30/M20. While the L30/M20 and L48 were only produced with the 12-bolt ring gear (barring an unusual special order), the rear axle data below attempt to summarize all documented rear axle codes for all 1967 and 1968 Camaros.

These rear axle data tables present and compare rear-axle ratio codes documented by four references: the 1983 edition of the GM Parts Manual (noted as "GM"), Alan Colvin's Chevrolet By The Numbers: 1965-1969 ("CBTN"), data from the US Camaro Club ("USCC"), and the 1972 edition of the Camaro-only parts catalogue from GM of Canada ("GMCA"). The codes in the tables begin by comparing the first three sources; to these is added a suffix to note the relationship of this code to the fourth source, as described below. The fourth data source used, the 1972 GM of Canada Camaro-only parts manual, is probably the single most authoritative and complete set extant, listing all Camaro axle codes in detail with supporting information. To the codes from the first three sources a suffix is added, indicating the extent of agreement and/or difference of these codes with the GMCA data. The symbols used are:

· Unemphasized uppercase characters - means that this axle code agrees between the first three sources. (An additional suffix of "*" means that the GM of Canada list also agrees.)

· Axle code in another uppercase font - means that there is a different interpretation of this code by another of the first three sources. All meanings are listed, with the CBTN interpretation in bold letters, the USCC meaning in italic letters, and the GM meaning in parentheses.

· Lowercase axle code - means this axle code is documented by only one of the first three sources. Lowercase bold codes are unique to CBTN. Lowercase italic codes are unique to USCC. Lowercase codes in parentheses are unique to GM.

· GMCA comparison - axle codes ending in * or # fully or partially agree with the GMCA list. The suffixes and their meanings are:

1."*" indicates universal agreement.

2."#" indicates agreement with one or more, but not all three, other sources.

3."+" indicates that this code appears in one or more of the other sources but not in the GMCA list.

4."-" indicates a disagreement with a GMCA code elsewhere in the list.

5."!" indicates a code unique to the GMCA list.

· Ring gear sizes - notes on ring gear size are based on the GMCA data.

There are cases where the disagreement between the sources is only in the year of application. For example, the QL code is in all cases shown as a 3.31 ratio 12-bolt positraction axle, but is described as a 1968 axle code by GMCA and as a 1967 application by the other sources. There may have been some cross-over applications in late 67 and early 68 models that led to this discrepancy. A very late 67 car with this axle has been documented. As more vehicles are documented, minor discrepancies such as this will be resolved.

Note that the 3.07, 3.31, and the 3.73 and higher ratios were only available with the 12-bolt ring gear. Note also that the 3.08 ratio was only available in the 10-bolt ring gear. The other ratios were available in both 10-bolt and 12-bolt rear ends, as noted.

 

1967 Rear Axle Codes

The 1967 PV code was also listed by GM, which agreed with the CBTN meaning rather than the USCC meaning.

1968 Rear Axle Codes

With only a couple of exceptions listed below, USCC is the same as GM, and so USCC codes are not specifically listed for 1968. The USCC exceptions to the 1968 GM listing: BC and BD are listed as 3.31, PT replaces PH.

Note also that the codes listed as "4-wheel disc brakes" do not appear in the 68 GM of Canada list, although codes QU, QV, QW, QX, QY appear in the 1969 listing as positraction axles with those same ratios. This difference in listing is explained by the fact that the 4-wheel disc brake axles were really 69 parts available in late 68 (for racing purposes) only as special order over-the-counter items.

Front and Rear Springs:

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.

Illustrated in this photo is the 1967 Mono-Plate springs, traction bar and 12 bolt rear shared by the the high performance L30/M20 combination, SS models and Z/28. Also notice the dual exhaust with crossflow muffler and dual resonators. This system was standard equipment on the SS and Z/28 models and optional for the L30/M20...

For 1968, the rear springs for these models were changed from Mono-Plate single-leaf to multi-leaf springs. Relatively late in Camaro development, the high-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 included a loss of traction. Camaro designers improved the situation on the 1967 models with the early year introduction of a traction bar (called a radius rod by the factory, and only used on the high-performance models: SS, Z28, and L30/M20) to limit the hard-acceleration wind-up deflection of the rear single-leaf springs.

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 traction bar combination of 1967 was replaced with multi-leaf springs. 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.
	Single leaf above proved to be incapable of handling the power of the L30 and L48...

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.

SPRING USAGE CHART:

*L48 with PG or one of the following rear axle ratios: 3.55, 3.73, 4.10, 4.56, 4.88.

Documented Performance:

L30/M20 performance was reviewed by "Road & Track" in the March 1967
issue, compared against the 289 Mustang and the 273 Barracuda. In standing start performance the L30/M20 thrashed the Mustang. Due to the higher gearing of the Plymouth test vehicle, the 3.23-geared Barracuda was equal to the 3.07-geared L30/M20 in the low-end, but the L30/M20 pulled away easily in the top end. 0-100 mph performance was 23.9 seconds for this L30/M20, a full second ahead of the 'Cuda and 3.1 seconds ahead of the Mustang. This despite the Camaro test vehicle having to perform with standard D78-14 (7.35 in wide) tires, while the Mustang and Barracuda were fitted with F70-14 (8.40 inch wide) and D70-14 (7.80 inch wide) tires, respectively. This article doesn't discuss the exhaust systems, but it is reasonable to assume that this L30/M20 test vehicle also probably had the standard single exhaust, rather than the optional dual exhaust. 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 abilities of the L30/M20 are essentially the same as the SS350.

Conclusion...

The L30/M20 is an unusual, and until now, previously not well documented, first-generation Camaro model. While the apparent rarity of the L30/M20 does not assure either increased desirability or worth, this technical summary does take a step toward raising awareness among the Camaro restoration community to this very interesting option package.

View foot notes and read about the Author...

Questions and comments regarding this article are welcome and encouraged.
Please click on image to email Rich Fields..

The author is indebted to Wayne Guinn for a number of items related to this article. Wayne is not only the host of this valuable Web page, he personally provided the illustrations for the article, and was a great help in research, discovering some of the more interesting background data. Additional specific valuable help was provided by Martin Foltz and Greg Davies. Thanks are also due to a number of helpful and knowledgeable members (too numerous to list) of the F-Body-Classic internet email list, who helped proofread an early draft of this article and thus reduced the error count. However, any remaining errors are my responsibility, however inadvertent.

And... Special thanks to Greg McGann and the Bell Internet for providing technical assistance in the design of this page...

Return to part one of this article.