Index

• The Engine
• The LM1 Drivetrain
• The LM1 Replacement
• LM1 vs L48 SS
• ID'ing the LM1

Introduction

The Engine

The LM1 engine was only available the first four months of the year, until the end of December 1968. In January of 1969, the L65 350 engine replaced it. It is unclear why the LM1 was discontinued in the Camaro. It has been proposed it was emissions related, but the engine was still available in other Chevrolet car lines. (The Camaro base 327 / 210 hp engine suffered a similar fate at the same time, being replaced by the 307 / 200 hp engine. These engine changes cause confusion in the factory and aftermarket literature. Most sources only list two of these four engines.)

The change to the 350 engine size from the 327 was part of Chevrolet's broader engine plan for the coming decade. The 307 would be replacing the 327 as the base V8 engine and the 350 engine would cover the mid-to-upper small-block power range.

In 1969, Chevrolet built 10,406 Camaros with the LM1 option, a little over 12% of the production for the first four months of the model year, but only 4.2 % of overall 69 production. For comparison, the base engine was 53% of production for the 1969 model year and the L65 engine (that replaced the LM1) was 21% of of production. The L30 option was ordered on just over 11% of 67 Camaros and 9% of 68 Camaros. So the sales rate of the LM1 was very similar to the L30 that it replaced, but the L65 had almost double the sales rate of the LM1.[1]

The LM1 Drivetrain

The base transmission for the LM1 was the heavy-duty MC1 3-speed manual transmission, built by Muncie. This was the same base transmission offered with all SS cars. All MC1 transmissions were floor shift.

LM1 cars ordered with the M20 4-speed received the superior Muncie 4-speed transmission with an aluminum case instead of the lower capacity and heavier Saginaw 4-speed transmission. (Note that M20 was not the name of the transmission but rather was the functional designation for any standard ratio 4-speed manual transmission.) The Muncie transmission combined with the Hurst shifter that was used in all 69 4-speed cars made for a great performing transmission.

These were marked changes from the L30 (327/275hp) engine that the LM1 replaced. The Camaro L30 powertrains only received the 12-bolt upgrade when ordered with the M20 4-speed transmission and then still used the lesser Saginaw transmission. Why these upgrades in powertrain configurations were done for 1969 is unclear, but it may have been due to the increased torque of the LM1 engine.

The LM1 Replacement

The standard axle for the L65 was the 10-bolt (though a few 12-bolts were used, mostly in the first few months of L65 production). The base transmission reverted back to the manual column shift (!) Saginaw 3-speed and the M20 transmission was now a Saginaw 4-speed again. The default axle ratios also changed on the L65, to the detriment of performance. The default ratio of a LM1/manual transmission powertrain was 3.31, whereas the L65/manual transmission default axle ratio was 3.08. The default ratios for automatic transmission went from 3.07 with the LM1 to 2.56 with the L65. The one feature that did not change was the L65 still received multi-leaf rear springs.

Again, the technical reasons for the downgraded drivetrain components are unclear, since the torque and horsepower output of the L65 should be very close to the LM1. There are two other possible reasons:
• Marketing - did people really want to pay the extra money for the drivetrain upgrades that came with the LM1?
• Profit margin - the cost of the drivetrain (namely the axle and the 4 speed transmission) could be reduced.

The L65 option price was reduced significantly compared to the LM1 ($21.10 vs $52.70) with almost the same horsepower rating. The jump in L65 sales rate (almost double the LM1 rate) proved that people were more sensitive to price than features under the car (features that most buyers didn't even know were there).

LM1 vs L48 SS

1. The main difference between the engines was the heads. The LM1 used the 3932441 heads that had a 76 cc chamber yielding a compression ratio of 9.0:1, while the L48 used the 3947041 heads that had the 63 cc chamber. The smaller chamber of the L48 caused an increase in the compression ratio to 10.25:1 and thus increased the power output.
2. The LM1 and L48 short blocks were the same; both used the same pistons, rods, cast cranks, and camshafts. LM1's have been found with both 2-bolt and 4-bolt blocks, though it appears that most were 2-bolt blocks. Most L48's appear to have used 4-bolt blocks, but a few L48 engines been observed with 2-bolt blocks. (There is no real functional difference between a 2-bolt and a 4-bolt block at these power output levels.)
3. There were minor differences in the distributor calibration, so the two engines used different distributors.
4. The LM1 exhaust system was 2" O.D., where as the L48 exhaust was 2.25" O.D.
5. The LM1 with manual transmission used the smaller 10.4-inch clutch, whereas the SS used the 11-inch clutch. (The smaller clutch was also used on Z28's, so it wasn't really a weakness.)
6. The LM1 and the L48 powertrains received the same default axle ratios: 3.31 for manual transmissions and 3.07 for automatic transmissions.
7. The SS package included disc brakes. Drum brakes were standard on LM1 cars, with power drums (RPO J50) and power discs (RPO J52) being available options.
8. The SS package included F41 special suspension, N10 dual exhaust, N44 fast ratio steering (if power steering was ordered), and F70x14 tires on 14x7 wheels. All of these features were optional on the LM1 except the wheels. The LM1 came with 14x6 wheels.
9. Appearance. The SS package included the D90 Sport Striping, SS badging, and the SS hood and hood insulation. The D90 stripe was an option on the LM1.
10. $$$$

The money difference could be pretty big, The cost was $52.70 for the LM1 engine option. For an LM1 with disc brakes, dual exhaust, and F41 suspension, it was $158.05 versus $295.95 for an SS350 (note that it was another $62.60 to upgrade the tires to the L48 tires). To that price, add the cost of any optional transmission ($175-$200) to either car. By adding the RPO D90 stripe on the LM1 car for $25.30, it even looked like an SS except for the hood and SS badging.

The SS350 was a more complete package, but no doubt about it, the LM1 gave you a lot of bang for the buck.

There was one notable ordering difference between the SS package and the LM1. The base transmission, the MC1 HD 3-speed transmission, was included in the the SS package. On the LM1, this transmission was a mandatory option for an extra $79. If any other transmission was ordered (which most people did), the transmission cost was the same for either engine.

The fact the the SS price included the MC1 transmission did affect the orders. To order a 4-speed on the LM1, it was only a $116 cost increment over the 3-speed; on the SS350, the cost increment was the full $195 price for the 4-speed. So most LM1 buyers spent the extra money and got a 4-speed over the 3-speed. LM1's with a 3-speed are not very common, whereas SS350's with 3-speeds are more common (though most have been converted to 4-speeds over time).

ID'ing the LM1

There was no special badging for the LM1 option, so the best way to identify an LM1 is via factory or dealer documentation (e.g. window sticker, invoice, protect-o-plate, etc) showing the options or via the original engine.

The LM1 engines for Camaro applications were stamped with the engine codes of HQ for manual transmissions, HR for M35 Powerglide transmissions, and HS for M38 Turbo 350 transmissions and should be appropriately dated for the car. The partial VIN should also be stamped on most engine pads (some of the later December cars may have the VIN stamped by the oil filter).

If the original engine and original documentation are gone, it becomes tougher to determine what the original engine was. Telling the difference between an LM1 and an L48 SS in this case is difficult and sometimes not possible.

LM1's were only built for four months in 1969 model year - from start of production until the end of December 1968. They were built at both the Norwood and Los Angeles plants. Most will not have X-codes on the cowl tag since that coding was introduced in mid-December on Norwood cars, but for those late December Norwood cars with an X code, it would be an X11 or X44. An SS350 car would be X11 or X55.

Several features were required on the SS. If they are missing, the car cannot be an SS, but the presence of them does not prove that it is an SS since they were optional on a LM1.

All LM1 and SS350 cars should have:

• 2 fuel lines due to the vapor return line for the Quadrajet carb
• 12 bolt rear axles (though 10 bolt axles had limited usage in some automatic cars) [2]
• rear brake line valve (note that usage of this valve was not always consistent)
• multileaf rear springs
• Muncie 4-speed transmission if a 4-speed
• Muncie 3-speed transmission if a manual 3-speed.

SS cars had:

• disc brakes
• dual exhaust
• SS hoods (cowl hoods were not available until January of 1969)
• wider wheels

Two of these four features were optional on the LM1 – disc brakes and dual exhaust. If the car has 2 fuel lines, 12-bolt, and a Muncie (if 4-speed), but does not have disc brakes and/or the dual exhaust doubler plate (coupes only, mounted on the driver's side rear frame rail), then it is a LM1 car.

If it does have discs and the dual exhaust doubler plate (coupes only), the results are inconclusive, it could be either a LM1 or a L48. The only thing left to check is the hood and hood springs, but these could have been changed over the years.

Summation

No, the LM1 was not a solid lifter terror on the street. But it was a performance model - a continuation and expansion of the 1967-68 L30/M20 performance legacy. The automatic and 3-speed manual cars were now included - the 12-bolt axle could handle any abuse the small block could deliver. The manual 4-speed cars received the notable improvement of the Muncie four speed with the Hurst shifter.

The LM1 was also a deal, especially considering the drivetrain upgrades that were included with the engine. The possible savings over the SS350 was a good chunk of change and you could order the options you wanted and pocket the difference. The SS350 was a more complete package, but with the LM1, you could end up with a sleeper of a car that was more than respectable on the street but didn't draw too much attention. Which, for some people, was the whole point.

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