So I bought a 69 Malibu Sport Coupe from a nice older woman who inherited it from her Dad who was the original purchaser in 69. Question is how do I identify if the engine is as the kind old lady told me L48 and very proud of that her dad had one, or as the now discovered build sheet says LM1. Everything looks as its been under the hood a long time including the air Cleaner label 350 turbo fire 300 Horsepower. Its not that I care the car seems to have plenty of power but would rather represent it correctly. how do I differentiate L48 to LM1 without tearing it apart, or what are the differences Heads, 2or4 bolt mains, etc.
Thanks in advance for the assist.

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. Both heads were produced with 1.94" valves. Externally the heads had different casting features on the front of the head. A picture of the front of the head might enable a quick determination of the head type without removal of the valve cover to reveal the casting number.https://www.crankshaftcoalition.com/...identification

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 were minor differences in the distributor calibration, so the two engines used different distributors.

Both engines used the quadrajet carb. Both used the same intake manifold.

Supply the numbers on the front pad of the engine behind the alternator. If the pad is dirty, try to clean the surface without resorting to abrasives. Typically, you don't want to scratch up the surface since the surface itself has broach marks that add to authenticity. The numbers on the pad will tell us when and where the engine was built, what engine it is, and have a partial vin code that should match the last numbers of your full vin code on the dash.

If your build sheet matches the car, most likely the car has an LM1 if it's still the original engine.. The PO may have installed L48 decals on the air filter lid.

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excellent answer and as soon as it warms up I'll do some investigating and let you know what I found...Thanks

Great post, Al. About 25 years ago I bought a '69 SS350 Nova with an original L48 350 and it had a 4-bolt block and 041 heads.

I have a 1969 300HP 350 from a 1969 station wagon and it came with 186 casting heads.
I still run the short block today never been bored and crank has never been turned and still has stock rods and rod bolts it is a 2 bolt block.
It has been abused by me for over 25 years many heads and cams have been in it and 4 sets of pistons.
280H and 58cc heads currently in it with flat tops.
It loves some RPM .

Great score Richard

My first car was a 69 L48 4 speed with a posi 12 bolt that I purchased before I had my license at 15 years old. About 1978, long before I knew what I really had. Optioned to the hilt with buckets and console. I often thought that the person that ordered it wanted an SS without the big block power. I called it silver with black interior, but was often corrected by friends that said it was silverish green since I'm a little color blind.

Once I did a rebuild to LT1 specs, that car put many big block cars to shame. The heads got the 202 valves and my own port job. I ran the LT1 cam straight from a Chevy dealer along with titanium valve keepers and LT1 springs. A set of Hooker headers and exhaust. I was in the 12's. About the same time, a buddy and me met Dale Thermos of NOS systems in Long Beach. We were into photography and we did his product catalogs. We'll we also got the latest greatest Nos systems available. With a completely hidden and plumbed system, I was in the 11's on slicks at 17 years old. Pretty good for those days with a small block.

I should have kept that car. But saw a 69 Z-28 I fell in love with so it had to go.

So the verdict is: Block Casting:3932388 Heads Casting 3932441 and Engine SN 197302745 T0905HS
So it is the original LM1 Engine and I'll have to figure a good combo to ramp up the pony power to Horse power. Good news is it runs on pump gas and air cleaner stickers are not always as they seem.

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and the block casting

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Engine code HS is 255 hp 350 LM1 with TH350 trans. I'm curious, does it have a 12 bolt diff?

Richard: the car is a great find, regardless of what 350 it was born with.

Headers, an RPM intake, a Holley 3310 carb, and a modest cam will wake that motor up a bit....if you care about that sort of stuff. (That's basically what I did to my first 1969 Malibu in high school/1990, although I swapped out the heads.)

Car is certainly cool enough in Factory form.

BTW: is it only us '69 guys who salivate over an L48? I think they're way cool.

I passed on one about a year before I found my current '69 Malibu....partly b/c I didn't realize what it was at the time. But mostly b/c it was on the other side of the Country. I kept photos of it and still think about that car from time to time. Lemans blue, white vinyl top, and parchment interior.

I spent over two years looking for my current Malibu. But that car and a '69 SS in Burgundy with a black top and interior, whose original owner was supposedly KIA in Vietnam shortly after purchasing it, have never left my mind and I half-a*s think of trying to track them down some day.....although I'm currently out of garage space.

Yes, big block guys don't get it until they get smoked by one.

Von, yes it has a 12 bolt, Ill explore what the numbers there tell me tommorow...wish I had a lift

LM1 350 255 HP 4 BBL. Option cancelled early in year because drag racers were gobbling them up. LM1 models were fairly cheap and they came with 12 bolts and muncie trans if you ordered 4 speed.

I know this because my father ordered a 69 camaro LM1 brand new and car was delivered to dealer with standard 350 2bbl 250 hp with saginaw trans/10 bolt. boy he was pissed and they said oh well. to settle the matter they had an LM1 impala on the lot and swapped intakes to give him a 4bbl & shut him up. Boy if he only knew about all the other stuff he didnt get along with that intake deal. Lost track of this car on long island in 1972. Anyone know where it is?

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I don't know where the car is, but I've heard many similar stories just as you describe.

Car was total strip down with a copo appearance. It was delivered with dog dish hubcaps Fathom green black buckets factory 4 speed non console car with manual steering manual brakes and 3:08 gears. The chrome reverse rims were added when new and it had 2 stewart warner gauges neatly cut into the center of dash pad. Purchased new at Amity chevrolet in amityville NY. Car was sold in 1972 locally. Kid came back to bitch about blowing the trans up shortly afterward. Never seen again. I have no vin or paperwork but would love to know if it is still out there