Author Topic: JM Coded Engine... has anyone ever seen a JM coded engine block?  (Read 10580 times)

firstgenaddict

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I have asked a few guys that deal in high performance big block chevrolet's and they have never seen one...
Wondering if anyone has seen a L89 Auto engine... ever?
James
Collectin' Camaro's since "Only Rednecks drove them"
Current caretaker of 1971 LT1's - 11130 and 21783 Check out the Black 69 RS/Z28 45k mile Survivor and the Lemans Blue 69 Z 10D frame off...
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KurtS

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #1 on: July 23, 2018, 04:03:06 AM »
About 4 or 5.
Kurt S
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Opium Motors

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #2 on: August 01, 2018, 05:50:15 AM »
JM 1969- 396/375hp Camaro w/ Aluminum Heads
Also
JM 1969- 396/375hp Nova
« Last Edit: August 01, 2018, 07:21:44 AM by Opium Motors »
1968 Camaro RS Convertible 327 4 Speed Corvette Bronze
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KurtS

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #3 on: August 01, 2018, 05:55:12 AM »
L89 is not believed to ever have been installed on a Nova. Camaro only.
Kurt S
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Opium Motors

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #4 on: August 01, 2018, 07:19:45 AM »
Your right the Nova never had the L89. They called it a L78 JM 396/375hp 4Speed
1968 Camaro RS Convertible 327 4 Speed Corvette Bronze
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Kelley W King

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #5 on: August 01, 2018, 12:18:28 PM »
Most Novas were really low end or option cars. The L78 was not really that expense of an option but the L89 was. Low end is probably why they just do not bring much money. If you look at them at the shows a clock is rare and AC is even rarer.
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X33RS

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #6 on: August 01, 2018, 12:36:45 PM »
In the early 80's I knew of a 69 SS Nova that had a JM coded engine in it.  I don't know if it was original to the car but the owner history was known at the time back to the original purchaser.  2 different friends of mine wound up with the car.  The original owner was a fellow out of Indiana that was drafted to Vietnam shortly after purchase.  He never returned home and his parents just parked the car.  Scott, a friend of mine,  found the car in the early 80's advertised for sale as an L89 with low miles.  That's when I first saw it.  Didn't run right and turned out the original owner had installed aluminum valve spring retainers (a common modification back then) and there were a couple of them failing and ready to drop a valve.  So he sold the car to a buddy of mine who was a competitive drag racer.  He pulled the engine for a refresh.  Other than headers it was left stock.  Was an automatic on the column and bench seat car.  Silver with black interior, and had 4.56 gears, but I don't know if those were original or not.  He actually raced the car with a pair of slicks and opened the headers.  The car clicked off 3 consecutive 11.90's passes and he put it back on the trailer.  Drove it on the street for a couple more years to various shows and cruises and then was sold to someone in New York with a car collection.  Lost track of it since and never heard of it for sale again.  I was going to purchase the car but was beaten to the punch.  Had protecto plate and other paperwork with it.   But I don't recall if the engine was original or not.  Everyone at the time believed it was a real aluminum headed car but back then it wasn't scrutinized like it is today either.  Wish I would have paid more attention to it at the time.

bertfam

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #7 on: August 01, 2018, 03:41:28 PM »
Quote
JM 1969- 396/375hp Camaro w/ Aluminum Heads
Also
JM 1969- 396/375hp Nova

Quote
Your right the Nova never had the L89. They called it a L78 JM 396/375hp 4Speed

The JM code was ONLY used on the 1969 Camaro L89 with the Turbo 400. It was never used on the 1969 Nova. The 1969 Nova L78 with the Turbo 400 was a JL code, the same as the 1969 Camaro L78 with the Turbo 400.

Ed

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #8 on: August 01, 2018, 05:53:36 PM »
Quote
JM 1969- 396/375hp Camaro w/ Aluminum Heads
Also
JM 1969- 396/375hp Nova

Quote
Your right the Nova never had the L89. They called it a L78 JM 396/375hp 4Speed

The JM code was ONLY used on the 1969 Camaro L89 with the Turbo 400. It was never used on the 1969 Nova. The 1969 Nova L78 with the Turbo 400 was a JL code, the same as the 1969 Camaro L78 with the Turbo 400.

Ed

My mistake, the Nova JM is not a L78 but did have a 396 w/L89 heads, I admit that mistake, I have no problem in admitting when I am wrong, getting old I guess....

Now, from the Novaresource.org they seem to be the CRG of Novas.

1969
8-cylinder (big block)
JF - 396cid (350hp) w/manual
JH - 396cid (375hp) w/manual
JI - 396cid (350hp) w/TH400
JL - 396cid (375hp) w/TH400
JM - 396cid (375hp) w/TH400 (L89 aluminum heads)
JU - 396cid (375hp) w/Powerglide
KA - 396cid (350hp) w/manual and HD clutch
KC - 396cid (375hp) w/manual and HD clutch
KE - 396cid (375hp) w/manual (L89 aluminum heads)

Clearly Nova did have a JM block.

Ok, I am not confrontational, I simply enjoy research and know that the learning never ends. My books have tons of penciled in information in the margins, for no source is ever perfect. I have found in my 40 yrs of working on muscle cars that there is always the exception to the rule.
1968 Camaro RS Convertible 327 4 Speed Corvette Bronze
1973 Corvette 454

bertfam

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #9 on: August 01, 2018, 06:18:43 PM »
No need for you to think you're being confrontational. We LOVE discussing things like this!! It's what we live for!

And to continue the discussion, there are a lot of WEB sites that show the JM code for the 1969 Nova, and while it "may" exist, none are known to have ever been built.

We at the CRG use original Chevrolet documentation for research because books, magazines and WEB sites are usually (more often than not) riddled with errors. The example below was taken from the September, 1968 Parts and Accessories Manual (P&A 25) showing what the engine codes were for each Chevrolet model in 1969. As you can see, there's no JM code listed for the 1969 Nova. However, while I never say never, without hard proof, I'm a disbeliever.

But even GM docs can be contradicting so we use several different GM resources to verify what actually happened at the time of manufacturer. Sometimes this can be really frustrating but usually, through a lot of digging, we can get to the truth! A good example of this frustration is the Dual Disk clutch option for the 1969 Camaro, RPO MA6). There are references to it in Chevrolet records, but again, none are known to have ever been built. The 1969 Corvette, yes (102 units), but not the 1969 Camaro.

If you have an original GM doc showing something different, please let us know. We're ALWAYS on the lookout for original GM documentation!

Ed

Opium Motors

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #10 on: August 01, 2018, 06:46:46 PM »
Most of my collection of books have already been moved to my ranch, my final destination with two barns for my cars. But I will dig out what I have and see what I can find.

1968 Camaro RS Convertible 327 4 Speed Corvette Bronze
1973 Corvette 454

bcmiller

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #11 on: August 01, 2018, 07:28:19 PM »
Yes I have heard rumors of L89 Novas for years. But remember that the heads were available over the counter and as stated, back then codes on engines were not scrutinized as heavily as today.

As rare as they might be, you would think at least one L89 Nova would have surfaced with documentation by now if they existed. I don't think they do.

And yes most of the Novas were “lower end” cars (bench seats, rubber floor mats) but damn with a little work they are FAST.  Remember Chevrolet would not let the 427 be factory installed in 69 like they allowed for the Camaro and Chevelle. Yenko did, and then called it “a beast” and “almost lethal”.   
Bryon / 1968 Camaro SS 396 coupe - now old school 468 big block
1967 Camaro RS/SS 396 coupe L35/M40 - 4 generation family project
Looking for 68 Camaro with body # NOR 181016

Opium Motors

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #12 on: August 01, 2018, 07:39:41 PM »
This is a 1970 but good information.

https://www.hemmings.com/magazine/mus/2008/06/1970-Chevrolet-Nova-SS-396-375-L89/1643771.html

...Chevrolet offered them as an upgrade to its hairiest version of the 396: the 375hp L78. Selecting the alloy heads changed the engine code to L89, but didn't up the horsepower rating--that remained at 375. As this was a pricey upgrade, particularly for something that didn't provide any extra power, not many Chevys were built with the L89 option....It took some digging, but Frendel was finally able to find a source that confirmed the availability of the L89 in the Nova and, more specifically, the CKT-code block as designating an L89 meant for a Nova.

I would love to know the source he discovered

So in 1969 you can special order L89 Heads for your 396, and if as above that is where they get the L89 Option. Now we need the proof of a JM block for Nova.
1968 Camaro RS Convertible 327 4 Speed Corvette Bronze
1973 Corvette 454

bcmiller

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #13 on: August 01, 2018, 07:53:14 PM »
People have been looking for many years, no proof has been found. 
Bryon / 1968 Camaro SS 396 coupe - now old school 468 big block
1967 Camaro RS/SS 396 coupe L35/M40 - 4 generation family project
Looking for 68 Camaro with body # NOR 181016

bcmiller

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Re: JM Coded Engine... has anyone ever seen a JM coded engine block?
« Reply #14 on: August 01, 2018, 08:39:28 PM »
Quote
Ok, I am not confrontational, I simply enjoy research and know that the learning never ends. My books have tons of penciled in information in the margins, for no source is ever perfect. I have found in my 40 yrs of working on muscle cars that there is always the exception to the rule.

Tell us about yourself.
Bryon / 1968 Camaro SS 396 coupe - now old school 468 big block
1967 Camaro RS/SS 396 coupe L35/M40 - 4 generation family project
Looking for 68 Camaro with body # NOR 181016

 

anything