Need help on determining LS6 motor

[Ole Greenie]

Hey ya'll...

I have a 70 CST S/S with a big block in it. I am trying to finally determine once and for all which motor I have in it. GM made a bunch of variants of BB motors and I want to know which one I have.

The motor as I understand it is a 454 LS6 motor. I can tell you that it has a Winters intake on it and it has solid lifters. I'm thinking it is a crate motor and fairly recent, not vintage because it has a 7.4 in the block casting.

The guy I bought it from said it was an LS6 but I am skeptical because it should run a bit quicker given about 450HP rating for a true LS6.

There is no stamping I can find to check the serial code but I do know that it is not a "CE" motor for replacement under warranty.

Any help from the engine Gurus would be great!
Thanks!

[71blksuper4x4]

The "real" ls6's have a casting number with the last 3 digits of 512. 512's were used in late 68-70 in 427's and 454's. I believe the 71-72 ls6 blocks are like a 289 block or something close. After that, I can't help you. They made ls6 crate motors until the early to mid 90's. Trevor

[Ole Greenie]

Thanks...Pretty sure this is not an original production run LS6 motor. The 7.4 in the casting on the passenger side of the block casting gives it away.

In talking with a few GM guys, the Winters intake with solid lifters seems to weigh to the LS6 side but the intake was also used on the L78 and L86 motors as well. Those were the 396 LS5 motors, I believe.

Did other crate BB motors come with solid lifters...or just the 450-475 LS6 motors?

Thanks again.

[geezer#99]

LS5 was a 454 rated at 360 HP. LS6 had a low rise intake to clear the hoodline on the vette and was used on the chevelle too. Square bore with a 780 Holley on it. L78 was a 396. L89 was an aluminum headed L78.
Some 427's came with solids. Can't recall which ones though.
Some blocks that are decked will show no numbers on the pad.
My 70 Chevelle with LS6 I had back in 78' had a ce block in it. Factory warranty motor. Original had 3 bad pistons in it. You should have square port heads with 11 to 1 forged pistons if it's an LS6.

[Ole Greenie]

Originally Posted by geezer#99

LS5 was a 454 rated at 360 HP. LS6 had a low rise intake to clear the hoodline on the vette and was used on the chevelle too. Square bore with a 780 Holley on it. L78 was a 396. L89 was an aluminum headed L78.
Some 427's came with solids. Can't recall which ones though.
Some blocks that are decked will show no numbers on the pad.
My 70 Chevelle with LS6 I had back in 78' had a ce block in it. Factory warranty motor. Original had 3 bad pistons in it. You should have square port heads with 11 to 1 forged pistons if it's an LS6.

Interesting, seems like I do have an LS6. I also have the low rise Winter's intake. Currently, has a 650 Holley which is getting swapped out tomorrow for an Edelbrock 750 electric choke. I will post pics when I get it done.

The SN stamp area is blank. There are no indicators/stampings on the deck to assist with identification. I wish there was a way I could take a look at the head ports to discern lineage but I would have to remove the intake.

Thanks for the info. Much appreciated!

[geezer#99]

IIRC there were numbers on a pad along the pan rail beside the starter too. A liitle harder to find. There is a way to identify square ports heads from the outside but I'll need to research that a bit more. Can.t remember for sure. Some marking on the head.

[bigsnookmaster]

Pull a valve cover and get a # off the head. I had an LS6 I bought off the original owner,70SS Chevelle, 450 hp. I believe the last 3 digits in the head casting were 290, but I'm not positive. If it's the real deal, it will be worth real money to the guy's restoring the Corvettes and Chevelles. You could probably trade for a nice LS conversion!

[Ole Greenie]

Update...Last night I removed the carburator to install a new Edelbrock 1411 I bought. Originally thinking that that the 650 Holley I had had plugged jets (no fuel filter!) and was not spraying but rather drizzling in fuel.

So after I got it off, I inspected it for functionality. I came to discover that only the primary side was working. The secondaries were not opening at all. After a bit of time I finally got the secondaries to open and close but they do not open with the throttle linkage. So all this time, I have been running with essentially a 2-barrel carb and only 325 CFM. Any takers as to why the secondaries would not open?

Anyway, I'll be installing the new 1411 750CFM today and will post pictures of the install. This thing should run pretty well after I dial in the tune. Maybe a 150 HP increase.

[Ole Greenie]

Originally Posted by bigsnookmaster

Pull a valve cover and get a # off the head. I had an LS6 I bought off the original owner,70SS Chevelle, 450 hp. I believe the last 3 digits in the head casting were 290, but I'm not positive. If it's the real deal, it will be worth real money to the guy's restoring the Corvettes and Chevelles. You could probably trade for a nice LS conversion!

Square port heads. Not much more to say...it is an LS6.

The swap with a nice LSX is a great idea and I will have to think about it since the LS6 motors have a huge appeal. I kind of like having the only LS6 powered truck around though. You won't find a true LS6 every day let alone in one of our trucks. I plan to occassionally show the truck so it may get quite a bit of attention once complete. The motor only has about 15,000 miles on it so it should last a pretty long time.

[Fitz]

Originally Posted by Ole Greenie

Square port heads. Not much more to say...it is an LS6.

The swap with a nice LSX is a great idea and I will have to think about it since the LS6 motors have a huge appeal. I kind of like having the only LS6 powered truck around though. You won't find a true LS6 every day let alone in one of our trucks. I plan to occassionally show the truck so it may get quite a bit of attention once complete. The motor only has about 15,000 miles on it so it should last a pretty long time.

Oh lots more to say! Not every square port 454 head was an LS6 head, but no oval port heads were LS6 heads! ALL of the big block heads in the table below are RECTANGULAR PORT heads. The only iron LS6 heads had the following last 4 digits in their casting numbers: 6074, 6492, 4025 and 4026. Only way to know is pull a valve cover and look.

Casting Years CID Chamber CC HP/RPO/Comments
3856208 1965 396 Closed 109cc 375hp/425hp z-16 chevelle
3873858 1966-67 396/427 Closed 109cc 375 L-78
3904391 1967 396/427 Closed 107cc L-71/L-72, 1.72
3904392 1967 427 Closed 106.8 430, 435 L-88/L-89, 1.72 ex
3919840 1967-69 396/427 Closed 107 375 L-78 425, 435 L-71/L-72, 425 COPO
3919842 1968-69 396/427 Closed 106.8 375 L-89 430, 435 L-88/L-89, 1.84 ex
3946074 1969-71 396/402/427/454 Open 118cc 375 L-89 430 L-88/ZL-1 425, 465 LS-6/LS-7
3964291 1969-70 396/402/427/ Closed 109cc 396/402/427/454 large or small spark plug
3964292 1970 454 Closed 109cc 450 LS-6,
3994025 1971 454 Open 118cc 425 LS-6,
3994026 1971 454 Open 118cc LS6
6258723 1971 454 Open . .
6272990 1970 454 Open 118cc service replacement mkIV
10045427 400/454/455 . . Pontiac/chevy aluminium small port /race
10051128 1990-94 454 Semi Open 72cc IP 400cc, bowtie, sym port
12363401 1996-up . Open 118cc bowtie aluminium mkIV gen.V gen.VI
12562934 2000-up 502 Open . gen.VI 502 marine
14011077 1989-94 454 Open 118cc IP 295cc, replacement, C port
14044861 1989-94 454 Open 115 425, 105.0cc, IP 380cc, bowtie, W port
14096188 1970-71 454 Open 118cc service replacement ls-6 markIV
14097088 1991-up 454/502 Open 118 .
24502585 1997 . . . olds/chevy aluminium

[71blksuper4x4]

291's are the 70' Chevelle ls6 head. The casting block number on the back of the engine on the driver's side should end with the last 3 digits 512. The 70' Chevelle LS6 motor is the true "ls6" that everyone talks about. The rest were lower horsepower ratings. The 512 blocks and 291 heads are what everyone desires. Chevy sold ls6 vettes in 71' with 425 hp. and also sold ls6-ls7 crate motors up until the early 90's before the 502's were introduced. Hope this helps ya out, and sounds like you got a fairly healthy engine regardless. Trevor

[Jacfourteen]

Get that thing running and see how it works with the other 2 barrels! I couldn't wait to see how much more power it will have.

[legendary]

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[Ole Greenie]

Ok here is an update for you all watching this thread.

I got the carb on and amid spending a few more hours than intended, She is running like a top. since I switched from a Holley 650 to an Edelbrock 750 (1411) I had to fab a new TV cable bracket for the 700R4, install a new TV cable and Edelbrock TV correct kit.

For those who don't know much about a Holley to Edelbrock switch, the throttle linkage is set about 3/4" further forward and 1/2" further left (outbound) than the holley I replaced. I did reuse the Holley TV cable bracket but it required cutting and relocating in accordance with the dimensions mentioned for trueness. This also afforded me enough adjustment room for the cable too.

Anyway, after it was all said and done, when the secondaries open, it acts like a turbo, especially in 2nd gear, and pulls real hard to 100mph. (That's when I shut it down.) It will spin the tires at 50 mph, though at that speed it gets kind of hairy.

The governor I have in it is one that does not let the engine reach it's true powerband, shifting at about 4300 rpm. It is a Bowtie Transmissions Level III 700R4 but I beleive it has the diesel engine regulator in it. So I will be looking for and installing a new governor that lets me get about 5500 rpm before a mandatory shift under WOT.

I don't want one that constantly shifts at rpm above 5000 but only under WOT. Any suggestions of what I should look for? Year and model cars?

Sure do like the sound of all barrels open! Pictures coming...

[Ole Greenie]

Here are a couple pictures of the install...






As you can see, this was taken before I hooked up the TV cable. Will post a couple of the welding done for the bracket.

[Ole Greenie]

Here are the pictures for the throllt and TV cable hook-up.







TV cable isn't completely true but I could not bring it into 100% in line due to the throw of the linkage. Not much room...

[406 Q-ship]

If that is an LS-6, it is one of the last run service replacement engines. It has a high rise square port intake on it, it doesn't mean the heads match but by the way you describe how it runs I believe that the heads are square ports too. It is a really late replacement service engine because GM dropped the low rise "corvette" intake in the very late 1980's and went to the intake used on the L-78/L-72 intake (high rise). I bought one of the last run LS-6 service engine in 1989 and it had a high rise L-78 style intake mainfold in it. Casting numbers on the service engine replacements can get weird and will not necessarily match old casting numbers. Check the front pad for the engine code would be the best option but not an end all. My LS-6 did have the 7.4 cast into it like the later GM blocks.

[Ole Greenie]

Originally Posted by 406 Q-ship

If that is an LS-6, it is one of the last run service replacement engines. It has a high rise square port intake on it, it doesn't mean the heads match but by the way you describe how it runs I believe that the heads are square ports too. It is a really late replacement service engine because GM dropped the low rise "corvette" intake in the very late 1980's and went to the intake used on the L-78/L-72 intake (high rise). I bought one of the last run LS-6 service engine in 1989 and it had a high rise L-78 style intake mainfold in it. Casting numbers on the service engine replacements can get weird and will not necessarily match old casting numbers. Check the front pad for the engine code would be the best option but not an end all. My LS-6 did have the 7.4 cast into it like the later GM blocks.

Thanks for that great information. The stars further align knowing that the person I bought this motor from (actually bought his truck and swapped motors) in 2001 said he installed it about the timeframe you had mentioned. Of couse it was a few years ago now so "that year" runs into the next in listening to him, but everything lines up correctly.

so I have a high rise intake. I also know I cant run less than 91 octane in it unless I further retard the timing.

Although a nice new LSX conversion is appealing, I think I will stick with the nostalgia of the BB LS6. I don't know of any others around here or on this board. Thanks again!