gtc131

Does anybody have the official GM engine specifications of the 454 LS-7?

I have tried googling, and searching the usual forums, but I gets bits and pieces of the picture, never the whole thing.

toddalin

Look in the '70 Assembly Manual. The LS-7 is shown (with 3 deuces ) under the options section with a big DISCONTINUED across the page.

gtc131

I have a 1970 Assembly Manual (published by Sequential Automotive Data, 1993) there appear to be no engine specifications per se.

Maybe my 1993 version is too “young”? Does the AM version you refer to with the 3 deuces have page numbers that I can cross-check?

Thanks!

TimAT

Ironcross has them.

What I have : Factory rated 454/460 stamp pad coded "XCH"

12.25:1 compression
Forged pistons,crank, rods with 7/16 bolts
Solid lifter cam (I' have the specs someplace- I have the ZL-1 cam in mine
I have aluminum heads too, I'm not 100% sure they came that way

toddalin

Actually, in looking deeper, the three deuces (option LJ2) were to be an option on the LS-5 (I would suppose), as the LS7 is spec'ed with a 4-bbl.

Assembly Instruction Manual '70 Mid America Corvette Supplies, 1975

Page K283, LS7 is noted.

Page K339 shows the 3x2 air cleaner and smog assembly (looks like the '67 3x2 air cleaner assembly) Option LJ2, Canceled

Page K340 codes for parts related to Option LJ2, Canceled

Page K341 shows "V-8 Engine 454 C.I.D 3x2 carburetors & Choke (Option LJ2), Canceled (although page K283 notes that the LS-7 gets a 4 Bbl Carb), Canceled

Page K342 details the air cleaner assembly for the 3x2, Canceled

Page K343 shows how the fuel and vacuum lines connect to the 3x2 and fuel pump, Canceled

Page K344 shows the smog pump set-up for the 3x2, Canceled

Page K345 shows the carb linkage assembly for the 3x2, Canceled

Page K346 details the carb linkage for the 3x2, Canceled

Page K361 details the LS7

Page K362 provides codes for LS7 assemblies

Page K363 details the carb, smog set-up and air cleaner assembly for the LS7, Canceled

Page K364 details the fuel line and choke set-up for the LS7

Page K365 details the vacuum set-up for the LS7. (Interesting that in the drawing, the air cleaner assembly looks like it may have been designed for cowl induction!)

Page K366 details the wireing for the LS7. (Was to use an amplifier (electronic ignition) assembly.)

Page K367 details the radiator support for the LS7.

Finally, Page K368 details the hood graphics package. Hood was to say "LS-7," similar to the "LT-1" graphic.

gtc131

Thanks for all of that typing Toddalin!!

Those page references accord with my 1993 Assembly Manual, however I'm actually chasing the official engine specs for the 460hp option -- i.e. the internals -- and, following a tip from another source, I have just found some of them in the March 1970 issue of Chevrolet Service News which is dedicated to "1970 Corvette Features".

gtc131

I gather the XCH is the correct code for the LS-7 block.

The March 1970 issue of Service News gives the compression ratio for the "460hp" option as 11.25:1, but does not give material data such as 4 bolt mains, aluminum heads, etc. I guess that material detail is in a parts list -- if you know the correct part numbers.

Also, there seems to be lots of mythical data out there just to confuse things. Maybe there is no such thing as the definitive specification, or perhaps it's lost in the archives of GM.

I guess what I really need is an Engine Assembly Manual ... if there ever was such a thing.

TheSkunkWorks

I'm sure someone will correct me if I'm wrong, but my understanding is that the Corvette LS7 would have been pretty much a 454 version of an L88 with the 2nd design aluminum heads and 12.5:1; tri-power was publicized, but 4bbl was actually planned. OTC LS7 crate engines had iron heads. At least, I think this is correct info.


TSW

wfo76

Production LS7
4-bolt block
forged crank, rods, pistons
11.25 to 1 compression
open chamber aluminum heads
mechanical camshaft .520/.550 lift
low-rise aluminum intake
Holley 800 vacuum secondary
standard open air cleaner
standard big block hood
transistor ignition

Crate LS7
4-bolt block
forged crank, rods, pistons
12.25 to 1 compression
open chamber iron heads
mechanical camshaft .560/.600 lift
no intake manifold, carb or ignition
engine suffix stamp XCH


Looks like the crate version with aluminum heads and the L88 carb/intake/hood
would have been a real screamer but that is not what was going to be built. The
engine would have basically been an 11.25 compression version of the 71 LS6
with a little more cam so a lot of power was left on the table by not using the
better L88 intake and hood. Somebody ought to build the full on 12.25 version
with the ZL1 .560/600 cam and L88 hood and see what it will do.

FRSTR90

I actually have the exact specs of the ZL-1/LS7 cam which are:
Lift (Zero Lash): .579/.620
Valve Timing
Intake:
Opening BTC: 62*
Closing ABC: 105*
Lash:.022 (with alum. heads)
Exhaust:
Opening BBC: 106*
Closing ATC: 73*
Lash:.024 (with alum. heads)

TimAT

Quote:
Somebody ought to build the full on 12.25 version
with the ZL1 .560/600 cam and L88 hood and see what it will do.

Wanna' see one?



I've got a video on the dyno too. The results were a real disappointment. 398 HP at 3800RPM then the flippin' thing started slipping on the rollers. And it was a one shot deal for a freebie, so no second chance.

gtc131

Thanks for all the info, guys.

My reason for asking is that my 1970 454 convertible has a crate LS7 in it (engine # T----XCH). The guy I bought the Vette from, and who owned it from 1982 through 2008, bought it without engine (the original LS5 was put into a speedboat) and decided to go the whole hog LS7 route following the specs to the letter, back in the good old days of leaded fuel.

According to him, and others who know him, the result was a beast that was unstreetable, with nothing under 4,000 and then an asphalt ripping tyre shredder from there to around 7,000. Just what you'd expect, I'd guess!

Over the ensuing years, and with the advent of unleaded fuel, he put a series of milder cams in it and lowered the compression to 10.5:1. He also added the L88 induction system, and that's where it is today, with me as the owner. It's a very fast street machine and thirsty to boot. Definitely a weekender.

Unfortunately, he doesn't seem to have kept all of the paperwork of the engine modifications over that 16 year period, so I'm trying to recreate and document it from square one -- hence my interest in the original GM specs as the basis.

Here it is today (note converted to RHD):

Ganey

Crate "LS-7" 12 C/R on dyno w/ headers
489HP @ 6000
481TQ @4000

gtc131

Found this sales receipt for an OTC LS-7 (part # 3965774) bought by somebody in December '89 for the princely sum of $2700:

GDaina

Tri Power intake was made, with a part number...I had one a few years ago, when I checked the part number, referenced the 4bbl manifold.

gtc131

Thought it may interest some to see that document:

TimAT

Interesting that GM would publish that page. The horsepower specs are all 460- which rumor at the time had it being the LS-7, yet that engine never made it to a production car. And same with the compression they're showing 11.25:1 Everything else I've seen points to the LS-7 being 12.25:1.

Don't get me wrong, I'm not questioning the validity of the document, I just find it interesting..

wer2xu

my car has a crate LS6 with a 3959180 cam, L88 Carb, aluminum intake, 1.7 roller rockers, and real L88 Hood...its good gobs of power, but gets somewhere between 5-10mph...I am a little nervous to take it above 4k rpm, as I have not seen all of the internals...


I have a set of aluminum heads, and all the parts to make TI ignition...wonder what it would be like when i get the heads on...more LS6, or more L88?!?

gtc131

Yes, this is another area of confusion surrounding the LS-7. On page 68 of his book “Corvette 1968-1982”, Mike Mueller says:

“Of the exotic 454 big-blocks initially mentioned in early plans for 1970 production, the aluminium head LS-7 came closest to reality. It was not only listed in assembly manuals and AMA spec sheets, it also made it into 1970 factory brochures and owner’s manuals, although some confusion existed as to what reality really was. Mundane black and white engineering papers and pretty color brochures listed compression at 11:25:1 and output at 460 horsepower. Like the early assembly manuals, the 1970 owners’ manual claimed 465 horsepower, as well as 12.25:1 compression. Solid lifters were a given.”

In his post above, wfo76 gives 2 specifications: one for “production” LS-7 and another for the crate version. Mueller alludes to a production version being tested by car magazines at SoCal’s Riverside Raceway in December 1969, unveiled by Duntov and Hufstader. That would have been not long before GM management canned the LS-7 production option.

Here is a page from my 1970 owners manual, showing the LS-7 option still listed (LS-7 is mentioned on many other pages in there, too):

wer2xu

that 70 owners manual still lists the 3 speed manual...Is the strike what killed the LS7 option?

I would imagine they had all the owners manuals, and brochures ready to go long before the cars were made, and did not want to throw them out...