1970 LS-7 engine

[Joe L.]

Re: 1970 LS-7 engine

Joe--

I think relying only on an old P&A catalog and ignoring the 1970 AIM, GM's submission of production specs to the Automobile Manufacturers Association (AMA specs), and the Chevrolet Sales Album and brochures has led you to an incorrect conclusion about what the advertised 1970 LS-7 was. I am drawing a distinction between the LS-7 that actually appeared in Corvette sales literature and that which may have been part of planning in 1969 and perhaps left some residual traces in the P&A catalog. I think there is evidence that the LS-7 was originally conceived as a 454 version of an L-88, but that it was later changed to a SHP street engine that could be advertised to the general public after the cancellation of the LJ-2 which would have been a 454 version of the L-71. I think this story is interesting because there is a general misunderstanding of the LS-7 featured in actual Corvette sales literature and that this episode represents the death of Zora Duntov's strategy of developing RPO engine parts to assist racers (that would then generate racing goodies in the P&A catalog) as a result of emissions regulations. I think the HD 454 which was not offered in the P&A catalog until at least 1973 was the beginning GM's new strategy of selling racing parts by placing them on the "Heavy Duty" parts list and plastering "FOR OFF-ROAD USE ONLY" labels on them because emissioms regulations were too great a barrier against the old RPO approach.

Let's examine some of the arguments that the LS-7 was a L-88 type racing engine.

The exact same thing was true for the 1970 LS-7. It was referred to in the P&A catalogs as HD (454). As I mentioned, the P&A catalogs contain only SERVICE parts for PRODUCTION applications (the only exception to this is some P&A catalogs which have a separate section for SERVICE-only high performance parts). So, if the P&A catalog reference to HD (454) does not refer to the LS-7, then what PRODUCTION application does it refer to?

Edward's comment #2 suggests that the LS-7 was planned as a 465 hp 12:1 CR engine which would be a 454 HD, and the AIM also refers to the LS-7 as a 454 HD, so there is no disagreement that the LS-7 name began as a code for the 454 HD. I don't know what year P&A catalog you are using, but other comments to this thread say 3965774 454 HD was not in the catalog until 1973. It was also not the same as the originally planned 454 HD in that it had open chamber cast iron heads that did not exist in 1970. This engine was newly manufactured in 1973 or later, labeled for off-road use only and was not a result of left over PRODUCTION parts. It was the beginning of the sale of heavy duty racing parts unrelated to production.

If the 1970 Corvette HD (454) or LS-7 used the "flat" intake manifold, then why does the P&A catalog specify a hood which is the type used for the 1968-69 L-88?

Again, I don't know what year P&A catalog you are referring to. It may be just an error, but it is possibly a remnant of the original plan for L-88 type LS-7 that was never purged from the catalog. The same goes for the console plate. However, the AIM shows a progression of cancelled and changed pages for the LS-7 option as it changed from a racing engine to a street engine. One of those page changes dated in May 1970 showed an ordinary 454 hood with an LS-7 decal presumably being substituted for the L-88 type hood. The engine now had a low manifold regardless of previous plans, and any P&A catalog after 5/70 listing the L-88 hood was simply not updated to the new LS-7 package. I think that is a source of the misinformation. I have included a photo of this AIM page, but I don't know where it will attach to this post.

There are errors to be found in the AMA specifications and these frequently involve situations in which a change was made "at the last minute".

The AMA specs were dated Feb 1970, after the cancellation of the the LJ-2, and describe a streetable LS-7, not the 12:1 CR, ZL-1 cammed race engine. The AMA specs cannot be dismissed as errors. They describe a consistent set of deviations from the race engine. They include:

1) CR of 11.25:1 --- The race engine would have been 12:1 or 12.5:1
2) Detailed camshaft specs for a modified L-71 cam --- All the lift and duration details are set out in several places in a table. They are internally consistent, and way different from the ZL-1 cam in the race engine. There is no possibility these differences are random error.
3) The distributor specs include a vacuum advance spec. --- L-88 type engines did not have an operational vacuum advance.
4) The carburetor was the same size as on the LT-1 and L-72, a 780 cfm. --- All L-88 type engines had a 850 cfm with larger 1.75" venturis.

In addition, another one of the change pages in the AIM shows the carburetor with the parts to install the manifold choke control. L-88 type engines had a spring around the choke rod to keep it permanently open; they did not have choke controls.

The Chevy spec pages in the Heritage site listed the engine height (oil pan to air cleaner) as the same for the LS-7 and the LS-5. This is consistent with the change page in the AIM specifying the same hood for the LS-5 and LS-7.

The specs GM gave the AMA which it in turn makes available to NHTSA are legal documents for which GM bears a responsibility for accuracy. The P&A catalogs are simply internal documents. If there is a disagreement, I'm betting on the AMA specs.

The most persuasive argument I can give that the advertised 1970 LS-7 was a street engine and not the race engine as originally planned is the way it was advertised.

It is well known that GM discouraged ordinary drivers from buying L-88s in 1967, 1968 and 1969. L-88s were not listed in the dealer sales albums, and they could not be ordered with radios or heaters (in 1967). The horsepower was misrepresented to make them appear less powerful than L-71s to further discourage the ordinary yahoos. GM made them for serious racers and knew that they were not suitable for ordinary driving. The 1969 L-88 engine was not even included in the AMA specs.

The 1970 LS-7 was featured in the Dealer Sales Albums , Ads and brochures in a big way. The aluminum heads and 460 hp were touted. Advertising 70 hp more than a LS-5 and 90 hp more than a LT-1 is not a way to discourage sales. There were no restrictions against radios, no mandatory F41 suspension or J-56 brakes. The manual transmission was a regular M-21 not a heavy duty M-22. It was advertised exactly like the 69 L-71 it was going to replace. Chevrolet did not appear to believe this was an engine an ordinary driver would regret buying and cause service nightmares. In contrast, the only 69 Corvette brochure I have seen that included the L-88 listed it outside of the regular power train table with a separate heading:
SPECIAL HIGH PERFORMANCE ENGINE - (OFF-ROAD APPLICATIONS ONLY)
and it identified the transmission as H.D. 4-Speed .

Finally, the failure to actually deliver any solid lifter 454's in 70 Corvettes is probably due the rigor and expense of emissions testing as suggested in Duke William's comment. I'm sure an emissions development and testing program for an individual engine cost at least $500,000 even in 1970. If the LS-7 were a L-88 type engine with expected sales of about 100 cars, the emission program would cost about $5,000 per car even if it could be made to pass. Why would GM choose to continue working on that kind of engine after canceling a 454 L71-like street engine with much greater sales potential? The answer of course is there is no way GM would do that. Unless, the LS-7 was a simpler L72-like street engine with enough sales potential to justify the emissions program and a better chance of passing than the JL-2. Of course, that is exactly the engine described in the AMA specs. It is the LS-7 advertised to the public in 1970, not the L-88 type engine designated LS-7 in the 1969 or earlier planning stage.

Patrick-------


The information I presented came from an April, 1970 edition of the P&A catalog. I am confident that it accurately reflects the scheduled parts content of the LS-7 or HD (454) as of that time. It's also true that later editions of the P&A catalogs drop most of the reference to parts for HD (454). That's to be expected as the HD (454) or LS-7 was never used in PRODUCTION. The LS-7 may very well have "morphed" into something other than it was originally intended as time went on. However, the only thing I am referring to is what the LS-7 was ORIGINALLY intended to be. Whatever it morphed into is totally irrelevant from a PRODUCTION perspective.

You noted that the hood drawing from the AIM is dated May, 1970. In the revision box it states "redrawn and redesigned". I'm quite confident that the original drawing included the high rise, L-88 style hood. This is all moot because neither design ever made it to PRODUCTION. Nevertheless, the original intention for the LS-7 was for an L-88 type hood and that would only have made sense if the original intention was for the engine to use a high rise manifold.

The GM #3965774 engine assembly was a SERVICE only engine assembly. While the part number dates from late 1969, I agree that the engine did not enter SERVICE availability until about 1973 or, possibly, later. It's also very possible that the specifications (and parts content) of the 3965774 engine assembly was revised over the 1969-73 period. That would be unusual, but it's possible. Cast iron open chamber heads were available as early as late 1969 using GM casting #3964291.

I'll give you an example of an error in the AMA specifications: the 1968 and 1969 AMA specifications for Corvettes specified that engines coupled with automatic transmissions used CCS exhaust emission control. However, all 1968 and 1969 Corvettes, regardless of transmission, were equipped with AIR exhaust emission control, including L-88 and ZL-1.

A couple of additional points:

1) The GM #3965774 engine assembly very closely met the specifications of the ORIGINAL LS-7 configuration---it had 12.25:1 compression, the 3959180 camshaft, a 5140 crankshaft, open chamber heads, and a Corvette oil pan. All of these attributes are in line with the earlier L-88/ZL-1. The only real difference was the use of cast iron rather than aluminum heads. The engine was not supplied with an intake manifold;

2) The engine that you describe that the LS-7 morphed into is, essentially, an engine which already had its own designation and that designation was LS-6.

[Bill M.]

Re: 1970 LS-7 engine

Finally, the failure to actually deliver any solid lifter 454's in 70 Corvettes is probably due the rigor and expense of emissions testing as suggested in Duke William's comment. I'm sure an emissions development and testing program for an individual engine cost at least $500,000 even in 1970. If the LS-7 were a L-88 type engine with expected sales of about 100 cars, the emission program would cost about $5,000 per car even if it could be made to pass. Why would GM choose to continue working on that kind of engine after canceling a 454 L71-like street engine with much greater sales potential? The answer of course is there is no way GM would do that. Unless, the LS-7 was a simpler L72-like street engine with enough sales potential to justify the emissions program and a better chance of passing than the JL-2. Of course, that is exactly the engine described in the AMA specs. It is the LS-7 advertised to the public in 1970, not the L-88 type engine designated LS-7 in the 1969 or earlier planning stage.

Interesting thread.

Another possibility for complexity reduction in the Mark IV world for 1970 is manufacturing (Tonawanda) was overwhelmed with changes. The 400 CID small-block was a new line for 1970 and had new automation features that were having issues. The Vega engine was right behind it.

[Duke W.]

Re: 1970 LS-7 engine

It seems odd that a new 1970 AIM page for the LS-7 hood decal would be released so far into the model year.

Another issue is the GM management decree that all 1971 engines run on unleaded 91 RON (equivalent to today's 87 PON) gasoline. I don't think that decree was issued until early 1970, which didn't give engineering much time to design and tool new pistons and cylinder heads for the high compression engines, so their was likely no choice but to scrap the "wish list" of engine configurations that were planned, but not yet released for the '70 and beyond model years and devote all resources to reconfiguring all high compression engines to low compression for the '71 model year.

It's always been my understanding that the original LS-7 as announced at the 1970 model year press introduction was a 454 CID, iron head version of the L-88.

Duke

[Patrick B.]

Re: 1970 LS-7 engine

Patrick-------


The information I presented came from an April, 1970 edition of the P&A catalog. I am confident that it accurately reflects the scheduled parts content of the LS-7 or HD (454) as of that time. It's also true that later editions of the P&A catalogs drop most of the reference to parts for HD (454). That's to be expected as the HD (454) or LS-7 was never used in PRODUCTION. The LS-7 may very well have "morphed" into something other than it was originally intended as time went on. However, the only thing I am referring to is what the LS-7 was ORIGINALLY intended to be. Whatever it morphed into is totally irrelevant from a PRODUCTION perspective.

You noted that the hood drawing from the AIM is dated May, 1970. In the revision box it states "redrawn and redesigned". I'm quite confident that the original drawing included the high rise, L-88 style hood. This is all moot because neither design ever made it to PRODUCTION. Nevertheless, the original intention for the LS-7 was for an L-88 type hood and that would only have made sense if the original intention was for the engine to use a high rise manifold.

The GM #3965774 engine assembly was a SERVICE only engine assembly. While the part number dates from late 1969, I agree that the engine did not enter SERVICE availability until about 1973 or, possibly, later. It's also very possible that the specifications (and parts content) of the 3965774 engine assembly was revised over the 1969-73 period. That would be unusual, but it's possible. Cast iron open chamber heads were available as early as late 1969 using GM casting #3964291.

I'll give you an example of an error in the AMA specifications: the 1968 and 1969 AMA specifications for Corvettes specified that engines coupled with automatic transmissions used CCS exhaust emission control. However, all 1968 and 1969 Corvettes, regardless of transmission, were equipped with AIR exhaust emission control, including L-88 and ZL-1.

A couple of additional points:

1) The GM #3965774 engine assembly very closely met the specifications of the ORIGINAL LS-7 configuration---it had 12.25:1 compression, the 3959180 camshaft, a 5140 crankshaft, open chamber heads, and a Corvette oil pan. All of these attributes are in line with the earlier L-88/ZL-1. The only real difference was the use of cast iron rather than aluminum heads. The engine was not supplied with an intake manifold;

2) The engine that you describe that the LS-7 morphed into is, essentially, an engine which already had its own designation and that designation was LS-6.

Joe ---- I made clear from the beginning that what I thought was interesting was the LS-7 engine actually in the Chevy sales brochures and how people would be surprised to know what it really was. Corvette enthusiasts have been tantalized for years by reading old ads about what could have been. The story of how it morphed into the equivalent of an LS-6 with aluminum heads and a hotter cam is a piece of Corvette history that has escaped coverage in all the Corvette history books I have seen. It still would have been the high point of street big blocks.

You are wrong about the 3964291 heads. They existed in late 69 all right, but they were closed chamber heads used on late L-71s.

The 3965744 engine appeared about the same time as the first Chevrolet Power book, and it represented GM's new way of marketing speed parts increasingly unrelated to production. The first books of the series quoted sections of the P&A catalog with high performance pieces originating in L-88s, ZL-1s, Z-28s and LT-1s while adding things like a newly manufactured iron head 454 HD that we see never really got close to production. The later books in the series were catalogs of items developed strictly for racing including unfinished castings of blocks and heads without any relation to production parts, like NASCAR stuff. I also think it is a significant piece of GM history that the failure to get the 454 HD racing engine into a 1970 Corvette (likely due to emissions requirement) seems to have stimulated the Chevrolet Power book era.

[Joe L.]

Re: 1970 LS-7 engine

Joe ---- I made clear from the beginning that what I thought was interesting was the LS-7 engine actually in the Chevy sales brochures and how people would be surprised to know what it really was. Corvette enthusiasts have been tantalized for years by reading old ads about what could have been. The story of how it morphed into the equivalent of an LS-6 with aluminum heads and a hotter cam is a piece of Corvette history that has escaped coverage in all the Corvette history books I have seen. It still would have been the high point of street big blocks.

You are wrong about the 3964291 heads. They existed in late 69 all right, but they were closed chamber heads used on late L-71s.

The 3965744 engine appeared about the same time as the first Chevrolet Power book, and it represented GM's new way of marketing speed parts increasingly unrelated to production. The first books of the series quoted sections of the P&A catalog with high performance pieces originating in L-88s, ZL-1s, Z-28s and LT-1s while adding things like a newly manufactured iron head 454 HD that we see never really got close to production. The later books in the series were catalogs of items developed strictly for racing including unfinished castings of blocks and heads without any relation to production parts, like NASCAR stuff. I also think it is a significant piece of GM history that the failure to get the 454 HD racing engine into a 1970 Corvette (likely due to emissions requirement) seems to have stimulated the Chevrolet Power book era.

Patrick-------



Yes, I was incorrect regarding the 3964291 cylinder head. It was a closed chamber design. The GM #3994026 was the first open chamber, cast iron head. However, it may have been available as early as mid-1970.

Regarding the AMA specifications and your belief that they are the the best and most accurate source of information, the AMA specifications are supposed to be relevant to PRODUCTION applications. The camshaft you mention which was described in the AMA specifications was never released to PRODUCTION or SERVICE and, as far as I know, never even produced. So, how could that reference in the AMA specifications be accurate or relevant to any PRODUCTION application?

Also, with respect to the 3965744 engine assembly, with the exception of cylinder head material, that engine consisted of all of the components which were cataloged for the HD (454) in the 1970 edition of the P&A catalog which I mentioned earlier.

[Paul D.]

Re: 1970 LS-7 engine

When I was working at a Chevy dealership over 30 years ago, a parts clerk gave me 2 decals in GM parts envelopes to put on my toolbox. I've still got the tool box but wish I had kept the parts envelopes! One was a LT-1 hood decal and the other was a LS/7 decal. Note that the decal I have features a forward slash (/) instead of the dash (-) like the AIM drawing. It reminds me of how ZL/1 usually appears in print. I wonder if it was just some marketing to go along with the over the counter engines or if it was meant for the production vehicles that got cancelled. The envelopes were regular blue and white parts envelopes with GM part #s on them and they were just large enough for the decals to fit in. The LS/7 decals are black letters with chrome or silver border and the letters are individual and solid. Just wish I had kept the envelopes for the part #s. Funny how those things didn't matter as much at 17/18 years old. Chip.

[Patrick B.]

[Patrick B.]

Re: 1970 LS-7 engine

For those who have not seen the "1970 Factory LS7 Specs" discussion on CF in C3 General, Stan Falenski, one of NCRS's top gurus on 68-72 Corvettes added a definitive observation yesterday. He reported that Chevrolet built a LS-7 pilot car in October 1969 that was displayed at a late Dec 69/early Jan 70 press event in Riverside CA introducing the 1970 Corvette and Camaro. It had an M-22 trans and a dual plate clutch but had a 11.25 CR engine, a low rise manifold, a standard big block hood (with 454 emblems), and an AM/FM radio. Another commenter reported that a Motor Trend article at the time said the pilot car had an L-71 cam.

By the time of the early 1970 sales brochures that called out the LS-7, the M-22 had been replaced by the M-21 and the dual disc clutch by a regular 11" single disc clutch with a heavier pressure plate.

It is pretty clear that the 70 sales brochure that seemed to tantalize Corvette fans with a race car offered to the public was really about Corvette's version of a Chevelle LS-6 improved with aluminum heads. It would have been the ultimate street engine of its day, but it was probably left behind because the efforts to get EPA certification for higher production engines took all the available man power as Duke suggested.

[Duke W.]

Re: 1970 LS-7 engine

How about a link?

Duke

[Patrick B.]

Re: 1970 LS-7 engine

https://www.corvetteforum.com/forums...ls7-specs.html

[Joe L.]

Re: 1970 LS-7 engine

For those who have not seen the "1970 Factory LS7 Specs" discussion on CF in C3 General, Stan Falenski, one of NCRS's top gurus on 68-72 Corvettes added a definitive observation yesterday. He reported that Chevrolet built a LS-7 pilot car in October 1969 that was displayed at a late Dec 69/early Jan 70 press event in Riverside CA introducing the 1970 Corvette and Camaro. It had an M-22 trans and a dual plate clutch but had a 11.25 CR engine, a low rise manifold, a standard big block hood (with 454 emblems), and an AM/FM radio. Another commenter reported that a Motor Trend article at the time said the pilot car had an L-71 cam.

By the time of the early 1970 sales brochures that called out the LS-7, the M-22 had been replaced by the M-21 and the dual disc clutch by a regular 11" single disc clutch with a heavier pressure plate.

It is pretty clear that the 70 sales brochure that seemed to tantalize Corvette fans with a race car offered to the public was really about Corvette's version of a Chevelle LS-6 improved with aluminum heads. It would have been the ultimate street engine of its day, but it was probably left behind because the efforts to get EPA certification for higher production engines took all the available man power as Duke suggested.

Patrick------

It's a bit difficult to come up with specs on an engine "that never was". However, the engine components described in your first paragraph would be, essentially, just as you mention-----an aluminum head version of the 1970 Chevelle LS-6. I just don't see how that could have or would have been designated LS-7. In addition, the engine components described in the first paragraph almost certainly would have been designated by Chevrolet as "special high performance" as was the 1970 Chevelle LS-6, the 1971 Corvette LS-6, 1967-69 L-71, 1966 L-72, and 1965 L-78.

However, early versions of the 1970 P&A Catalog do not specify any components for a 1970 454 with special high performance. They do specify components for a 454 with HD. The only other Corvette engines which Chevrolet ever designated as "HD" were the 1967-69 L-88 and 1969 ZL-1. Among many others, the following components were specified for the 1970 454 HD:

camshaft-----GM #3959180 (same as 1969 ZL-1)

pistons-------GM #3976014 (12.25:1 compression ratio)

cyl head------GM #3946072 (as as L69 L-88 and ZL-1)

So, if the above components did not apply to the 1970 LS-7, what engine designation did they apply to?

[Stan F.]

Re: 1970 LS-7 engine

Joe,

If I had to guess, I believe that the LS-7 pilot car was built in late October of 1969. It showed up for the second 1970 press preview at Riverside (CA) in late December 1969 or early January 1970. It had the 11.25 to 1 compression engine (lower than the 12.00 to L-88), standard big block hood (won’t accommodate a high rise manifold like the L-88 used), fan shroud (not available with L-88), dual disc clutch (not available with L-88), vacuum secondary carburetor (same part number as LS-6, not available with L-88), radio (not available with L-88)... Definitely not “HD” in the sense that the L-88 was.

LS-7 may have started off as a 454 version of the L-88, but that isn’t what it ended up. I’m not sure what date your parts list is dated (my guess is early), but by October 1969, LS-7 was finalized as a special high performance street engine. There was an actual example running around so that’s difficult to argue with.

Regards,

Stan Falenski

[Patrick B.]

Re: 1970 LS-7 engine

The collapse of the plans for various 454 engines for Corvettes in the face of new emissions requirements and the burden of certification testing of all engines to be used in 1970 Chevrolets is an interesting bit of Corvette history. We know that the original plans called for 454 versions of the L-88, ZL-1, L-68, L-71 and L36, under the names LS7, LT2, LJ1, LJ2 and LS5. Various GM documents and other sources, not just the parts book, are necessary for the understanding of what happened. The 1970 AIM has remnants documenting the successive cancellations of most of the planned engine lineup and the change in the LS7 body from the high L88 air induction hood to the regular big block hood with LS/7 decals. The CF thread whose link I supplied earlier has a time line for these events. The L-88 versions must have been the first to go. There was little chance they could pass emissions testing and little pay off for the effort even if they could. The culmination of these actions is represented in the early 70 sales brochure. There is the base LS5 and the 460 hp aluminum head LS7 without the accompanying F41, J56, air induction hood, radio restriction or 12.25 CR that would be expected of the original LS7 race engine. The LS7 nomenclature was now being used for a special high performance street engine not a HD race engine.

The Chevrolet Service News dated March 1970 was a supplement to the 1970 Chassis Service Manual for 1970 Corvette information because the 70 Chassis Manual retained 69 Corvette info (since 69 Corvettes were still in production). This supplement described the new SHP LS7 as 11.25 CR with a vacuum secondary 780 cfm Holley and an idle speed of 750 rpm with manual trans or 700 rpm with automatic. It also still listed the oddball street mechanical cam with .520/.550 gross lift.

The March 1970 service information was consistent with the January sales brochure and the pilot LS7 car presented to the press at the 1970 Corvette and Camaro introduction at Riverside CA. If any remnants of the HD race engine remained in the 1970 parts book, I suspect that was Duntov's effort to do racers a favor, and the pistons were the only new part. Duntov must have expected the fall back SHP LS7 to make it through the regulatory hassle since it was nearly identical to the Chevelle LS6 engine in production by this time. Here is a picture of the SHP LS7 engine in the pilot car.

[Joe L.]

Re: 1970 LS-7 engine

Joe,

If I had to guess, I believe that the LS-7 pilot car was built in late October of 1969. It showed up for the second 1970 press preview at Riverside (CA) in late December 1969 or early January 1970. It had the 11.25 to 1 compression engine (lower than the 12.00 to L-88), standard big block hood (won’t accommodate a high rise manifold like the L-88 used), fan shroud (not available with L-88), dual disc clutch (not available with L-88), vacuum secondary carburetor (same part number as LS-6, not available with L-88), radio (not available with L-88)... Definitely not “HD” in the sense that the L-88 was.

LS-7 may have started off as a 454 version of the L-88, but that isn’t what it ended up. I’m not sure what date your parts list is dated (my guess is early), but by October 1969, LS-7 was finalized as a special high performance street engine. There was an actual example running around so that’s difficult to argue with.

Regards,

Stan Falenski

Stan------


The parts information I provided is sourced from the April, 1970 edition of the 1953-70 Corvette P&A Catalog.

That edition makes no mention anywhere of a SHP 454. The only 454 variants mentioned anywhere are (454) (presumably referring to the LS-5 and cataloging component parts that would be expected for an LS-5) and 454 HD. Among other parts cataloged for the 454 HD are the the ones I referred to above which are consistent with 1969 L-88 and ZL-1 (except pistons which are, of course, 454 specific but which I have confirmed are 12.25:1).

I would fully expect that any component changes made from the engine built around October, 1969 would have been correctly cataloged by April, 1970.

It is possible that the specs for the LS-7 engine were markedly revised over time and an engine that was originally designated as HD "morphed" into an engine that, by GM standards, should have been designated SHP. That would be unusual but I suppose it's possible.

On the other hand, if the components designated for 454 HD did not refer to the LS-7, then, as I've mentioned several times previously, what engine RPO did they refer to?

By the way, the first mention of a 454 SHP in a Corvette P&A catalog was the first edition of the 1971 catalog which specifically referred only to the 1971 LS-6 engine. Furthermore, although the LS-6 was initially scheduled to be carried over to the 1972 model year, no mention of the 1972 LS-6 or its components is found in the first edition of the 1953-72 P&A catalog dated September, 1971 suggesting just how timely the P&A catalogs are.

[Stan F.]

Re: 1970 LS-7 engine

Joe,

I have no doubt that the part numbers/dates are what you say. The elephant in the room is the lone LS-7 Corvette that was built… If pressed my thinking is that the LS-7 started out as 454 version of the L-88 and then morphed (however unlikely) into more of a street engine. That’s the only thing that accounts for the HD parts list and later, an engine that would more appropriately be called a special high performance version.

As always Joe, your feedback is appreciated!

Regards,

Stan Falenski