1970 LS-7 engine

[Patrick B.]

Some of the comments in the recently revived string on LS-6 Corvettes seemed to suggest that the advertised but never sold 1970 LS-7 Corvette was a 454 version of an L-88 or ZL-1. I think it was really something much milder-- a 454 substitute for the street high performance 69 L-71/L89.

First of all, it was advertised and appeared in early Corvette Brochures and in the Chevy dealer Sales Album. The "heavy duty" L-88 and ZL-1 engines for racing were never advertised this way. The brochures advertised that it had aluminum heads and was rated at 460hp. The AMA and other specs at the GM heritage center fill in a lot of the other details. First of all it had a streetable 11.25:1 compression ratio, probably increased from the 427 L-71 to take advantage of the aluminum heads reduced tendency to ping on marginal gas. Unlike the L-88, it had a distributor with a vacuum advance (and a very aggressive centrifugal advance). It used a Holley carb with the same size venturis as the LT-1 (hence a 780 cfm carb not the 850 cfm L-88 carb). The oil pan to air cleaner height was the same as the LS-5. Therefore it would use the low LS-6 manifold and fit under the regular LT-1/LS-5 hood. However, unlike the L-89 it would use the open chamber aluminum heads with 1.88" exhaust valves rather than 1.84" exhaust valves in the closed chamber aluminum heads of the L-89. The most surprising fact in the AMA specs was the cam. Instead of the L-78, L-72, L-71, LS-6 street mechanical cam with .5197 gross lift, intake and exhaust, it used a variation with the same .5197 intake lift but a greater .5498 gross exhaust lift. It is also surprising that this slightly improved street mechanical cam never made it to the over-the-counter speed parts sold by GM.

So, it appears that the differences between the LS-6 for the 70 Chevelle and the LS-7 intended for the 70 Corvette were that the LS-7 would use open chamber aluminum heads with 11.25 CR while the LS-6 used cast iron closed chamber heads with 11.00 CR and that the LS-7 would use a cam with more exhaust lift. Both were hot street engines. Unfortunately the LS-7 11.25 pistons and the hotter street cam never made to the parts department.

However, the parts department is responsible for the idea that the LS-7 would have been a heavy duty racing engine. From at least the early 70's GM sold a 454 HD engine under part number 3965774 (pad suffix XCH). It had 12:1 CR, ZL-1 cam and a cast iron version of the open chamber ZL-1/L-88 heads. The parts dept also sold under part number 3981820 a 454 with 11:1 CR and cast iron closed chamber heads identified as 1970 LS-6.

Some time around 1980 GM began selling a 454 with the 70 LS-6 short block (closed chamber 11:1 CR pistons and LS-6 cam) but with the cast iron open chamber heads. This combination had a compression ratio of 10.2:1. It was similar to the 71 Corvette LS-6 but it had iron heads and higher compression pistons. It was sold under part number 366250 and had a pad suffix of XAA.

Until about 1986, the 12:1 CR 454 was simply called the 454 HD. However, in the 1986 HD parts list the 454 HD (3965774) is now called an LS-7 and the hybrid 10.2 CR open chamber 454 (366250) is now called an LS-6. These designations are purely parts catalog names and neither the over-the-counter LS-6 or LS-7 are the same as the 1970 LS-7 or LS-6 or even the 1971 LS-6 intended or installed in real cars. No wonder the LS-7 is such a misunderstood chapter in Corvette history.

[Mark E.]

Re: 1970 LS-7 engine

Interesting.

Weren't BB open chamber heads on low compression, '71 and later cars? So if you're right, then the '70 LS-7 would have been the first BB with open-chamber heads? And with higher compression?

The 1970 AIM shows three big blocks: LS5, LS7, and LJ2. LJ2 sheets are titled "V-8 Engine 454 CID 3X2", and the diagrams look like a L71 Holley tri-power set up.

Does anyone know more about the cancelled LJ2?

UPDATE: I Googled "LJ2" and found a bunch of stuff including: http://blog.garagistry.com/2014/08/g...secret-do.html

Below is an excerpt; can anyone confirm its accuracy? I don't know about the LS5 originally designated for Chevelle only. Also, this is the first I've heard of LJ-1 and LT-2. Has anyone else?

Based on available information, Chevrolet was reviewing several 454 CID variants. The LS-5 and LS-6 were designated for Chevelle only production, the others for Corvette only (LS-7, LJ-1, LJ-2, LT-2). The LS-7 may also have been available for other models:
LS-5 - 4bbl 390 HP
LS-6 - 4bbl 450 HP
LS-7 - 4bbl 465 HP (12.5:1 CR vs LS-6 11:1 CR conflicting info regarding iron or aluminum heads)
LJ-1 - Tri-Power 10.2:1 CR ??? HP (awaiting confirmation of LJ-1 designation or only LJ-2)
LJ-2 - Tri-Power 11.0:1 CR 460 HP (awaiting confirmation of aluminum or iron head)
LT-2 - 4bbl All aluminum similar to the 427 ZL-1

Although the LS-7, LJ-2, and LT-2 never made it to production, they were listed as possible options in GM documents.

[Patrick B.]

Re: 1970 LS-7 engine

The Tri-Power LJ-2 is illustrated in the 1970 AIM with a notation that it was cancelled on 10/3/69. The same drawing also notes that LJ-1 was cancelled on 6/16/69. The LS-7 was included in the AIM. It even shows a revision as late as 5/19/70 with a different air cleaner and the elimination of the A.I.R. system. The LS-7 is described as a 454 HD in the AIM, but it must have changed character as a 460 hp replacement for the LJ-2 upon its cancellation. The assembly would be mostly the same regardless of compression ratio and cam. The carburetor installation page was also redrawn on 5/19/70.

[Douglas L.]

Re: 1970 LS-7 engine

Below is an excerpt; can anyone confirm its accuracy? I don't know about the LS5 originally designated for Chevelle only. Also, this is the first I've heard of LJ-1 and LT-2. Has anyone else?

First I'm hearing of them. Sounds like 454 versions of L-68 and L-71 kinda of how LS-5 is to L-36. Looks like they decided to abandon the 3X2 set-up completely for whatever reason and used the LS-6 as a L-71 replacement. Did some thinking about it and I, like Patrick, think the LS-7 was going to be a replacement for the L-89(maybe a bit hotter) and the LT-2 was the super hot L-88/ZL-1 option.

On a side note-those 180 headers on the LT-2 mule in above link are wild. I've really only seen 180 headers before on a Pantera. The sound clip sounds so different, really changes the tone of a old crossplane american V-8.

[Duke W.]

Re: 1970 LS-7 engine

I believe the reason many of those engine options were canceled was emission certfication - both federal and California. That's a lot of cost for what would be low volume options. At the same time it's odd that the LS-6 was emission certified in the A-body, but not Corvette.

The "bundle of snakes" exhaust system on the Ford GT-40 yields 180 degree intervals on each pair by combining the inside two cylinders of one bank with the outside cylinders of the opposite bank, and this configuration gives 180 degree exhaust pulses on any cruciform crank V-8.

A flat crank yields 180 degree intervals on each bank. It's essentially two four cylinder engines on a common crank 90 degrees out of phase. Each four cylinder bank has an unbalanced second order vertical shaking force that you are probably familiar with if you have ever driven a small four-cylinder sedan, especially one from the seventies or eighties. It creates that "booming" sound as the vibration resonates in the body cavity. I've calculated that the peak force generated by my Cosworth Vega engine is about 15g at 233 Hz (7000 revs), which has caused every stamped sheet metal part on the engine to break at one time or another and caused the voltage regulator pins to wear that created an intermittent over-voltage condition. (It took me a while to figure that one out.)

On a flat crank V-8 it nets out to a second order horizontal shaking force whose peak magnitude is the square root of two greater than the peak in each bank. On a small engine it can be mostly isolated with engine mounting, but as engine size increases it's tougher to isolate.

I think the current Ferrari flat crank V-8 is up to 4.5L, and I understand an upcoming hot Mustang will have a high revving 5-6L V-8 with a flat crank. It will be interesting to see the engineering solution to isolate the significant unbalanced horizontal shaking force from the body.

Duke

[Joe L.]

Re: 1970 LS-7 engine

Some of the comments in the recently revived string on LS-6 Corvettes seemed to suggest that the advertised but never sold 1970 LS-7 Corvette was a 454 version of an L-88 or ZL-1. I think it was really something much milder-- a 454 substitute for the street high performance 69 L-71/L89.

First of all, it was advertised and appeared in early Corvette Brochures and in the Chevy dealer Sales Album. The "heavy duty" L-88 and ZL-1 engines for racing were never advertised this way. The brochures advertised that it had aluminum heads and was rated at 460hp. The AMA and other specs at the GM heritage center fill in a lot of the other details. First of all it had a streetable 11.25:1 compression ratio, probably increased from the 427 L-71 to take advantage of the aluminum heads reduced tendency to ping on marginal gas. Unlike the L-88, it had a distributor with a vacuum advance (and a very aggressive centrifugal advance). It used a Holley carb with the same size venturis as the LT-1 (hence a 780 cfm carb not the 850 cfm L-88 carb). The oil pan to air cleaner height was the same as the LS-5. Therefore it would use the low LS-6 manifold and fit under the regular LT-1/LS-5 hood. However, unlike the L-89 it would use the open chamber aluminum heads with 1.88" exhaust valves rather than 1.84" exhaust valves in the closed chamber aluminum heads of the L-89. The most surprising fact in the AMA specs was the cam. Instead of the L-78, L-72, L-71, LS-6 street mechanical cam with .5197 gross lift, intake and exhaust, it used a variation with the same .5197 intake lift but a greater .5498 gross exhaust lift. It is also surprising that this slightly improved street mechanical cam never made it to the over-the-counter speed parts sold by GM.

So, it appears that the differences between the LS-6 for the 70 Chevelle and the LS-7 intended for the 70 Corvette were that the LS-7 would use open chamber aluminum heads with 11.25 CR while the LS-6 used cast iron closed chamber heads with 11.00 CR and that the LS-7 would use a cam with more exhaust lift. Both were hot street engines. Unfortunately the LS-7 11.25 pistons and the hotter street cam never made to the parts department.

However, the parts department is responsible for the idea that the LS-7 would have been a heavy duty racing engine. From at least the early 70's GM sold a 454 HD engine under part number 3965774 (pad suffix XCH). It had 12:1 CR, ZL-1 cam and a cast iron version of the open chamber ZL-1/L-88 heads. The parts dept also sold under part number 3981820 a 454 with 11:1 CR and cast iron closed chamber heads identified as 1970 LS-6.

Some time around 1980 GM began selling a 454 with the 70 LS-6 short block (closed chamber 11:1 CR pistons and LS-6 cam) but with the cast iron open chamber heads. This combination had a compression ratio of 10.2:1. It was similar to the 71 Corvette LS-6 but it had iron heads and higher compression pistons. It was sold under part number 366250 and had a pad suffix of XAA.

Until about 1986, the 12:1 CR 454 was simply called the 454 HD. However, in the 1986 HD parts list the 454 HD (3965774) is now called an LS-7 and the hybrid 10.2 CR open chamber 454 (366250) is now called an LS-6. These designations are purely parts catalog names and neither the over-the-counter LS-6 or LS-7 are the same as the 1970 LS-7 or LS-6 or even the 1971 LS-6 intended or installed in real cars. No wonder the LS-7 is such a misunderstood chapter in Corvette history.

Patrick-------



GM #3965774 is a late 1969 era part number. It was not released for SERVICE at that time but it existed from that time. It was released for SERVICE sometime between 1973 and 1975.

Many of the parts for the HD 454 (i.e. the 1970 LS-7) were carried in the P&A catalogs from 1970 and later. I surmise this occurred because the engine cancellation as an RPO occurred after GMSPO had developed the catalogs and/or after they had inventoried the LS-7 parts (and wanted to sell them).

Some examples:

The camshaft cataloged in the 1970 Corvette P&A catalog for the HD 454 is the same GM #3959180 as shown for the 1969 ZL-1.

The piston cataloged for the HD 454 was GM #3976014 and was uniquely applicable to the 1970 HD 454.

The connecting rod for the 1970 HD 454 was the GM #3969804. As a matter of fact, this was the very first application of this rod which became known as the "1969 L-88/ZL-1 rod". Actually, the original PRODUCTION and SERVICE rod for the 1969 L-88/ZL-1 was GM #3959187. It was discontinued and replaced by the 3969804 in July, 1970. The 3969804 is a superior rod to the 3959187.

The 1970 HD 454 did not use the same intake manifold as the 1971 LS-6. It used a manifold of GM PART #3977610. This was a high-rise manifold, not the "flat" style used for the 1971 LS-6 (and other 1970-72 SHP Chevrolet big blocks). The 1970 HD 454 used hood GM #3966673. This is the "L-88/ZL-1 style" hood and, in fact, replaced the original L-88/ZL-1 hood, GM #3934160, in August, 1971. There would have been no need for such a hood if a "flat" style manifold had been intended for use on the HD 454.

[Patrick B.]

Re: 1970 LS-7 engine

Patrick-------



GM #3965774 is a late 1969 era part number. It was not released for SERVICE at that time but it existed from that time. It was released for SERVICE sometime between 1973 and 1975.

Many of the parts for the HD 454 (i.e. the 1970 LS-7) were carried in the P&A catalogs from 1970 and later. I surmise this occurred because the engine cancellation as an RPO occurred after GMSPO had developed the catalogs and/or after they had inventoried the LS-7 parts (and wanted to sell them).

Some examples:

The camshaft cataloged in the 1970 Corvette P&A catalog for the HD 454 is the same GM #3959180 as shown for the 1969 ZL-1.

The piston cataloged for the HD 454 was GM #3976014 and was uniquely applicable to the 1970 HD 454.

The connecting rod for the 1970 HD 454 was the GM #3969804. As a matter of fact, this was the very first application of this rod which became known as the "1969 L-88/ZL-1 rod". Actually, the original PRODUCTION and SERVICE rod for the 1969 L-88/ZL-1 was GM #3959187. It was discontinued and replaced by the 3969804 in July, 1970. The 3969804 is a superior rod to the 3959187.

The 1970 HD 454 did not use the same intake manifold as the 1971 LS-6. It used a manifold of GM PART #3977610. This was a high-rise manifold, not the "flat" style used for the 1971 LS-6 (and other 1970-72 SHP Chevrolet big blocks). The 1970 HD 454 used hood GM #3966673. This is the "L-88/ZL-1 style" hood and, in fact, replaced the original L-88/ZL-1 hood, GM #3934160, in August, 1971. There would have been no need for such a hood if a "flat" style manifold had been intended for use on the HD 454.

This is exactly the source of the confusion about the LS-7 that I was trying to address. I disagree with your characterization of the HD 454 as the 1970 LS-7. One is a racing engine and the other was meant to be a street engine.

The 454 HD SERVICE engine that the parts catalog began in about 1986 to refer to as the LS-7 is not at all the same 460 hp engine described in the AMA specs (Feb 1970) and advertised in the Corvette sales brochures under the name LS-7. The 454 HD is more or less a cast iron second design L-88 racing engine stroked to 454 cubic inches with a 12:1 CR. The almost PRODUCTION 1970 LS-7 is a special high performance street engine with aluminum heads, 11.25 CR and a low manifold. It would be identical to the 71 Corvette LS-6 except for higher compression pistons and a slightly modified cam (neither of which ever became SERVICE parts).

To add further confusion the LS-7 nomenclature may have originally described an L-88 type engine during the early planning of the 1970 model year when the LJ2 tri-power SHP street engine was still in the running (and in the 1970 AIM). However, when the 1970 specs were submitted to AMA in February 1970 the LJ2 engine was gone, and a single 780 cfm 4bbl aluminum head 11.25 CR SHP street engine was listed under the name LS-7. This is the intended PRODUCTION 1970 LS-7 and it is much different from the SERVICE 454 HD. The facts I am citing are all available in the GM Heritage website under the 1970 Corvette info, the 1970 AIM, the 5th addition Chevrolet Power book, and the 1986 Chevrolet Heavy-Duty Parts List.

[Mark E.]

Re: 1970 LS-7 engine

Patrick,

If you're LS-7 street engine theory is correct, then could the LJ2 just be the tri-power version of it? Similar to L36 - L68 relationship for '67- 69? ..

[Patrick B.]

Re: 1970 LS-7 engine

Patrick,

If you're LS-7 street engine theory is correct, then could the LJ2 just be the tri-power version of it? Similar to L36 - L68 relationship for '67- 69?

Yes, although it seems that the LJ-2 was the first intended SHP 460 hp street engine for 1970 Corvettes and the LS-7 was the planning name for an L-88 type engine with a nominal 465 hp rating. After the LJ-2 was dropped, I think the LS-7 name was used to designate an LJ-2 type engine simplified with one 4 bbl replacing the Tri-power (maybe in the hopes simpler emissions testing). It is more like an L-71 being simplified to an L-72, less bling but arguably a more reliable engine with just as much power.

[Joe L.]

Re: 1970 LS-7 engine

This is exactly the source of the confusion about the LS-7 that I was trying to address. I disagree with your characterization of the HD 454 as the 1970 LS-7. One is a racing engine and the other was meant to be a street engine.

The 454 HD SERVICE engine that the parts catalog began in about 1986 to refer to as the LS-7 is not at all the same 460 hp engine described in the AMA specs (Feb 1970) and advertised in the Corvette sales brochures under the name LS-7. The 454 HD is more or less a cast iron second design L-88 racing engine stroked to 454 cubic inches with a 12:1 CR. The almost PRODUCTION 1970 LS-7 is a special high performance street engine with aluminum heads, 11.25 CR and a low manifold. It would be identical to the 71 Corvette LS-6 except for higher compression pistons and a slightly modified cam (neither of which ever became SERVICE parts).

To add further confusion the LS-7 nomenclature may have originally described an L-88 type engine during the early planning of the 1970 model year when the LJ2 tri-power SHP street engine was still in the running (and in the 1970 AIM). However, when the 1970 specs were submitted to AMA in February 1970 the LJ2 engine was gone, and a single 780 cfm 4bbl aluminum head 11.25 CR SHP street engine was listed under the name LS-7. This is the intended PRODUCTION 1970 LS-7 and it is much different from the SERVICE 454 HD. The facts I am citing are all available in the GM Heritage website under the 1970 Corvette info, the 1970 AIM, the 5th addition Chevrolet Power book, and the 1986 Chevrolet Heavy-Duty Parts List.

Patrick-------


The regular P&A catalogs, especially those from the late 1960's and 1970's, did not usually carry SERVICE-only, high performance parts in the regular pages of the catalog. In the P&A catalogs, the L-88 was always referred to as "HD (427). The ZL-1 was referred to as "alum. cyl. and case". These engines were NEVER referred to in the P&A catalogs as "L-88" or "ZL-1".

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? Yes, I know the LS-7 never made it to PRODUCTION. However, it was scheduled as a PRODUCTION application and apparently made it into the P&A catalogs on that basis. Therefore, the parts shown in the P&A catalogs are those parts scheduled for use in the PRODUCTION HD (454) application and that application could only have been the LS-7. Parts for "racing only" or "experimental" applications rarely, if ever, are cataloged in the regular SERVICE parts sections of P&A catalogs.

The SERVICE engines you described were SERVICE-only pieces and were never carried in the regular SERVICE parts sections of the P&A catalogs. As such, they may very well be non-PRODUCTION configured and they may very well be loosely referred to as "LS-6" or "LS-7".

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? The "flat" manifold works perfectly well with the standard 68-72 big block hood.

One more thing: 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".

[Joe L.]

Re: 1970 LS-7 engine

Patrick,

If you're LS-7 street engine theory is correct, then could the LJ2 just be the tri-power version of it? Similar to L36 - L68 relationship for '67- 69? ..

Mark-------


Apparently, the TJ-2 was a 454 cid version of the L-71. I do not think it was to be a tripower version of the LS-7.

[Joe L.]

Re: 1970 LS-7 engine

One more thing:

The 1970 P&A catalogs specifies console trim plate GM #3976375 for "1970 Corvette with H.D. (454)". This trim plate is inscribed "454" and "LS-7". This pretty much confirms that for 1970 GM defined the HD (454) as the LS-7.

I should also mention that the catalog lists trim plate GM #3976374 for "1970 Corvette with Sp. H/per (454)". This plate was inscribed "454 cu. in" and "460 HP". I figure this must have been the also still-born TJ-2. If so, the TJ-2 must have been a 454 cubic inch version of the L-71 and not a tripower version of the LS-5.

[Tom B.]

Re: 1970 LS-7 engine

They did refer to parts as being L88 and ZL1 in the Heavy Duty parts list and in Chevrolet parts department bulletins. An example would be Chevrolet Parts and Accessories Department "Hotline" Bulletin 73-53 dated 12/7/1973. It is a revision of the H.D.parts section of P&A 30A. Cams blocks and other parts are listed as L88 1st design, 2nd design, H.D., ZL1 ect. There is nothing in this bulletin listed as LS7. That's a separate bulletin.

"Hotline" Bulletin 73-32 dated 7/25/73 is Service Parts and Tune Up Specs for 3965774 LS7 engine. This probably corresponds closely to the release of pn#3965774 for service or in anticipation of the release. Of interest is that there is no intake manifold in the parts list. Everything else is listed from valve covers to pan and damper to clutch. That makes me believe that the engine was intended to use a previously available production intake like the LS6, L88 or aftermarket intake of your choice, depending on intended application.


Tom

[Joe L.]

Re: 1970 LS-7 engine

They did refer to parts as being L88 and ZL1 in the Heavy Duty parts list and in Chevrolet parts department bulletins. An example would be Chevrolet Parts and Accessories Department "Hotline" Bulletin 73-53 dated 12/7/1973. It is a revision of the H.D.parts section of P&A 30A. Cams blocks and other parts are listed as L88 1st design, 2nd design, H.D., ZL1 ect. There is nothing in this bulletin listed as LS7. That's a separate bulletin.

"Hotline" Bulletin 73-32 dated 7/25/73 is Service Parts and Tune Up Specs for 3965774 LS7 engine. This probably corresponds closely to the release of pn#3965774 for service or in anticipation of the release. Of interest is that there is no intake manifold in the parts list. Everything else is listed from valve covers to pan and damper to clutch. That makes me believe that the engine was intended to use a previously available production intake like the LS6, L88 or aftermarket intake of your choice, depending on intended application.


Tom

Tom------


Yes, the section you referred to is the separate section of the P&A catalog which I mentioned above. That section, found in some editions of the regular P&A Catalogs, was, basically, a forerunner of the GM High Performance Parts Catalog which came along later. That section contains both PRODUCTION and SERVICE-only high performance parts and does use some different terminology. However, the fact remains that the regular pages of the P&A catalogs contain only parts applicable to PRODUCTION applications. Of course, some of those parts may also be considered "high performance" parts and also included in the separate section.

[Patrick B.]

Re: 1970 LS-7 engine

Patrick-------


The regular P&A catalogs, especially those from the late 1960's and 1970's, did not usually carry SERVICE-only, high performance parts in the regular pages of the catalog. In the P&A catalogs, the L-88 was always referred to as "HD (427). The ZL-1 was referred to as "alum. cyl. and case". These engines were NEVER referred to in the P&A catalogs as "L-88" or "ZL-1".

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? Yes, I know the LS-7 never made it to PRODUCTION. However, it was scheduled as a PRODUCTION application and apparently made it into the P&A catalogs on that basis. Therefore, the parts shown in the P&A catalogs are those parts scheduled for use in the PRODUCTION HD (454) application and that application could only have been the LS-7. Parts for "racing only" or "experimental" applications rarely, if ever, are cataloged in the regular SERVICE parts sections of P&A catalogs.

The SERVICE engines you described were SERVICE-only pieces and were never carried in the regular SERVICE parts sections of the P&A catalogs. As such, they may very well be non-PRODUCTION configured and they may very well be loosely referred to as "LS-6" or "LS-7".

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? The "flat" manifold works perfectly well with the standard 68-72 big block hood.

One more thing: 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".

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.