Whose 1970 LS-5 exhaust manifolds have AIR holes??

[David P.]

The 70-72 TIM&JG states that 1970 LS5 passenger side exhaust manifolds between serial numbers 6000 and 8000 "may have drilled and tapped AIR holes plugged with machine thread recessed square hole plugs." Of course, there is no other AIR gear on the 1970 LS-5. This topic is strictly about the manifold holes/plugs.

My March 9 build #5864 LS5 car has these AIR holes as described.20140123_175905.jpg Any other LS-5s have this outside the 6000-8000 range called out in the TIM?

My hope is to strengthen the info going into the 5th edition 70-72 TIM, whenever it may be developed.

Thanks-

[Steven S.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Hi David. My 1970 LS5 is a convertible, VIN #9998, and does not have any AIR holes in the exhaust manifolds. It is a very original car, with 58k miles, with the POP, Tank Sticker, and Dealer Invoice. The engine and transmission have never been out of the car, with all of the mechanical parts dated 1970 and numbers matching, and the complete original interior. Just one repaint about 20 years ago that has held up very well.

Hope this helps for the next TIM.

Steve

[Warren F.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

I had three 1970 LS5 coupes, the VIN' s were 6664, 7272 & 8373, none had plugs in the stock exhaust manifolds.

[David P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

70CorvetteLS5 100.jpg
Here's the passenger side manifold with AIR holes/plugs on a very early LS5 car, VIN 194670S400180. Driver side manifold is the no-hole config as expected per the TIM.
Another Cortez Silver car too, incidentally.

My working hypothesis is that these passenger side manifolds were left overs from earlier production and were installed in discrete/discontinuous groups of LS-5s until they ran out somewhere in the 8000 range, sometime in early April, 1970.

[Joe L.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

[ATTACH=CONFIG]50598[/ATTACH]
Here's the passenger side manifold with AIR holes/plugs on a very early LS5 car, VIN 194670S400180. Driver side manifold is the no-hole config as expected per the TIM.
Another Cortez Silver car too, incidentally.

My working hypothesis is that these passenger side manifolds were left overs from earlier production and were installed in discrete/discontinuous groups of LS-5s until they ran out somewhere in the 8000 range, sometime in early April, 1970.

Dave-----

The passenger side manifold used for 1970 was the same as that used for 1966-69 Corvette big blocks. All 1968-69 Corvettes were equipped with AIR. So, there's every expectation that there may have been a lot of the manifolds already drilled and tapped for the fittings. In order to use them for the 1970 model year, they would have to be plugged and I expect that' just what happened. In fact, the drilled and tapped manifolds may have been manufactured in some early anticipation that they would be needed for the 1970 model year. In those early years, a lot of the emissions regs and strategies to meet them were in a "state of flux".

On the other hand, the driver side exhaust manifold was new for 1970 model year Corvette big blocks. So, there would have been none of these "left over" from any earlier model year and, thus, no reason for these to have been drilled and tapped for AIR. The first use of these manifolds for an application with AIR was 1971 LS-6. However, thereafter, all 1972-74 Corvette big blocks were equipped with AIR. Only 1970-71 LS-5 were AIR-free.

[David P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Joe,

... and AIR-free is wonderful, from a "one less system that I have to restore/maintain" standpoint. Thanks for the background summary too. My goal is to collect some examples of sequence #s that have this config in order to provide some info that may be useful during the 5th edition TIM revision, as well as to satisfy my own curiosity. Cheers-

[Terry M.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Dave-----

The passenger side manifold used for 1970 was the same as that used for 1966-69 Corvette big blocks. All 1968-69 Corvettes were equipped with AIR. So, there's every expectation that there may have been a lot of the manifolds already drilled and tapped for the fittings. In order to use them for the 1970 model year, they would have to be plugged and I expect that' just what happened. In fact, the drilled and tapped manifolds may have been manufactured in some early anticipation that they would be needed for the 1970 model year. In those early years, a lot of the emissions regs and strategies to meet them were in a "state of flux".

On the other hand, the driver side exhaust manifold was new for 1970 model year Corvette big blocks. So, there would have been none of these "left over" from any earlier model year and, thus, no reason for these to have been drilled and tapped for AIR. The first use of these manifolds for an application with AIR was 1971 LS-6. However, thereafter, all 1972-74 Corvette big blocks were equipped with AIR. Only 1970-71 LS-5 were AIR-free.

When I first disco0vered this anomaly it was for later serial numbers than the single sided examples cited and it was engines with plugged fittings on both sides. My speculation was that there was a batch or two of exhaust manifolds drilled and tapped in anticipation of the LS7 that never came to be.

Now we see these early single sided examples and Joe may have provided the genesis for them.

[Bob P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Ok I'm going to add to the mystery surrounding the plugged exhaust manifolds on 1970 LS-5's. My car has never had the engine pulled out of it according to all previous owners in which there were only 2. My car was built on January 14,1970, it is VIN 194670S400876, another very early car. It has plugs in both the passenger side manifold and the driver side manifold. Neither have plugs like the 2 pictured above. The passenger side has a plug with a square male fitting on the end and the passenger side actually has what looks to be brass plugs in it. I believe the casting dates of the exhaust manifolds are on the engine side and I'm not too sure how easy they are to check, but I'll see if I can find them. I can also post pictures if anyone is interested!

[Kenneth B.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Ok I'm going to add to the mystery surrounding the plugged exhaust manifolds on 1970 LS-5's. My car has never had the engine pulled out of it according to all previous owners in which there were only 2. My car was built on January 14,1970, it is VIN 194670S400876, another very early car. It has plugs in both the passenger side manifold and the driver side manifold. Neither have plugs like the 2 pictured above. The passenger side has a plug with a square male fitting on the end and the passenger side actually has what looks to be brass plugs in it. I believe the casting dates of the exhaust manifolds are on the engine side and I'm not too sure how easy they are to check, but I'll see if I can find them. I can also post pictures if anyone is interested!

I believe my 70/454 SN 7601 also has plugs. I bought it from the original owner. When I rebuilt the engine I took picts. of them. I think I sent or showed them to Terry M back in the day because the JM said thay were undrilled. Corvette is back in MI. & I will check when I go back when the damn snow & cold are gone. Don't know the casting dates but they were before the Corvettes build date. I will look for the picts.

[David P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Gents, I'd love to see those pics! Especially Bob's, but since we're in the same chapter I'll probably have a chance to see them in person

[Joe L.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Ok I'm going to add to the mystery surrounding the plugged exhaust manifolds on 1970 LS-5's. My car has never had the engine pulled out of it according to all previous owners in which there were only 2. My car was built on January 14,1970, it is VIN 194670S400876, another very early car. It has plugs in both the passenger side manifold and the driver side manifold. Neither have plugs like the 2 pictured above. The passenger side has a plug with a square male fitting on the end and the passenger side actually has what looks to be brass plugs in it. I believe the casting dates of the exhaust manifolds are on the engine side and I'm not too sure how easy they are to check, but I'll see if I can find them. I can also post pictures if anyone is interested!

Bob-----

There should be dates on the rear side of the manifolds. They might be a little difficult to see but I think you should be able to see them from under the car, possibly with the aid of a small mirror. The left side will be very difficult, though. The right side might be easier.

With the style plugs you described, I really doubt that the plugs (and manifolds) are original. I especially doubt that the brass plugs are original; I don't think the factory would have used such plugs.

[Kenneth B.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

My plugs were NOT brass. I will look for the picts. I also recall that only one side had plugs but I cant recall which. The plugs look like the ones in the post with the pict in the thread #4 with female square plugs.

[Bob P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

Guys I would post my pictures but for some reason I can't get them to load. I'll try and get the dates off the manifolds today.

[Chris H.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

My car, VIN 531, build date Jan 5, has plugs on the passenger side but none on the drivers side.

[Bob P.]

Re: Whose 1970 LS-5 exhaust manifolds have AIR holes??

My driver side exhaust manifold has part number 3880827 cast into it on the front side along with LH and GMT. I wasn't able to locate a cast date on the back of the manifold, but I was able to find on the back side the numbers 827 with an LH next to it, which I assume is the last 3 numbers of the part number. This is a manifold that was used through 1969 production on all 427 engines. The exhaust manifold on the passenger side has part number 3880828 cast into the front of it, which is correct for all 1970 454's. I haven't located a date on this manifold either. My car had a aftermarket side exhaust system added to it by the 2nd owner at some point. I know that side exhaust was not offered in 1970 as a factory option so it is possible that the 2nd owner put a 1969 exhaust manifold on the driver side so that he could purchase a 1969 side exhaust system for the car. This would make sense, since the car had under car exhaust on it originally and since the drivers side exhaust manifold was new for 1970 the under car exhaust system would have been different for 69 and I'm sure that Chevy wouldn't have put a 69 exhaust system on a 70 car! Since he bought a aftermarket side exhaust system, I don't know why he just didn't by one for a 70, unless it was available at the time. Guess I have another part to by when I start my restoration on this car! Still curious why I have the brass plugs on the driver side manifold?