1969-70 SMOG PUMP

[Kenneth B.]

what is the difference between the 1969 & 1970 smog set ups beside the dates

[Norris W.]

Re: 1969-70 SMOG PUMP

For one thing, some 70's didn't have smog. My 70' LS5 4 speed air convertible doesn't have it, and I did an owner search when I bought the car about 20 yrs ago and everybody in the line said it came that way. It has non smog exhaust manifolds dated consistently with the rest of the car, which everybody in the chain said had never been replaced.

It may be common knowledge among the 70 experts, but I've never known why some did and some didn't when apparently ALL '69's did, and although my '71 LS5 coupe with similar equipment had the pump and hardware gone, presumably by a previous owner, it had drilled manifolds with plugs.

I haven't thought about it in a long time, but I'd like to know the reason, especially since the LS5 & LS6 Chevelles of the same time period had the pumps.

[Sal C.]

Re: 1969-70 SMOG PUMP

As far as the small blocks are concerned the only difference between the two years would be the thickness of the pulley spacer and possibly the pulley itself. Otherwise it's exactly the same.

[Joe L.]

Re: 1969-70 SMOG PUMP

Sal-----

I agree 100%.

[Joe L.]

Re: 1969-70 SMOG PUMP

Norris------

Yes, all 1968 and 1969 Corvettes had the AIR (i.e. "smog pump") emissions system. For the 1970 model year, ONLY the LT-1 had AIR.

Your 1971 LS-5 did not originally have AIR, either. So, I don't know why it had manifolds with AIR fittings. It's possible that they were supplied this way from the factory. Although unusual, some have been "documented". If so, though, the plugs utilized usually have indented SQUARE wrench provisions and not external or internal hex.

1972 LS-5 DID use AIR. Are you sure the car was not a 1972 instead of a 1971?

As far as why, here's the deal: first of all, don't assume that because a 1970-71 Corvette did not have a "smog pump" that it did not have exhaust emissions control. All 1968 and later Corvettes had exhaust emissions control. It's just that all exhaust emissions control did not involve an AIR system for the 1970 and later model year Corvettes.

Exhaust emissions control for some applications was provided by carburetor and distributor modifications. This was called the "controlled combustion system" or "CCS". This was a lot cheaper than the AIR system. However, it was much more performance-robbing. For most applications, it was cheaper to use the CCS system and forego the AIR system. The performance loss for most applications was not that big of a deal.

For example, during the 1968-69 period, most Chevrolets with automatic transmissions used the CCS system, while most with standard transmission used the AIR system. Corvettes, being a performance-oriented car, got the AIR system for ALL 1968-69 applications.

By 1970, apparently Chevrolet engineering felt that it would be ok to use the CCS system for most Corvette applications and that exhaust emission requirements could be met without degradiung performance too much. However, for the only special high performance engine released for Corvettes in the 1970 model year, the LT-1, the AIR system was chosen due to it's lesser effect on performance where ultimate performance was desired.

The same thing held true for 1971. Non-SHP Corvette engines received the CCS system whereas the SHP, LT-1 and LS-6, used AIR.

Some folks think that AIR is a performance-robbing system. That's completely untrue. Yes, it does require a small amount of power to drive the AIR pump. However, the engine can otherwise be designed and tuned for maximum performance and still meet exhaust emissions standards. The AIR system is THE WAY TO GO for performance AND emissions control. In fact, it's still used to this day on many applications.

[Norris W.]

Re: 1969-70 SMOG PUMP

Yes Joe, ABSOLUTELY sure on the second car being a '71, and it does have externally hexed plugs. I'm also sure that the car has THE original motor, but what I'm NOT sure of is that it has original dated exhaust manifolds. I'll have to check first time I get in the mood to roll around under it. Like most of my cars, I bought this one sometime in 80's/early 90's when some of this stuff was WAY cheap, but I don't recall the details now without looking closer, especially on cars that I'm not all that interested in anymore. The '71 was a 100K mile car when I found it, and I never bothered to run a title history, so I don't know much about it except for original drivetrain components and zero damage history.

[Joe L.]

Re: 1969-70 SMOG PUMP

Norris-----

The external hex head plugs in the AIR fittings are not typical of factory installations in those small number of cases in which plugs were used, at all.

For 1971, there were only 2 LS-5 engine suffix codes that I know of-----"CPH" for manual transmission and "CPJ" for THM-400. Both of those codes were engine assemblies that did not have provisions for AIR. If you have some other hitherto unknown code, I suppose it's possible it used AIR. But, if it has one of these 2 codes, it did not originally have AIR.

Also, if the emissions label is still present on the car (located near the master cylinder), that will provide very useful information. The only codes for 1971 LS-5 that I know of are "AZ" and "AV". Both of these codes denote an engine equipped with CCS. In fact, it's stated right on the label. So, if you have either of these codes on your label, the car was not originally built with AIR. If you find some other hitherto unknown code on the label, then other possibilities present themselves.

[Kenneth B.]

Re: 1969-70 SMOG PUMP

MY 70 early March 454 has the pluge in the manafolds. I bought the Vette from the origional owner. Terry McMannan took pictures years ago when he was at my house looking at my 72 ZR-1.

[Joe L.]

Re: 1969-70 SMOG PUMP

Ken-----

Yes, early 1970 would be the ones that I would most expect to see with the factory-plugged manifolds. Tonawanda was either using up 1969 manifolds (all of which were the AIR fitting type) or there was a shortage of the non-fitting manifolds at changeover time.

What is the configuration of the plugs? I would expect internal square head.

[Terry M.]

Re: 1969-70 SMOG PUMP

The other possibility is Tonawanda was using exhaust manifolds intended for the still-born LS7. It would be interesting to find the casting dates on some of these early 1970s BB exhaust manifolds with the AIR fittings.
BTW the approximate vehicle date range of these manifolds is in the 1970-72 TIM&JG.

[Kenneth B.]

Re: 1969-70 SMOG PUMP

JOE
My pluge recessed sq. holes