69 L46 versus 70 L46-smog /no smog. Why?

[Mike E.]

Per the JG and my limited personal experience, the 69 L46 came with smog (AIR) equipment, while the 70 did not. Anyone know why?

[Duke W.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

You're dealing with four different L-46 configurations - two model years and federal and California emission standards, which were tighter than federal.

AIR was an expensive system, so the engineers endeavored to meet emissions requirements without AIR if possible via carburetor and distributor calibrations (fuel and spark advance maps). In some cases California configurations needed AIR while the federal configuration of the same basic engine did not. Also, it is tougher to meet emissions requirements with a manual transmission due to the "hydrocarbon spike" that occurs when lifting off the throttle to shift, so the same basic engine configuration may have required AIR with a manual, but not with an automatic.

The above are general considerations on early emission control. For the '69 model year there were four different Corvette engine configurations, two of which were manual only, so that makes for six configurations that had to be tested for federal and CA emissions - 12 total for just Corvette. Then add for all the other model lines. This is why engine/transmission/axle combinations were limited as the seventies progressed.

Meeting emissions standards at the least cost kept the engineers very busy in that era. Dave McClellan discusses the difficulty in getting all the various configurations certified in his book, and in some cases there was a question of whether or not they'd have a product to legally sell at the normal beginning of the new model year.

Duke

[Mike F.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

In 1970 Chevrolet added TCS (Tranmission Controlled Spark) to the Federal L-46 engine (I belive most if not all other engines got them as well). Chevrolet also added an ECS (Evaporative Emissions Control System) to the California cars, which was RPO code NA9.

TCS - Prevented vacuum advance to the distributor in 1st & 2nd gear. (Fed & CA cars)
ECS - Was a charcoal(?) canister mounted on the drivers side, near the rear of the lower inner front fender. for the gas fumes. (CA cars only)

Perhaps these "smog" additions allowed for the elimination of the A.I.R. pump?

[Terry M.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

In 1970 Chevrolet added TCS (Tranmission Controlled Spark) to the Federal L-46 engine (I belive most if not all other engines got them as well). Chevrolet also added an ECS (Evaporative Emissions Control System) to the California cars, which was RPO code NA9.

TCS - Prevented vacuum advance to the distributor in 1st & 2nd gear. (Fed & CA cars)
ECS - Was a charcoal(?) canister mounted on the drivers side, near the rear of the lower inner front fender. for the gas fumes. (CA required)

Perhaps these "smog" additions allowed for the elimination of the A.I.R. pump?

There Mike; I corrected it for you.
I have actually seen more NA9 1970s delivered outside California than those delivered in California, but I am sure if I lived in California my perspective would be different. Regardless' NA9 was not California only, but rather California required.

[Mike E.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Thanks for the input, Duke, but I was pretty much aware of the issues of the day. I guess I should have emphasized I was looking for greater specificity. Why exactly did the 70 L46 not need AIR while the 69 did? Mike, I appreciate your reminding me that TCS was introduced in 70, and that it could have been part/all of the reason. I'm also wondering about the effect/non-effect of the "gizmo" (dashpot?) on the 70 carburetor. This was 70-only wasn't it? Did it play any part in the emissions picture? Photo of that attached.
P3282626.jpgP3282627.jpg

[Edward J.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Mike, The dashpot would help slow the closing of the throttle and help keep the engine from stalling when you let the accelerator pedal up suddenly, It would slowly close throttle once the lever contacts the button. This way the no loss of power steering and power brakes. Carburetors did awful things once Emissions were introduced.

[Terry M.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Thanks for the input, Duke, but I was pretty much aware of the issues of the day. I guess I should have emphasized I was looking for greater specificity. Why exactly did the 70 L46 not need AIR while the 69 did? Mike, I appreciate your reminding me that TCS was introduced in 70, and that it could have been part/all of the reason. I'm also wondering about the effect/non-effect of the "gizmo" (dashpot?) on the 70 carburetor. This was 70-only wasn't it? Did it play any part in the emissions picture? Photo of that attached.
[ATTACH=CONFIG]55925[/ATTACH][ATTACH=CONFIG]55926[/ATTACH]

The purpose of the dashpot is, as Ed states, to slow the closing of the throttle plates on release of the accelerator, but the reasoning is a little different. It is an emissions part; in that when the throttle plates are suddenly completely closed the air is shut off to the engine and the HC emissions at the tail pipe will momentarily spike. The dashpot prevents that spike.

[Bill M.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Per the JG and my limited personal experience, the 69 L46 came with smog (AIR) equipment, while the 70 did not. Anyone know why?

Probably cost. The '70 did have emissions controls and the '70 standards were more stringent than '69.
Meeting the tougher standards without using AIR probably saved a few $.

[Kevin G.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Could it be simply that the 1970, L46 was NOT considered a High Performance engine, like the LS 5?

[Mike F.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Could it be simply that the 1970, L46 was NOT considered a High Performance engine, like the LS 5?

The LT-1 was the only 1970 Corvette engine delivered with A.I.R. system installed. Base engine, L46, LS5, no A.I.R..

[Kevin G.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Yes, only the "High Performance" engines received the AIR systems.

[Jim T.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Thanks for the input, Duke, but I was pretty much aware of the issues of the day. I guess I should have emphasized I was looking for greater specificity. Why exactly did the 70 L46 not need AIR while the 69 did? Mike, I appreciate your reminding me that TCS was introduced in 70, and that it could have been part/all of the reason. I'm also wondering about the effect/non-effect of the "gizmo" (dashpot?) on the 70 carburetor. This was 70-only wasn't it? Did it play any part in the emissions picture? Photo of that attached.
[ATTACH=CONFIG]55925[/ATTACH][ATTACH=CONFIG]55926[/ATTACH]

Mike my original owner 1970 base engine 350/300 with turbo 400 did not have this "gizmo" (dashpot) on its Rochester.

[Terry M.]

Re: 69 L46 versus 70 L46-smog /no smog. Why?

Mike my original owner 1970 base engine 350/300 with turbo 400 did not have this "gizmo" (dashpot) on its Rochester.

Dashpot only goes with 1970 Manual transmission.