I'm in the process of putting together a 283 specifically built for high-RPM racing, but it will need to pass the sniffer test. It will have no EGR and no AIR injection but will be running two catalytic converters (for sniffer test/street use). I'm in the process of throwing up some cam choices for the engine but I need to know if they will get pass a sniffer test for a post 1973 model year (78 specifically).
First cam:
Adv. dur : 284/296
@ 0.050" : 240/246
Lift : .507/.510"
LSA : 110*
Second cam:
Adv. dur : 294/306
@ 0.050" : 250/256
Lift : .519/.523"
LSA : 110*
I was throwing around the idea of a Commander 950 with a 4bbl TBI unit but more than likely it will be wearing a Holley 4150 or hopped up Rochester M4ME. Lemme know what you guys think about passing the sniffer test or about 283 combos.
First cam:
Adv. dur : 284/296
@ 0.050" : 240/246
Lift : .507/.510"
LSA : 110*
Second cam:
Adv. dur : 294/306
@ 0.050" : 250/256
Lift : .519/.523"
LSA : 110*
I was throwing around the idea of a Commander 950 with a 4bbl TBI unit but more than likely it will be wearing a Holley 4150 or hopped up Rochester M4ME. Lemme know what you guys think about passing the sniffer test or about 283 combos.
five7kid
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May 4, 2026
"Conventional wisdom" says stay under 210 duration to keep overlap down. With larger LSA, you can go higher (my cam has 216/228, for instance, with 112 LSA).
For a 283, the overlap is magnified vs. a 350, for instance. So, I'd think you're in a little too deep, even with two cats. A feedback induction system may help some, but if it keeps the mixture lean enough at idle to pass sniffer, throttle response probably won't be too impressive.
For a 283, the overlap is magnified vs. a 350, for instance. So, I'd think you're in a little too deep, even with two cats. A feedback induction system may help some, but if it keeps the mixture lean enough at idle to pass sniffer, throttle response probably won't be too impressive.
I may have to soon come to the reality that I might have to have two cams for my engine. One for emissions testing and the other one for my racing needs....
Supreme Member
I can't see how you're going to get that to pass with no AIR. It might be possible with it, especially if you could get an extra-large-diameter pulley for it, and only put the belt on at test time.
I have always found it far more convenient to have 2 complete engines; dodges the tuning hassles.
I have always found it far more convenient to have 2 complete engines; dodges the tuning hassles.
That's the other option I may have to come to. I might have to swap the emissions-legal engine for the test and then swap in the 283 after testing; because it's becoming quite evident that I won't be able to pass the test with my ideas. They don't do a visual check here so I'm not at all concerned about what the engine looks like, but only how it performs out the tailpipes...