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I have a stock 77. L48 automatic
I must pass CA smog every 2 years. I am
interested in adding power but want to avoid spending too much and or causing a huge change back to smog compliant job every 2 years.
I already have true dual exhaust.
I did basic stuff to add power, tune up , set timing as per Lars’ paper. Thinking high flow cats could be the very next thing on the list to add a bit of power for very little cost. High flow cats seem to be as cheap as $50 each.
These flow master brand are only $61 each and look very similar to stock cats ( regarding visual inspection) my hope is to pass smog without the modified vehicle referee process.
has anyone already switched to high flow cats without any other changes? Did it add power, was exhaust note changed?
Last edited by Greengear; Oct 23, 2018 at 10:07 AM.
They better have that Ca EO # stamped on them or you will fail the visual trust me on this. They run more than the same cat without it just what we have to deal with out here.
Any modern cat is better than the original GM one. Catco, magnaflow, plenty of choices out there.
I got failed as the pn on mine was changed/updated to another....even proving that I still failed the visual with "someone I knew". Its not worth their income to risk passing some guy for $60. The days of that kinda disappeared
Pretty sure magnaflow and flowmaster are sponsors here on the board, page one of them.
Walker has been around a long time too
IMHO, the single biggest power inhibitor of late C3 smog motors is the stock CAT. You literally have the first car I've heard of on here that still has stock cats. You need to do what you need to do to get rid of that thing.
It's truly horrifically terrible.
Adam
Last edited by NewbVetteGuy; Oct 23, 2018 at 12:13 PM.
I have a stock 77. L48 automatic
I must pass CA smog every 2 years. I am
interested in adding power but want to avoid spending too much and or causing a huge change back to smog compliant job every 2 years.
I already have true dual exhaust
Does your true dual exhaust have two modern CA legal cats? If so, you're good to go. Don't mess with it anymore. If not, that's what you need to do. I'd be surprised to find that you sourced a stock cat for your second intermediate pipe.
Does your true dual exhaust have two modern CA legal cats? If so, you're good to go. Don't mess with it anymore. If not, that's what you need to do. I'd be surprised to find that you sourced a stock cat for your second intermediate pipe.
good point. I took the previous owners word for it that it had ancient 70’s pellet style cats. I think they are already upgraded. See pic
Those don't look like EO'd cats - they were probably replaced many years ago. That said, is that 2.5" pipe? Looks smaller but my photo measurement capabilities aren't the best.
If the car has a stock engine, that system is pretty good for your needs. 2.5" would improve it, maybe a few HP. Headers would be a much bigger win or other engine mods. I'd leave it alone, for now.
Those cats are technically legal as long as the cats were installed prior to the law change mandating E.O.'d cats, but some smog shops will give you grief over it. Not a problem until it is, of course.
Last edited by Shark Racer; Oct 24, 2018 at 12:02 PM.
I have a stock 77. L48 automatic
I must pass CA smog every 2 years. I am
interested in adding power but want to avoid spending too much and or causing a huge change back to smog compliant job every 2 years.
I already have true dual exhaust.
I did basic stuff to add power, tune up , set timing as per Lars’ paper. Thinking high flow cats could be the very next thing on the list to add a bit of power for very little cost. High flow cats seem to be as cheap as $50 each.
These flow master brand are only $61 each and look very similar to stock cats ( regarding visual inspection) my hope is to pass smog without the modified vehicle referee process.
has anyone already switched to high flow cats without any other changes? Did it add power, was exhaust note changed?
Some years ago Magnaflow used my 81 to build their cat back exhaust prototype. They dynoed the car before and after. The gain was approx. 13 hp. On an 81 that is almost 10%.
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Hi flow cats or stock
