long tube headers: emmissions?

[sothpaw]

Can anybody who has done long tube headers confirm
that they screw up emmissions? Even with the cats still
in place? Why is this?

--I've always assumed I can't do the headers because of the
emmissions testing here.

 

[oldace84]

Would love some Hooker's, longtubes....but totally illegal out here in Southern CA.
Just not worth the hassle of installing then trying to get thru the smog nazi's.....
tony

 

[vader86]

You could buy the headers and try to fit some bullit cats in there, be willing to do some welding though. If your emissions arent too strict, you can get away with it, just gotta have the cats on there.

 

[sothpaw]

what's too strict?

They run it on the dyno at speeds from 0-40. It's not
just a tail pipe test.

 

[Trance_LT4]

Maryland emmissions......I got my long tube headers done after my smog test. I've got less than a year before my next one is due, so I can't tell you yet, but I'm gonna try to get it smogged as is right now.

 

[sothpaw]

bullet cats?

Trance,

Do you have to run bullet cats from Random? I thought it was
physically impossible / impractical to fit the stock cats on there
with long tubes.

I'm trying to cost out headers. I figure $800 for the manifolds,
$300 for the bullets (if I must), and $100 for install/pipe fabs.

 

[Trance_LT4]

I'm not using bullets from Random tech. I'm using two 12 inch cats I ordered from summit. Catco, I think the name is. They were like $40 a piece.

 

[Eagle85C4]

One of the problems I see is that the stock exhaust is set and calibrated to produce emissions at or below a certain level for Clean Air purposes. In addition to providing extra oxygen to help the converter maintain temp at or around 600 degrees, the air pump also reduces the percentage of the emissions by changing the ratio of oxygen to emission gas. In a nut shell the air pump introduces air into the exhaust to dilute the emissions at the tail pipe. It does not change the amount of emissions just the ratio. By changing the amount of flow in the exhaust without changing the amount of air from the pump causes the ratio to change and allow more emission and less oxygen causing the emissions test failure. If it is possible to cause the air pump to inject more air into the exhaust increasing the oxygen to emission ratio it would lower the emissions at the pipe and fool the test. But the oxygen sensor would also have to be calibrated to not change the air/fuel mixture when it see's more oxygen in the exhaust. It may be possible to inject air into the exhaust downstream of the sensor where it won't effect the sensor but diluting the emissions allowing it to pass inspection.

 

[sothpaw]

Eagle,

...so it sounds like just change the headers/cats is not enough
to pass emissions, I'd also have to make the air pump work
more? Do you know anyone that's tried this? Sounds not too
complex.

If modding it to pass is too hard, I'll simply lean more towards
doing a cam. I like headers because of the torque potential.

 

[Vettelt193]

I didn't think you got an exhaust system yet.... when looking at exhaust, the lowest flow point is what will kill power, headers won't give you much (if any) power at all without doing something else to the exhaust to free it up

 

[sothpaw]

you're right

I know it'd be better to do headers& exhaust. But I didn't
know I'd get little/nothing from headers /cats w/ stock
mufflers.

There's a guy on corvetteforum who did the LT4 Hotcam, then
headers with substantial gain, he doesn't mention new mufflers
or exhaust.

I'll go back and check with him.

 

[Vettelt193]

I would be very surprised if he didn't do some other exhaust mod... the stock headers actually flow very well, the exhaust is the weak point... another thing to think about is the labor. headers are not easy to install, especially compared to a standard exhaust system

 

[sothpaw]

yes, but...

If I do the headers in combo with the ported heads, they
will already be off!

I like the big torq. gains I've heard advertised for headers +cam.
I have a book showing ZZ9 cam and headers +muffler on an F-body, LT1. The gain in hp and torq is all over the useable range,
not just at the top.

Of course, that car had ported heads already.

 

[Vettelt193]

You can't compare F-body to your car... they have a factory manifold, not the shorty header style. F-body cars get huge gains from headers, ours do not

 

[tntcorvette]

you can pass emission with long tube headers, cats and the rest of the smog stuff on there.