I'm replacing my y-pipe this Friday with a custom mandrel bent unit from a local exhaust shop, and will be eliminating the cats.

My question is concerning the thermactor system. I asked the guy at the shop what they do about the air tube, and he says they just crimp it off. What are the drawbacks of this, if any? I was told that the computer will throw a continuous memory code, but it wont affect driveability.

Opinions?

 

Well Id suggest removing the pump then, otherwise itd be building pressure forcing air into a crimped tube. Unnecessary drag on belt at that point I say.

 

Is there a pump delete pulley I can get in order to do that?

 

I meant to ask this in the first post also. The shop want's to make me a pipe 2-1/4 from the manifolds to the Y, and then 3" back from there.

Is 3" too much pipe for a basically stock 351W?

 

No that sounds basically just like the Bassani y pipe. Except I think the bassani is 2.5" into 3".

 

And yeah there is a Smog delete pump, You can either get that, which is basically an idler puller or I've read that you can just run a shorter belt and eliminate it that way as well. The Mustang 302 pump delete is the kit that you can use if I remember correctly.

 

get the pump delete. finding the correct length belt is a pain in the ****. i left my unhooked SP on since i couldnt get the correct belt. I would for sure get a hi flow cat on there. they are cheap and will keep you very legal not to mention you wont loose any performance by running one. and like mentioned just pull the rest of the tubing and such out. Leave the TAB/TAD sensors plugged in but vac lines unhooked. also keep your egr hooked up to the manifold and sensor connected.

 

The air injection to the catalytic converter is not constant. You don't need to do anything to the tube... disconnect it at the diverter valve behind the passenger side cylinder head and remove the check valve, tube etc. The air injection is downstream of the O2 sensor at that point so there is no concern over codes thrown.

However, if you remove the smog pump and Thermactor system completely, THEN you will deal with thrown codes because the system also pushes fresh air through the exhaust just downstream of the exhaust valves in the heads. (That's the whole reason the diverter valve exists behind the cylinder head because it alternates the flow from the cat to the heads and vice versa). The lack of fresh air injection at this point WILL distort the readings the O2 sensor gets since this injection point is upstream of it. This has the potential to thrown codes because the air that the system adds is something the computer will "miss" if its not there.

 

Thank you everyone for giving me options to consider. I did in fact go look at the pump delete pulley as suggested here. I have also looked into a shorter serp belt.

greystreak, your explanation of the other functions of the thermactor system, and your suggestion on just which parts I need to remove, is most in line with what I'm trying to accomplish. A good performing exhaust system in a state that doesn't have smog concerns. The rest of the truck I want functioning as close to "as designed" as possible. I want the computer happy, with all the systems intact as much as possible.

If I disconnect the pipe at the diverter valve, won't I have to "cap" it there or something? What will prevent the air that is normally pumped that way from just being pumped into nothingness (and un-muffled)?

Thanks for your help guys.

 

No worries about the air that would normally be pumped down the tube to the cat. It gets pulled into the smog pump and dumped right back out at the diverter valve once the tube is removed. Its not like there is anything in it but the same air that got pulled into the pump three feet forward of where it leaves the diverter. Noise isn't a factor either as I recall. If you feel there is enough "noise" from the open end of the diverter, you could put a short length of hose on it and stuff the open end of the hose with a piece of foam or a chunk cut from a breather filter. That would "deaden" any noise from the open hose. I intend to do this to the diverter in mine when I finish the 4.9L swap as i will be deleting the catalytic converter that is clogged and no longer functioning properly.