1988 F 150 302 automatic 2 wheel drive EEC-IV . Once I have long tube headers and dual exhaust where do I relocate o2 sensor? One other question. If you have dual exhaust do you have two cats and two mufflers? Thanks

 

To have a true dual exhaust system, you would have to have two cats and two mufflers. However, there are many people out there that are running a dual system after the cats--aka catback system. Put the O2 sensors back where they were, as close as you can get them.

vernon

 

Is that a 3 wire or 2 wire O2 sensor? If it's 3 wire it's heated, and you could probably get away with putting it in one of the collectors. If it's a 2 wire, you'll either want to get coated headers, or run header wrap. Header wrap can be detremental to header life though.

You want it as close as possible to the exhaust ports. Not only to keep it heated up, but to keep the transport delay as low as possible. Transport delay is the time between when the computer makes a change and when the O2 sensor sees the results of that change. Obviously, the farther down the exhaust stream it is, the longer it will be before the computer will see the changes. Since the computer is preprogrammed with a specific transport delay per engine RPM, placing the O2 sensor in a different location can cause problems.

So I'd say put it in one of the collectors. Jegs or other places sell a weld-in O2 sensor fitting. Be sure if you have a 2 wire sensor to either use coated headers or wrap 'em.

How do I know all this?

I installed a Holley EFI system on my FE 390. The instructions for that system explain a lot of fuel injection information. I drilled a hole in the collector of the passenger side header, and welded the O2 sensor fitting in. It needs to be angled upwards so that it doesn't collect moisture. The kit came with a 3 wire sensor so I was OK with regular unwrapped headers. I was also able to program in the transport delay.

On to the next question:

The way I would do it, is if you have emission testing, run a true dual exhaust system, with two aftermarket high flow cat converters. Then a crossover pipe, then the two mufflers. (dont skimp on muffler quality, I've been bitten before) It'll cost more to do it this way, but I think that will provide the best results.

Just the way I understand things.

Edit: Whatever you do, dont put the O2 sensor behind the cat converter! It wont work as it should.

 

The ideal place would be in a crossover pipe after right after the longtubes. It will read from both sides of the engine this way.

 

Thanks for all the replies. I have a three wire o2 system so that is good to know based on the information you supplies me. One other question has occurred to me. If my current single exhaust system has two catalytic converters. Will it be enough to put a catalytic converter on each pipe as well as a muffler. I am planning to have a true dual exhaust. If I were to do this. What effect on my emissions do you think this will have? Thanks again for the inofrmation and suggestions.

 

Hrm. Usually the two converters have different materials in 'em, and filter different things. What you'd have to do, is put on two aftermarket units, as they filter everything in one unit. Then, on the one hand, the exhaust would be flowing through each cat slower, allowing it to sit on the element longer, filtering it better. On the other hand, an aftermarket unit might not filter out the bad stuff as good as a factory one, in the name of flow. Also, having long tube headers will cool the exhaust more before it ever gets to the cat converters. There again, coated or wrapped headers will negate this. Converters work best when they're good and hot. So you're losing some efficiency there. The overall effect, as I predict it, will be a very slight increase in emissions over the stock system. Probably still well within any emissions testing limits though. With coated headers, it'll probably be just as good as or better emissions than the stock setup.

 

Thanks for your reply. I gather that coated headers is the way to go. If I understand correctly you are saying the cats go on as close to the headers as possible and than later down the pipes the mufflers,one on each pipe. The o2 would go in an H pipe. The H pipe should be infront of the cats or do you think it would be best to put it behind the cats? If it is behind than the o2 sensor should go infront of the cats. Can the o2 senser go into the long tube part of the header just before it conects with the pipe?

 

You can do like every shop in this town does, put the sensor in about the stock location in the pass side pipe, it worked fine there before it will work the same with the duals. You can go with or without the H on this setup, your choice. You could also go with a dual in dual out magnaflow as they have an X pipe built into them.

 

Put the sensor in the header collector on the passenger side like 351M said. Then, put the cats as close to the headers as possible. Then the H or X pipe, whichever you choose to run. Then the mufflers. Locate the mufflers as close to the front of the system as possible though, so all the moisture gets cooked out of them and they dont rot out inside.

So heres the order:

1. Headers with O2 sensor on passenger side
2. Cats
3. H or X pipe
4. Mufflers
5. Tailpipes

 

Thanks for all the information. I have gone online to look for headers. There are quite a few for a 302. Is there a particular brand that you feel is better than others. I am not really after making it louder I just want the performance. Is it to big of a compromise on performance to not put on mufflers that will not increase the noise? Thanks in advance.

 

Well, I have Hedman's on my 390. They fit good. I'm not entirely familiar with what fits well on 302's though. I'd look for a set with smaller primary tubes to promote low end torque and to get the gasses down to the O2 sensor as quickly as possible.

As far as I understand it, the maximum HP you'd gain from using performance mufflers is about 5hp. Hardly worth the headaches from the drone and noise. Use quiet mufflers. Keep it quiet.

 

Pretty much any mufflers will add more power, any turbo muffler should net almost as much power as a straight through with the proper size pipe. If you go with a straight through or other reall free flowing muffler,like Edelbrock go with 2"-2.25" pipe if you go with super turbos or the like go with 2.25". I would presonally say go with the Cherry Bomb Turbos, fairly quiet at cruise speeds without the drone but still sound nice uptop.