Run Straight LT's?
 

I've heard mixed reviews.

I would like to know, for a car that will see very little street time and mostly strip, is it safe to run Straight Pacesetter Longtube headers? Will there be any problems w/ the Front O2 sensors?

There will be problems with the front O2 sensors unless you clamp on about 18" of extra 3" tubing. They have more of a chance to be exposed to fresh air, which would cause your car to go insaneo-rich.

Could not agree more :nod:

no way i could just run straight headers then? could a good tune avoid that problem?

If need be what size/diameter pipe should i use for the Pacesetter merge collector?

Well you could but your o2's will fuck up at some point cause of all the fresh air. People have run open headers for decent periods of time. I wouldnt personally run them no more than a few days without any extentions.

is it to amount of fresh air while Off or while being used? or while plugged in or what... I mean the O2's have been off the car in my garage which is pretty open...on there own w/ nothing by them. Does this mean the fresh air from opening and closing the garage door could have ruined them? I dont really understand that? if someone could explain

We are talking about while its running, idling especially.

Whats the big deal on getting some scrap pipe from an exhaust shop and clamping it on there? You seem dead set against it. :jest:


What we are saying, is the best tune in the world would likley be SCREWED by the fact that the O2's wont be able to read as well as they should. You will need some 3" pipe, probably have to get them to stick it in the expander as well so it will slip over a piece of 3" pipe. You can rent a pipe expander from autozone i think.

They mean that while the car is running they get super hot. and without any extentions the cold fresh air will get to them.

so would they have a better chance in the hot summer then? or makes no difference?

LMAO get some extra pipe on there!!!!

your exhaust is about 800 degrees. 30 degree change due to weather is nothing.

You can run straight headers if it's going to be a track-only car or if you have the balls to drive it on the streets. It will be loud as hell, but you can do it. They way it's done is by tuning the car with EFILive, HPTuners, etc. What you do is shut off the fuel trims and closed-loop operation. In essence, this eliminates the feedback from the front O2's and your car will run in open-loop all the time. This is kind of like how carb'd cars work. They don't learn from rich or lean conditions, so you will lose that safety factor. But, cars ran that way for how many years? 80? 90? Anyway, back to open-loop. Your car switches to open-loop (from the factory) while it's waiting for the O2's to warm up or in situations where there's a greater load on the motor (WOT). The only thing different is you'd be running this way the whole time. The most important thing to remember is, during open-loop the PCM is commanding an AFR without knowing if it is right or not. That's why it is important for the tune to be accurate.

It can be done. :)

Interesting, so by not having the closed loop, what could happen? you said safety? I would really like to know more on this- I'm sure others will too.

Well, environmental changes can cause slight changes in air fuel ratios as well as new mods (like adding headers). I'm sure those aren't the only factors, but probably the biggest two. The safety you are losing is the PCM's ability to adjust for those changes.

Basically, closed-loop works kinda like this...there's a grid of fuel trims (cells) that represent different driving conditions (low rpm/low load, high rpm/med. load, WOT, idle, etc.). The percentage the PCM increases/decreases the trims for the conditions is determined by the front O2 feedback. For example...

Let's say the PCM is commanding an average AFR of 14.63...and based on the feedback from the O2's, it finds your AFR is really 15.0. So, the PCM then says, "If 15.0/14.63=1.0253, then increase (because I'm lean) the fuel trim cell for this driving condition by 2.53%."

This is done over a hundred times each minute and called short term fuel trims (STFT). The average of the STFT's is recorded for each condition and becomes a long term fuel trim (LTFT) if it is consistently rich or lean. The tricky thing about LTFT's is when you transition to WOT (open-loop) and you have negative LTFT's, it will not subtract any fuel. But if you have positive LTFT's, it will add them to it's fueling calculation. This is because the PCM is guessing the AFR in open-loop. So, it's saying if I'm lean in several conditions during closed-loop, I need to assume a lean condition at WOT (open-loop) whether it's lean or not.

Make sense?

So what would it be really bad to run open headers with the O2s unplugged even for a day untill i get the 12" pipes done?
-Joel

My frend attempted to fire up his camaro w/o the O2 sensores being plugged in, the car backfired popped and blow smoke and flame out of his headers. so I personally wouldnt take that risk...

Now for my question does the Pipe have to be welded or can it be slip fitted w/ a clamp of some sort to the headers?

My friends and I just installed Pacesetters on my Z and it started/ran just fine for 10 minutes without any O2's. I didn't even get an SES light. As long as the car is relatively stock (just bolt-ons), you will be fine. When you step up to H/C mods, you definitely need a tune before you can run without O2's.

Why risk problems? Put some extensions on there and wake neighbors up to your delight. Just watch out for officers. Open headers sound awesome. Just my .02

to my previous post do the collectors need to be welded to the extensions?

no they don't