FAST question about open headers.

[Z-OwNer]

I figured I'd try this on your guys board since you seem to be the most knowledable about FAST. I just recently did a forged 396 build up with heads cam and all that junk. I have longtube headers which I would like to run just open headers with no y-pipe or anything like that. Is there any way to set up the FAST so it will run ok like this? Because it cant get a correct reading from the wideband 02 if its right there at the open part of the header correct. I just dont want to ruin the engine by driving it like this.

 

[bobc455]

Where were you thinking of putting the O2 sensor? How far up the collector could you put it?

-Bob Cunningham
bobc@gnttype.org

 

[bruce]

Originally posted by Z-OwNer
I figured I'd try this on your guys board since you seem to be the most knowledable about FAST. I just recently did a forged 396 build up with heads cam and all that junk. I have longtube headers which I would like to run just open headers with no y-pipe or anything like that. Is there any way to set up the FAST so it will run ok like this? Because it cant get a correct reading from the wideband 02 if its right there at the open part of the header correct. I just dont want to ruin the engine by driving it like this.

You want at least 10" of pipe between the sensor and the end of the collector.

I have a portable WB that I use.
It's 16" of tubing with the sensor 6" from one end. I have a strap and hose clamp so that I can strap it onto the exhuast pipe, and when installed it reaches 6" up the pipe, and still has the 10" on the other side. I'd suggest you weld up a deal something like that and then just weld that into your current collector.

You'll just be primarily reading a couple cylinders, but that's the only way to get by without running anything but a collector I know of.
HTH

 

[Z-OwNer]

I am an extreme noob when it comes to this side of things (the computer and tuning) Does the car run in closed loop when it first starts up and then switches to open loop and thats when it starts getting info from all the sensors and such. It runs solely off the computer tune at first though right? Having an open exhaust makes it keep compensating indefinitely with more fuel because it thinks there is way to much air for the amount of fuel right? If this is the case (lol which probably is no since i dont really have much of a clue) Is there a way to keep the car in closed loop all the time so that I can atleast drive the thing for now? Its been over 2 years

 

[bobc455]

>>I am an extreme noob when it comes to this side of things (the computer and tuning)

I would highly recommend taking some time and learning how it works. The computer is great, but if you don't know how it works then you could (minimally) be missing out on some performance! I would do some reading- look at the FAST website, for starters, and maybe some magazine articles and such. Oh yeah, and read this forum! Lots of good information here.

>>Does the car run in closed loop when it first starts up and then switches to open loop and thats when it starts getting info from all the sensors and such.

No, the opposite. You have to wait for the O2 sensor to heat up, and for the engine to get up to temperature, before you will get meaningful readings from the O2 sensor. Before this, it will be relying on the pre-programmed parameters to "blindly" keep it running.

>>It runs solely off the computer tune at first though right?

It always runs off of the computer tune- sometimes it just slightly adjusts the mixture a bit to make the O2 sensor happy. But it is always looking at the internal tuning tables first.

Having an open exhaust makes it keep compensating indefinitely with more fuel because it thinks there is way to much air for the amount of fuel right?

That's why the point has been raised about how far up in the header you can place the O2 sensor. If you put it too near to the outlet, you will get raw air from the atmosphere mixed in with your exhaust, screwing up your O2 readings. If you can put the sensor far enough away from atmosphere, you can probably run fine.

This begs the question, however about the car- are you only going to be racing it? Most guys here run a full exhaust, so the sensor placement isn't much of an issue. If you can't get it far enough up the collector, I'm not sure you will even be able to get reliable readings from the O2.


>>If this is the case (lol which probably is no since i dont really have much of a clue) Is there a way to keep the car in closed loop all the time so that I can atleast drive the thing for now? Its been over 2 years

Once the sensor is warmed up, you can run in closed-loop all the time. I think you would hear a unanimous recommendation from the other readers, however, that you should tune your VE tables so eventually the O2 sensor is only making very slight corrections, and the engine isn't dependant on the O2 just to keep running. Only then will adjustments to the AE etc. be meaningful. That is to say if you can even get the O2 to function! Can you add some length to the exhaust system just to dial in the FI?

-Bob Cunningham
bobc@gnttype.org

 

[Z-OwNer]

Originally posted by bobc455


I would highly recommend taking some time and learning how it works. The computer is great, but if you don't know how it works then you could (minimally) be missing out on some performance! I would do some reading- look at the FAST website, for starters, and maybe some magazine articles and such. Oh yeah, and read this forum! Lots of good information here.

>>No, the opposite. You have to wait for the O2 sensor to heat up, and for the engine to get up to temperature, before you will get meaningful readings from the O2 sensor. Before this, it will be relying on the pre-programmed parameters to "blindly" keep it running.

This is what I was talking about. Is there a way to force the car to stay in open loop. It might not be exact but it will atleast run alright correct? Right now with open header it just keeps dumping more fuel and more fuel till no end right?

>>It always runs off of the computer tune- sometimes it just slightly adjusts the mixture a bit to make the O2 sensor happy. But it is always looking at the internal tuning tables first.

Thats what I was trying to say, Im just wondering if there is a way to keep it from compensating because it will be getting false readings.


>>That's why the point has been raised about how far up in the header you can place the O2 sensor. If you put it too near to the outlet, you will get raw air from the atmosphere mixed in with your exhaust, screwing up your O2 readings. If you can put the sensor far enough away from atmosphere, you can probably run fine.

This begs the question, however about the car- are you only going to be racing it? Most guys here run a full exhaust, so the sensor placement isn't much of an issue. If you can't get it far enough up the collector, I'm not sure you will even be able to get reliable readings from the O2.

The O2 bungs are pre-welded into the headers. The car will be driven a few times a week. But at the track or racing around it will be pretty much open header. There will be two electric cutouts so I am just trying to figure out if its going to work is all.

>>Once the sensor is warmed up, you can run in closed-loop all the time. I think you would hear a unanimous recommendation from the other readers, however, that you should tune your VE tables so eventually the O2 sensor is only making very slight corrections, and the engine isn't dependant on the O2 just to keep running. Only then will adjustments to the AE etc. be meaningful. That is to say if you can even get the O2 to function! Can you add some length to the exhaust system just to dial in the FI?

I plan on for now (until I figure out what I want to do with the exhaust) bolt an offroad pipe to the header which should give over a foot of pipe so that I can see if its doing ok. I guess I could drive around with that on there and that would give me the recomended 10 inch min.

Thanks for the info guys, any and all suggestions are appreciated.

 

[bobc455]

>> This is what I was talking about. Is there a way to force the car to stay in open loop. It might not be exact but it will atleast run alright correct?

Yes, just uncheck the box that says "closed loop enable" in Calcom- it is under the "Closed loop parameters" under A/F ratio.

>>Right now with open header it just keeps dumping more fuel and more fuel till no end right?

No. There is a limit that you can set in Calcom for how much fuel the closed-loop will add- typically 10% or so. Look at "correction limits" under the A/F ratio menu in Calcom.

>> The O2 bungs are pre-welded into the headers. The car will be driven a few times a week. But at the track or racing around it will be pretty much open header. There will be two electric cutouts so I am just trying to figure out if its going to work is all.

If you use a header extension (or off-road pipe?), that will probably get enough length to get accurate O2 readings.

It seems to me from some of these questions that you have never even opened the Calcom software, and don't understand how the ECM works. You REALLY ought to become familiar with it! (It's okay, it won't bite!)

-Bob Cunningham
bobc@gnttype.org