Quick question

[1984Rampage]

When you upgrade to a larger exhaust do you need to have your computer recalled for the exhaust?

[NAJ]

When you upgrade exhaust or air intake the controller you are allowing the engine to breath easier.The controller will see the additional air flow thru the Map Sensor voltage and will adjust fuel enrichment accordingly.
Unless you upgrade the injectors and turbo or other engine mechanical components where the controllers normal parameters cannot compensate for the mods upgraded contoller programs are not needed.

[detobias]

much as I hate to disagree with the uber-NAJ, I found on my modded TII that if you make significant increases in the flow capability of your engine, then the stock cal/MAP won't accomodate that, and you will run lean at WOT

the reason (as I understand) is that the computer look-up table *calculates* an air flow rate (and then accompanying fuel flow rate) based on the MAP reading and RPM, assuming a stock engine configuration

if you make significant improvements in flow to your engine (ported exh. & intake mani, ported head, oversize valves, no cat/muff, larger exhaust, etc.. or all of the above as I have done) then your engine will be flowing MORE air at the same MAP reading... BUT the computer does not know this

if you are just making one or 2 small changes, then this is probably not an issue; your increase in flow capablity is small, probably only 1-3%

if the TD's had a more advanced engine management system like the MAF system used in DSMs and most other "modern" engines, it would be directly reading the air flow, instead of calculating it

just keep an eye on your WOT A/F (you do have an A/F gauge right!?) and if you are running a bit lean, get an AFPR and turn up your fuel pressure a smidge

[Tbone]

NAJ is correct when assuming closed loop operation (when the oxygen sensor is dictating the A/F ratio). It's hard to fool the computer into running anything but stoich (14.7 A/F) when in closed loop. However, in open loop (under any boost at all or at wide open throttle) the computer contols the A/F ratio through the MAP sensor, rpms, and air temperature. Just as detobias said. So it is easy to throw off the A/F ratio when running open loop. You can increase air flow through porting, larger exhaust, etc. Or you can simply fool the map sensor or air temperature sensor by using a resistor or petentiometer (to change the A/F ratio). I did this on my NA Saturn and I was able to run so lean that the car would stumble and not accelerate. It was a neat experiment but I never did see the mpg increases I was expecting.

[1984Rampage]

Well what I did was order a stage three cal from fwd-performance and told cindy that everyhting was stock. I ordered this before I decided I was gonna upgrade my exhaust. Now I am putting on a full 2.5" exhaust and am wondering if Im gonna have any problems?

[crazymadbastard]

I think the cal assumes a free flowing exhaust but check with Cindy. I think you are ok.