Rule of thumb for AF changes with change from full exhaust to open headers?

[cjshaker]

I was wondering if there was a rule of thumb on making jet changes when you go from full exhaust to open headers? I know when removing an air cleaner assembly, you generally should jet up 2-4 sizes, depending. But I don't recall seeing or hearing anywhere how much of a change you'd need, if any, with going from a full exhaust to open headers. It's a 2 1/2" exhaust, so there is a fair amount of restriction there. Or is it not an issue with exhaust?

[Drew Pojedinec]

Assuming no major restrictions with the air cleaner or the exhaust you shouldn't have to change much if at all.

Due to it being difficult to measure what restriction there may be, I'd say it depends on the current setup how much you need to change something.  If I had a car like yours and was going to drag week, I think I'd buy an extra set of metering blocks.
Have one set up for the street and one for the strip with larger jets and PVCR's.

[jayb]

I think it depends totally on the combination, and the restrictiveness of the exhaust.  A wideband A/F is your friend here...

[cjshaker]

 There's no unleaded high octane (above 93) available locally, so I typically run a few gallons of 110LL to stay safe, and the lead doesn't play well with sensors. And I don't feel like grinding off the ceramic coating to weld in a bung on my headers.

I guess I'll have to experiment with a collector extension for a bung, back the timing off a couple degrees, run some basic 93 for a bit and see what happens. I wonder if a sensor would get an accurate reading if it were only placed in a short extension before the exit?

[BattlestarGalactic]

I put a WB in my wagon this past winter.  It only reads correctly after going down track.  At idle or slow moving it reads way lean(not enough exhaust flow over it).
I put it in so I could see what it does with the 1850's on it and then when I get the 735's done I can see where the tune is at and jet it similarly.

[jayb]

The wideband O2 sensors will run quite a while with leaded fuel, so not to worry there.  Having them close to the exit of open headers will effect the reading significantly, though, unless you are at WOT.  Maybe some long collector extensions, with the bung welded right up at the front, would work for track purposes.  Mine seem to work at the track, upstream about 14" from the end of the collector.

[Falcon67]

If you are going to put it much past the end of the header flange (collector end) I would use a heated sensor.  For tuning the street car I have a bung located right past the flange in the collector extension.  Also, I just run one with the laptop until I get the carb tuning where I want it, then put it back in the drawer.  No need to run around with it all the time. 

[cjshaker]

I can put the sensor within an inch or so of the flange, and using a longer extension for an accurate reading wouldn't be a problem. Sounds like a good plan.

And yes, this is for track purposes only. I know my street tune is fine, but wasn't sure how much things would change by removing the exhaust for track duty. And Chris, I remember you mentioning removing them after you were done, which is my plan. No reason to keep them once I know for sure.

Larry, does yours have recording capability? I'd assume it isn't real easy trying to read the meter while rowing gears and keeping the car straight   Can anyone recommend one that does have recording capabilities?

[jayb]

This one datalogs; I think the LM-2 "basic" kit may require a hookup to a laptop during datalogging, but the complete kit has its own memory card that you can download the data from later.  Its easy to hook up an RPM signal also, so that you are seeing how A/F changes with engine speed.

http://www.innovatemotorsports.com/products/lm2.php

[Tobbemek]

INNOVATEMOTORSPORTS is definitely the way to goo, and the newer improved Bosch 4.9 wide band lambda unit .

[cjshaker]

Thanks for that info and link, Jay. I like the RPM logging capability to go along with the AF logging. Do you know if it can receive RPM data from an MSD unit? Maybe from the tach trigger or from a digital unit like the 7AL? If not, I'll contact Innovate and ask them.

[jayb]

Pretty sure that it will receive the RPM data from the MSD.

[Drew Pojedinec]

Logworks takes all sorts of inputs, even oil pressure, water temp, battery voltage, rpm, etc.

[BattlestarGalactic]

I just wait til 8th mile mark when I stop shifting to see what it is reading.  Likely not doing much right til then being at the near end of the collector(with no extension).  That is when the motor starts pulling.

If you don't want to data log, use a go pro?  If you mount it near the tach, you can watch it easily enough with a quick glance. 
I know right now it is reading 11.9 pulling high gear through the lights.

[cjshaker]

I think I'd rather data log. The GoPro will come in handy for several other things, but gathering some info about the RPMs would likely be useful also, and might show other issues such as tire slippage. Or it might even be useful for when I switch to a Soft-Lok in helping determine how much clutch slippage is happening.

Logworks takes all sorts of inputs, even oil pressure, water temp, battery voltage, rpm, etc.

.

I'll check them out Drew. Like I mentioned above, I have considered getting into some data logging for future plans, where things like engine rpm and driveshaft rpm could be useful in sorting out clutch adjustments. I don't race with any regularity, so it comes down to my own wits and asking guys on here. I haven't looked into any multiple input loggers, but had planned on it sometime in the future.