Odd behavior
 

Something I found a bit odd the other day was I was running with my elect cutouts open on the freeway and when I closed them it seemed to gain noticeable hp. You would think the fuel injection would like open headers. I’m going to record the event with the data logger and see if there’s some adjustment that can be done to the fuel table to compensate. Curious.

Depending on the location of your o2 sensor; with the cutouts open the exhaust may be scavenging some fresh air up the exhaust causing a lean o2 reading. The efi will temporarily add excess fuel until the sensor sees what It needs to see, likely when you close the cutouts.

Pretty common in the old days to add fuel when the exhaust cut-outs were open, even with carbs. We had Fuel/Air meters at Holley and actually designed a couple of systems to add additional fuel under some conditions by turning a dial under the dash.

These systems were called the Holley Mile Dial System and the Quarter Mile System.
(I think I still have 3 or 4 new systems designed for the Holley Carbs on the shelf.
They used a Duty Cycle Solenoid to add the extra fuel to the main circuits (or remove it) in a Mile Dial System).

There is a bunch of bad info out there about how the systems worked. You had a knob that had 10 different settings and each setting changed the duty cycle of the fuel solenoid. Somewhat like changing the pulse width of a Fuel Injector with a computer today.

There is some discussion of it in one of David Vizards several books on carburetion...one written long after the things vanished from the catalogs. He used it as a dyno tool to go from guesstimated to perfect jet choice quickly. It might actually be much easier to use now, with readily available aftermarket oxy sensor based mixture gauges.

A EGO sensor can be confused by open headers if the calibration is not optimized for that mode of driving as well as the closed cut-out mode. It can be confused even by being installed in the wrong location in a header system.

Tom V.

Yeah I admit I wasn't watching the a/F before and after closing the cutouts. It was a definate bump after closing them though. They are fun just for the wow factor but I'd guess my DynoMax ultras do as good or better of a job anyway through the mufflers.

As stated already, probably getting erroneous readings from the o2 sensor with them open. You need a minimum of 18” of pipe aft of the o2 sensor. If the cutouts are within that range, there’s a likely chance the sensor is seeing reversion in the form of fresh air, causing a rich run situation.

I know last summer when at the track on e=the first day I purposely kept the cutouts closed the first day then opened the second day with no other changes to see what difference they would make. there was definitely a half second difference in time with what I had with the cut outs opened and closed before I opened the bottle valve.

This result is a dead giveaway that Whatever rpm you where freeway running at it must of #1) still been below the rpm of your motors peak torque, and #2) still have been below the point of where the Exh flow out of the motor needed the full amount of flow area that your Exh system has available.

In short, opening the cut outs which shorten the tuning lenght of the Exh system by however much shifted the rpm of peak torque to a higher point that the motor was not running at!

Have this result on an engine dyno, o2 reading went all weird when running open headers as apposed to the muffler system they have,
also could seen the bottom end torque was down compared to having mufflers. It did get better with higher rpm, made 5 hp more at 6200 with open.

We run electric cutouts on a few cars here, and have 02 bungs before the cutouts.

They are fun, and effective at the track.

You shouldn't have to revamp fuel tables with EFI if it's self learning. What might be going on is what has already been mentioined, the 02 readings the computer is taking is too close to the cutout and giving false readings, and the computer might be over compensating for the changes. Might have to move the 02 sensor if there is any room to do that.

Cutouts actually work pretty good with the carburators, since I'm at 5,000 feet anyway I run them a little on the rich side of things so the cars stay safe when we drive off the mountain. Cleans right up though if I pop the cutouts open.

I'd bet the o2s were picking up air with the cutouts open.

When my LS setup was open header, it hated life unless I disabled the o2s.

Opening my cutouts produced 23 extra hp on the dyno...no efi.

I think I have just about 18" from the cutouts to the sensor. I am running 4 tube headers and the cutouts are mounted right on the end of the X-pipes. Probably just the ecu trying to adjust the A/F making the difference. I'll try and pay attention to the monitor next time and see if it shows the anomaly.

How fast is it at self tuning? Might take a bit to adjust?

Or like mentioned, disabling the 02's and run in a speed density tune is what I used to do on some of the LS tuning. But you have to have a safe tune nailed down and takes quite a bit of data logging.

Don't know if these new throttle body injection units have that ability in the software.