Those with EFI or WB AFR

bingo2 · #1 (**permalink**) 12-19-2010, 01:34 PM

I'm considering EFI for my for my car.

The exhaust system in a 4 piece affair; primary header, collector, muffler and turn down. The collector is bolted to the primary, the muffler is a slide fit over the collector and the turn down slides over the muffler end.

The ideal placement for the O2 sensor would be near the end of the collector however, there isn't enough room between the collector and the body panel to mount the bung and sensor at the preferred angle of 10-15 degrees up from horizontal.

I'm curious to know where anyone has mounted the sensor and at what angle.

jdean · #2 (**permalink**) 12-19-2010, 02:34 PM

The compromises in mounting the O2 in a Cobra are:
1) To get it sampling from all 4 pipes means putting it just after the collector....which makes it farther from the exhaust valve than the recommended 20" or so.
2) It is hard to mount them facing up from horizontal in a Cobra because of not enough clearance between the pipe and the body. Mine are mounted about 15 degrees down from horizontal, just behind the collector. I think the idea of facing upward is to keep moisture from collecting in the tip and then freezing.

They will work fine like this. Almost all Cobras I have seen have them mounted just after the collector and then either horizontal or downward a bit. I have seen some where it was mounted closer up but only in one pipe. I dont like that idea either.

lamaluv · #3 (**permalink**) 12-20-2010, 07:34 AM

Mine is now a three stage exhaust system. I can change the side pipe/muffler to open pipes for the track quickly. My O2 censor is near horizontal just after all four pipes meet at the collector.

Dick

vector1 · #4 (**permalink**) 12-20-2010, 07:51 AM

watch your slip-fit connections, unless you make them airtight the o2 reading is going to be unuseable.

DonC · #5 (**permalink**) 12-20-2010, 08:57 AM

It sounds like you're looking at a system that uses WB 02 sensors. The primary difference between WB and NB sensors is that WB have their own internal heaters and can be mounted just about anywhere in the exhaust stream with the primary consideration being a position that gives you the best access to the entire exhaust stream. NB sensors fall into the 18-20 inch from the port range to get them hot enough to read accurately.
Mounting the sensor at the horizontal or above is to keep condensation from gathering on the tip of the sensor and corroding it.
The common problem with our cars is that, in general, the collector is so close to the body there isn't room to install the sensor where it will be hidden from view. About the only way to get the necessary vertical range placement is to cut a port in the body behind the collector that allows the sensor to protrude inside the body. Not an ideal location but that's about all you've got to work with. Short of that your only other option is to mount the sensor below the horizontal but be prepared to replace it every so often when it gets fouled.
DonC

bingo2 · #6 (**permalink**) 12-20-2010, 09:38 AM

Thanks to those who replied.

DonC, you are correct the system does use a WB O2 sensor.

The system I'm looking at is the FAST EZ EFI, its been around for a couple of years now and appears to be very stable and offers some user input for fine tuning. I already have a fuel return system on the car so the installation should be fairly straight forward.

Jerry Clayton · #7 (**permalink**) 12-20-2010, 09:56 AM

In my gallery is a couple of pics of some Cobra type headers/pipes I built for a 32 ford I built for a customer--Fast controller with Hilborn stack type injection---
Photo MVC-657f shows a close up of the collector during fab and MVC-824e if enlarged you can see the hole where the bung is lined up with a piece of tubing that is welded thru the boxed frame structure which allows clearance and access to the O2 sensor.

Sorry but the MVC 657f photo is on ClubHotrod----was at the top of the page when I signed on today!!!

Barry_R · #8 (**permalink**) 12-25-2010, 07:39 PM

Not sure how it would impact function. By why do you need to have the sensor directly centered to the collector pipe? You can mount it horizontal and down lower from the centerline of the pipe an inch or so by extending/notching the mounting bung on an angle.

RICK LAKE · #9 (**permalink**) 12-26-2010, 06:34 AM

Bingo2 I have been running FI system for 14 years. It's a speed pro setup. IMO run a wide band O2 sensor. It seams to have a better ability to handle Large camshafts with small LSA. The ideal spot is 8-12" after the collector. If you have an O2 sensor in the pipe It is recommended That the sensor be horizonal or on a down postion. Rick L.

cobracrazy · #10 (**permalink**) 12-26-2010, 01:08 PM

all very good advise, here's more:

if you must use slip fit collectors like most of us, try some exhaust heat wrap to reduce the leakage common to slip fit setups. Like mentioned above, that leakage will affect the quality of the information the sensor collects. If you're going to weld bungs, weld an extra bung while your at the welder. That way if you have it dyno tuned with a wide-band you can compare results with your ECM.