Exhaust Q's
 

Ok here's the deal. I have a 81 with a p79 head which in turn has round ports for exhaust. I ordered a coated header from MSA and ended up getting a square port non-smog. Before I send it back is there a way I could use this? I've done the search and have found out that the square port header will fit on the round port head, but I was wondering about the egr and O2 sensors....can they be eliminated. Of note, I do have a 76 motor sitting in my garage that with the ecu. It also has the N47? intake(correct me if I'm wrong) would any of this be of value to make this header work? thx in advance for your patience.

you really only need the o2 sensor which can very easily be welded in place. they sell o2 bungs at most part stores. the egr can be blocked off at the bottom using a 3/8 npt plug. as for the n47 intake, dont they have egr's also? if so its no benefit.

or you could use a O2 simulator and not have to do any of that, but then again you wont be getting any info like the real o2 sensor would do

unless u need to pass smog, why need an 02 sensor, i have absoutely no emissions on my motor the only thing on my n47 intake s the fuel rail.

Thanks for the quick replys! I'm gonna be pulling the motor out to do some cleaning/painting soon so I figured if it was gonna be apart, now would be the time to swap intakes and so forth. Any ideas on what kind (year) gasket I need? Especially being a square port header on round port head? I'll probably have the o2 bung welded on farther down the exhaust as this header is ceramicoated.

if the o2 is welded further down (at the point where all 6 pipes connect) then you will need a heated o2 sensor, they cost more, and will require some extra wiring. the best part is it will read all 6 cylinders instead of just the one. the o2 is needed in any car with it. this is how the ecu computes the fuel going into the engine and makes maximum power

Yes, definetely go with the heated O2.

Actually, the 02 just does a certain percentage correction of what the air flow meter reads.

I'm curious how you guys would control the heater circuit of this heated 02 sensor.

On all the time, on only at idle (best idea) or on a timer?


On the head topic, I've bolted plenty of 280zx turbo manifolds to p79s as well as n47 maxima heads with no problems.

when I first installed headers when my car was NA I had no O2 plug so I just left it unplugged.

The car ran fine but I got about 16/17mpg and it ran RICH all the time. the car was more powerful and economical with the O2 sending a signal to the ECU.
milage bumped back up to about 22/23mpg

My suggesion is though: send it back!
Are you running a stock engine, stock cam, stock intake but with maybe a throttle body and K&N filter up front? (like most people) Just run the factory exhaust manifold and put a 2.25 inch pipe from that all the way back with your choice of muffler. That's plenty good.