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Discussion Starter · #1 ·
Hey All,
I combed the forums (and the web) for 2+ hours to find a member's post that mentioned after he installed the 2 piece '72(ish) manifold on his S3 he lost some low end power but the high end was nice and smooth.

I can't find that post and subsequent solution. I just installed a 72 2-piece manifold using a new center and mid muffler section from IAP. Had the O2 bung welded in after the Y, etc. All went well, but noticed the lack of power on the low end.

I think it could be that my O2 sensor may not be heating up all the way since I didn't hook up the white wires(power) to my heated sensor yet(black wire is connected) Is this the issue? The O2 is not getting hot enough to help me run smooth at low rpms?

Anyone remember that guys post? I'd like to ask him what he did to resolve. No pics yet. Sorry Tifosi!

Thanks in advance!
 

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Is it a case of lack of smooth, or lack of power?
Those are more or less two different animals.

Regarding the O2 sensor, the only time its actually relevant to the ECU is when the TPS is off the idle switch and in the lower half of travel and you are at steady state throttle.
The rest of the time its being more or less ignored because you're idling (ECU reverts to an independant idle map) or you're accelerating or decelerating (vacuum/load levels cause the ECU to go into open loop power mode which is also an independant map or you've let off the throttle and put it back into the idle map)

In any event it really wouldn't effect the low end specifically unless things were going stupid rich or stupid lean without it (doubtful unless there are other issues involved such as false air or ignorantly high fuel pressure or the like really screwing with the overall mixture)

I'm fairly convinced that the problem has nothing at all to do with the O2 sensor IOW.

When you say center and mid section cans, what do you mean onnconna I can only imagine there is only one middle in anything to begin with :)

Do you mean an expansion chamber or catylist in the front position and a new can in the center section?

What are you running at the rear section?

If your answers are 'expansion chamber', 'new center can' (especially if of a free flow variety), and 'stinger tailpipe' when the system that came off was 'old catylist', 'old center can' and perhaps even 'old rear can', then I would expect a percieved loss of low end power because you took a high back pressure system and replaced it with a much lower back pressure system that scavenges besides.

Back pressure to a point can help with a bit more low end torque, but not enough to really quibble about when compared to the benifit its removal gives at the other end of the spectrum. (too much backpressure of course can create the proverbial 'banana in the tailpipe' situation and should be avoided)
 

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Discussion Starter · #3 ·
I suppose it's a lack of smooth (on the low end). It sputters a bit and then when it hits the higher rpms it gets faster and smoother. Clear as mud, ey?

And yes, I do mean the expansion chamber(no cat) in the front position and a can in the middle. I retained the rear can section, because I haven't ordered the stinger yet. YET!!

Thanks for the info on the O2, I'm now enlightened.

So, knowing that I do have the rear can, and adequate back pressure, where do we go from here? Do you remember that guy who posted the same issue? I'd like to query him on his solution. If he figured it out.

70+ degrees today but kept the Alfa at home. My "hot - no start condition" continues. 12V relay to starter is one of my last projects this season. Well, that and some front end work - knocking when hitting holes and when reversing (then hitting brakes). Posted this issue last year, I think you said it was some upper ball joints or something because I replaced both tie rods on both sides and that didnt fix it.
 

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Right off the top of my head I don't recall the manifold thread you speak of, but perhaps it'll come to me later.
Still trying to work out how changing the manifold could effect low end performance though unless you dropped a lot of backpressure by swapping the cat for an expansion chamber.

Are you positive that there's no false air leaks?
Including perhaps something in the AFM to plenum ductwork that might not open up until the engine heaves a bit on the mounts?

The suspension knock is prolly the castor arm bushing at the upper control arm end in need of replacement.
 

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Might also want to check to see if the VVT solenoid is working. The in line fuse is often a problem (corrosion).
 

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I would also check that you in fact have a working MAP sensor. (behind the side panel of the passenger side, looks like a silver mushroom). This expensive to replace guy sets ignition timing advance. It can have been disconnected by the PO to stop annoying "whistle" leaks. or vacuum line just disconnected period.
I replaced my S3 manifold with a two piece S4. I have a free flow Magnaflow 94004 and then a glass pac CherryBomb followed by a Stinger. It goes...and sounds great.
My thoughts are that the empty "can" you are using in place of the CAT may be the tuning issue...too much volume?
Also the 02 sensor could play a role at low revs if it is finito..was it gummedsooted up? when you reinstalled it? does the bung let it in far enough? did you damage it?
Just my $.02(CDN).
TTFN Elio
 

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Discussion Starter · #7 ·
OK, following-up to complete the circle.

The lack of power or sluggish acceleration was due to either of 2 things(or both):

I got around to connecting the heated O2 sensor, only had the black wire hooked up AND I replaced my OVS (bought new one from Matt Brady, who advertised them on this BB).

After these upgrades the car accelerates MUCH smoother! Thanks for a nice product, Matt. And thanks to you all for getting me on the 3 wire heated O2 sensor.

Thanks again to Tifosi who correctly diagnosed my issue with the knocking sound in the front end. It is the caster arm bushing. Ordered a new one from IAP and having it replaced on Monday.

Thanks all!
 

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I replaced the broken original '86 exhaust manifold with the '74 two piece manifolds, a 74 front pipe with O2 bung installed, replacing the front can with a new universal cat, reused Cisam center and reused Ansa rear. I didn't notice a drop off of low end performance
 
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