Ferrari Mailing List: Re: Mondial Exhaust and Tach Sensor Questions

[Doug and Terri Anderson (dnt]

Hello Rick - sorry, don't know the where fores and why fores of the two sensors - but as far the cats go - absent them - you'll be noisier.  Not a true Tubi though.

 

Perhaps a good reason to keep your cats, but, off the car, is if you are in smog state and replacements have got to be expensive.

 

Come smog time - put the cats on for visual inspection and the emission point of the exam.

 

Will the [exhaust] manifold run hotter?  It should and here's why.  During the intake exhaust cycle, there is a brief time, TDC, that both valves are open - the exhaust system having had the last charge rushing down the pipe pulls in the new intake charge and gets it going into the cylinder.  A portion of this new charge also runs down the exhaust pipe - say a foot for augments sake.  Now the piston is running down and finally pulling some vacuum and the charge down the exhaust pipe is reversed and also pulled into the cylinder.  The valve timing being what it is should hang open only long enough while the fresh charge is available before shutting.  If it all works as planned, the cylinder gets a full intake charge.  In theory.

 

Now lets run the same scenario as before but less back pressure - the intake charge is still pulled down the exhaust pipe at TDC but this time - no back pressure - and the new charge runs down the pipe two feet and not the one foot as designed.  When the piston descends and pulls back the fresh charge back from the exhaust pipe, only a foot and not the whole 2 feet of fresh charge gets sucked back in - ergo - a lean charge.  A lean charge runs hotter.  A lean charge, if you are in a smog state, contributes to a very high NOx problem.  Not that you'll be any competition for a Chinese Long March Rocket or one of their  Jianghuai fine autos.

 

Increase the fuel pressure and CO % rating and you should be OK.

 

It gets a little complicated, but some cars actually use this trick to pull in exhaust gases to cool off the combustion mixture and those engines don't have an EGR valve.  BUT they do have real screwy valve timing.

 

Onward -

DOUG

 

----- Original Message -----

From: rick Baumgartner

To: DOUG

Cc: The FerrariList

Sent: Monday, August 30, 2010 2:05 PM

Subject: [Ferrari] Mondial Exhaust and Tach Sensor Questions

 
Hi Boys,
Wondering if anyone out there has had any experience with catless pipes?
 
I have a 87 Mondial 3.2 and was thinking of installing the cat pipe eliminators. Does it really give you better throttle responce? How much louder is the exhaust? Is there any issue with the increased temperature at the manifold from having a lower back pressure?
 
Also need to replace the sensor that drives the tach. One of you had mentioned that its the same sensor that is used to sence TDC and not the timing one . These sensors are identical. One close to the front cyclinder bank and one closer to the rear (rear of car) cyclinder bank. Does anyone know which is the position of the TDC sensor?
 
Thanks a bunch guys.
 
Rick
 
    

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