Hi All, I have a 1990 348tb that I normally run with two catalytic converters, and so the timing was set (during the engine out) to the values deemed for catted engines. Last week, my car failed its emissions test, and one cat was identified as the culprit so yesterday, I removed both cats and replaced them with test pipes that came with the car... and now I like the new sound so much, I don't want to go back if possible. My question is... what effect does it have on an engine when running without cats (other than the obvious environmental impact)? My analysis, based on my limited understanding, is that there will be less back-pressure, so the exhaust gasses (heat) will exit the exhaust system faster and the engine will run a bit cooler. Wrong or right? DF
If you retain the O2 sensor in the test pipes, the only "real" effect is environmental. Your garage, clothes and neighborhood will stink of fuel. If you take the O2 sensor off, then you can have a bunch more stuff being affected depending on your MAF screw (CO screw) settings. Look at the maintenance manual (you can download it from my server http://public.me.com/mbussadori), but you should se the MAF screws to give you about 250-300 PPM for hydrocarbons and I think .6% CO. You need to sample from each bank (the O2 Sensor socket is a good place) as the exhaust tips are a mix of both banks, so the ECU has a calibration while in open loop (when the 02 sensor is disconnected). You will also have your CEL's come on if you do that (not on the Motronic 2.5 cars), so you may want to unscrew the bulbs... The back pressure etc. well, in theory, you're right, but if you look at the cat, the core body is much wider than the inlet and the outlet. That is intentional so that if you added the frontal area of the little walls the structure of the cat's core is made up by and subtracted that from the frontal area of the widened core part of the cat, you would not have less than the area of the inlet and outlet pipes. On a new cat the net effect is minimal, less the turbulence. On an old cat, where the cells get clogged and narrowed then it does become more prevalent. If you want a great replacement to the Ferrari factory ones and much more expensive X-ost, Stebro, tubi or whatever, I built metallic core (look at http://www.ferrarichat.com/forum/showthread.php?t=212160) which when flow tested showed less than a percentage point of flow restriction (within the instrument's precision tolerance) and put them on my car - aside from a core meltdown when one of my MAFs freaked and poured fuel (they were glowing bright yellow and only one collapsed) they have been working perfectly for about a year. Marco
The previous owner of my 84 QV Mondial took out the cats. He had been a long time owner of various V12 Ferrari's and thought the cats were why the Mondial, which was new at the time, didn't perform like his older cars. I couldn't tell you the difference in performance or sound. I can tell you neither my garage or neighborhood smell like gas. It passes the New York smog test easier than my non-modified 430.
It can depend on the model. Some ferraris will run very cleanly even without cats and easily pass state emissions tests - my 3.2 mondial does exactly that. No adverse smells or issues at all. You should give your 348 a tune up and see how she does at the emissions testing station (assuming you're not inclined to buy a CO sniffer yourself and test). As mentioned above, you should retain the O2 sensor in the test pipe - this is critical to proper running/mixture. Removing the cats does away with a major source of heat in the engine bay. Yes, your car will run cooler, and be rid of a potential source of ignition of unburnt fuel. Provided you can pass state emissions test, it's an all around good move!
This is a good thread and I've considered going catless as well. Question: How extensive is the re-timing/tuning after installing test pipes on my '88 Mondial? Will I need to degree the cams? Thanks
I can second the experence of Cliffbeer. The O2 sensor should be retained and there are no diveability or bad smells with the cats removed. My car had a bad fuel rail pressure regulator and as the system would adjust itself, the cat got so hot that it melted the driver side tail light lense. The engine compartment is much cooler and the sound now with the tubi is very nice...very very nice! Jeff Pintler 89 348tb, 86tr
Hi Wade, Not sure what you mean here. Your question assumes there is a re-timing/tuning drill to run to deal with the absence of cats. My 3.2 runs excellent with very low emissions and good A/F ratio throughout the full range with no re-timing/tuning. With the O2 sensor installed the engines normal ECU-based A/F adjustment will continue to work just fine. Of course, if you want to degree the cams just for fun....
