Guest jdllaugh Posted February 21, 2002 Share Posted February 21, 2002 Is it legal to go without a catalytic converter in a 240z when swapping in a late-model engine? I assume the rules vary from state to state. I'm in Oklahoma, which doesn't currently have an inspection system, but I would like to know what the rules are generally. What percentage horsepower gain is likely from running without the cat? Quote Link to comment Share on other sites More sharing options...
Guest greimann Posted February 22, 2002 Share Posted February 22, 2002 It is against federal law to remove a properly functioning catalytic convertor on a vehicle that was originally equipped with one. If your car was not originally equipped with one and you have a modern engine, and no state inspection, you are probably in the clear. With the high flow monolythic convertors on the market, there is no real HP loss by having one (or two) installed. If you are using one of the old pellet style, those things are a real cork in the system and you loose a lot. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted February 22, 2002 Share Posted February 22, 2002 I, of course, did not check my local laws before scrapping the ZX exhaust when I transplanted my '82 motor into my '78. The '78 used regular gas and had no cat - the '82 used unleaded and had a cat. In Colorado, they do an exhaust sniff test for cars prior to '82 and check for the emissions equipment. They are getting lazy and not looking at EGR and carbon canisters, but they always check gas caps and cats. Of course they check the equipment for the vehicle, not the engine, so mine passes visual every time (sniff test is another thing ). So not being familiar with the laws, I've done it and the state doesn't seem to care, let alone even notice. Quote Link to comment Share on other sites More sharing options...
Len Posted February 23, 2002 Share Posted February 23, 2002 James; It is nice to not have inspections anymore. Just wait they'll return someday. I plan on running a 3" exaust on my 1983 280ZXT I will weld a straight pipe about 24" long with flanges on either end in the middle of exaust (where the cat was located). So in the future if I need to; I can unbolt the straight pipe, weld up same lenght cat and replace with the cat if needed. Len Quote Link to comment Share on other sites More sharing options...
Kennysgreen280zt Posted March 7, 2002 Share Posted March 7, 2002 A few years back Sport Compact Car (scc) was doin cat and exhaust tests on a 240sx. They accually lost 2 hp without the cat on. They gained what they called "uncontrollable noise" my $.02 ~Kenny Quote Link to comment Share on other sites More sharing options...
Guest jdllaugh Posted March 8, 2002 Share Posted March 8, 2002 I have heard that opening up your exhaust system too much can hurt performance. Torque more than HP. That's especially true on 4 bangers like the 240sx. After doing research, I would say I'm not going to gain much in the way of HP from just removing the cat. My current plan, very much subject to change, is to replace the stock engine in my '72 240z with a 3800 Series II V6 out of a Camaro/Firebird. They're supposed to be 200 hp stock. I'm hoping with free flowing intake and exhaust, some porting and polishing and other tweeks, I can get that into the range of 230-240 (flywheel) hp. In a car as light as the 240z, that should make for a fun autocrosser/track toy. First, tho, I have got to fix those rusty floors! Quote Link to comment Share on other sites More sharing options...
Len Posted March 8, 2002 Share Posted March 8, 2002 James and Kenny I'm building my exaust systum along the turbo theory of best exaust is No exaust! I've also heard that for N/A engines a bit of backpressure is Goooooooooood!!!!!!!!! And for me a 3" systum won't have much backpressure even with a Cat. I just figure I should have two extra 3"flanges and 24" of 3"pipe left over so what the heck go for it! Oh yea James I'm heading to your town this weekend for my 13 yr. old son's soccer tournament! (the games will be in Jenks). If I see a 240Z I'll wave(but if its your current project it will prabably be in your garage!!!!!!!!!!!! Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted March 10, 2002 Share Posted March 10, 2002 in california if you install a late model engine into a chassis that did not have a cat you dont have to run a cat.the reason is the older car does not have heat shields for cat.but if you use a 96+ engine with no cat you will get trouble codes because obd 2 has cat effiency monitor (downstream o2) sensors.cat back pressure is due to design and pipe diameter.na cars usually need a little back pressure but any exhaust system on a turbo usually slows down exhaust flow-slower turbo spool up.i run a 3" system with mandrel bends and a non baffled muffler on my 77. Quote Link to comment Share on other sites More sharing options...
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