Guest Roger NE Posted October 7, 2013 Share Posted October 7, 2013 (edited) I'm about to fit a 2JZ-GE in my Mk3 Supra (replacing the very similar but unreliable 7M-GE engine) I'm planning on using the stock Mk3 Exhaust. Just like the Mk4 N/As, the Mk3 SOMETIMES has a small cat on the downpipes, but USUALLY has a large main Cat at the end of the downpipes, where it joins to the main exhaust. But here's the point . . . my 1991 car never had a Cat on the downpipes, but when I tried removing the MAIN Cat the performance (especially at low revs) was poor. Then someone advised me that the engine was designed to have the back pressure from that main Cat, which is why the Non-Cat stock exhaust (fitted by Toyota to some models) has a box instead of a Cat at the end of the downpipes. (apparently that box is not at all restrictive, but just provides the correct standing waves for the engine) So 12 years ago I fitted one of these Mk3 Non-Cat downpipes that comes with the extra box attached (readily available from stock exhaust suppliers), and the performance was good again . . . in fact much better than when there was a Cat. Therefore my plan for the new engine is to cut and weld the twin downpipes on my Mk3 Exhaust onto the pair of downpipes that come from the Mk4 Manifold, thereby keeping that "Cat replacement Box" in place. I'm figuring that if I removed it, I might see the same DROP in bottom end performance. So that's my question . . . . I wonder if anyone else has noticed this when they've removed all the Cats from an N/A Mk4? Would appreciate any comments from knowledgeable people. Edited October 7, 2013 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
skippyboyo1 Posted October 7, 2013 Share Posted October 7, 2013 Nope. Everything gets better, get them out. The end Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted October 7, 2013 Share Posted October 7, 2013 (edited) Nope. Everything gets better, get them outThe problem is that some people told me that would be the case with the 7M engine . . . but it wasn't . . . there was a noticeable loss in low rev torque Sure, the top end was much better without the Cat . . . But only when I fitted the new Catless downpipe with the extra box did it get back to normal lower down the rev range . . . and I still had the same improvement at high revs as without the Cat. Plus why would Toyota bother making that special downpipe with the extra box if it wasn't desirable to maintain the performance on a Catless system? I can't imagine that the issues are much different with the 2JZ-GE than the 7M-GE . . . Anyway, I'd certainly appreciate other feedback / comments Edited October 8, 2013 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
trebor69 Posted October 7, 2013 Share Posted October 7, 2013 The only difference I noticed was on top end .......oh and the noise obviously Quote Link to comment Share on other sites More sharing options...
David P Posted October 7, 2013 Share Posted October 7, 2013 No cats and 2.5" exhaust system suits the 2JZ-GE, which fortunately, doesn't need cats for MOT. Quote Link to comment Share on other sites More sharing options...
Al Massey Posted October 7, 2013 Share Posted October 7, 2013 No cats and 2.5" exhaust system suits the 2JZ-GE, which fortunately, doesn't need cats for MOT. It depends on what the registration is off the car not the engine Quote Link to comment Share on other sites More sharing options...
David P Posted October 7, 2013 Share Posted October 7, 2013 The registration document can/should be updated, which would show the GE engine code and all is well in the land of MOT. Quote Link to comment Share on other sites More sharing options...
Slam Posted October 7, 2013 Share Posted October 7, 2013 No cats and 2.5" exhaust system suits the 2JZ-GE, which fortunately, doesn't need cats for MOT. A wise old man told me this once :secret: Quote Link to comment Share on other sites More sharing options...
Slam Posted October 7, 2013 Share Posted October 7, 2013 It depends on what the registration is off the car not the engine Someone told me that recently Quote Link to comment Share on other sites More sharing options...
Al Massey Posted October 7, 2013 Share Posted October 7, 2013 The registration document can/should be updated, which would show the GE engine code and all is well in the land of MOT. I spoke to an MOT guy the other day regarding this as my new build will be an NA/T but in an S reg car and he said it goes off the car reg. Will have to look into this further then. Quote Link to comment Share on other sites More sharing options...
Monkpower Posted October 7, 2013 Share Posted October 7, 2013 My old NA was full decat and I had no problems getting an MOT. As the NA was never made for the UKDM they were only ever JDM imports so it wasn't recognised on the UK MOT database. It got run through as an older vehicle. Double check with your MOT place to be sure though. My old NA was loud but sounded great! Noticeable gain on the top end with maybe a little sacrifice of low end torque. I was running a 3" system though. Better to stay with a 2.5" system for overall driveability. Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted October 8, 2013 Share Posted October 8, 2013 (edited) Appreciate the input guys . . . Well low end torque is more important to me than any extra top end . . . which is why I'm concerned about this As I mentioned, I'm not planning to have any Cats (as I don't have any at the moment) . . . but I think I'll probably keep that extra box that replaces the main Cat on the Mk3 exhaust system. And yes, it's the age of the CAR, not the engine, that counts when it comes to MOT emission tests. Out of curiosity, what ratio is the diff on a Mk4 N/A? I ask because Mk3 N/As were fitted with a 4.3:1 diff, but in my opinion that made the car absurdly highly geared . . . so years ago I changed mine to a 3.73:1 diff, which made it much more drivable. Edited October 8, 2013 by Roger NE (see edit history) Quote Link to comment Share on other sites More sharing options...
Al Massey Posted October 8, 2013 Share Posted October 8, 2013 Appreciate the input guys . . . Well low end torque is more important to me than any extra top end . . . which is why I'm concerned about this As I mentioned, I'm not planning to have any Cats (as I don't have any at the moment) . . . but I think I'll probably keep that extra box that replaces the main Cat on the Mk3 exhaust system. And yes, it's the age of the CAR, not the engine, that counts when it comes to MOT emission tests. Out of curiosity, what ratio is the diff on a Mk4 N/A? I ask because Mk3 N/As were fitted with a 4.3:1 diff, but in my opinion that made the car absurdly highly geared . . . so years ago I changed mine to a 3.73:1 diff, which made it much more drivable. Think it depends on the diff, and either NA or auto for the ratios bud. Regarding torque and decatting. I was double decat, 3" straight through with a manifold and the low end torque was amazing. Would often pull away easily from other NA's Quote Link to comment Share on other sites More sharing options...
David P Posted October 8, 2013 Share Posted October 8, 2013 Supra N/A diffs are 4.083:1. Quote Link to comment Share on other sites More sharing options...
Guest Roger NE Posted October 8, 2013 Share Posted October 8, 2013 Supra N/A diffs are 4.083:1. So lower than a stock Mk3 N/A, but higher than I now have fitted I think I'd find 4:1 diff would still make the car too highly geared . . . especially as the 2JZ is more powerful (around 230 bhp vs 200) Even with my existing engine, 3.73:1 feels just right through all the gears (my original diff made it feel like someone had put a 3 litre engine in a car with gear ratios for a 2 litre engine!) Quote Link to comment Share on other sites More sharing options...
straightsix Posted March 10, 2014 Share Posted March 10, 2014 I spoke to an MOT guy the other day regarding this as my new build will be an NA/T but in an S reg car and he said it goes off the car reg. Will have to look into this further then. I know this is a late post (I've not been around for a while) but this may clear up engine swap and MOT issues..... I had to MOT my Supra after the V8 conversion. One MOT tester failed it on emissions as he did a cat test on it. I argued with him and eventually had to contact VOSA directly who confirmed: "If you have a 1994 vehicle fitted with a 1992 engine, the emissions test must be carried out to 1992 standards. You, as the presenter of the vehicle for test, must produce a document (can be a letter from yourself or from a garage who completed the conversion), stating the vehicle details that the engine was from and if possible chassis number etc. It is not the tester's job to question the document - he needs to keep a copy of it for his records should he be inspected by VOSA himself and he is in no way expected to police the conversion himself - only to test the vehicle based on the condition and the information he is supplied." "If you fit an engine from a 2000 registered (for example) car into an older vehicle, then the emission test will be as for a 2000 registered car and would need appropriate emission controls in place (ie cats)." I duly typed up a letter stating that the intake and ECU (the emission control system) fitted to the car was from a 1992 Toyota Soarer and presented the car for retest with the letter and details of the people I spoke to at VOSA. Test passed and MOT on the car no problem. In Roger's case, I would make sure you clarify the 2JZGE came from an imported Supra although you have to bear in mind that Lexus used 2JZGE and they will be on the MOT database. Quote Link to comment Share on other sites More sharing options...
Al Massey Posted March 10, 2014 Share Posted March 10, 2014 I know this is a late post (I've not been around for a while) but this may clear up engine swap and MOT issues..... I had to MOT my Supra after the V8 conversion. One MOT tester failed it on emissions as he did a cat test on it. I argued with him and eventually had to contact VOSA directly who confirmed: "If you have a 1994 vehicle fitted with a 1992 engine, the emissions test must be carried out to 1992 standards. You, as the presenter of the vehicle for test, must produce a document (can be a letter from yourself or from a garage who completed the conversion), stating the vehicle details that the engine was from and if possible chassis number etc. It is not the tester's job to question the document - he needs to keep a copy of it for his records should he be inspected by VOSA himself and he is in no way expected to police the conversion himself - only to test the vehicle based on the condition and the information he is supplied." "If you fit an engine from a 2000 registered (for example) car into an older vehicle, then the emission test will be as for a 2000 registered car and would need appropriate emission controls in place (ie cats)." I duly typed up a letter stating that the intake and ECU (the emission control system) fitted to the car was from a 1992 Toyota Soarer and presented the car for retest with the letter and details of the people I spoke to at VOSA. Test passed and MOT on the car no problem. In Roger's case, I would make sure you clarify the 2JZGE came from an imported Supra although you have to bear in mind that Lexus used 2JZGE and they will be on the MOT database. Brilliant answer, and would clear up a lot. So if you have an older engine in a newer car, write a letter, if you have a newer engine in an older car, don't say a word Quote Link to comment Share on other sites More sharing options...
straightsix Posted March 10, 2014 Share Posted March 10, 2014 Yep. As VOSA stated - it's not for the tester to argue or prove/disprove the engine's age if you provide written confirmation from yourself. All they have to do is make sure they have copies of all the information and test it accordingly as it is presented to them. I had quite a few arguments with the testing station when they said initially said they couldn't pass it without a letter from Toyota! I even checked MOT tester forums and VOSA had quoted the same on those to several testers that had questioned the issue. Basically, emissions wise, the car can only be tested to it's oldest part (the fact that my engine block was a 1996 LS400 made no difference as the ECU was from a 1992 Soarer) Quote Link to comment Share on other sites More sharing options...
garethr Posted March 10, 2014 Share Posted March 10, 2014 ..."If you fit an engine from a 2000 registered (for example) car into an older vehicle, then the emission test will be as for a 2000 registered car and would need appropriate emission controls in place (i.e. cats)..."That is incorrect. http://www.motinfo.gov.uk/htdocs/m4s07000301.htm Vehicles fitted with a different engine must be tested to the requirements of whichever is older the engine or the vehicle. Quote Link to comment Share on other sites More sharing options...
james_cbr Posted March 10, 2014 Share Posted March 10, 2014 what about a 97 facelift car with a early 2jzgte fitted ? Quote Link to comment Share on other sites More sharing options...
straightsix Posted March 10, 2014 Share Posted March 10, 2014 2JZGTE had cats from factory so they would have to be there. You need something pre Aug 1992 for no cats on a 'UK spec' car Quote Link to comment Share on other sites More sharing options...
straightsix Posted March 10, 2014 Share Posted March 10, 2014 (edited) That is incorrect. http://www.motinfo.gov.uk/htdocs/m4s07000301.htm Vehicles fitted with a different engine must be tested to the requirements of whichever is older the engine or the vehicle. Just going on what VOSA told me when I phoned them up. I was on the phone so many times I had a direct number! I'll have to find the info out as I was told that the emissions were engine based and therefore you couldn't stick a newer engine in an old car without the appropriate parts needed (cats, dpf, etc.) I did go round in circles reading everything and that's why I phoned them Edited March 10, 2014 by straightsix (see edit history) Quote Link to comment Share on other sites More sharing options...
straightsix Posted March 10, 2014 Share Posted March 10, 2014 It's getting awkward though - as new law for DPFs on diesel vehicles - If you remove it, it will fail. You can bash out the insides and have it mapped out but insurance is void as you've tampered with the emission control system. Quote Link to comment Share on other sites More sharing options...
james_cbr Posted March 10, 2014 Share Posted March 10, 2014 Mines an import na doing tt converstion Quote Link to comment Share on other sites More sharing options...
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