Idnevno Posted July 29, 2003 Share Posted July 29, 2003 just made my exhaust a couple weeks ago. 3" downpipe, to 5" exhaust out the side of my car. i noticed that off the line acceleration changed it is not as fast off the line but when i hit 25 pounds of boost the car slams your head into the seat. if anyone has any ideas on what i can do to make up for the off the line acceleration would be greatly appreciated. if anyone wants to see some pics let me know and i will try and figure out how to post them. - D Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 29, 2003 Share Posted July 29, 2003 My L28ET with 3" exhaust (rear exit, Dynomax muffler) will build boost as soon as you load the motor with the clutch - 3500 rpm launch, practically zero lag. What turbine are you running that will drive 25psi of boost? It sounds like you've optimized for top end flow, and there may not be anything you can do for your lag. Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted July 29, 2003 Share Posted July 29, 2003 DELETE Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted July 29, 2003 Share Posted July 29, 2003 DELETE Quote Link to comment Share on other sites More sharing options...
DavyZ Posted July 29, 2003 Share Posted July 29, 2003 "The best muffler for a turbo is no muffler." Turbos like as little exhaust/muffling as possible. As for the 5" tip, well.... Davy Quote Link to comment Share on other sites More sharing options...
Idnevno Posted July 31, 2003 Author Share Posted July 31, 2003 ok well lets see where do i start??? the rear end is 87 300zx posi with 4.10 gears. everything is solid mounted, i have 240 tokico springs on my 280 strut housings so my car is bout 2" off the ground. i have cut into the tunnel and relocated the rear sway bar in order to fit my exhaust in there. it is 3" off the downpipe it goes into a 3" in3" out dynomax race magnum round muffler to a 3" mandrel bent 90 into 5" for bout 1.5 feet and out the side of the car in front of the pass tire. i have cut out part of the body and the seatbelt bucket in order to tuck it up in there. as for the fuel and ignition. it is stock fuel setup and MSD 6AL with the boost retard i have the timing set at 2 degrees to compensate for boost pressure. the flywheel is a lightweight aluminum one. i run no intercooler at the moment presently but i am running a custom water injection setup that i made. i am also running a switch setup i made to fire off the cold start injector whenever the car sees 4 pounds and over of boost. not sure bout the turbo?!?! i believe the cam is a stock turbo cam not toooo sure though. the head is a P90A one with hydraulic lifters....i have pictures of my car but i do not know how to attach the pics to a reply!?!?! if anyone can help it would be greatly appreciated. the coolest thing is when it backfires!!!!! i shoot flames roughly 2 - 4 feet out the side of the car all depends on how hard i run the car depends on how large the flame is.. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted July 31, 2003 Share Posted July 31, 2003 I'd be curious what your mixture is across the rpm band at full load. Your ignition timing is set to 2* BTDC? With stock turbo EFI, that setting is 20* BTDC. Or are you just talking about your BTM setting? Either the timing or the fuel mixture could be keeping the torque low until you hit full boost. I can't believe the cold start injector is doing much for you... You are running a stock fuel system at 25 psi? That sounds dangerous actually - you won't get but 250 hp, and you can max out the fuel injectors by 12 psi, or 14-15 without an intercooler. I really can't imagine just the exhaust addition hurt performance - it sounds postively UNrestrictive. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted July 31, 2003 Share Posted July 31, 2003 Ditto to what sleeperZ said... Unless somehow you have some restriction in your exhaust, it shouldn't hurt performance, high end or low end. Maybe the extra power/spoolup has caused something to come loose, break, etc. and it just happened at the same time as adding the new exhaust...? Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted July 31, 2003 Share Posted July 31, 2003 Call me a skeptic, but there are too many contradictions. This coming from someone who also runs about 25psi boost. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted July 31, 2003 Share Posted July 31, 2003 My stock turbo blew up the trust collar bearing when it hit 20+psi Quote Link to comment Share on other sites More sharing options...
Idnevno Posted July 31, 2003 Author Share Posted July 31, 2003 hey scottie if you want i should be taking my Z to daytona for spring break next year. i hope to have some of the bugs figured out by then. in terms of contradictions i would like to know what you think is contradicting because your opinion comes highly respected to me. i believe my injectors are stock non- turbo but not too sure. the intake and head have both been extrude honed. the exhaust is anything but restrictive. the turbo is a stock 83 280zx turbo of which i have had a ceramic bearings machined into it. the old brass?!? ones did not hold up at all above 12 - 14 psi. the water injection is shooting water into the compressor side of the turbo which turns to steam to keep detonation down. the timing i set at 2 degrees with the vacuum hose disconnected. i am also retarding the timing 1 degree for every pound of boost. i am jumping the cold start injector when i see 4 pounds or more of boost. i start to come down from running real rich around 16 pounds i just start hitting the red zone (lean) with the air fuel gauge at 20 pounds at 25 pounds i start to detonate. i am also running 108 octane gas as well to get this to work successfully. my next step hopefully is to convert over to the 300zx electronics. any suggestions or help would be greatly appreciated. it's just kind of odd it might be coincidence though from doing exhaust and now a stumble under acceleration until 1500 - 2000 rpm. i am considering dropping my fuel pressure from 42 psi at idle down to 30 or 35 but i am worried about high end fuel pressure and getting enough pressure when i run high boost levels. right now at 20 pounds boost i am seeing 68 psi fuel pressure. Quote Link to comment Share on other sites More sharing options...
yo2001 Posted July 31, 2003 Share Posted July 31, 2003 Bring it to Reynolds, GA in Sept. 14th. I'm sure everyone want to see it. Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted August 1, 2003 Share Posted August 1, 2003 It sounds to me like you need a good engine managment system, injectors and a better turbo. The stock EFI unit was NEVER intended to be used that way, and you are damn lucky nothing has exploded on you running that lean with stock non-turbo injectors! And running that hot with a stock turbo! Please don't take it the wrong way, but I don't you can tune this system. If I was to guess, I'd say you can't be making more than 220 hp to the wheels. With a stock Z31 computer, stock turbo injectors, intercooler and a better turbo, I put down over 250hp at 15 psi of boost (stock motor). Others have put down the same with stock turbos running only slightly higher boost. Quote Link to comment Share on other sites More sharing options...
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