80LS1T Posted July 12, 2006 Share Posted July 12, 2006 My service writer has an 03' 350Z that he put a turbo kit on 2 weeks ago and the motor started knocking 3 hours later. We finally got the approval from Nissan for a short block and if needed a long block. I removed the engine today and found that #2 pistion oiler was broke off and there was bearing material in the oil pan. #2 cylinder was only at 110 PSI compression were as the other 5 were at about 170PSI, obvioulsy damage was done. My theory is that since the PCM was not programmed for the cams he had is that it ran lean under WOT. "Jim Wolf" said that the cams wont affect A/F ratios. If I'm not mistaken pretty much all cars, including the 350Z, dont look at the O2 sensors under WOT and just run off fuel maps that are programmed into the PCM. So if the cams were bigger and allowing more air into the cylinders but the PCM wasn't programmed for those cams it would run lean, correct? My question is if he lowers his compression to say 8.5:1 or 8.8:1 with forged pistons and went with forged rods would his lower end be pretty safe? Apperently the 3.5L is only good to about 420HP before it goes. If he lowers his compression obviously he's going to loose some power if he leaves it at 8psi but since the compression is lower he could up the boost some then correct? He doesn't want to blow this new motor! And for you engine builders out there, if he does goe with new rods and pistons he should have the whole rotating assembly balanced right? Thanks guys! Guy Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted July 12, 2006 Share Posted July 12, 2006 I don't think the cams caused a lean condition... It was more than likely tuning (probably running lean and detonating. Running a lower compression will not save you from running lean and detonating, appropriate air/fuel ratios and correct timing for boost will. You can run more boost on pump gas safely as long as the supporting mods are there (fuel, boost retard) with lower compression. I suppose it would be an ideal time to install rods and pistons while the engine is out of the car, if he intends to make more than 400 rwhp. Quote Link to comment Share on other sites More sharing options...
Phantom Posted July 12, 2006 Share Posted July 12, 2006 If I remember correctly the achilles heel of the Z33 motor is the connecting rods. If you go to forged rods & pistons, ARP bolts and replace your bearings while it's apart the bottom end should be able to take more HP/TQ. If you drop the CR to around 8.5:1 then you'll be able to run significantly higher boost presures. With a good intercooler I would imagine 18-20 pounds of boost would be achievable. The key once all this is done though is to get it to a good dyno tuner and get it set up properly. If he had spent the $500 to do that originally he'd probably still be running fine with the original equipment. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted July 12, 2006 Author Share Posted July 12, 2006 I don't think the cams caused a lean condition...It was more than likely tuning (probably running lean and detonating. So even if the PCM was programmed for stock cams and he had different ones in there(bigger ones), that wouldn't cause it to go lean under WOT? If he does go with lower compression pistons and better rods will he have to balance the rotating assembly? Or can we just put the new pistons and rods in the new engine(obviously after we check the piston to cylinder clearances and rod bearing to crank clearances)? Thanks Guy Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted July 13, 2006 Share Posted July 13, 2006 you can spend $1,000,000 on that car -but if the fuel supply doesnt follow the amount of air put out by the turbo it will continue to blow up.maybe another computor to control additional injectors?the usual aftermarkit crutch okie rig on a turbo kit is to raise the fuel pressure under boost.maybe install a innovate motorsports wide band o2 kit and do some datalogging.throwing aftermarkit parts on late model cars usually doesnt work the way its supposed to.my opinion would be to put another computor to control another injector in each throttle body.since i work as a ford dealer tech i will to you what happens to fords when owners play with them-warrenty voided. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted July 13, 2006 Share Posted July 13, 2006 So even if the PCM was programmed for stock cams and he had different ones in there(bigger ones)' date=' that wouldn't cause it to go lean under WOT? [/quote'] The cams would have to be SIGNIFICANTLY bigger to cause that much of a lean condition at lower boost levels. I am ass-uming that the boost wasn't turned up over 6-7 psi... I would lean toward the tuning and fuel delivery to be the culprit in this case. Just my .02 Regards, Mike Quote Link to comment Share on other sites More sharing options...
80LS1T Posted July 13, 2006 Author Share Posted July 13, 2006 since i work as a ford dealer tech i will to you what happens to fords when owners play with them-warrenty voided. Hehehe, well since he's the service writer for Nissan and I'm the guy installing the new engine supplied by Nissan that wont be problem! One of the perks I guess! As for fuel supply, it has a "bigger" fuel pump(walbro 255 I beleive) and bigger injectors. The boost is maxed out at 8 psi by the waste gate spring. Part of the kit is sending the stock PCM in and having it "reflashed" for the turbo kit, so theoretically it should have been ok if the cams weren't a factor. I am just finding it hard to believe that the tune was so far off that the engine "blew up" 3 hours after the install, seems like it should have lasted longer than if it was tune properly? Guy Quote Link to comment Share on other sites More sharing options...
ww Posted July 13, 2006 Share Posted July 13, 2006 I am just finding it hard to believe that the tune was so far off that the engine "blew up" 3 hours after the install, seems like it should have lasted longer than if it was tune properly? You answered your own question. Was it dyno tuned with a wide band O2 after everything was installed? If not, it doesn't have to be too out of tune to smoke a piston. Were the new injectors flow tested and matched? You could have a good O2 reading and still have an injector that's running lean even at full duty cycle and kill the engine. Quote Link to comment Share on other sites More sharing options...
80LS1T Posted July 13, 2006 Author Share Posted July 13, 2006 No since it only ran for 3 hours he never got it to the dyno. The guy that installed the kit "was reading the o2 sensors with a scanner after the install and said it was ok"....someone should tell him that the o2 sensors arent widebands!(this guy is the other tech I work with, yeah he's a tool!) Guy Quote Link to comment Share on other sites More sharing options...
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