My Rear Mount Turbo Fabrication
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Joined: Dec 2002
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From: USA
prior to my 'test' at sebring:
once i realized that i was leaking all the boost away i rewelded / leak checked each piece and the fun began,
used my cobb accessport to monitor afr - could only do 2nd / 3rd runs so 4th / 5th were unknown territory - had the accessport zip tied to the dash so i could watch it on the track
used my scangauage hp estimator and that only showed about a 50% hp gain - so i figured i was maxing at ~ 360 whp so engine would be safe - i knew things could go wrong but i thought i would destroy the turbo not the motor
fixed my oil smoke issue by getting a voltage regulator for the oil pump for the turbo / that system worked great - isolated from motor oil - could watch oil temp / pressure and adjust the pressure with the regulator - didn't get the full 8 hour test this time but no more spyhunter smoke clouds either
at sebring:
so was ~10mph faster after each straight - i normally am at 125-130 (indicated/ actual is minus some wheel sizing) and was at 140(indicated) at the end of the straight the lap before - had backed off a bit this lap because i was behind someone so ~135ish when it blew covering rear wheels with oil, some puckering but undies remained clean
there was a very bad knock as i coasted around 17 and into the pits - that knock turned out to be a very bent rod that due to shortening was causing piston to hit crank shaft weights with each revolution - i first had just ordered 1 piston / connecting rod to replace the broken one (plus rings / bearings / 4 valves / oilpan/ gasket set) because the others looked good (while IN the motor) had it together and was spinning it by hand and that knock was still there, so took it all apart and found the bannana rod - figured if 2 of 6 were bad then all needed to be changed
once i realized that i was leaking all the boost away i rewelded / leak checked each piece and the fun began,
used my cobb accessport to monitor afr - could only do 2nd / 3rd runs so 4th / 5th were unknown territory - had the accessport zip tied to the dash so i could watch it on the track
used my scangauage hp estimator and that only showed about a 50% hp gain - so i figured i was maxing at ~ 360 whp so engine would be safe - i knew things could go wrong but i thought i would destroy the turbo not the motor
fixed my oil smoke issue by getting a voltage regulator for the oil pump for the turbo / that system worked great - isolated from motor oil - could watch oil temp / pressure and adjust the pressure with the regulator - didn't get the full 8 hour test this time but no more spyhunter smoke clouds either
at sebring:
so was ~10mph faster after each straight - i normally am at 125-130 (indicated/ actual is minus some wheel sizing) and was at 140(indicated) at the end of the straight the lap before - had backed off a bit this lap because i was behind someone so ~135ish when it blew covering rear wheels with oil, some puckering but undies remained clean
there was a very bad knock as i coasted around 17 and into the pits - that knock turned out to be a very bent rod that due to shortening was causing piston to hit crank shaft weights with each revolution - i first had just ordered 1 piston / connecting rod to replace the broken one (plus rings / bearings / 4 valves / oilpan/ gasket set) because the others looked good (while IN the motor) had it together and was spinning it by hand and that knock was still there, so took it all apart and found the bannana rod - figured if 2 of 6 were bad then all needed to be changed
That might be because at lower throttle positions the stock ECU gives out a much higher timing than at WOT
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From: Illinois
I am also wondering how it was tuned, and close you think the tune was to being dialed in. I am in a position where I built a beta stage setup and am a bit hesitant to test it out. Its my DD so I'm kinda screwed if I mess it up.
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From: ocala, florida
rebuilt NA engine break in going fine,
changed oil at 250 miles and filtered old oil thru a coffee filter [took a while] and no tiny shavings
gets better +1 mpg since redo, no oil lost yet either
letting memory fade in my wife's mind before i go bolt the turbo back on,
will spend a bit more time playing with the tune next time - i rushed it to get to my track date with bad results, figured [hoped?] that if afr was good then life would be good....
if anyone has a 350z turbo base tune for the cobb accessport i'd happily use it as a starting point !
changed oil at 250 miles and filtered old oil thru a coffee filter [took a while] and no tiny shavings
gets better +1 mpg since redo, no oil lost yet either
letting memory fade in my wife's mind before i go bolt the turbo back on,
will spend a bit more time playing with the tune next time - i rushed it to get to my track date with bad results, figured [hoped?] that if afr was good then life would be good....
if anyone has a 350z turbo base tune for the cobb accessport i'd happily use it as a starting point !
You might want to post in tuning section - sorry I don't know much about the access port. AFR's mid 11s and timing in the low teens at most at peak torque might still not save you on a high compression motor on a race track. Did you lower compression this time around? If not, you might want to use race gas next time you go out on a track or invest in W/M injection. Kudos on doing all this work yourself! 
Any updates on this. I just read this whole thread, very interesting. I would like to hear more on the blowing a motor when backing off the throttle, since im about to start mapping out my boost build.
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Aug 6, 2021 06:19 AM
