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sorry it's taken so long. On so many levels, I'm sorry. Due to my hectic work schedule (out of town most days of the week doing contractor work) I barely get any time to work on my car on the every-other-weekend home. I'd uploaded a base tune I'd worked up with the 127# bosch injectors and a 3bar speed density tune. My VE was modified but not the idle areas. It would start but then die quickly. Here's what I'd put on my other thread about using my HPTuners software to get the engine running ....
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Well, Finally got to do some tuning. The poor car has been waiting for me to get 10 minutes to do anything to it since I started my contract in Dallas back in June.
So, getting everything buttoned up and the 3bar SD flash in its initial incarnation, I uploaded it. I turned the key on and off 5 times to let the pumps fully prime the fuel system, said a prayer and cranked it. She started right away but had a very weak idle, stumbled then died. I tried cranking it again and it would just repeat. Sometimes it would backfire before idling a little. I thought it sounded like lean mis-fire. Trying to open the Throttle body a bit to add some air only made it die quicker. I tried logging it but it was running too brief a time to really discern anything. After a few more minutes, I had to go back to Dallas. Phock... But on the flight home, I remembered running into something like this (lean, weak idle. Wouldn't stay running) on my LT1 after I went from a MAF 1 bar based tune to a 2 bar. I had 60# injectors with that tune but putting 60# in the injector constant made it run like my 5.3. I ended up setting the Injector constant(IC) to something around 34# to get her to run correctly. This, being on the OBDI pcm of the LT1, made sense. But I wondered if I was running into a similar issue with my current 127# injectors.
I started pulling up Denmahs 3 bar tune and noticed he had his IC set to some offbeat poundage like 49#. This strengthened my idea that I might need to drop my IC to something less than 127, by a few pounds at a time, flashing the file, then seeing how I idled.
When I got back from Dallas today, I quickly dropped the IC from 127 to 120, uploaded and then tried to start it. Hmm... it *is* better, though still dying. I dropped it 3 more pounds, uploaded the flash, then started it again. Hey, that's definitely better. I dropped it down to 113#, uploaded it and started it. It now idles like a champ.
I have a lot more to do before I can get more tuning time in but I was elated that I found out what was going on.
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I set the IC back to 127 and went thru my VE table. I increased it from the stock 5.3 settings to Denmahs 3 bar and she fired right up and idled.
I'd sent my 2 year old PT7675 to Forced Inductions.com for repair after finding the turbine had a binding point in rotation. I thought it would be a simple repair but be advised, Precision Turbos does not supply parts to outside parties for repairs. Thus, it takes repair facilities quite a bit of time to source the parts from similar turbo companies. I sent my turbo in the last week of November and I'm told it was being shipped yesterday (Jan 28th) This is not Forced Inductions fault, but rather a combination of bad timing (PRI, a performance parts get together event where vendors showcase/review new products was in December) and Precision Turbos stance on supplying parts.
The issues that Jose (at FI.com) said were afflicting my PT76
The compressor wheel was way out of balance. This was news since I bought it brand new. One thing to note, I'd ordered a non-billet version but after the sale, I got a call saying, "Hey, this already has a Billet wheel on it so you'll need to give us an extra $200 bucks or wait till we get the version you wanted". Not being the patient type, I paid the extra money. But in light of this non balanced discovery, it makes me wonder if someone just slapped the billet wheel on it before sending it. Hmm...
Now, I'd always read/heard that turbo drains needed to have a decent drop before entering the pan, but... my hotside put the turbo just above the harmonic balancer height by a bit, so the turbo drain was (a) short at about 3 inches and (b) near parallel to the pan drain. So with that configuration, I put a -10 an elbow off the bottom of the turbo and sent it off to the pan. I drove it like that from 2008 till 2014 and it never seemed to be a problem for either the original turbo (TC 76) or the PT7675. However, Jose said that was a bad idea and that oil had caked up inside the turbo and had been getting past the seal. To alleviate that problem on my new build, I ordered a Turbowerx pump yesterday and will let that handle turbo oil scavenging issues.
Jose also found that the wheel was hitting the housing, probably at maximum PSI. But this, he said, was because the clearance at manufacturing or assembly had too close of a tolerance. They were going to CNC that problem away.
I'm hoping this mild winter will continue so I can get this car on the road soon.
Another point to bring up, when updating the tune and MAP sensor to 2 or 3 bar, there are tune aspects of the MAP Linear and Offset that are extremely important to have right.
I bought the first 3 bar map sensor I saw for sale in the Ls1tech.com classifieds and put it in , thinking, "Well, that's done. Lets fire it up!". Well, it would only start and die. Turns out the Map Linear and offset defaulted by HPTuners setup was way off what this MAP sensor required. Once I (finally) found the right settings, it starts up and idles fine without all the backfiring, etc. When sourcing your 2 or 3 bar map sensor, request either the data sheet of the Linear/Offset values. If you can't get either, you may find yourself chasing a ghost when tuning.
Dang, I didn't realize I hadn't updated this in so long.
Recent developments...
Bought an MSD 2 step.
Built a switch/button to independently arm 2-step, Transbrake and Line Lock, all activated/deactivated by a single momentary switch in my ash tray cavity.
Swapped the tune to E85
Got a Dennys Nitrous ready driveshaft w/1350 yokes front and back.
Installed 3.08 gears, thinking it would load the turbo better and increase my 1/4 mile MPH.
Raced it with the Vigilante 9.5" TC at the local track. Got a 11.3 @ 120mph because it was blowing thru the converter (shift rpm was only dropping 200 to 300 rpm during shifts). Contacted Precision Industries to see if they could restall my Vigilante. They looked up the records on the last restall( I had them restall the original setup from 2800 to 3800, or so I thought). He said, "Yes, I see we restalled it to 4,300". My eyebrows shot up. Damn, that's why it blows thru the converter. Ray Cahall told me my TC stall and gear were all wrong for my setup. I re-installed 3.55 gears and bought a new PTC torque converter. When I took it to the track I got a 10.6 at 128.9mph, 1.5 sixty foot. This was at 17psi. Now this was driving to/from the track without taking out the tools in the hatch or changing fuel or taking out the interior. I'd set the air pressure in my M/T drag radials (315x35x17) to 17psi before leaving my house.
The car is running great now. I have spent a lot of time tuning it with my HP Tuners Pro and I couldn't be more happy.
However, all you guys know how it goes... We're never 'done'. There's always something we want to improve on the car, no matter how perfectly it runs.
Purchased, not installed yet but during this winter...
Griffin stand up radiator and Derale fans
Twin GT35 turbos
An On3 78mm turbo (incase I want to 'twin' the PT76 and On3 78mm turbos)
A pair of stock Ls1 Camaro exhaust manifolds to weld up the hot side.
Things I'll have to do before long...
Either get some Ford 9" ends put on my Ford 8.8 differential (along with new axles, etc) or sell the Hybrid 8.8 and get a built 12 bolt/9". My 8.8 only has 28 spline Strange axles.
Invest in some suspension pieces. I have some QA1 shocks and BMR heavy duty sway bar, plus subframe connectors, but that's about it.
Last edited by mightyquickz28; 09-04-2017 at 08:05 AM.
Now, I don't *know* this but I was told by my differential guy that you can't get 35 spline axles into those GM 10 bolt legs. Mine is a 'hybrid' of the 8.8 center section and my stock GM 10 bolt legs.
Originally Posted by MY_2K_Z
Instead of getting rid of your 8.8 why don't you just upgrade to like a 35 spline carrier and get custom axles?
New personal best tonight at Lebanon valleys test n tune. 96 Z28 w/ turbo 5.3 TH350. Street legal, driven off the highway, onto the track, pump gas (E85).
I set the two-step back down to 3000 RPM because last week at 3500 it just blew off the drag radials. It was getting like 5 PSI at that RPM, but with it back down to 3000 RPM it was building 2 psi. First pass I messed up and took off in second gear with the trans brake. Tires went up in smoke but once it caught it flew. 1.71 60 foot (meh..) 6.5 et @ 112.46. I let off the gas after I passed the 8th mile mark and started putting on the brakes and it still turned a 10.8 ET @ 95mph.
Next pass, got my act together and took off in first 1.61 sixty foot, 6.4 ET @ 112.28 MPH. Once again I let off after the 8th Mile and started putting on the brakes and still turned a 10.8 @ 91 mph.
After that I just took off my helmet without turning off the engine from the last pass and drove home. The car is so much fun to drive!
Two On3 GT35's with stainless steel Turbine housings .80 A/R, v-banded on Turbo input.
Twin Turbo Intercooler with dual 2.5" in/out.
Truck manifolds (both are passenger sides) facing forward, V-banded, cut and welded by me.
Two Tial 50mm wastegates.
Complete new 2.5" intercooler piping, cut and welded by me.
Downpipes are 3.0" to the floor pan, then straight 2.5" (ie: no mufflers) all the way back to the Borla tips. Cut/Welded by me.
Installed a Junkyard 4L80E with stock Torque Converter. (a PTC TC is in my shop, just haven't installed it yet.)
Installed ICT dual port front timing cover to use for turbo gravity drains.
Took me 3 of the past winters working anywhere from 30minutes to an hour or two a day each winter, interrupted constantly by life, on these twins.
Was it worth it? After a day or two of popping off couplers, and changing the wastegate springs from 14 to 10 and now 8#, YES.
I can't say that the exhaust note is sexy or racy. To me, it sounds like an old farm truck with glass packs. But the boost and how early it comes on and how quickly it escalates is just astonishing compared to the already impressive previous PT7675 single.
Last edited by mightyquickz28; 04-12-2020 at 05:11 PM.
10-05-2015, 12:25 PM
We're never 'done'. There's always something we want to improve on the car, no matter how perfectly it runs.
