GMT900 6.2 PPV Build Log

[swathdiver]

This is good data, you will see further down the timeline soon that it was down on power with the cam before I went and put a turbo on it. BTR estimates something like 60-70bhp with the cam in a 6.2, I expected at least 400whp on the dyno and had a suspicion something was up. It ties in with the blowby I observed.

Stellar idea, don't fear the gear! I've not yet decided what gear ratio I'll settle on when replacing this 3.08, maybe a 4.10? Need to pick between a eaton trutrac or yukon dura-grip too.

The non-ppv wheels that came with the car were on 265-65-18 tires. If I wasn't on these 18s, I don't know if the 4pot brakes would have fit under them. Wheels are on the list however. You mentioned going down the track, what size rear tire have you run? Anything in the 28x12.5 or even 31x12.5 range? Trying to get a grasp for what would fit.

It is a billet 278mm converter, part number 07-09-07-2A. I think with my end goal of 6-700whp its a good addition to the build. Even better it came with the car when I bought it. I am glad that the 6L80 was gone through, rebuilt and some choice upgrades done like this converter and clutches. The horror stories I've read about stock converter/stock tune 6L80s blowing up is a bit scary.

Turbochargers don't like to pull on gears like naturally aspirated cars do. 3.42s or 3.73s at most would be my recommendation.

We run that size tire on my pickup that makes 375 horses. We run Michelin Defenders on both of them.

For those higher horsepower motors, the heavier billet converters are necessary for durability even though they cost a little more horsepower to turn. As for the JMBX, well, we're still running them without issue, half a million miles on 3 trucks so far.

 

[Joseph Garcia]

Very nice build thread, and I wish you the best of outcomes with your modded truck. It is an incredible thrill when you give it the throttle and the truck leaps forward like a bullet in response.

 

[ls3_ppv]

The problems continued with the ebay turbo kit and the tune. First up, I couldn't make more than 2-3psi of boost before the car starting cutting out and falling on its face. We messed with the tune and got it running good enough that I felt I could take it up to Kentucky again for LSfest East this year and have some pros look at it. TTS (The Tuning School) was at the event this year and we signed up for a dyno session to have some instructors go through the tuning process with us and work on getting the PPV to run better.

We have arrived at Beech Bend raceway for LSfest, don't mind the cracked dash.

Got a campground crib too:

And got to see some cool builds:

Unfortunately, the dyno session got cancelled and my hopes of getting a solid tune vanished. We did get the instructors to help fix a couple quick things and give us some pointers on what is needed to scale the MAP sensor properly, verify injector data was loaded correctly and fix this odd long crank startup that happens after each calibration flash. Beggars cant be choosers so itll have to do until I can get a pro to really dial this thing in. We were on the lightest wastegate spring at this point so I could peak maybe 4psi of boost on a crappy ebay wastegate after the MAP was scaled correctly. I took notes, talked to some more people smarter than me at all the vendor booths and made a checklist of things I needed to do.

1. Get a better wastegate
2. Get a better BOV
3. Hire a reputable tuner
4. Swap out the truck MAF for a better resolution LS3 card style MAF sensor

Time to head back home, we got work to do!

 

[ls3_ppv]

Its Thanksgiving 2022 now and we've made some progress on the checklist from LSfest.


Truck style MAF-------------------------------------------------LS3 card style MAF

Also discovered the rubber 90 degree boot coming off the throttle body was sucking in during operation so I took the opportunity here doing the MAF swap to rework this whole intake pipe with an aluminum 90 and the MAF bung welded into the straightest section of pipe here.

Also got the JDM bov installed. Things are looking good.

Also got this amazing shot helping to pickup this c6z from Utah and driving it back home.

 

[ls3_ppv]

Time to tackle the wastegate, this ebay one was coming apart. We are now in April of 2023 and work has been a bear so the PPV got sidelined for a bit until I could address the wastegate and tune.

Dang she thicc! Got me a turbosmart powergate 60mm

chopped off the 38mm wastegate flange, hogged out the hole

Should be zero issues now dumping boost and holding spring pressure with this 60mm. Its nearly as big as the turbo!

Also finally caved in and got a fancy catch can. After talking to the Might Mouse owner at LSfest two years in a row and asking all kinds of questions, I got the gen 5 XL can with -10AN fittings.
Let's call this PPV PCV rev. 4 and final PCV configuration. I love this, it works, its easy to drain and observe oil level and combines everything my rev. 3 setup did into a clean package with additional capacity. I feel likeI've made a string of good decisions to dial this PPV in up to this point now, things are looking pretty good!

 

[ls3_ppv]

Its now July 2023, been driving it for a few months and partying with this little 62mm turbo. It's on spring pressure at about 6-7psi at this point and I am racking up miles as much as I can and saving up my pennies for a regear and trutrac. Unfortunately, I start hearing a tapping noise and dig in to investigate. I got these carnage pics to share, its a major heart break.

Yuppp thats valve contact on that underside of the exhaust valve there, rockers destroyed every single valve tip, there's metal EVERYWHERE!

 

[ls3_ppv]

I was left scratching my head here but had a good idea to reach out to BTR since the pushrods, rocks, springs, retainers are all BTR and maybe they can work through some root cause analysis with me.

What you are looking at is an email from Kyle@BTR telling me that THE Brian Tooley was able to identify that I had 1.8ratio LS7 rockers in these LS3 heads. The second picture is the LS7 rocker on the left sitting next to a stock LS3 rocker on the right. 1.8 ratio rockers no worky in 1.7 ratio heads. Notice the wear pattern on both. WOW!

Well, problem identified. I can fix this but I do not trust this block anymore. It's coming out and getting sent to the machine shop for some work and a rebuild.

Its now October 2023. Assembly after a rehone, crank turned .010 and balanced, block decked .005, ARP rod bolts, new piston rings w/ upgraded steel top ring gapped to .024 and .026. All new bearings. Re-used the camshaft.

Some choice upgrades while its apart. -10AN turbo oil drain bung off the oil pan and another -10AN bunch for the driver side PCV connection.

I have already popped an AC line from being too close to the turbo hotside and extended that line away. I also extended the heater core lines and relocated the passenger side battery ground from the front to the rear of the passenger cylinder head. I was in heat management mode, this stuff sucks to work with and I probably should have wet the fiberglass but under hood temps are down and I haven't had any more issues with lines around the turbo T4 flange. Next time I'd look at cerakote or some high temp paint perhaps.

 

[ls3_ppv]

PPV is back together, running smooth. Guess what, there's no more idle blowby! I have vacuum at the oil fill cap, its no longer sputtering coming to a stop too! I think its time to get something better than an LSfest campground tune on this thing. I reach out to PCM Of NC at a friend's recommendation for some help to start turning the power up and get a remote tune. I didn't have easy access to a dyno session and liked the ability to send logs back and forth a few times to get the tuning dialed in. My buddy's recommendation was great, this shop is easy to work with and very flexible as I've worked through these issues and made various upcoming upgrades.

Its now December 2023, the PPV has some miles and is out of break-in. I stumble across this thread: 9.5SF Swap and source a $120 denali rear end. I decide to rebuild it with all new races, bearings, seals, brake hardware, rotors, pads, everything but new suspension bushings and in she goes. I get as far as setting backlash and first time around installed the crush sleeve backwards, I phoned a friend that is big into offroad stuff and he knows a few things about setting up an axle. Once he discovered my backwards crush sleeve, everything went back together smoothly.

Big upgrade going from an open diff/1310 yoked/8.5"/3.08 gearing to g80 locker/1350 yoked/9.5"/3.42 gearing rear end. I think some of the other people in this thread will be pleased I finally did a re-gear, and frankly so am I. It helped tremendously with drivability, converter flashing, gave me some traction control and I don't need to worry about breaking this heavy duty 9.5" semi-float axle adding any more power. A++ would do this mod again!

 

[ls3_ppv]

Last mod to finish out December right before the new year I upgraded some cosmetics. Steering wheel was coming apart at the top and trim top layer was peeling off. Lets fix that with a new steering wheel and emblem.

This was also pretty inexpensive compared to other vehicles I have that I have shopped steering wheels for. Normally something like this id expect to be in the $700+ price range. This was $250 from a seller called Revesol-USA on ebay, they even have a carbon fiber option now!

 

[ls3_ppv]

Also snagged a black leather center console from a yukon. The donor car was a non-denali so I wouldn't get something with woodgrain and it had to come tear free, I got lucky at a junkyard about 25 minutes away that had this for $70. Steam cleaned it and treated the plastic and leather.

Side by side comparison

Jumpseat already pulled out.

New console installed. There is no provision in the PPV for the rear ac controls anywhere but you can tap the front cig lighter plug wiring to enable the additional DC outlets in this console to work.

 

[ls3_ppv]

April 2024, the PPV is chugging along. I am working on the back and forth revisions and datalogs with the remote tuner and trying to iron out some minor shifting issues during various throttle loads. But of course, you can't sleep on the deals. I was crusing FB marketplace and happened upon a VSracing 78/75 billet gen2.5 series turbo. .96AR T4....well uhh thats exactly the upgrade this PPV needs. That 64mm ebay turbski is choking this 6.2 motor out in the upper rpms, guy wanted $200 for it with less than a dozen 1/4 mile passes on it before he upgraded. He already tapped it for a boost reference push lock fitting at the outlet and oil fitting came with it. Even offered to deliver it to me, buddy how could I not!?

So anyways, its time to get serious about some power...

Also a good time to heat wrap that downpipe. This stuff really sucks to work with but its a big difference in under hood temps.

I also take a quick peak under the valve covers and make sure things aren't going sideways on me again. She's mint bud!

 

[ls3_ppv]

Retune the PPV and with a new motor and turbo I just want to rack up some miles on this thing. We head back to LSfest again in September 2024 as the PPV has been trouble free since April and about 8000 miles now. Some interesting match ups on the track at Beech Bend raceway lol

PPV makes the trip there and back but I'm noticing that the oil pressure is tending lower. About 18psi at hot idle now when it used to be closer to 30psi. I change oil and send out for a blackstone oil analysis, lead levels are slightly elevated.... for tracking here were lead levels all 8000 miles.

Mileage / Lead PPM
300 / 5
2200 / 2
5211 / 3
8039 / 7

Blackstone flagged the 5ppm and 7ppm reading which indicated it was higher than universal averages and we needed to keep an eye on it as lead is from bearings.

Disaster strikes....again in December 2024. Different failure mode, same headache. Before I pull the motor again its confirmed with a mechanical gauge. 14psi cold idle, 4psi hot idle.

Out she comes, yea PHQ is right lol.

Camshaft bearing #4 has left the chat...

I also mic'd out the oil clearance on the other bearings and they are all above the service limit of .005" and consensus is you really want something in the neighborhood of .002-.003 on new cam bearings. A little self-clearancing by the lifter on that #4 bearing.

I am not going to lie, I am pretty disheartened at this point. I consult with the machine shop on wtf has happened here but at 8000miles there is no warranty. If you have been following along, you will remember that the only thing I reused was the camshaft and while its journals were the proper size I didn't trust it any more. Also found that the rear oil galley barbel slid aft and an O-ring on it had failed. A momentary drop in pressure when this happened I suspect caused the mayhem. This oil pump was fighting for its life to save this motor, that camshaft bearing sliding aft but staying partially in place allowed oil to keep things lubricated enough to prevent a bigger disaster. Cylinder bores, lifter bores, all bearing surfaces otherwise have zero damage. I'm not excited to spend two Christmas seasons rebuilding this turd, its certainly not my preference. But the story doesn't end here...we must keep going!

 

[ls3_ppv]

Let's get after it, this PPV isn't going to whoop me. And that cam, don't trust that. It's also not suited for a heavy SUV and boost. Let's go back with a Sloppy Mechanics "The Best Cam" LOL

Shopping list:
Durabond coated cam bearings PN: CHP-25T
Summit racing main bearings PN: SUM-172310
Summit racing race series coated rod bearings PN: SUM-663HC010
Melling HV HP oil pump PN: MEL-10296
BTR LS9 Multilayer Head Gaskets PN: BTR22033-2
Sloppy 219/225 cam


If someone wants to calculate the compression now here's the info I know:
deck height: 9.240 in.
block decked .005in.
heads milled .001in.
Piston Volume +3cc
Combustion Chamber Volume 70cc
Gasket thickness: 0.055in
Gasket bore: 4.1

I am coming up with a 10.6:1 compression ratio.

Interesting set of ACL...er I mean summit racing rod bearings I got...

Staying organized

Going through the heads, all valves seal up. No repeats of last year's fiasco.

Freshhhhhhhhhh

Been fighting a pesky leak at the back of each exhaust manifold, found they were both slightly warped. Got those resurfaced and problem solved!

 

[ls3_ppv]

I am a big fan of "while you are in there" mods. If you look at my earlier post installing the turbo kit, you will see that the driver manifold is a stock truck manifold with the 3 stud flange. Lets v-band the whole exhaust, fix the crappy flex section in the cross over and make things a bit more blue.

V band welded to end of driver manifold

Screw it, new cross over build. Fancy double walled accordion style flex piece from vibrant performance.

My boy being a major help getting this fitted and welded up!

Beautiful new crossover, fits better than the one that came out and shouldn't leak from the new driver side v-band or flex section ever again.

And lastly, lets add some color to these valve covers. They came out beautiful, my painter buddy was asked to make it something blue and came up with this from a mix of some Lemans Blue BMW paint leftover from one of my other projects and some colors he had. He killed it!

 

[ls3_ppv]

Time to drop it back in, I am so ready to put this thing back on the road and boil some more tires!

Dropped it in with other valve covers, didnt want to damage these freshly painted ones. Once it was in and bolted up to the bellhousing, I swapped them out.

Hell yea, we got oil pressure now boys!

Man does it feel good to have this thing back out on the road, temps and oil pressure are solid.

 

[ls3_ppv]

Christmas came and my wife...I mean Santa brought me some goodies. New Dashskin dash cover and headlights landed. She's seen the headache I've been through and also drives this car from time to time and wanted to get me a little something.


Like every GMT900 vehicle, the dash cracks. Luckily I had all the pieces still and plastic welded everything up to reinforce it the best I could before putting the topper on.

Installed and silicone setting up, I put about 20 books and tension rods on this thing to hold it down for 24 hours. The smell lingered around for about a week.

All cleaned up and out on the road, this turned out very nice. No more rattling!

 

[ls3_ppv]

Headlights are clapped out with some LED bulbs that blind everyone and the plastic is cloudy. These new units came from an amazon seller Auto Dynasty for $105, I opted for the OEM style halogens with clear reflectors, clear lenses and black housings. Also tossed the LED bulbs out and installed some Sylvania silverstar ultras.

Before:

After:

At some point I replaced the missing front lip on this thing too, that was less than $40 delivered to my door and installed in 5 minutes. This PPV headed into 2025 with a newly rebuilt motor, new cam, new crossover, new headlights, new front lip and new dashboard topper. I get it retuned and work through break-in and tune revisions with the remote tuner again. This thing is getting dialed in and looking better and better. I snapped a picture during the snowday we caught here recently and it was looking good that day.

 

[Miami-Dade]

Excellent work!!

 

[RooTBeeRthe1st]

I need to fix my dash still...was thinking something similar