Jump to content

2021 GMC Sierra AT4 6.2L Supercharger build

SierraStorm21
 Share

Recommended Posts

SierraStorm21 Enthusiast

SierraStorm21

Posted
Posted

I searched for about a year, including posting here looking for references, and finally found someone who had a solid reputation to do it and pulled the trigger on purchasing the Whipple in June of 2023. However he was 3 months backed up, so it didn't go in till middle of September 2023 and I got it back a few weeks later when I returned from vacation.

 

At the urging of the shop owner, I opted for the Trans tuning as well and I'm certainly glad I did.  There was a few hiccups along the way, mostly logistics between HP Tuners and Whipple, but in the end it was all sorted out. I also splurged and got the red version.

 

It certainly pulls and I had a lot of fun driving back home and since. The tune he did on the Transmission made a world of difference too. Shifts are crisp and in the earlier gears, harder and more concise. When just driving around town, it shifts earlier in the RPM range and I like it alot. The SC itself is pretty quiet. I can hear it because I'm used to it, but friends I've taken for a ride can't really tell unless I point it out. I wish it had more of the SC whine, but I can live without it. Like AEMedic mentioned in his SC build, I think the Whipple tune leaves some to be desired. It has some surging and I mostly notice it under light loads up any incline at cruising speeds. It's like it doesn't know what to do under certain circumstances. It's a minor annoyance for now which I plan to have tuned out later this year.

 

Since around 1000 miles, I've had the AFE CAI, Borla S-type cat back exhaust and the Edge Pulsar LT module installed. I knew the truck felt fast, but I really didn't know how fast. I bought a dragy several weeks before I drove it up to have the work done and got a baseline of what the truck could do in 0-60, 1/8 and 1/4 in a spot I've found that is 3/4 mile long and is around 112 feet in elevation. Did about 12 runs over several days. They were all done earlier in the morning and with 3/4 to full tank of fuel. I also should note that I have the 6.5' bed on mine.

 

When I got it back, I did the same thing over a few days and was pleasantly surprised at the results. Attached are a few screenshots.

 

While I love it, I feel like the Whipple tune is pretty conservative and while I get that and the reasons why, I think I want a little more. In discussing this with the shop that did the work, he suggested the next step would be meth injection kit with a slightly smaller pulley and a custom tune. He said he might be able to get another 30-50 rwhp by custom tuning alone, but that using meth injection would allow for a reduction of the intake temps and stresses throughout, and also allow easier tuning. He said they do alot of those kits on a multitude of rigs.

 

I'm on the fence about whether to move forward with it and would love to hear from those that have more knowledge and wisdom about the subject than I certainly do. I've done a little research and it makes sense. I just don't know if I want to deal with having to fill up the reservoir and more importantly, wonder if doing so would cause other failures in the drivetrain. I should add that this is my 'sports car' if you will and not a daily driver

 

2021 GMC baseline.jpg

2021 GMC SC.jpg

SC.jpg

2021GMC.JPG

SCEmblem2.JPG

  • Like 3
Gangly Senior Enthusiast

Gangly

Posted
Posted

Thanks for the nice writeup and great pictures.  12's is a VERY respectable number for a 1/2 ton truck in the quarter-mile, impressive!

  • Like 2
  • 1 month later...
kodiakdenali Enthusiast

kodiakdenali

Posted
Posted

Thanks for sharing!

Awesome setup and solid numbers.

I know it will be really difficult to judge because it got the blower at the same time, but what was your impression of the transmission tuning? it shifts earlier in the rpm range? is the same true for when your truck is in sport mode? Usually holding out the gears a bit longer is desirable, but it all depends on so many factors. I’m not a fan of the factory shift program on this transmission. it certainly gets the job done, but I’ve always felt like it could be improved. Although if you tell the truck you really want it to go it can. Especially in sport mode I can get some very snappy shifts when I’m on the throttle but as soon as you let off its back to sloppy gear changes. The manual says in that sport mode is essentially an arming type system. as in even when you're in sport mode it only gets sporty when it detects that you’re driving more aggressively and not all the time. There’s definitely a lot of variation in how it shifts, but I can’t get it to shift the way I want it to consistently. Tuning is probably the answer.

SierraStorm21 Enthusiast

SierraStorm21

Posted
  • Author
Posted

The shifts are much more defined and felt in the lower gears...1-4. It shifts sooner and crisper under light to medium loads. WOT is the same and the shift points there are probably the same as stock when doing that. You just feel it shifting unlike the stock tune where I could hardly tell.

 

The 1-2 and 2-3 are very definitive and even 3-4 you can feel. After that they are less felt but you can still tell. At first I was going to have him lighten the 1-2 because it was pretty harsh. Especially on the drive home and hitting Portland rush hour traffic. I'd get going 15-20mph and then have to let off the gas again just as it shifted and it'd jerk my head a bit. However after some time it's softened up a bit and I've grown to like it. 

 

I'm always in Sport mode anymore. I think I drove it home in normal, but the shifting wasn't any different between the two from what I recall. 

  • 6 months later...
SierraStorm21 Enthusiast

SierraStorm21

Posted
  • Author
Posted
2 hours ago, johnnyquick said:

May I ask which shop you used?

EPC racing in Spokane, Wa seems to be knowledgeable about the installs AND  more importantly to me the dyno tuning.

That's who I used. They are great. I found them by just searching online and then @kodiakdenali referred me to them as well. Unfortunately they are a 12 hour round trip for me.

Just so your aware, doing the Whipple gets you the Whipple static tune. There is no customizing it beyond that. Whipple encrypts it so he's unable to see what they've done.

 

If you want to do the Whipple and a custom tune, that's something different where he has to start from scratch essentially. If this were my daily driver, the Whipple tune is pretty good and fairly refined. It leaves some HP on the table as I've mentioned previously, but if you want a good amount of power and reliability, the stock Whipple tune is fine. His trans tuning brings it all together though imo. If this were my daily, I might have it adjusted slightly to be less harsh on the 1-2 and 2-3 shifts, but for me, it's great.

  • Like 1
Aubie_01 Enthusiast

Aubie_01

Posted
Posted

I remember seeing that the aluminum driveshafts on the K2 trucks could come apart above a certain speed (and saw the pictures).  Is that a concern with these trucks?

kodiakdenali Enthusiast

kodiakdenali

Posted
Posted

EPC had one from a 2019 under his desk. Wish i took a picture of it. Broke right in half. Said it happened around 140. I had him leave my speed limiter at 125. 

  • Like 2
  • 8 months later...
SierraStorm21 Enthusiast

SierraStorm21

Posted
  • Author
Posted
5 minutes ago, johnnyquick said:

So, did you go with the Alky?

I did, but I'm not sure I'd do it again for a few reasons.

I have to keep the Windshield Wiper fluid reservoir 2/3 or more full in order to not have a cavitation problem with the system when driving. So I fill it up every time I go to drive it.

 

That's apparently due to the angle and design of the factory reservoir where the feed comes out and EPC offered to make a custom reservoir, but I decided against it. I even had a leak a few weeks after it was done and had to drive it back up there to have it resolved. The problem was that the fittings Alky sends aren't a perfect fit for a truck setup. So they came up with their own custom fittings solution and it's been rock solid since.

 

Secondly it's not something that is going to be maintenance free. It's kind of complex setup with a pump in the fender well and modules under the dash and while I understand the concept, it's not something I want to mess with. Additionally, since I'm not local to the shop that did it, if anything were to go wrong, I'd have to deal with it on my own or find a way to get it 5.5 hours to the shop or find someone else closer, which I have not yet found.

For the positives, it's like a mini NOS boost when it engages, kind of fun. Additionally, it's cooling down the intake temps and lastly, it's keeping everything clean internally. 

I'd probably opt for a different route, like a DoD delete with new pushrods, lifters, springs and cam. But that's going to be much more costly.

I might end up doing that in a few years anyway and that point, decide whether to keep the Alky or remove it.

  • Like 1
johnnyquick Enthusiast

johnnyquick

Posted
Posted (edited)

Doing a Texas Speed dod delete kit and custom cam designed for use with the supercharger, and putting on Long tube headers and a heavy duty driveshaft as per LMR in Texas.

I am hoping to end up with 650Hp at the crank with all this and dyno tune with TCU tune as well.

Did you get any dyno numbers on yours?

Funny thing is wifeys Escalade V smokes everything I have came across yet, this fueled my upgrade plans to the tilt...lol Unless I REPO the V from her that is🤩

BTW, just coming off warranty in 1500 Miles thus I am free to mod to the max now. 

Edited by johnnyquick
SierraStorm21 Enthusiast

SierraStorm21

Posted
  • Author
Posted
1 minute ago, johnnyquick said:

Doing a Texas Speed dod delete kit and custom cam designed for use with the supercharger, and putting on Long tube headers and a heavy duty driveshaft as per LMR in Texas.

I am hoping to end up with 650Hp at the crank with all this and dyno tune with TCU tune as well.

Did you get any dyno numbers on yours?

 

Yeah that's the way to go.

 

I did, stock was 347.3 WHP / 388 /WTQ and after both the Whipple, Alky Control and custom tune, I was at 554 WHP / 504 WTQ. Using an online calculator, it estimates I'm at 670 HP / 610 TQ at the crank.

Who are you going with to do it?

  • Like 1
johnnyquick Enthusiast

johnnyquick

Posted
Posted
17 hours ago, SierraStorm21 said:

Yeah that's the way to go.

 

I did, stock was 347.3 WHP / 388 /WTQ and after both the Whipple, Alky Control and custom tune, I was at 554 WHP / 504 WTQ. Using an online calculator, it estimates I'm at 670 HP / 610 TQ at the crank.

Who are you going with to do it?

Same guy as you in Spokane is the plan!

kodiakdenali Enthusiast

kodiakdenali

Posted
Posted

Just stopped by over there to say hi and have him do a quick checkup on my setup yesterday. Couldn’t possibly recommend him more. Supercharged at around 2500 miles I think, a bit over 40k now. It's has been flawless.

  • Like 2

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share
Go to topic listing

  • Latest Articles

  • Posts

    • Atlas
      Wow I'm in a pickle. (Broke down truck) and a story.

      By Atlas · Posted

      So, do I go elbow-deep on this thing or list it for sale and play dumb? Seems to "runs good."   I'm about $1200 away from having: -a rebuilt injector ($300) -a new cat ($250) -a new cat back exhaust (OE style) ($300) -a new AC compressor ($200) -AC refrigerant charge ($150)   In theory, this should rectify the obvious detracting issues from its value and operability. Cold AC with a non-squeaking AC pulley both sounds and feels good. An exhaust that isn't cut/hacked in 17 different places and doesn't vibrate on a crossmember would make it sound and feel less janky. A working cat would help the stink, and will save the earth, but *if and only if* the fuel system is working properly, which would also address the intermittent "rich" CEL.   Heard a good one... CEL for "Rich condition" means you haven't spent enough money on the truck lately, and it's letting you know.   Rebuilding the injector would seem to be the most important part. Replacing the cat would be secondary. I don't think mine is plugged or overly restricted, but it might be a little restricted? I have no good way to tell other than seat of the pants feel. I hate the smell.   The current theory is I have a rich idle problem: A bad fuel pressure regulator, or a leaking injector(s) being the highest probabilities. I already replaced the FPR but that doesn't mean its replacement isn't also bad. It was a new part from Dorman, but the packaging looked like it had been sitting on a shelf for 20 years.   This is the (single) upstream O2 sensor shown at idle. I'm getting a lot of "rich" it seems. Sometimes it stays high like that and doesn't drop down. That makes me think it's processing injector leaks or a partially stuck open injector.     Other times it looks like this. Nice oscillations between rich and lean, which is what I think it should be. Under load and at speed, the oscillations are nice and tight and uniform looking, high and low.     Fuel trims suggest the PCM is compensating pretty hard at idle to pull fuel out. But it's not enough to trip a CEL. Something about slowing to a stop: brake vaccum booster, EGR, or the EVAP purge is delayed, or there's pooled fuel in the intake again that's draining into a cylinder is enough to set the CEL. Of course, in two days of driving, it hasn't set. I was hoping to actually look at the freeze-frame data when it sets. IAT is high because it's idling on an 83 degree day here.  
    • Another JR
      Gasser Subforum Has Been Quiet - - So, Regenerative Braking and Using L10

      By Another JR · Posted

      Have considered installing a DC to DC charger in your camper to replace your isolator?  
    • newdude
      Gas fill door

      By newdude · Posted

      Common failure.  You need to replace the fuel door housing.   The painted cover transfers over to the new housing.  To remove the old one there is 4 spots where you poke the plastic to release it.  
    • newdude
      Gasser Subforum Has Been Quiet - - So, Regenerative Braking and Using L10

      By newdude · Posted

      No such thing as regenerative braking on a pure ICE vehicle.     Regenerative braking is the re-capture of energy from electric motors and stores it in the battery pack.  So hybrids, PHEV and EVs have regenerative braking.     What you are seeing is the charging system changing modes is all.  Its likely entering charge mode for some sort of reason is all.  All of the charging modes will be listed below.   As for L10 vs D.  L10 turns off automatic grade braking.  L10 puts you in control of grade downshifts where in D it will automatically do it based on brake pedal position and other factors.  Otherwise L10 and D drive exactly the same aside from that one aspect.    Battery Sulfation Mode The BCM will enter this mode when the interpreted Generator output voltage is less than 13.2 V for 45 minutes. When this condition exists the BCM will enter Charge Mode for 2–3 minutes. The BCM will then determine which mode to enter depending on voltage requirements.   Charge Mode The BCM will enter Charge Mode when ever one of the following conditions are met:   Windshield wipers are ON for more than 3 s. Climate Control Voltage Boost Mode Request is true, as sensed by the HVAC control module via serial data. High speed cooling fan, rear defogger, and HVAC high speed blower operation can cause the BCM to enter the Charge Mode. The estimated battery temperature is less than 0°C (32°F). Battery State of Charge is less than 80%. Vehicle speed is greater than 145 km/h (90 mph) A current sensor malfunction exists. System voltage is determined to be below 12.56 V When any one of these conditions is met, the system will set targeted generator output voltage to a charging voltage between 13.9–15.5 V, depending on the battery state of charge and estimated battery temperature.   Fuel Economy Mode The BCM will enter Fuel Economy Mode when the estimated battery temperature is at least 0°C (32°F) but less than or equal to 80°C (176°F), the calculated battery current is less than 15 A and greater than −8 A, and the battery state-of-charge is greater than or equal to 80%. Its targeted generator output voltage is the open circuit voltage of the battery and can be between 12.5–13.1 V. When fuel economy mode is active, the generator is not charging, only maintaining open circuit battery voltage. The BCM will exit this mode and enter Charge Mode when any of the conditions described above are present.   Headlamp Mode The BCM will enter Headlamp Mode when ever the head lamps are ON (high or low beams). Voltage will be regulated between 13.9–14.5 V.   Start Up Mode When the engine is started the BCM sets a targeted generator output voltage of 14.5 V for 30 s.   Tow/Haul Mode (if applicable) Pressing the Tow/Haul Mode button located on the center stack, the vehicle system voltage is raised and the remote (non-vehicle) battery will be charged. Having the headlamps on will raise the system voltage and if the Tow/Haul button is applied it will not serve any purpose. The voltage is regulated between 13.9-14.5 V.      
    • jaszr2
      Active Grille Delete

      By jaszr2 · Posted

      Hello from Australia Just sharing that there is now a way to delete the active shutters entirely with just a plug in module. Opens up tons of room to light bars etc.

  • GM-Trucks.com Clubs

  • Popular Contributors

×
×
  • Create New...