Converting an L8T hood to a functional L5P intake (functional hood scoop).

revrnd · October 8, 2024

Re: Hoods, Hood Scoops & Marketing...

Didn't the 'post MCE' GMT800 HDs (@ least the Chevs) have a higher profile hood than the LDs? Then near the end of the model run, the 1500s got the higher profile.

As we worked to retool for the GMT900 during GMT800 production, a future Silverado and Sierra were brought in for display. There were a couple of GM staffers from the States answering questions. I noticed that the GMC had quite a depression in the hood when compared to the current hoods @ the time. I asked 1 of the guys the reason for the 'rain catcher'. 'It's in case they want to add a hood scoop (copying the Tacoma). I replied w/, "How about making tailgate cables that last?" That did not go over well. This was after the multi million recall which affected my truck @ the time. It suffered a broken cable when I dropped a snowmobile ramp on it. Thankfully I wasn't loading a sled as the tailgate didn't hit the bumper. As it was a black plastic hood scoop (non-functional?) was added to the Sierra HDs

Then you have the K2XX truck that differentiated the diesels from gassers w/ a functional hood scoop...

And now w/ the T1XX the braintrust says all HDs get the scoop...

TBH, if my truck didn't come with the non-functional hood scoop, it wouldn't have bothered me in the least.

Epsilon Plus · November 17, 2024

A little heat gun massage may have us back in business.

Stay tuned.

Epsilon Plus · November 17, 2024

PITA Hemholtz resonator is the next hurdle. Accordian plenum is a touch small and out of place. Will need to make a custom tube and get rid of that massive thing.

Epsilon Plus · November 17, 2024

It's only a 1.5 foot run. As ghetto as it sounds I might try a Fernco and 4" PVC run and if it works wrap it in carbon fiber tape or at least it will be a mock up for a spendy silicon pipe. I don't mind losing the big ugly Hemholtz. Will allow more intake noise. Just need to adapt (or delete) the PCV feed from the valve cover in that case.

Epsilon Plus · February 25, 2025

Got it functional. Been driving around for a couple days without a big fake Toyota scoop on the hood and it feels pretty good .

That said, it was definitely a B. The battery, the intake piping, and the oil cooler line are the biggest obstacles here. Everything else drops right in.

So with this I found out that diesels use a shorter H6 battery vs H7. About 1.5" different in length. Since my stock AGM battery is somehow still dropping 12.75v at rest after 3.5 years in Arizona, I can't bring myself to spend $250 to replace it. I chopped a couple tabs off in the battery tray (that I saved and can weld back on if needed) that allowed me to shift the battery back and then I trimmed the battery fuse block tray thing on the corner to allow the ants rearend fit. Unfortunately, the top cover is going to have to stay off until I get that smaller H6 battery in there. Kudos to GM for burying the battery in the back corner of the engine bay and taking the damn handle off it. Real fun to play with

Next was the intake piping. The TB is very close to clutch fan bracket. A custom intake pipe will need to be made that adapts to the TB and immediately short 90s or 22s away from that. I didn't want to spend another $180 on Airaids intake pipe kit with whoknows how many $20+ silicone couplers so I just used a 4" to 3.75" cup and choked it down on the stock Hemholtz resonator bellows. No leaks, no codes. Dirty engine bay. Hemholtz looks a little sideways in this pic, probably didn't have it on the pass side tab mount yet.

So, still some work to be done in the future. Need to make a custom intake tube that looks cleaner and delete the Hemholtz and need to address the battery area. Other than that, it's sucking hood air, baby!

Epsilon Plus · February 28, 2025

Pryme · February 28, 2025

38 minutes ago, Epsilon Plus said:

The intake air temp stock seems to always be the same as ambient. So would you call this just a ram air because I don’t see it being a cai?

Epsilon Plus · March 1, 2025

Ram air would only happen at jet aircraft speeds. Something like this would be beneficial under full towing load on a hot day up a hill or something.

More beneficial with more mods (supercharger, large cam...etc).

Mostly it's just to know that it's not a big fake scoop anymore and that up until the airbox part, it was simple drop in swap stuff.

Griffs55 · June 13, 2025

On 3/1/2025 at 2:31 PM, Epsilon Plus said:

Ram air would only happen at jet aircraft speeds. Something like this would be beneficial under full towing load on a hot day up a hill or something.

More beneficial with more mods (supercharger, large cam...etc).

Mostly it's just to know that it's not a big fake scoop anymore and that up until the airbox part, it was simple drop in swap stuff.

Did you notice any boost in power or fuel economy?

Epsilon Plus · June 17, 2025

No. The gains, if any, won't show themselves until after headers, cam, proper unrestrictive tune, anything that makes the engine truly breathe better.

Maybe one day I'll get rich and stick 2" primary headers, an LT2 cam, and a real tune on the truck but I don't think the 10.5-11mpg I average now is going to get any better

Epsilon Plus · July 27, 2025

H6 battery size worked perfect. Clipped a centering pin off the bottom of the hold down and grinded off two tabs inside the battery tray that were meant to hold the original longer H7 size. With that done, the H6 slid into factory diesel position complete with a pre tapped hold down bolt hole. This allowed the perfect factory clearance of the diesel airbox to battery and allowed me to snap back down the battery/fuse cover.

Everything is zipped up and fully functional, so here it is. The worlds first (I guess) L8T with fully functional L5P intake. I suppose if I wanted to keep playing with it I could make a custom intake tube and ditch the Helmholtz resonator, but for now I'm happy. Full parts list and bullet point how-to to follow as soon as I find time.

EXSlider400 · July 28, 2025

Excellent job I’d much rather use factory parts. This is the next thing on my list. Let us know if you notice any MPG or other changes. Thanks again.

Epsilon Plus · August 7, 2025

Ok, so after identifying and tracking down the last part I needed (the intake portion under the vanity vent that is a closeout to the bare hood), I finally have a completed parts list. Without further ado:

84520314 - Bright Chrome Hood Ornamentation Vent
85126004 - Rear Intake Air Duct
84684674 - Front Intake Air Duct
84670713 - Intermediate Intake Air Duct
85614333 - Air Cleaner
84182769 - Hood Insulator
84496061 - Front Intake Air Duct Cover
85135957 - Front Intake Air Duct Adapter
11611677 - Hood Insulator Retainer (11)
11612035 - Push-Pin (4)
11570015 - M6x1.0 Cage Nut (8)
11570173 - M6x1.0x30mm Flanged Bolt (8)
Non-GM: Straight Reducer Coupler Silicone Hose ID 3-3/4-inch to 4-inch 4-Ply with Stainless Steel T-Bolt Clamp for Turbo/Intercooler/Intake Piping - This is for clamping the large side to the airbox and sticking the small side in the stock airduct and synching it down on it.
H6 Battery

My total cost shipped for everything was $671.95. The prototype GM kit for this that was never released is listed at $820+ About double the cost of an S&B. The value of having a functional hood? Priceless. You could probably save a bunch of money going to a junkyard and gutting a hood for the intakes, grab the airbox, the vanity hood vent thing that sucks to buy since its an accessory and therefore overpriced...etc.

Yeah, yeah, cue all the "it doesn't do anything! Stock is fine! Waste of money!". Yes. I'm well aware of the target demographic of this truck. Settle down Grandpa, some of us like to hotrod, mod and experiment with stuff. Remember what that was like?

I shipped some things to the house through GMpartsdirect and other things I bought through parts.gm official and sent to the dealer. Things like the hood insulator are like $35 total dollars amazingly but obviously its a million dollars to ship, so that's a good dealer item. The (4) push pins are to hold down the aforementioned "Air Duct Adapter" under the vanity Vent. The nuts and bolts are for bolting the intake to the hood. Sizes are listed because these little things cost a fortune from GM but are super cheap through Amazon (get the push pins there too. Look the part number up you'll know what they are. Now that the hood has a proper closeout to the intake who knows, maybe I'll get some super-duper power from it. Looks like its very engineered with little deflectors and what-not placed in it for smoothing.

For those that take this on. Maybe wait until you need a battery or if you plan to do this mod, replace your stock H7 with an H6 size. There are two standoffs inside the battery tray that you can grind off so the battery will slide back all the way. After that, the front hold down goes back with it and there is a threaded hole for it. Top hold down remains. Other than that, the major DIY part of this that doesn't just drop in is heating up the front of the diesel airbox where it interferes with the oil cooler pipe with a heat gun and pressing it back with a can or something contoured.

Post questions in this thread. Also, if you make a custom intake tube to the TB post that too so I can copy it lol. We'll need a SAE J2044 quick connect fitting to deal with the PCV and a silicone coupling that fits over the 3 & 7/8 TB. Need about 14" of intake piping. Probably a sharp 90 off the TB to clear the clutch fan bracket then a straight shot to the airbox if we're lucky. Hopefully don't need 22s to make the angle.

Cheers.

Edited August 7, 2025 by Epsilon Plus

mrjulian416 · August 28, 2025

On 8/7/2025 at 7:15 PM, Epsilon Plus said:

Yeah, yeah, cue all the "it doesn't do anything! Stock is fine! Waste of money!". Yes. I'm well aware of the target demographic of this truck. Settle down Grandpa, some of us like to hotrod, mod and experiment with stuff. Remember what that was like?

But, it doesn't do anything. Stock is fine. Seems like a waste of money.

I kid, I kid