- +True 100% bolt-on install for 2020-2026 GM HD trucks — no drilling, cutting, or welding
- +Demon Model 730 stainless triple horns, Kleinn's loudest at a rated 157.8 dB at 150 PSI
- +200 PSI 6450RC waterproof compressor rated for 100% duty cycle
- +Full onboard-air package: 1/2-inch Max-Flow line, 24-foot hose, inflates up to 39-inch tires
- +Spare tire location is retained — no trade-off under the bed
- +Extended two-year warranty on the 6450-series compressor and 730 horns
- −Expensive at $1,299.95, and the horns alone are $599.95 of that
- −157.8 dB rating is published without a test distance
- −No chord frequency (Hz) data for the three trumpets
- −Kit page itself doesn't restate tank capacity or dB — specs are split across Kleinn's component pages
- −Easy to confuse with the separate GMHD-734 kit for 2007-2019 GM HD trucks
Methodology
This review aggregates publicly available information from manufacturer specifications, retailer listings, and verified user reviews. We do not perform hands-on testing. Last reviewed: August 23, 2026. Specs below come from Kleinn’s official 2020-2026 GM 2500HD/3500HD kit page and Kleinn’s component pages for the Demon 730 horns and 6450RC compressor, plus Kleinn’s official installation demo video. Every source is listed at the end.
Quick verdict
The Kleinn GMHD20-734 is one of the most complete factory-engineered train horn packages you can bolt onto a late-model GM heavy-duty truck, and it earns a 4.3/5 from us. You get Kleinn’s flagship Demon 730 stainless triple horns, a 200 PSI waterproof compressor rated for 100% duty cycle, and a real onboard-air system that inflates up to 39-inch tires — all on vehicle-specific brackets that require no drilling, cutting, or welding. The $1,299.95 price is serious money, but compared with piecing together the same components separately (the horns alone sell for $599.95), the kit math is defensible. Our main gripes are documentation, not hardware: the loudness rating has no test distance, and the kit page scatters key specs across other Kleinn pages.
What it is
The GMHD20-734 (SKU KL GMHD20-734) is a vehicle-specific train horn and onboard air system engineered for 2020-2026 Chevrolet Silverado and GMC Sierra 2500HD/3500HD trucks. This review covers that generation only — Kleinn sells a separate, similarly named GMHD-734 kit for 2007-2019 GM HD trucks, and the two are not interchangeable.
It is the top variant on Kleinn’s GM HD page. The same product page offers three configurations: the Model 730 system reviewed here ($1,299.95), a Beast Series Model 230 system with ABS horns and a 150 PSI compressor (KL GMHD20-230, $999.95), and an air-only system with no horns (KL GMHD20-OBA, $799.95). The 734 version pairs the Demon Model 730 — Kleinn’s loudest published horn, a stainless-steel triple rated at 157.8 dB when fed 150 PSI — with the 6450RC compressor and a 1/2-inch “Max-Flow” air line. The whole system mounts under the truck on powder-coated steel brackets, Kleinn’s page emphasizes “clean, stealth, under-truck mounting,” and the spare tire stays where it is. Shipping weight is a substantial 80 lb, which tells you this is a full air system, not a pair of trumpets and a hose. The kit is listed in stock on Kleinn’s site as of this review. This is a kit for an owner who wants both maximum horn output and working onboard air — tire inflation, air tools — from one installation. For the broader brand picture, see our Kleinn reviews hub and our Kleinn vs HornBlasters comparison.
Specifications
| Spec | Value |
|---|---|
| Part number | KL GMHD20-734 |
| Fitment | 2020-2026 GM 2500HD/3500HD (Silverado / Sierra) |
| Horns | Demon Model 730, triple trumpet, stainless steel & zinc alloy |
| Rated output | 157.8 dB at 150 PSI (test distance not disclosed) |
| Horn rack dimensions | 22.5” L × 18.5” W × 7.25” H |
| Compressor | Kleinn 6450RC, 200 PSI, 100% duty cycle, waterproof/submersible |
| Air tank | 3-gallon class steel tank (capacity not restated on the 2020-2026 kit page) |
| Air line | 1/2” Max-Flow high-flow line |
| Tire inflation | Up to 39” tires; 24-ft quick-connect hose + luminescent-gauge inflator |
| Solenoid | VX6003 electric solenoid valve (Demon 730 spec) |
| Install | 100% bolt-on — no drilling, cutting, or welding; spare tire retained |
| Shipping weight | 80 lb |
| Price | $1,299.95 (Kleinn direct, in stock) |
| Warranty | 1-year limited kit warranty; extended 2-year on 6450-series compressor and 730 horns |
A note on the two numbers buyers care about most: the 157.8 dB figure comes from Kleinn’s standalone Demon 730 horn page, which discloses the pressure (150 PSI) but not the microphone distance — see our guide on advertised vs real-world decibels. The 3-gallon tank size likewise comes from retailer listings for the 734 kit family rather than being restated on the 2020-2026 kit page itself.
What’s in the box
- Demon Model 730 stainless-steel triple train horns on a vehicle-specific rack
- Kleinn 6450RC waterproof 200 PSI, 100%-duty-cycle air compressor
- Steel air tank with fittings
- Powder-coated, vehicle-specific bolt-on mounting brackets
- 1/2” Max-Flow air line and pressure switch (automatic compressor control)
- Complete wiring: relay, wires, loom, and fittings
- Heavy-duty 24-ft kink-resistant air hose with quick-connect couplers
- Tire inflator with glow-in-the-dark luminescent gauge
- Quick-connect coupler relocation kit with 12-ft airline and fittings
- Kleinn canvas storage bag
Pros
- Genuine 100% bolt-on engineering for one specific truck platform — no fabrication, no drilling, no welding
- Demon 730 stainless horns are Kleinn’s loudest published model, and the rating discloses its pressure (150 PSI)
- 100%-duty-cycle 6450RC compressor can run continuously — no thermal-cutout wait between tank refills
- Doubles as a legitimate onboard-air rig: 39-inch tire capability, 24-ft hose, quick-connect inflator included
- Spare tire stays in place, which vehicle-specific kits don’t always manage
- Two-year extended warranty on the two most expensive components (compressor and horns)
Cons
- $1,299.95 is a significant premium over universal triple-horn kits of similar loudness class
- No test distance published with the 157.8 dB rating, so cross-brand comparison is guesswork
- No chord frequency (Hz) data for the trumpets
- The kit page itself omits tank capacity and dB — you have to chase Kleinn’s component pages for them
- Part-number confusion risk: GMHD-734 (2007-2019) and GMHD20-734 (2020-2026) are different kits
Alternatives
- Kleinn GMHD20-230 (Beast Series) — same page, same bolt-on brackets and truck fitment, but with ABS Beast 230 triple horns, the 150 PSI 6350RC compressor, 1/4” line, and 35-inch tire capability for $999.95. The sensible pick if you want the fitment without the flagship price.
- Kleinn SDKIT17-734 — the same Demon 730 + 6450RC architecture packaged for 2017+ Ford Super Duty trucks; our full review is at /reviews/kleinn-sdkit17-734/.
- HornBlasters Conductor’s Special 544 Nightmare — the main cross-brand rival for maximum loudness with a big air system, though it’s a universal kit rather than a bolt-on; see /reviews/hornblasters-conductors-special-544-nightmare/.
Install / compatibility notes
Pin your generation first. This kit is P/N KL GMHD20-734 and fits 2020-2026 GM 2500HD/3500HD trucks. If your truck is a 2007-2019 Silverado or Sierra HD, you need Kleinn’s separate GMHD-734 kit, which is sold on a different product page. Ordering by the “734” alone is how buyers end up with brackets that don’t line up.
The system is electrically a standard 12V install: the included pressure switch cycles the compressor automatically, and the relay, loom, and wiring come in the box. The 6450RC is waterproof/submersible, which matters because everything lives under the truck in road-spray territory. Kleinn’s official demo video for the GMHD20 system walks through the mounted layout on the truck. Because the horns are plumbed with 1/2-inch line and fed up to 200 PSI, this kit sits at the top of the pressure range we cover in our train horn PSI guide — and the 100%-duty compressor spec is exactly what our duty-cycle explainer recommends for onboard-air use. After mounting, do a first fill and leak check before buttoning everything up (our bench-test guide covers the routine). For horn-only detail on the Demon 730 itself — finish options, solenoid, BlastMaster upgrade — see our standalone Demon 730 review.
A last buying note: at 80 lb shipped, freight damage is worth checking for on delivery, and the bag-and-inflator accessories make the bed-mounted quick-connect genuinely usable for trail airing-up — the use case we detail in train horn onboard air uses.
Sources
- Kleinn — Direct Fit Train Horn and Onboard Air Systems for 2020-2026 GM 2500HD/3500HD — official kit page: SKU KL GMHD20-734, $1,299.95, variants (GMHD20-230 $999.95, GMHD20-OBA $799.95), 6450RC 200 PSI compressor, 1/2” Max-Flow line, 39” tire inflation, included items (24-ft hose, luminescent-gauge inflator, coupler relocation, wiring, storage bag), bolt-on/no-drill claims, spare-tire retention, 80 lb shipping weight, stock status, warranty terms
- Kleinn — Model 730 “Demon” Stainless Steel Triple Train Horns — horn rating (157.8 dB at 150 PSI; 159.6 dB with BlastMaster upgrade), stainless/zinc construction, 22.5” × 18.5” × 7.25” rack dimensions, VX6003 solenoid, 200 PSI max, $599.95 standalone price, 2-year warranty
- Kleinn — Model 6450RC waterproof air compressor — compressor specs: 200 PSI, 100% duty cycle, submersible, $299.95
- Kleinn — Train Horn & Onboard Air System for 2007-2019 GM 2500HD/3500HD — the separate previous-generation GMHD-734 kit, cited for the generation/part-number distinction
- Offroad Alliance — Kleinn GMHD-734 Train Horn and Onboard Air System — retailer cross-check for the 734 kit family’s 3-gallon steel made-in-USA tank and previous-generation fitment
- YouTube — KLEINN GMHD20 TRAIN HORN AND ONBOARD AIR SYSTEMS FOR 2020-2024 GM 2500HD/3500HD (Kleinn official channel) — manufacturer demo of the mounted GMHD20 system layout
Train Horn Hub aggregates publicly available data. We do not test products in-house. All trademarks belong to their respective owners.
The GMHD20-734 is the right pick for a 2020-2026 Silverado or Sierra 2500HD/3500HD owner who wants Kleinn's loudest horn plus a genuine 100%-duty onboard air system in one no-drill, vehicle-specific package — just confirm the GMHD20 part number, because the similarly named GMHD-734 fits the previous truck generation.
Frequently asked questions
Quick answers to the questions people ask most about this topic.
- How loud is the Kleinn GMHD20-734 really?
- The kit's Demon Model 730 horns are rated by Kleinn at 157.8 dB when fed 150 PSI, with no test distance disclosed. Treat that as a manufacturer rating rather than a field measurement — real-world loudness at the curb depends on mounting location and tank pressure.
- Will the GMHD20-734 fit my 2018 Silverado 2500HD?
- No. The GMHD20-734 fits 2020-2026 GM 2500HD/3500HD trucks only. Kleinn sells a separate GMHD-734 kit for 2007-2019 GM HD trucks on a different product page, and the mounting brackets are not interchangeable between generations.
- Can the GMHD20-734 inflate truck tires?
- Yes. Kleinn rates the 734-series system for tires up to 39 inches, driven by the 200 PSI, 100%-duty-cycle 6450RC compressor. The kit includes a 24-foot quick-connect air hose, a tire inflator with a luminescent gauge, and a coupler relocation kit.
- Do I lose my spare tire with this kit?
- No. Kleinn's product page states the spare tire is retained — the compressor, tank, and horns mount under the truck on vehicle-specific bolt-on brackets without displacing the spare.
- What warranty does the GMHD20-734 come with?
- Kleinn lists a one-year limited defect warranty on the kit, with extended two-year coverage on the 6450-series compressor and the Model 730 horns.
