- +All-metal, chrome-plated trumpet built for exposed roof mounting
- +Chrome front pedestal bracket supports the 28-inch trumpet against vibration
- +Front deflector cover and rubber gaskets for rain, bugs and roof leaks
- +Air feed enters through the horn base, so no hose shows on the roof
- +Wolo states the 90/100 PSI test pressure behind the 130 dB rating
- −Wolo's own page lists two frequencies: 285 Hz and 320 Hz
- −No test distance disclosed for the 130 dB rating
- −Horn only: compressor, tank and valve are extra
- −Wolo recommends a two-horn set with the 825, doubling the horn cost
- −Three-month factory warranty with a $10 return-shipping fee
- −Out of stock at Wolo and NAPA on 10/10/2026, with no public owner reviews
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 10/10/2026. For the Wolo 820 Giant we took the core specifications from Wolo Manufacturing’s current Model 820 product page and the official Model 820-825 installation sheet, which also states the warranty terms. We cross-checked price, finish and availability against NAPA’s listing, and we used Wolo’s pages for the matching 825 high-tone horn, the 827 low/high set and the 820-858 Giant Pro kit to fill in context. NAPA shows no customer ratings for this horn yet, and we found no substantial owner reviews, so this review leans on published specs rather than user reports. Every figure below traces back to a source listed at the end of the article.
Quick verdict
The Wolo 820 Giant is a single, 28-inch chrome trumpet built to bolt onto a truck roof. Wolo rates it at 130 dB at 90/100 PSI but does not say at what distance. It is a horn only: no compressor, tank or valve in the box. We rate it 3.2/5. The all-metal chrome build, front support bracket and rain deflector make sense for a roof-mounted horn. Against that, Wolo’s own spec sheet contradicts itself on frequency (285 Hz in the title, 320 Hz in the spec table), the factory warranty is only three months, and Wolo advises installing the 820 as a pair with the 825 high-tone horn for the best sound. That pair costs more than one horn. In our editorial opinion, buy it for a classic big-rig roof-horn look if you already run onboard air. Don’t buy it as a cheap route to a train-horn chord.
What it is
The Giant is Wolo’s roof-mount truck air horn line. The Model 820 is the low-tone version, and the Model 825 is its shorter high-tone partner. Per Wolo’s product page, the 820 is “all metal construction chrome plated throughout.” It ships with a chrome-plated metal front pedestal support that Wolo says helps “eliminate trumpet vibration at high speeds and on the roughest roads,” plus a front deflector cover to keep rain, road dirt, snow and bugs out of the trumpet. The air feed enters through the base of the horn, so no hose is visible above the roof line once it’s installed.
The retail box in Wolo’s product photo labels the 820 “Low Frequency,” “Roof Mount Air Horn” and “Requires an onboard air system.” That framing matters. This is a single-trumpet truck air horn, not a three- to five-chime locomotive-style chord horn like most products on this site. One trumpet gives one note. Wolo’s own page states: “For best sound results, always install the Giant as a set one high tone and one low tone.” The two-horn set is sold as the Model 827, and the 820-858 Giant Pro is a complete kit with an air system.
Who it suits: pickup, semi and RV owners who want a visible chrome roof horn and already have (or plan to buy) a compressor, tank and valve. If you’re still choosing between this kind of horn and a multi-trumpet kit, our train horn vs air horn guide explains the difference.
Specifications
| Spec | Value |
|---|---|
| Model | 820 Giant (low tone) |
| Type | Single-trumpet roof-mount air horn |
| Sound output | 130 dB at 90/100 PSI (test distance not disclosed) |
| Frequency | 285 Hz in the product title and 320 Hz in the spec table, both on Wolo’s own page (see note below) |
| Horn size | L 28 in. × W 8-1/4 in. × H 4-1/2 in. |
| Weight (listed) | 7 lb |
| Shipping dimensions (listed) | 30 × 6 × 10 in. |
| Construction | All metal, chrome plated (NAPA lists a stainless steel trumpet with chrome finish) |
| Air inlet | Flexible inlet hose with brass fittings, connected through the horn base |
| Valve / solenoid | Not included |
| Power source | Onboard air system (compressor + tank), sold separately |
| Wolo-recommended air systems | Models 840, 858 or 860 |
| Wolo list price | $129.99 (shown out of stock on 10/10/2026) |
| NAPA price | $118.23 with free shipping (shown out of stock on 10/10/2026) |
| Warranty | 3 months per Wolo’s instruction sheet; NAPA’s listing says 1 year |
| UPC | 080217008204 (per NAPA) |
About the frequency conflict. Wolo’s Model 820 page carries “285 Hz” in its title but “320 Hz – Low Range” in its spec block. The Model 827 set page, which pairs an 820-style low tone with an 825 high tone, gives the low horn as 285 Hz and 28-1/2 in. long, and the high horn as 330 Hz. On the standalone 825 page, Wolo labels its 330 Hz horn “Low Range.” The 820 description also says the Giant “produces a powerful high tone truck horn sound,” text that matches the 825 page word for word. Our reading is that 285 Hz is the more likely figure for the low horn, since two Wolo pages agree on it. Still, the manufacturer hasn’t settled it publicly, so confirm with Wolo’s tech line before you buy if pitch matters to you.
What’s in the box
Per Wolo’s product page and NAPA’s listing, the standalone 820 includes:
- One chrome-plated Giant low-tone trumpet
- Chrome-plated metal front pedestal (trumpet support) bracket
- Front deflector cover against rain, dirt, snow and bugs
- Flexible inlet hose with brass fittings (thread end pre-wrapped with Teflon tape, per the instructions)
- Stainless steel mounting hardware
- Rubber gaskets for a watertight roof installation
- Instructions in English and Spanish
Not included: a compressor, air tank, solenoid or lanyard valve, air line from the tank, wiring, or the matching 825 high-tone horn.
Pros
- All-metal, chrome-plated construction intended for exposed roof mounting in all weather
- Front pedestal bracket supports the long trumpet against vibration at speed
- Front deflector cover and rubber gaskets address rain, bugs and roof leaks
- Air feed enters through the base, so no hose is visible on the roof
- Wolo states the operating pressure (90/100 PSI) behind the 130 dB rating
- Stainless mounting hardware and a simple six-step install sheet
Cons
- Wolo’s own page lists two different frequencies (285 Hz and 320 Hz)
- The 130 dB rating has no stated test distance
- Horn only: compressor, tank and valve add a lot to the cost
- Wolo recommends running it as a pair with the 825, which doubles the horn cost
- Three-month factory warranty with a $10 return-shipping fee on claims
- Out of stock at both Wolo and NAPA on 10/10/2026, and no public owner reviews
How loud is “130 dB” here?
Wolo publishes 130 dB “with 90/100 psi,” which is more than many budget brands disclose. It still leaves out the measurement distance, and the distance changes the number a lot. For context, Wolo gives the same 130 dB at 90/110 PSI for the four-trumpet 853 Philly Express, and 125 dB for the self-contained 845 Road Warrior DD. The numbers are only comparable within Wolo’s own catalog, and only if Wolo used the same test setup across models, which it doesn’t say. A single trumpet also produces one note, so even at a similar dB rating it won’t sound like a chord horn. Our guide to advertised vs real train horn dB explains why spec-sheet figures rarely match roadside measurements.
Alternatives
- Wolo 825 Giant (high tone): same Giant body at 24-1/2 in. long, listed at 330 Hz and 130 dB, $129.99 at Wolo. It isn’t a substitute so much as the partner Wolo tells you to install alongside the 820.
- Wolo 827 Giant Pro set: a low-tone and a high-tone Giant with a heavy-duty 12-volt solenoid valve, listed at $249.99 (12 lb listed weight). If you plan to follow Wolo’s own advice and run a pair, this is the cleaner buy. You still need an air system.
- Wolo 820-858 Giant Pro kit: the 820 bundled with Wolo’s 858 Tornado air system and a 12-volt solenoid, listed at $329.99. It includes everything needed to sound the horn.
- Wolo 845 Road Warrior DD: a single chrome trumpet (125 dB, 275 Hz, 21-1/2 in.) with its own direct-drive 12-volt compressor, $158.99 at Wolo. It suits buyers who want a deep roof-style horn without installing a tank.
- Wolo 853 Philly Express: four compact chrome trumpets (290/421/548/648 Hz, 130 dB at 90/110 PSI) for $119.99. It’s the better pick if you want an actual chord for roughly the same horn-only price.
Wolo’s smaller 12-volt horns, such as the 417 Long Horns and the 619 Big Bad Max, are self-contained factory-horn upgrades rather than roof horns. All Wolo models we cover are on the Wolo brand hub.
Install / compatibility notes
You need a complete air system. Wolo’s page states that the Giant “requires an on-board air system” and recommends its Models 840, 858 or 860. Per Wolo’s pages:
- Wolo 840 Turbo
- 5.5 L tank, 2.03 CFM, 12 A, 80 PSI on / 110 PSI off, $249.99
- Wolo 858 Tornado
- 2.5 gal tank, 2.55 CFM, 21 A peak, 33% duty cycle at 100 PSI, $264.99
- Wolo 804-EV valve
- 12 V solenoid, 2.9 A, brass fittings for 1/4 in. O.D. hose, $51.99
The horn itself has no electrical parts. It needs a valve between the tank and the horn’s inlet hose: a 12-volt solenoid such as the 804-EV if you want to sound it from a button, or a lanyard valve for a pull-cord setup (Wolo sells the lanyard version of the kit as the 821-858). Wire the solenoid through a relay and a fused feed. Our train horn relay wiring guide covers this, and solenoid valve sizing explains how to match the valve to the line. For compressor choice in general, see our compressor buying guide and how big an air tank you need.
Roof mounting means drilling. Wolo’s installation sheet calls for these steps:
- Choose a spot where the front of the horn is unobstructed so the sound projects straight ahead.
- Use the horn’s rubber gasket as a drilling template, then bolt the horn down with the supplied hardware, tightening the screws evenly.
- Fit the rubber molding strip into the front trumpet support bracket, slide it onto the narrow part of the trumpet, and use the bracket as a second drilling template.
- Bolt the support bracket down, again with its rubber gasket to prevent water leaks.
- Thread the flexible inlet hose into the horn base. Don’t remove the Teflon tape, and avoid kinks or sharp bends that reduce airflow and can change the sound.
- Connect the other end of the hose to the valve fed by the onboard air tank.
Drilling a cab roof is permanent, so seal every hole and route the air line away from heat. See our guides on where to mount a train horn on a truck and train horn waterproofing. A 28-inch trumpet suits full-size pickup, semi and RV roofs better than small cabs. Measure your roof before ordering. Horn-use rules vary by state, so check our state legality pages before you sound it on public roads.
Warranty logistics. Per Wolo’s instruction sheet, the three-month warranty covers the original purchaser. Claims need the product returned prepaid with the original bill of sale, a short description of the problem, and a $10 check or money order for return shipping. NAPA’s listing advertises a 1-year warranty, so if a longer term matters, confirm with the retailer which terms apply to your purchase.
Sources
- Wolo Manufacturing — Model 820 Giant Low Tone product page — 130 dB at 90/100 PSI, conflicting 285 Hz / 320 Hz frequency, 28 × 8-1/4 × 4-1/2 in. size, 7 lb weight, shipping dimensions, all-metal chrome construction, front pedestal support and deflector, included items, recommended air systems, pair-installation advice, $129.99 list price, stock status, product photo
- Wolo Manufacturing — Model 820-825 Giant installation instructions (PDF) — six-step roof-mount procedure, gasket and bracket templates, Teflon-tape and hose-kink cautions, three-month warranty, $10 return-shipping fee, tech support line
- Wolo Manufacturing — Model 825 Giant (high tone) product page — 330 Hz, 24-1/2 in. length, 130 dB, $129.99, recommended Model 840 air system
- Wolo Manufacturing — Model 827 Giant Pro low/high set — 285 Hz low / 330 Hz high, 28-1/2 in. low-tone length, 12-volt solenoid, $249.99, 12 lb
- Wolo Manufacturing — Model 820-858 Giant Pro kit — 820 bundled with the 858 air system and 12-volt solenoid, $329.99
- Wolo Manufacturing — Model 821-858 Giant Pro lanyard kit — lanyard-valve version of the Giant Pro kit with the 858 air system
- Wolo Manufacturing — Model 858 Tornado compressor and 2.5-gallon tank — 2.55 CFM, 21 A peak, 33% duty cycle at 100 PSI, $264.99
- Wolo Manufacturing — Model 840 Turbo compressor and tank — 5.5 L tank, 2.03 CFM, 12 A, 80/110 PSI switch points, $249.99
- Wolo Manufacturing — Model 804-EV 12-volt solenoid air valve — 12 V, 2.9 A, brass fittings for 1/4 in. O.D. hose, $51.99
- Wolo Manufacturing — Model 845 Road Warrior DD — 125 dB, 275 Hz, 21-1/2 in. horn, direct-drive compressor, $158.99
- Wolo Manufacturing — Model 853 Philly Express — 130 dB at 90/110 PSI, 290/421/548/648 Hz, $119.99
- NAPA Online — Wolo Giant Air Horn 820 — $118.23 with free shipping, stainless steel trumpet with chrome finish, roof-mount pedestal, inlet hose and hardware included, 1-year warranty claim, UPC, out-of-stock status, no customer ratings
Train Horn Hub aggregates publicly available data. We do not test products in-house. All trademarks belong to their respective owners.
The Wolo 820 Giant suits truck and RV owners who already run onboard air and want a classic chrome roof horn with a single low note. Buyers after a train-horn chord or a complete kit should look at the 827 set, the 820-858 Giant Pro or a multi-trumpet Wolo instead.
Frequently asked questions
Quick answers to the questions people ask most about this topic.
- How loud is the Wolo 820 Giant?
- Wolo rates the 820 at 130 dB with 90/100 PSI of air pressure but does not disclose the distance the measurement was taken at. Treat it as a manufacturer claim rather than a figure you can compare directly with horns rated at a stated distance.
- Is the Wolo 820 285 Hz or 320 Hz?
- Wolo's own Model 820 page lists both: 285 Hz in the product title and 320 Hz in the spec table. Wolo's Model 827 set page also gives the low-tone Giant as 285 Hz, so that figure has more support, but confirm with Wolo before buying if exact pitch matters.
- Does the Wolo 820 come with a compressor or valve?
- No. The standalone 820 includes the horn, a chrome front support bracket, a deflector cover, a flexible inlet hose, stainless mounting hardware and rubber gaskets. You need an onboard air system (Wolo recommends its Models 840, 858 or 860) plus a solenoid or lanyard valve. The 820-858 Giant Pro kit at $329.99 bundles the horn, an 858 air system and a 12-volt solenoid.
- Should I buy one Giant or a pair?
- Wolo's product page advises installing the Giant as a set of one high tone (Model 825, 330 Hz) and one low tone (Model 820) for the best sound. Wolo sells that pair with a 12-volt solenoid as the Model 827 for $249.99.
- What warranty does the Wolo 820 have?
- Wolo's installation sheet gives the original purchaser a three-month warranty against defects in materials and workmanship. Claims require a prepaid return with the bill of sale and a $10 check or money order for return shipping. NAPA's listing advertises a 1-year warranty, so confirm the terms with your retailer.
