---
title: "Bentley 4½ Litre "Blower" · HICONIUM"
description: "Tim Birkin and Amherst Villiers put a Roots supercharger ahead of the radiator, nearly doubling the 4½ Litre's road output. Original road cars, team cars, later conversions and modern Continuations require separate pricing."
canonical_url: https://hiconium.dev/vehicles/bentley/41-2-litre-blower
image: https://hiconium.dev/og/vehicle/bentley/41-2-litre-blower.png
---

> HICONIUM · Index: https://hiconium.dev/llms.txt · Every page: append `.md` or send `Accept: text/markdown`.
> Path: [Home](https://hiconium.dev/) › [Vehicles](https://hiconium.dev/models) › [Bentley](https://hiconium.dev/manufacturers/bentley) › 4½ Litre "Blower"
> On this page: [The price and the proof](#the-price-and-the-proof) · [Model readouts](#model-readouts) · [Documented sales](#documented-sales) · [Birkin chose pressure where W.O. Bentley chose capacity.](#overview-heading) · [Technical specifications](#technical-specifications) · [Powertrain](#powertrain) · [Chassis](#chassis) · [The people behind the car](#the-people-behind-the-car) · [Sir Henry "Tim" Birkin](#sir-henry-tim-birkin) · [Amherst Villiers](#amherst-villiers) · [Dorothy Paget](#dorothy-paget) · [Woolf Barnato](#woolf-barnato) · [Member instruments](#member-instruments)

![A dark green Bentley 4½ Litre Blower, front three-quarter view on a british-green field with an amber band](https://hiconium.dev/images/cars/bentley-41-2-litre-blower/hero-wide-2560.jpg)

# 4½ Litre "Blower"

Supercharged against W.O.'s judgement

Tim Birkin and Amherst Villiers put a Roots supercharger ahead of the radiator, nearly doubling the 4½ Litre's road output. Original road cars, team cars, later conversions and modern Continuations require separate pricing.

1929 to 1931 · 55 built · Cricklewood and Welwyn

## The price and the proof

Indicative road-car band $3.5M–$7M · typical $5M · 2 documented road sales · 2 recorded sales on file. Modeled values are not observed sales. Nothing here is investment advice.

Confidence: low. The two strongest documented USD sales are from 2007 and 2015, while a third result shows the discount for a production car rebuilt in team style. Public trades are too sparse and old for a tighter current band.

USD; original factory-supercharged road cars with documented identity. Team cars sit outside the band.

Original road cars and Birkin team cars are separate markets; later conversions are not Blower comparables.

Valuation method and source rules: [HICONIUM standards](https://hiconium.dev/standards). Observed auction results across the wider market: [Market terminal](https://hiconium.dev/market).

### Model readouts

2 documented anchors. model v1 · seed bentley-41-2-litre-blower. Compound annual growth is modeled price CAGR; S&P 500 is a price index without dividends. Forecast quantiles are not investment advice.

| Window | This car* | S&P 500 | Gold |
| --- | --- | --- | --- |
| 1Y | +107.4% | +18.8% | +21.9% |
| 5Y | +86.7% | +11.4% | +17.6% |

| Series | Deepest drawdown | Window |
| --- | --- | --- |
| This car* | -0.6% | Feb 2020 → Mar 2020 · recovered Apr 2020 |
| S&P 500 | -20.3% | Dec 2021 → Oct 2022 · recovered Dec 2023 |
| Gold | -18.9% | Feb 2026 → Jul 2026 · not recovered |

| Horizon | P10 | P50 | P90 |
| --- | --- | --- | --- |
| +6M | $4'772'180 | $5'204'054 | $5'675'011 |
| +12M | $4'862'392 | $5'416'435 | $6'033'608 |
| +24M | $5'056'369 | $5'867'554 | $6'808'877 |

### Documented sales

2 recorded. Every public sale on this file, newest first. Amounts keep the recorded currency. Source links appear only when the catalog stores a public auction-lot URL.

| Date | Chassis / label | Class | House | Venue | Amount | Currency | Basis | Source |
| --- | --- | --- | --- | --- | --- | --- | --- | --- |
| 2026-07-25 | 2026 | Road | Iconic Auctioneers | BRDC Classic 2026, Silverstone, UK | £393'750 | GBP | incl. buyer's premium | [https://www.iconicauctioneers.com/1927-bentley-4-litre-blower-rec17068-1-silverston-0726](https://www.iconicauctioneers.com/1927-bentley-4-litre-blower-rec17068-1-silverston-0726) |
| 2016-10-07 | bonhams · Knokke-Heist, Le Zoute · hammer | Road | bonhams | Knokke-Heist, Le Zoute | €8'000 | EUR | hammer | [https://cars.bonhams.com/auction/23596/lot/7/bentley-412-litre-blower-childs-car/](https://cars.bonhams.com/auction/23596/lot/7/bentley-412-litre-blower-childs-car/) |

Published sold totals are recorded without currency conversion. An unsold 2022 high bid and continuation cars are excluded from the ledger.

## Birkin chose pressure where W.O. Bentley chose capacity.

W.O. Bentley opposed supercharging the 4½ Litre. Tim Birkin pursued it with independent engineer Amherst Villiers, secured chairman Woolf Barnato's approval and found the racing budget through Dorothy Paget.

Fifty road cars were required for homologation. Birkin & Co. developed four team cars at Welwyn Garden City; production chassis and engines came through Bentley, while the team cars carried stronger parts and up to 240 bhp in race tune.

The Blower set pace and lap records but did not deliver a period endurance victory. Its market identity rests instead on the small production run, the external supercharger and the surviving documentary boundary between factory-supercharged cars and later conversions.

| Highlight | Detail |
| --- | --- |
| The blower sits outside | Villiers mounted the crank-driven Roots unit between the front dumb irons, ahead of the radiator. The carburettors feed it from one side and a long induction trunk carries the charge back to the engine. |
| Fast, but no endurance win | Birkin's No. 2 car fought the supercharged Mercedes at Le Mans in 1930, then retired with a dropped valve. Bentley's own archive states that no period Blower won an endurance race. |
| Fifty, four, then fifty-five | Bentley describes 50 public homologation cars and four Birkin team cars, while other factory summaries give 55 period Blowers and five competition cars. Prototype and chassis accounting explain the one-car difference; this dossier uses Bentley's 55-car headline. |

| Label | Value |
| --- | --- |
| Built | 55 period cars |
| Road cars | 50 homologation |
| Team cars | 4 Birkin cars |
| Supercharger | Amherst Villiers Mk IV |
| Endurance wins | None in period |

## Technical specifications

### Powertrain

| Label | Value | Note |
| --- | --- | --- |
| Engine | 4'398 cc inline-four | 100 mm bore, 140 mm stroke; fixed cast-iron head |
| Valvetrain | Single overhead camshaft, 16 valves | twin ignition |
| Supercharger | Amherst Villiers Mk IV Roots type | crankshaft-driven and mounted ahead of the radiator |
| Road output | 175 bhp at 3'500 rpm | Bentley factory Heritage Collection figure |
| Team output | 240 bhp at 4'200 rpm | factory figure for Team Car No. 2 |
| Transmission | 4-speed manual | close-ratio D-type on team specification |

### Chassis

| Label | Value | Note |
| --- | --- | --- |
| Frame | Pressed-steel ladder chassis | team cars used the 117.5 in wheelbase; production tourers commonly 130 in |
| Suspension | Solid axles and semi-elliptic leaf springs |  |
| Brakes | Bentley-Perrot mechanical drums | 15.75 in on Bentley's team-car specification |
| Road performance | 97.8 mph · 0 to 60 mph in 15 s | factory figures for demonstrator GH 6951 |
| Team performance | 125 mph | factory figure for UU 5872 in racing trim |

## The people behind the car

### [Sir Henry "Tim" Birkin](https://hiconium.dev/people/sir-henry-tim-birkin)

Project leader and works driver · Birkin & Co.

Pursued the supercharged 4½ Litre, organised the independent team and drove Team Car No. 2 at Le Mans in 1930.

### [Amherst Villiers](https://hiconium.dev/people/amherst-villiers)

Supercharger engineer

![Portrait of Amherst Villiers](https://hiconium.dev/images/cars/bentley-41-2-litre-blower/people/amherst-villiers.jpg)

Designed the crank-driven Roots-type installation mounted ahead of the radiator.

### [Dorothy Paget](https://hiconium.dev/people/dorothy-paget)

Team financier · Birkin & Co.

Funded Birkin's independent team of supercharged competition cars.

### [Woolf Barnato](https://hiconium.dev/people/woolf-barnato)

Bentley chairman · Bentley Motors

![Portrait of Woolf Barnato](https://hiconium.dev/images/cars/bentley-41-2-litre-blower/people/woolf-barnato.jpg)

Approved the production programme that made Birkin's cars eligible for competition.

## Member instruments

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