# Engine RPM — Acoustic Tachometer

> Acoustic tachometer for measuring engine RPM by analyzing sound. (iPhone/iPad app by Real-Time Specialties.)

- Source: https://appshunter.io/ios/app/engine-rpm/id340401811 (this page in markdown: same URL + `.md`)
- Developer: [Real-Time Specialties](https://appshunter.io/developer/335568332)
- Category: Utilities, Productivity
- Price: $8.99
- Rating: 4.00/5 from 35 App Store ratings · 64 written reviews indexed
- Age rating: 4+
- Requires: iOS 12.0 · 3 MB
- Languages: American English
- Released: 2009-12-02
- Data updated: 2026-08-30
- Monetization: free
- User reviews in markdown: https://appshunter.io/ios/app/engine-rpm/id340401811/reviews.md

## What is Engine RPM?

Measure the RPM of an engine by analyzing the sound it makes.  Engine RPM listens to the sound of a running engine and uses advanced signal processing algorithms to extract the frequency of that sound and calculate the RPM.

This app is primarily for setup and diagnostics of engines.  After setting the the number of cylinders and whether the engine is a 2-stroke or 4-stroke engine, the app can work with any internal combustion engine, from diesel tractors to aircraft engines to motorcycles to chainsaws.  To use the app you must set an expected RPM range to guide the analysis algorithms to the correct RPM.  A real-time graph of the autocorrelation graph is displayed to help in troubleshooting and adjusting the expected RPM range.

The analysis requires a clear sound from the engine without excessive interference from extraneous sounds. Do not expect to read the RPM of an engine while other things are making too much noise at the same time.  The analysis also requires that the RPM be stable.  It cannot read the RPM of an engine that is rapidly accelerating.  For this reason, and because of the need for adjusting the expected RPM range, this app should not be considered a drop-in replacement for an operational tachometer.

Setup options include update periods from 93 milliseconds to 1.5 seconds, one to 12 cylinders, 2-stroke or 4-stroke, low-pass filtering, and signal clipping.  The overall RPM range is 400 to 90,000 RPM (although at any one time, the operational range is typically +/- 30% around a nominal expected RPM).  Precision is usually about +/- 10 RPM.

## Key features

- Acoustic RPM measurement
- Engine sound analysis
- Supports 2-stroke/4-stroke engines
- Configurable cylinder count
- Real-time autocorrelation graph
- Adjustable update periods
- Low-pass filtering

## Chart rankings

- #194 in Top Paid · Utilities (US App Store)

## Recent user reviews (10 of 64)

All indexed reviews: https://appshunter.io/ios/app/engine-rpm/id340401811/reviews.md

### 5/5 — Helpful

*2026-03-02*

Like others I used this to measure rpm on my lawnmower. It helped me diagnose a problem and saved me a trip to the repair shop. Worth the fee in my case - saved me some time and money.

### 1/5 — Did not work

*2025-08-10*

Needed to monitor and adjust the idle on my motorcycle.
Did not once register a live rpm reading.
No matter what settings I adjust it still held the same 4 digit reading in red.
I placed my phone even directly behind the exhaust and the number read the same even tho I raised and lowered the actual rpm.

I had hoped from the review I read that this would be my savior but instead just a loss of money.

### 5/5 — Fonctionne super bien

*2025-06-23*

Il faut bien faire ses réglages avant !

### 3/5 — Can’t save config

*2025-05-25*

Good app to troubleshoot, but after find the good parameter the app don’t have option to save parameter

### 5/5 — Engine RPM

*2024-07-16*

I just replaced my old mechanical tachometer on my Isuzu 4 cylinder marine diesel on my sailboat with an electrical one driven thru the alternator and Balmar MC 618 regulator.  Following the instructions on the tach and the RPM app it all danced perfectly and accurately!  Simple accurate!

### 5/5 — Works Well - Works as Described

*2024-06-10*

Was a little concerned when noticing most reviews are very old. Pleased to report it worked very well when setting the speed of my old two stroke Lawn Boy mower.  As the author and other purchasers have noted, works best with a constant engine speed and no background noise.  Also verified my Ranger’s idle speed with it’s tachometer, spot on.

### 5/5 — Great concept. Great execution. Great price!

*2023-03-27*

The Tiny Tach tachometer I’ve been using in my small engine work wasn’t extremely expensive, but it’s finicky and difficult to use when I’m tuning something like a chainsaw. 
This app, after a couple minutes glossing over the instructions, was almost intuitive to get to function. It will be really nice to be able to set this down and have both hands free to operate the throttle and adjust carburetor settings on equipment now. Large, easy to see display and controls plus other features I haven’t even gotten to will make my work SO much easier!  Thanks guys, for all your hard work. I’m totally happy with the price!

### 1/5 — Frustrating

*2022-04-20*

I just want my 9 dollars back. Sick of trying to get this to work.

### 5/5 — Very good

*2021-10-11*

Must have for small Eng repair shop to check quick for idle rpm. Works awesome. You have to set you cylinders and 2-4 strokes then it works like a charm. Highly recommended

### 4/5 — Got my snowblower working

*2021-01-03*

Was able to dial in my snowblower RPMs no problem. I do think the app should have the cycle/number of cylinders option right on the Home Screen, I think that would help out. Also, would be nice if it had good enough response times to react to transient surges, really it’s only useful for steady RPM values. But overall, did what I needed for much cheaper than a small engine tach.

## Frequently asked questions about Engine RPM

### What does Engine RPM do?

Engine RPM measures the revolutions per minute (RPM) of an engine by analyzing the sound it produces. It uses advanced signal processing to extract the engine's sound frequency and convert it into an RPM reading. This makes it useful for engine setup and diagnostics.

### How accurate is Engine RPM?

The app typically offers a precision of about +/- 10 RPM. However, accuracy depends on factors like engine sound clarity, lack of interference, and stable RPM. It's important to set an expected RPM range to guide the analysis algorithms for optimal results.

### What types of engines can this app measure?

This app can work with any internal combustion engine, including diesel tractors, aircraft engines, motorcycles, and chainsaws. You can configure the number of cylinders and whether the engine is 2-stroke or 4-stroke to tailor the analysis.

### Is Engine RPM a replacement for a physical tachometer?

No, this app should not be considered a drop-in replacement for an operational tachometer. It requires stable RPM and a clear engine sound without excessive interference. Adjusting the expected RPM range is also necessary, making it more suited for setup and diagnostics than real-time operational monitoring during rapid acceleration.

### What are the setup options for Engine RPM?

Setup options include adjustable update periods (93 milliseconds to 1.5 seconds), setting the number of cylinders (1 to 12), specifying 2-stroke or 4-stroke operation, enabling low-pass filtering, and signal clipping. You also need to set an expected RPM range for the analysis.

## Version history (last 5 releases)

### 2.5 — 2023-09-13

* Optional Low-Pass Filtering to suppress high frequency interfering sounds.
* Optional signal rectification to transform high frequency percussive bursts into low frequencies that were otherwise too low to be detected by the microphone.
* Older unreliable modes of operation were removed (auto ranging and tracking) in favor of the more reliable Hint Band mode.
* Built-in help is greatly expanded.

### 2.4.1 — 2020-07-01

Fixed a problem with Settings visibility when Dark Mode is used in iOS 13.

### 2.4 — 2020-06-18

* Improved signal analysis calculations, making envelope detection unnecessary.
* Use of speaker in "Match RPM sound" mode is louder.
* Revised time-stamp in logging to reflect time of day.
* Configurable logging interval.
* Improved help files.

### 2.3 — 2016-05-27

1. Sample times up to 3 seconds for measuring lower RPM.
2. Envelope detection option.
3. Sound-generating option for manually matching to the engine sound.
4. More extensive help files for each setting option.

### 2.2 — 2015-11-17

iOS 9 compatibility issue fixed.
Added user-configurable sample lengths for faster-changing RPM.
Improved analysis algorithms for better sensitivity and noise rejection.
Added a logging function for saving RPM readings over time and sending them by e-mail.

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All apps by Real-Time Specialties: https://appshunter.io/developer/335568332

## Related topics

[engine rpm](https://appshunter.io/ios/topics/engine-rpm) · [tachometer acoustic](https://appshunter.io/ios/topics/tachometer-acoustic)

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-30.*