Dyno Testing a Stock Aston Martin DB9

How much power does my 2005 Aston Martin DB9 really make?   It certainly makes ‘enough’ – the car is not lacking for performance.  Lately I’ve been curious about a few ‘bolt on’ performance upgrades that I want to try out.  To know if they make any difference, I want to know the actual power my car make now that its 15 years old and has 44,000 miles on it.   I need a Baseline performance test.

I can open the owners manual in the glove box, and right there in Section 13 is a beautiful graph where Aston is expounding that it makes 450 bhp and that 82% of the Torque is available above 1500 RPM.  Terrific, but I’m not sure I trust any manufacturer to tell the whole truth and nothing but the truth.   I wanted to measure it myself [if you are a regular reader of this blog, you know by now I gotta be me].

The Plan

In order to find out I sought out a local shop to perform a Dynamometer Test of the car.    Also known as a rolling road, a Dyno test will measure the power and torque where the rubber meets the road.

My plan is to return to get another Dyno test performed after each performance upgrade, and to compare it to this initial Baseline set of values.  Science. For comparison Dyno testing to be meaningful, you need to try and keep everything possible the same.  Fuel, test rig, technician, etc.

Finding a Dyno shop took some considerable effort.  To start with, I wasn’t sure where to look.  Googling returned options, but I found that most of the places had gone belly up.  I presume its a side effect of factory cars with 700 bhp being available now.

I took my car to Travis of Snail Performance.  He uses the Mustang 150 Dynamometer at M45 Automotive in Auburn, California.   Travis and M45 are part of the tuning scene for fast Subaru’s, and fortunately my DB9 would fit the rig.

During each visit Travis runs the car through three (3) power pulls, going from idle to max RPMs when the power starts to fall off.   We have the car well warmed up, in Sport Mode, A/C system completely off, and the pull is done in third gear only.

Why third?   Glad you asked.  We want to be in a gear where the Dyno and gearing work the engine hard to its maximum effort.  But, we don’t want the pull to take an overly long time running engine temperatures through the roof (like 6th gear).   During the baseline test we found that in 4th gear the ultimate power measured was slightly higher, but the pulls took longer and heat build up (soak) was beginning to influence the results.   We tried again in 3rd gear and the car was happier.  It might leave a few bhp unaccounted for, but my key aim was comparisons of the changes, not maximizing some number.

Baseline Results

Travis ran the car through three pulls and gathered data.   Each run isn’t identical, but very close.  Here are the results of the best run listed against the previous two Dyno tests.

Peak Values

These are the numbers that get all the press, but are really only achieved at a very high RPM where we rarely, if ever drive the engine:

  • Power – 376 bhp at 5500 rpm
  • Torque – 368 ft-lbs at 4800 rpm

Average Value

  • Avg. Power – 278 bhp
  • Avg. Torque – 329 ft-lbs

What is average power?  As Travis explained to me, it’s a better representation of the overall engines performance.  What use is a performance improvement that’s only change is adding 10 bhp between 6,000 and 6,500 rpm?  It might be something if you drive at redline all the time (tracking the car), but useless for any other purpose.   Average power is the average across the entire RPM range.  Area under the curve.   Accounts for all the gains mid-range, top end, etc.   Raising the average power is a measure of increasing the overall performance of the engine.

Why isn’t it 450 bhp?

Why aren’t the numbers anywhere near what Aston claims is the engine power and torque in the manuals?   Another good question. We are measuring ‘at the rear wheels’, meaning where the rubber meets the road (literally).  The rear wheels are on rollers, and the rollers are the measuring tool of the Dyno.    Manufacturers published engine power is always of just the engine sitting on a testing stand coupled directly to the Dynamometer.   The difference is all the loss attributed to the drivetrain between the engine and road wheel.   The transmission, the differential, the drive shafts, axle shafts, wheel bearings, brake rotors, etc. all create losses in the system (all the time) and reduce the amounts of power and torque that actually make it to the rear wheels.    There is no way to precisely know how the rear wheel measured numbers relate to the engine power without actually removing the engine and testing it separately.  As a rule of thumb, most people generically quote about 15% power loss through the drivetrain.   If the stock DB9 engine is listed as 450 bhp by the manufacturer, you can roughly expect about 85% or 382 bhp to make it to the road.   From my results showing 376 peak bhp in this baseline run, that would be about 16.4% power loss through the drivetrain if you believe the engine makes 450 bhp as Aston claimed.  Again, for my upcoming testing purposes this is comparative, so this isn’t that important.

Aston Martin DB9 Power and Torque Graph included in the Owners Manual – NOT measured at the rear wheels

What’s next?

Velocity AP GT4 Airbox Delete Kit

The first step in my quest for 50 more BHP is to install a Velocity AP GT4 Airbox Delete Kit.   Getting more power from an engine involves improving its breathing, allowing it to suck more air in and blow it out easier.   The GT4 Airbox Delete Kit helps with breathing in.  It will remove the original airbox and air filter and replace it with a high performance setup that Aston Martin was fitting to the GT4 performance cars.    I’ve written up a whole article about it  here – check it out!

After I fit this kit and head back to the Dyno, I’ll publish the results in another article [Coming soon].


Of course, watching a Dyno test is a lot of fun.  Being in the room is even more visceral.   Something I would recommend if you have a Dyno shop near you.  Here is a short video of the test, and Travis discussing the results.

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