I am in the process of evaluating several ‘bolt on’ performance changes for my DB9. Ultimately I am hoping to achieve power levels similar to a DBS (they are essentially just the same engine). In this article I am testing the changes that come with fitting a Velocity AP GT4 Airbox Delete Kit (check out my other article on how to fit one). This is a popular modification that promises less weight and better breathing to make more power. Its that last claim we are testing here.
I’m not a fan of seat of the pants claims like: “Ya, I bolted that on and it sure feels faster, but I haven’t had it tested.” Placebo effect. Make a change that you think will make the car faster, your brain wants to believe its faster. I’m also a skeptic of manufacturers claims that aren’t backed up by published scientific test data. Boggles my mind why they don’t do that. Do they not actually test their upgrades before selling them? If they do, why don’t they take a few minutes to publish the results? Make believers of us. Well, you know me, I gotta know for certain, and now you will know.
This is the second trip to the Dynamometer for my DB9 to test the changes (and each visit is a fun visceral event). In my first trips we recorded data for the Baseline Performance – what was the existing power of my original car? My car is about 15 years old and has about 42,000 miles on it, and is in top shape, well-tuned and maintained. Check out this article and video on how I found out.
For comparison Dyno testing to be meaningful, you need to try and keep everything possible the same. Fuel, test rig, technician, etc. I’ve done just that. I’ve been taking my car to Travis of Snail Performance. We are using the Mustang 150 Dynamometer at M45 Automotive in Auburn, California. 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 and 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 measure 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.
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 – 372 bhp at 5600 rpm
- Torque – 369 ft-lbs at 4750 rpm
- Avg. Power – 275 bhp
- Avg. Torque – 328 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.
How does it compare?
How does the cars performance with the Airbox Delete Kit installed versus the Baseline test? Here is the overlay Graph.
- Blue = Stock Baseline Performance
- Red = Airbox Delete Kit Installed
A small incremental improvement at best. There was no change in peak power, and a minor improvment in peak Torque. Where there is a notable improvement is in the more practical and usable mid-range power. Between 2400 and 3400 RPM there is as much as 6 more ft-lbs of Torque and 3 bhp. That’s roughly a 2% improvement.
|Baseline||Airbox Delete Kit|
|Torque (ft-lbs)||Peak||366 @ 4750 RPM||369 @ 4750 RPM|
|Midrange||311 @3145 RPM||317 @ 3145 RPM|
|Power (bhp)||Peak||372 @ 5400 RPM||372 @ 5400 RPM|
|Midrange||186 @ 3145 RPM||189 @ 3145 RPM|
The next step in my quest for 50 more BHP is to work on exhaling better, removing a restriction in the exhaust flow. I will be fitting a Secondary Cat Delete kit (SCDK). Check out my articles on how to fit one here. You can also check out the power increase the SCDK makes in this article.
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.