The Ampera is an EREV, this means that after the battery is depleted a petrol engine generates electricity to power the electric motor and recharge the battery with the excess power produced.
A very clever system that is more efficient than an hybrid power-train and allows the car to be used purely electric during the week and use it without any range anxiety during the weekends, as it only needs to fill up with petrol in case I need to drive more than the electric battery range allows.
GM did an amazing job making the Ampera quiet, and even the 1.4 liter petrol engine is very quiet when operating. In it's slowest (not sure how many RPM) I measured 44 dB inside the car, the same as the C6 with a 2.7 liter V6 diesel engine. The only issue is when accelerating hard with the battery depleted, the engine sounds agricultural, it's a 4 cylinder engine.
So my idea was to start deadening the engine compartment as it was the easiest place to apply Dynamat and the place where I was sure I would get a positive result reducing the engine noise.
Dynamat on the bonnet
Like all cars the Ampera has soundproofing applied to the bonnet, but unlike my two other cars this soundproofing was very thin and light. Removing it showed that I had decent space to apply Dynamat Extreme.
Also there was a type of foam between the metal sheets that make the bonnet / hood. This has 3 benefits, decouples the metal sheets avoiding rattles, gives them strength to avoid resonance and since it closes entire areas that would be open avoids an echo chamber that would amplify any noises. Clever thinking!
After cleaning the area I started to apply Dynamat on the holes in the middle and the ones where the windshield washer jets are. Still had some old Dynamat, I really prefer the silver to the new one in black. Dynamat Extreme is not supposed to be visible, so not sure why the change of colour.
Unlike other areas where upon knocking on the metal it sounds well dampened, in the bonnet I would get some faint metal resonance. Not anymore, now it sounds very solid.
As always, after putting the original soundproofing back in place it looks stock, that's how it's supposed to be.
The engine on the Ampera has a cover, so my idea was to add Dynamat Extreme to that as well. I had good results in the C6, so it was a no-brainer.
I tough it was odd that the engine cover was bolted in place, but Americans do things differently from us folks here in Europe.
After removing the bolts I saw that it was still fixed in place, with two air tubes attached to it. Removed those and boy was I in for a surprise.
It weighs a lot and seems to be part of the air intake, with almost no space for Dynamat to be applied. But it wouldn't make any difference, it is so thick and heavy that it already mutes a lot of noise coming from the engine.
So, me being me, I gave it a good clean and put it back in place without any deadening done.
My main quest was to quiet down the petrol engine. I did a measure before and got 44dB inside the car. After this the sound meter is oscillating between 42.5 and 43dB, so a great result. I didn't take any measurements on the highway with the engine on, but it sounds very muted under high acceleration and inaudible under normal normal.
I tested the car on idle with just the electric engine, so I will get noise for the aircon compressor and some fans to keep the battery cool. Before this the meter was also oscillating but between 28.5 and 29dB, now it oscillates between 28 and 28.5dB. It's not much, but to put these values in perspective, just by me breathing normally the meter would jump to 30dB.
With everything powered down the meter goes down to 26dB, shows how quiet it really is. Shame I didn't make the same measurement in the C6 for comparison.
Also I didn't add an entire sheet of Dynamat, probably about 700g of Dynamat Extreme applied, very small weight increase for these results. Very happy!
Done in 11 of February, 2018