Manual BRZ sounds different than automatic one.
 

Hi everyone, me and my friend both have bone stock BRZ, but we've experienced that their engine sound is significantly different and it really bug us why. We are speaking of general "engine" sound in cabin. Mine is MY15 manual and his is MY14 automatic. The manual one has deeper and rougher tone in low rpm and it turns into rich mechanical high tone screaming in high rpm. While the automatic one seems a bit quieter and from low to high rpm tone doesnt change much and is more high pitched all the way up. Because we have nice toyobaru community here in Czech rep. we've tried other manual BRZs to find out if its just mine that makes nicer sound or if its a general feature of manual ones. It turned out that sound of mine (manual) is absolutely normal, even though there was a suspicion that rougher sound was because of nearing engine death that occured during months of observation (I'm already back on road with same sound). (Un)fortunately we dont have many automatic BRZs around to test if his sounds as it supposed to, so I'm asking a question: Can the sound be so different "just" because of a transmission or is there any other reason to it? I also got to say that this is not asking for a help to resolving the issue as we think its just feature of each car and both cars are alright. We are just curious why its like that. Thanks!

TL,DR - Stock manual and automatic BRZ sound different. No mods, sound tube in, cca same age and mileage. Why?

TL,DR summary.. Since the manual transmission and automatic transmission are infact different... different materials have different sound resonances. Not to mention transmission mounts/bushings make ALL the difference in the world for sound too. I got aftermarket transmission bushings and mine has more low end rumble in the cabin due to the vibrations. All of that is taken into account when comparing two completely different products.

interesting observation

I want to swap mine to an auto now, mine is too loud.

If in "lower RPM" you are referring to operation below 2000, the manual transmission will clatter quite a bit. Normal.


If you're talking about manual transmission whine, that's not normal for the TL70. It's common, but not normal.

Put solid transmission and differential mounts on the automatic, it'll help "liven" the sound up ;)

Thank you, that make sense. We were not sure how much design and construction differences were behind these two cars except the transmission itself and how much it affects the "engine" sound heard in cabin. He wont be happy as he already has an automatic and hoped that he could "fixed" it easier than buying some proper exhaust system :D

Have you checked the sound tube grommet in the passenger footwell to see if somebody put the plug in the automatic? The grommet is made so that the cigarette lighter plug from the glove compartment is an exact fit, so that you can plug the sound tube to reduce the engine noise reaching the cabin.

We use our cars kinda extensively so "low" means something from 2000 to 4500, where the sound changes a bit. We were aware of transmission whine and other strange noises that manual makes, which we kinda excluded from our observation and we've focused on other sounds related to what could be described as general engine sound. Not saying that we (or our ears) were able to differentiate them entirely. Our observation was full of surprises, mostly from my friend who didnt believe the amount of different sound transmission itself makes. Like trying to shift in second gear in freezy temperatures. Still thank you for response.

Yeah, that was the first think that come to my mind. Both tubes are in place, and both are open, not blocked by anything. We even have the same carpets :D I also had the plug in before (wanted to try it on 2000km trip, what difference it makes), and I think it would still sound louder and richer than automatic, which is sad :D

In that case, a couple of other things come to mind:

You mentioned yours is a 2015 and his is a 2014, but you didn't indicate the miles. An exhaust system's sound will change over its lifetime. Is there a difference in the number of miles on these cars?

If not that, then I'd suspect it has something to do with the fuel flow as controlled by the computer. I drive long distances and use the cruise control quite often. I have noticed that the engine tone sometimes changes when I engage or disengage the cruise, even at the same speed and RPM. When the computer takes over, the engine gets quieter.

With the automatic, the computer is always in control. Since the manual is putting more of the decisions in the driver's hands than the automatic, perhaps the computer allows more fuel to flow for the manual to be ready for the driver's inputs, whereas the automatic's computer can reduce the fuel flow since the shift points will be more predictable. With different fuel flow, you'd get a different sound.

Oh, one other idea. Have you looked at his air filter? A dirty air filter will reduce the flow of air, and the computer will pull back the flow of fuel to maintain the correct air/fuel ratio. A dirty air filter can make an engine run quieter.

By sound you mean the auto sounds slower than the manual?

Shots fired.

We had quite similar guess, because the difference how engine sounds like is the one intake would make. But he is just one maintenance service ahead (me 65K, him 75K kms). So his air filter is like two months and 10K kms older. Which probably wont make that much difference.