I am thinking of getting the 75mm HKS single exhaust. I currently have the HKS dual exhaust with the large cylindrical resonator removed and a test pipe. It is pretty damn loud. So I am hoping the 75mm single won't be a ton louder than mine since I have the resonator removed on my dual.

I know superchargers make the exhausts louder so hopefully someone here has one that can chime in.

Also some say the larger diameter exhaust like that can actually lose power on supercharged setups due to lowering boost levels with less back pressure. What do you guys think?

 

I have one and it's nit too loud. I feel it's loudest when I first start the car and let it warm up. I actually will be looking for a quieter exhaust solely because I live in California and don't want more tickets. Our cops in so cal are a pain!! If u wanna buy hit me up

 

I'm CT sc'd on 8lbs btw.

 

Have you had any other exhausts to compare it to while sc'd? How bad is highway cruising drone? Do you have it with a test pipe and is there any rasp?
If I get one I might try and add another resonator or something after the test pipe.

 

 

False. You might lose some power, but it wont be becuase of boost loss associated with a larger exhaust which is losing back pressure. Pressure/boost is unused power potential. If your exhaust cant expel the gasses efficiently you will build/show more pressure/boost and net less power as a result.

A single is more efficient at expelling the gasses becuase it has less obstruction which creates turbulence, you don't want a turbulent exhaust system, the least bends/splits and consistent sizing throughout the better, also the engine produces pulses when it fires, how big/forceful depends on the power the motor makes. Too small a diameter pipe and the pulse can be squeezed too much causing overheating and power loss, a pipe that is too large will make the exhaust pulse expand too much and create turbulence in an otherwise beautifully efficient designed exhaust system. The idea is to find the appropriate diameter pipe for the power/pulse your engine produces. Back pressure is a bit of a myth, its about efficient gas pulse scavenging.

So far my 60mm dual exhaust has netted me some efficient numbers for my power level. I'd gain a few if it were a single, but the point I'm making is the size pipe and how the pulse scavenging works. My observation with my own car is that once we get over 375whp, the 60mm starts to get a bit cramped, at 400whp, I think a 70mm is about right. A 75mm may not provide any power if not lose some from the pulse scavenging aspect, but that is just a guess, definitely switching from a duel to a more efficient single is the right direction and may offset too large a diameter choice. There is a few factors at play obviously. If you make the switch, be sure and post up your numbers, assuming you stay with the same boost.

 

Ok yeah. Trying to decide if it is worth switching to the HKS 75mm single. I currently have the HKS dual which is 60mm and a 60mm test pipe. I just made 406whp at 12 psi on my tune yesterday.

If I do get the exhaust I would bring it with me for a before/after tune I think. But if I only would gain 10hp and get lots more drone etc it wouldn't be worth it for me. Would have to be some pretty decent gains to be worthwhile.

 

Depending on the Dyno, those could be really great numbers considering your set up. I wouldn't expect much making the exhaust change myself. If you changed your header and match the test pipe size you would be further ahead, then up the boost some more. We are running basically the same system. Mines a Tanabe. 60mm test pipe and stock header. Amazing the stock size flows as well as it does to be relatively efficient on a car with nearly twice the power. Removing the cat has the biggest single impact I think over header or cat back when under 400whp.

Another option might be to just pick up a used inexpensive 70mm single of some type and call it good, match the TP size if you can. I think you will get more bang for your buck this way without going nuts. I'd do this myself but I'm not willing to compromise my sound level and looks of a single for 15hp at best.

 

sorry for the slight thread jack here, but the SC + more free flowing exhaust issue is something that I have also been wondering about. From looking at alot of dynos here, it looks like people actually make more on a 60mm vs a 70mm or larger. I seem to recall Evans saying that SC owners should think twice about modifying the exhaust system as a drop in pressure = drop in hp. Besides the initial drop in power due to loss of pressure, wouldn't a more efficient exhaust system yield more gains per psi than a more restrictive one?

 

Well, look how I see this on SC'd cars compared to Turbo. The stock S2000 header +'s exhaust geometry is so efficient compared to a tubo manifold header and 3" that I'm willing to bet that if you put a pressure sensor to measure back pressure on the turbo-header vs the stock manifold at 11psi the back pressure will be higher on the turbo setup. Even a big T3 wheel .96 stg 5 exhaust housing will offer more restriction than a 60mm straight pipe.