older car idle...

electric cutouts + cams.

my GT had mac 3in cat-back, the h-pipe hollowed out with the PI headswap, that sounded mean and loud, on my Cobra i just have the mac 2 1/2in catback and it sounds meaner. if i were you i'd try checking out the 2 chamber magnaflow or mac mufflers.

i nice set of headers would most likely help. ditto the cutouts too

keep the 1 chamber flows and get headers.. long tubes and a off road x with 1 chambers will be LOUD

Bill9000 said:

OK, not to start a thread that someone else probly has at one time... but...

I have 1-chamber flows and an off road H-pipe, and I love the way the car sounds when it's pulling, but hate it at idle, it's so smooth and quiet, that until stepping on it, nobody would notice that it isn't stock.

I want to increase the volume of the idle. (I am aware that cams would make it sound lopey, and I'm planning on that)

but I used to have a big block chevelle, and it only had 2-chambers on it, and it was 25 times louder at idle than my stang. I realize it's a lot more cubic inches, but there's got to be something to make these newer cars sound like real cars!!!!

would headers help?

any ideas anyone?

Click to expand...

I have come across this too, and I don't really know the answer. I have some theories but they don't always seem to add up.

My TR7 V8 is fairly modded - high lift cam, big 500cfm Weber 4brl carb, stage 1 heads, upgraded fuel pump and so on. It also has some massive full out competition spec exhaust manifolds on it (headers), leading into Y pipe and a single straigh-thru 3" silencer (no Cats, this setup is almost identical the British Leyland Works Rally cars). However on tickover it is reasonably sadate, even revving it doesn't make it as loud as some of the 4 cylinder cars that buzz around. However if you go off down the road and get some load on the engine it is a different story altogether. Reckon you can heard it at over 1/2 mile away as a norm.

Where as my XJS V12 has stock manifolds with the stock mid pipes and large restrictive silencers (1 per bank). All I have done is remove the rear silencers and replace it with a length of straight pipe either for each bank. Now at tick over it is REAL LOUD, like vibrates the windows in my house loud. But once it has a bit of load on the car as you go down the road it is no where near as loud as the TR7.

My theory is this:

Apart from the obvious restrictions in silencer type and cats I can only fathom 2 other reasons for the volume discrepancy at idle and open throttle.

1. The pipe diameter. A larger diameter would I guess act like a larger diameter wind musical instument, so thus produce a lower note. However it may well appear quieter as the exhaust gasses won't be moving as fast down the pipe because of the increased bore size. To then increase the volume you would then have to increase the flow rate down the pipe. (cams, heads, intakes - not sure really just guessing).

2. The location of the silencers in relation to the tail pipe. On My TR7 the only silencer is a rear box with the 3" tail pipe coming straight off of it about 4" from the end of the silencer.

Something similar to this:


Where as with the XJS the silencers are in the middle of the car. Although it is a V engine it has two seperate exhaust system (ie not joined by a H, X or Y pipe). So for simplicities sake it could be viewed as having two Straight 6 exhaust systems on one car, the pipe work is also is stock dimensions which is quite narrow, I would guess circa 2" diameter tubing.

The flow characteristics must be different between having only 4" of pipe from the silencer to the outside (tail pipe) as opposed to having 3-4 feet when the silencers are in the middle of the car. If it is changing the flow characteristics then it must also be changine the noise too.

Example of XJS exhaust setup: