Exhaust Drone on the highway - Ford Forums

**donuts2001** · 12-31-2002, 08:24

Hey Fella's, after a lot of work on my motor and my 4 speed Auto transfusion she's finally on the road(not without teething problems though! Need new wheel bearings now. argh) and I took her up to 100km/h today and she's sitting at around 1500RPM and I have a 3.23 Diff.

So I'm wondering if I put a 2.5" exhaust in it how much droning there would be cruising on the highway? My friend has driven in his friends VK commodore which had a 2.5 zorst and he said the continous noise on the highway was unbearable.

So could anyone out there that has had a 2.5" tell me where the exhaust noise mostly kicks in(RPM wise) and if they have any problems on the freeway, etc.

Cheers

NZ · 12-31-2002, 15:13

I have a Cat Back 2.5' exhaust with a custom made muffler. I find it to be really good and the only drone I can get it to do is around 2500 - 2700rpm. Since I have a 5 speed, It is really good for cruising.

EvilEA · 12-31-2002, 15:20

just ask the person your getting the exhaust off, they will be able to put on a muffler that has minimal drone, this is the problem that i was afraid of, i wanted the performance gain of a bigger exhaust system, without the drone.

I was told its possible, it all lies in the muffler that you get installed.

Hope this helps, Good luck

Scott.

JG33PY · 12-31-2002, 15:25

had the same problem from about 80km/h to 100km/h. put a resonator on just after the diff. still drones a bit, but no where near as bad. i'll definatly go twin next time.

WBT56 · 12-31-2002, 16:17

Quote:

Originally posted by donuts2001
and I took her up to 100km/h today and she's sitting at around 1500RPM and I have a 3.23 Diff.
Cheers

Are you sure your speedo and tacho are correct? 1500RPM sounds too low for a 3.23 diff. Anyone else get this result with this combination? Will become relevant when chasing a drone at a certain RPM if the figure you quote is wrong.

Troutman · 12-31-2002, 17:01

Quote:

Originally posted by WBT56
Are you sure your speedo and tacho are correct? 1500RPM sounds too low for a 3.23 diff. Anyone else get this result with this combination? Will become relevant when chasing a drone at a certain RPM if the figure you quote is wrong.

I noticed that too. I have a 5 speed manual and 2.77 diff, and it indicates close to 2,000 rpm at 100. However, I know my speedo is inaccurate so I'm actually doing 5 km/h over 100 at that speed. (and can be fined in Vic too

)

JG33PY · 12-31-2002, 17:17

1500rpm for me is about 80km/h after the converter locks. 100k is about 1900rpm...5.0litre with standard diff and 16x225x50 tyres.

**donuts2001** · 12-31-2002, 19:47

Quote:

Are you sure your speedo and tacho are correct? 1500RPM sounds too low for a 3.23 diff. Anyone else get this result with this combination? Will become relevant when chasing a drone at a certain RPM if the figure you quote is wrong.

Tacho is correct, Speedometer is slightly out(3.08 speedometer gear with 3.23 Diff) but I was doing around 107km or so and keeping up with the rest of the traffic.

I can check the tacho again at this speed if no one believes me... but I'm 99% sure thats the reading it was giving me. I've put in a 4 speed Auto from a ex-chaser which looks like it's been reconditioned recently. The way I figure it, the tacho reading would be based on how well your transmission passes the engine power down to your wheels. I've also got a balanced tail shaft, head gaskets been changed and a XR6 cam put in. (oh yeah and bonus leaking exhaust flange and whistling wheel bearings :| )

Trust me she had lots more go in her too... Probably could have taken her up to the limit

Fairlane Boy · 12-31-2002, 23:43

just a straight through 2.5" zorst on mine gave a bad drone at about 100km/h. when i had cats.. very different now tho, down to about 85km/h. which is fine. cant here it at 80, cant here it at 90.. juuuust perfect.

WBT56 · 01-01-2003, 00:28

Quote:

Originally posted by donuts2001

I can check the tacho again at this speed if no one believes me... but I'm 99% sure thats the reading it was giving me. The way I figure it, the tacho reading would be based on how well your transmission passes the engine power down to your wheels.

Check the tacho again, for your own benefit. (and your wallet) Nak302's figures sound about right. Most 3.08 diff O/D autos seem to do about 1750-1950 RPM @ 100KM/H. The tacho reading will be based on how efficiently the box transmits power, yes, but it will never beat direct coupled figures.(work out theoretical RPM @ speed using O/D ratio like a manual). The reason for knowing it is right is this: If the maths says you should be doing, say 1850RPM, and your tacho says 1500RPM, then if you give it lots through the gears, say 5500RPM according to your tacho, then it's really doing 6780RPM. Not pretty.