Exhaust Drone on the highway - Page 2 - Ford Forums

Martin · 01-01-2003, 00:49

Single muffler here, no drone to speak of at any rpm in any gear.

Some would describe it as loud though, but I dont mind it....

**donuts2001** · 01-01-2003, 02:54

Quote:

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

Sorry but the Tacho is right... and I've checked today with my digital multimeter which has a tachometer feature built in. The Tacho in my car is giving the right reading. I can't remember exactly where the RPM was(because I'm trying to drive! lol), but it was DEFINATELY below 2000RPM... somewhere around the middle.

Seems the only way to prove this is with a photo. After I get my wheel bearings done tommorow, I'll get my friend to take one of the dash while i'm at 100km/h.

01-01-2003, 04:25

i have an ef xr6 with a 3-inch cat back exhaust, no extractors, and i only get a bit of drone at around 101-106km/hr. Anything below or above that is noise free :)

Dunno if i should get extractors on her though, might drone too much...

crodarian · 01-01-2003, 04:31

i got an ED 6cyl with a 4sp. I have a 2.5" zorst, one muff, pacemakers and 2.5" cat, and there is no drone till around 2500-3000rpm. I have 3.08 diff and i rev at about 1700-1800 at 100km/h, so there is no drone when cruising, only when giving it some does it sound sweet

**donuts2001** · 01-01-2003, 05:48

Okay took her for a drive tonight, and can verify it sits at about 1650-1750RPM at 107km/h(should be high enough for any speedo error).

Yes it has a 4 speed Auto, Yes it has a 3.23 Diff(as stated on the diff itself) and yes my tacho is working correctly.

Just goes to show different Auto's have different transmission of power to the wheels. Will take a photo if there are any misbelievers

TopGhia · 01-01-2003, 11:26

Quote:

Just woundering through

Maybe you should "wounder" towards a dictionary

psproule · 01-01-2003, 15:28

Donuts - different autos (of the same breed) don't have different transmissions of power. I have an EL I6, 4 speed auto, 3.23 diff and 16" wheels with 50 series rubber. 100kph = 1800rpm, both by maths and on the road observations.

Unless an auto is worn and there is some band / clutch slip the tranny is similar to a manual in it's transfer of drive. They use real gears with real teeth - but in a planetary gearset and thus cannot vary their ratios beyond those available. For the BTR93LE in the EL the ratios are 2.39:1, 1.45:1, 1.00:1, and 0.68:1 (I'm not sure but I think the 85 and 95 are the same).

The slip referred to in auto trannys is in the torque converter. The torque converter allows a torque multiplication effect to take place where an increase in engine revs at the input will provide more static torque at the output, even if the output shaft is stalled. The maximum revs you can pull with the output stalled is called the stall speed. A higher stall speed means more available torque but higher engine revs which isn't good for fuel economy when tootling around town. Ever seen / heard a high stall equipped car? Some of them sound like they have to pull 4000RPM before they move away from traffic lights. Great for drags though as you can get the motor on song.

Modern torque converters are usually equipped with a lock up clutch (as in 4 speed auto Falcons etc) which, when engaged, locks the torque converter into a solid 1:1 drive. This promotes better fuel economy and drops drive losses through the transmission. You will feel the converter lock up in a BTR 4 speed under part throttle in 3rd and 4th gears, usually above about 60kph in economy mode and 75ish in power. It unlocks when changing ratios or under heavier throttle applications when more torque is required.

Thus when in 4th cog with the lock up applied you have a direct and fairly solid 0.68:1 ratio through the transmission.

So for some maths (and it could get messy here as I hate maths)... mostly rounded to 2 decimal places....

I have a wheel diameter of 651mm

Circumference (distance wheel will travel per revolution) = 651 x PI = 2045.2mm

Final drive ratio = 3.23 (diff) x 0.68 (4th cog) = 2.20:1

Number of wheel revolutions per km = 1000 / 2.0452 = 488.95

Number of wheel revolutions per 100km = 100000 / 2.0452 = 48894.97

Number of engine revolutions per 100km travelled = 2.20 x 48894.97 = 107568.94

If travelling at 100km per hour number of engine revs per minute = 107568.95 / 60 = 1792.81 - close enough to 1800rpm.

If anyone feels like checking the maths please go for it - I could be wrong.

Pat.

blueoval · 01-01-2003, 16:03

Cant argue with your evaluations psproule! Sound right to me!

WBT56 · 01-02-2003, 00:42

Quote:

Originally posted by blueoval
Cant argue with your evaluations psproule! Sound right to me!

I agree also. Right on the money.

Aaron_EF8 · 01-02-2003, 06:43

www.fordmods.com has a gearbox/diff/tyre calculator thing that seems to be very accurate, maybe try that?