exhaust

[Vart]

could a bad sounding exhaust cause excessive fuel consumption?

i think its full of holes but the rusted on muffler (came with car and sounds shat) makes it hard to tell. would it mean i use a lot more fuel cause even driving without getting the econ gauge into the red seems i return only 30 mpg. the manual says i should get about 50 mpg on motorways, i seem to get 300 miles per tank top whack. i was hoping for more...........

i presumed reasonable economy happened at the first thick line on the econ gauge.

on a similar note are all 5th gears for 1.7 340's totally lame. mine refuses to be economic at all at anything less than 85 where the mpg is poverty stricken anyway.

thanks

regards

vart

[redline]

if your exhaust is full of holes the lack of back pressure may cause you to have to work the engine harder and therfore be less economical

[jtbo]

I'm not sure about backpressure, but each exhaust pulse generates vacuum into exhaust port side and this vacuum kind of sucks exhaust gas out from cylinder. Now if you have bad leaks there will be not this vacuum effect at all, there is only athmosperic pressure 1bar.

Sport exhaust manifold (is it called tube headers?) will make extra power by increasing vacuum by putting each exhaust pulse even space, that is why every tube need to be exactly same lenght, so there is constantly similar vacuum available when exhaust valve is opened, while with stock exhaust manifold situation varies a bit as there is longer distance to exhaust gas to travel from exhaust port to end of exhaust manifold.

Also carbs need to be retuned if exhaust is changed to different, mosly exhaust manifold, but also mufflers may affect to carb micture.


At least this is how I have understood thing to be

To original question I can anser yes. I had bad leak between exhaust manifold and 2 to 1 collector part, they did not found it in garage and it just was getting worse and worse.

After I replaced 2 to 1 part it was much quieter, I made very good care to sealing connecting surfaces and I did found out that garage has been lazy, there is these 3 knuts and 3 bolts, well these 3 bolts should be attached to exhaust manifold all times, but they were not, they were attached to knuts and were not tightening enough.

I hope that I don't need to visit garage never again

Also luckily 360 exhaust parts are very cheap.

[classicswede]

A blowing exhaust can cause an increase in fuel consumption. 30 mpg is not all that bad for combined consumption but on a run it should be better.
Step no1 is to fix the exhaust and step no2 is to get your fuel mixture checked.

Dai