What paints/techniques do I need to get this look?

[Monty]

I'm doing a replica stock build of a car that's been well taken care of, but has some miles on it.  I'll probably try the Tamiya powders for the chassis, but the exhaust is what I'm trying to nail down.  Here's the real car's exhaust:

If possible, post a pic of an exhaust system where you used the paints etc you're recommending.

[Snake45]

Do some net research on the "salt technique" used for weathering by military modelers. Looks like something that might work for this. (I've never done it so can't comment on it personally.) 

[SfanGoch]

I use a stainless steel or steel metalzer base. Then, I stipple Vallejo Hull Red, German Camouflage Black, Leather Brown, Red and German Camouflage Orange in varying amounts to achieve a rusted finish. This is a 1/35 Detroit Diesel 8V-92TA for the Hobby Boss M1070 HET tractor.  I wanted a heavily rusted look for the turbo system as seen in a reference photo.

 

[cobraman]

Would that Rustall product do a good job on that ?

[SfanGoch]

Unlike RUSTALL, using paints to create the effect doesn't require clay powder which isn't permanent.

[EngineerBob]

Similar to SfanGoch, I spray paint the part with a base of dark metallic or red oxide (depending on how rusty I'm going for) and then stipple paint a variety of rusts, oranges, and yellow inexpensive craft acrylics and then top coat with flat clear.

[jaymcminn]

I used a stippled technique as suggested above for the exhaust on my Alfa 8c before masking with rubber cement and spraying a black top coat to simulate rust breaking through the black paint. As a finishing touch I used the Tamiya "rust" weathering powder to blend the stippling and tone down the black.

 

[Bainford]

Check out the Rust Antiquing Set from Sophisticated Finishes.

[kjohan]

This is the underbody of ongoing build of Italeri Ferrari 259 GTO
Concerning the exhaust:
The plastic was moulded in medium grey.
I brushed firt Humbrol Matt Rust  no 113, not fully even coverage, some variation
Thereafter a couple of unsystematic rounds with Gunmetal grey gloss metallic. no 53
When the paint started to dry gave it some "stabs" here and there with the brush

Hope it works with rhe photo this time

[SfanGoch]

Poifect!

[Oldcarfan27]

Take a look at Steve Guthmiller's current '68 Coronet project (page 21) and see if this is the effect you're looking for on your exhaust.