Purple exhausts

v8alex · Post by **v8alex** » Sat Dec 22, 2007 9:38 am

I have some stainless pipes on my RV8. Once running, the primaries turned from silver to gold - fine. I've noticed recetly they now have purple patches on them, particularly near the exhaust ports.

Is this a sign of running too hot ? i.e. mixture incorrect - too lean or rich ? Or is this nothing to be worried about ?

Alex

ian.stewart · Post by **ian.stewart** » Sat Dec 22, 2007 9:54 am

It could easily be a sign that as you get ysed to the engine/car you start to drive it a bit harder, aot you are using it at WOT or near for continious lengths of time

v8alex · Post by **v8alex** » Sat Dec 22, 2007 10:31 am

I've not driven the car yet, just built the engine and have it idling in the garage, Max rpm so far is 3,000. I've used less than 2 gallons of fuel so far, so very little running time to date.

Alex

ian.stewart · Post by **ian.stewart** » Sat Dec 22, 2007 11:06 am

The only real way to test the mixture is use a sniffer or Lambda, if you are really serious temp probes in each exhaust port,
Personally I would be thinking the colouring is not a problem, A well tuned engine running on open pipes can often be seen to have a cone of blue flame exiting the the pipe, Even with my engine set up very slightly rich I would expect the pipes to glow at the exhaust ports,
I would think the colouring to get more pronounced as you run the engine, the blue spots that you describe could quite easily be grease from your fingers burning onto the pipe, Next time you see a big bike with stainless or chromed exhausts have a look and see where the colouring starts to drop off and turn to light straw, sometimes as much as a foot of discoloured pipe can be seen,

5000SE · Post by **5000SE** » Sat Dec 22, 2007 11:33 am

ian.stewart wrote:Next time you see a big bike with stainless or chromed exhausts have a look and see where the colouring starts to drop off and turn to light straw, sometimes as much as a foot of discoloured pipe can be seen,

I was about to say the same, and most bikes tend to run a bit rich anyway!

v8alex · Post by **v8alex** » Sat Dec 22, 2007 12:59 pm

I did think it might be grease from fingers as I'm still grubbing around the engine area and the manifolds make great handles.

One of my mates at work has a custom bike with some pretty serious chrome pipes - I'll take a look.

Thanks

Alex

Ian Anderson · Post by **Ian Anderson** » Sun Dec 23, 2007 9:45 pm

Alex

I had a similar thing when I satrted the RV8 3.9 EFi in the GT40

The Stainless headers discoloured very badly and I had wiped off the finger prints with white spirit

I don't know what fuel system you are using but if Hotwire there are 2 tune resistors - one says look at lambdas and the other does not - it made a hell of a difference to the emissions when we got the right one!

Also found that the timing adjusted accurately cooled down the headers

Ian