Exhaust fumes normal?

[MB750]

A couple weekends ago I was out and about in the Cobra, working up the break-in miles. I noticed at lower speeds and stop-n-go traffic that the exhaust smell was becoming somewhat intrusive. At highway speeds it's non-existent (obviously), but at lower speeds with the wind blowing in the right direction the smell was pronounced enough to be clearly noticeable.

I know I've got a custom exhaust, but it does ditch out in the same location as the standard side pipes. Is this normal? It's got me designing a rear exit set of tail pipes.

[cv2065]

Running too rich? Initially, I had a small issue like that but I tuned it out where I can now be in the garage while it’s warming up with no issues. Adjust for a leaner mix or check your timing.

[edwardb]

With my first couple builds with carbs, yes exhaust smell was there. I typically pushed the cars out of the garage before starting so not to fill the garage with fumes. Once warmed up they were better and as long as I kept moving not objectionable. These were well tuned carbs and probably pretty typical. With my Coyote builds, a complete non-issue. I haven't used any of the aftermarket EFI systems. I suspect they're better than carbs but I don't know.

[Mike.Bray]

With my first couple builds with carbs, yes exhaust smell was there. I typically pushed the cars out of the garage before starting so not to fill the garage with fumes. Once warmed up they were better and as long as I kept moving not objectionable. These were well tuned carbs and probably pretty typical. With my Coyote builds, a complete non-issue. I haven't used any of the aftermarket EFI systems. I suspect they're better than carbs but I don't know.

I would tend to agree it's a carb issue. My Cobra has stack EFI and I've never smelled any exhaust fumes. My Camaro has side exhaust with a carb (for now) and I can smell fumes when I'm stopped and have the window down.

[Jeff Kleiner]

Some odor is pretty normal, both carbed and EFI. If it's really overwhelming though then yes,as others have said take a look at your fuel mixture. Often when an exhaust smell is mentioned it is immediately assumed that it's running rich but actually it can be the opposite---lean condition can lead to misfire which will also send unburnt fuel into the exhaust. Lean will not only stink but will also burn your eyes. Take a look at the plugs; black =rich, white=lean.

Jeff

[MB750]

Thanks everyone. As far as the tune is concerned, I've got it tuned right where I want the AFR's, which means around 13:1 at low speed cruise. I have a wideband gauge right on the dash. While it's a little richer than an EFI system would allow, it's not pig rich. And the plugs come out mostly white, maybe a little bit of a tan color.

As much as I'd rather NOT do, apparently adding cats can take some of the smell out of the exhaust.

[MB750]

Running too rich? Initially, I had a small issue like that but I tuned it out where I can now be in the garage while it’s warming up with no issues. Adjust for a leaner mix or check your timing.

I gotta say, after I had the head milled to raise CR, I just shoved the dizzy back in and haven't confirmed the total timing yet. It's close, but not optimal.

[JMD]

Definitely check timing and reconsider AFR ratios as those are two main factors that can cause exhaust smell if your mixture isn't burning completely. Timing that's excessively retarded can cause that, but maybe not if your O2 sensor is still reading in the acceptable range.

I have a Sniper 2 and never had an issue with excessive exhaust fumes, even while idling in the garage. I would double check your AFR at idle if that's where you're noticing it most. You can go quite lean at idle without hurting anything and there's really no reason to run it rich at idle unless you have a wild cam. I've run anywhere between 13.8-14.5 at idle and never noticed significant fumes. I wound up leaving idle at 14.1:1 and have absolutely no smell at all under normal circumstances.

I'd also double check all spark plugs...maybe you have a cylinder that's not firing properly and have unburnt or only partially burnt fuel coming out the exhaust? Maybe on the opposite side from your O2 sensor?