Can high speeds expel carbon build-up through exhaust?
08-07-2011, 01:29 AM
#16
Based on experience, I think it does burn off.
Years ago, bought an 84 TL in LA and drove back to Denver starting out on Friday afternoon. Drivers from LA to Vegas must have been on crack as 100 mph was just keeping up. Stopped in Vegas for fuel then onto Denver across the desert. The stretch from Vegas to Salina was much the same pace.
The stretch from Salinas UT to Grand Junction is as open as it gets once you come out of the hills and after running over 120 for quite a while, decided to see what top end was.
By this time, it was middle of the night and pitch black. Running along at 155 for a while, I looked out the rear view mirror and saw a trail of sparks that seemed like they were several hundred feet long.
Obviously, it startled me enough that I slowed down thinking something was dragging from the rear but they went away below 100 mph and no odd sounds so I continued on.
My only explanation was that the carbon in either the chambers or entire exhaust system had finally heated to the point of combustion.
Years ago, bought an 84 TL in LA and drove back to Denver starting out on Friday afternoon. Drivers from LA to Vegas must have been on crack as 100 mph was just keeping up. Stopped in Vegas for fuel then onto Denver across the desert. The stretch from Vegas to Salina was much the same pace.
The stretch from Salinas UT to Grand Junction is as open as it gets once you come out of the hills and after running over 120 for quite a while, decided to see what top end was.
By this time, it was middle of the night and pitch black. Running along at 155 for a while, I looked out the rear view mirror and saw a trail of sparks that seemed like they were several hundred feet long.
Obviously, it startled me enough that I slowed down thinking something was dragging from the rear but they went away below 100 mph and no odd sounds so I continued on.
My only explanation was that the carbon in either the chambers or entire exhaust system had finally heated to the point of combustion.
08-07-2011, 12:17 PM
#17
Race Director
Based on experience, I think it does burn off.
Years ago, bought an 84 TL in LA and drove back to Denver starting out on Friday afternoon. Drivers from LA to Vegas must have been on crack as 100 mph was just keeping up. Stopped in Vegas for fuel then onto Denver across the desert. The stretch from Vegas to Salina was much the same pace.
The stretch from Salinas UT to Grand Junction is as open as it gets once you come out of the hills and after running over 120 for quite a while, decided to see what top end was.
By this time, it was middle of the night and pitch black. Running along at 155 for a while, I looked out the rear view mirror and saw a trail of sparks that seemed like they were several hundred feet long.
Obviously, it startled me enough that I slowed down thinking something was dragging from the rear but they went away below 100 mph and no odd sounds so I continued on.
My only explanation was that the carbon in either the chambers or entire exhaust system had finally heated to the point of combustion.
Years ago, bought an 84 TL in LA and drove back to Denver starting out on Friday afternoon. Drivers from LA to Vegas must have been on crack as 100 mph was just keeping up. Stopped in Vegas for fuel then onto Denver across the desert. The stretch from Vegas to Salina was much the same pace.
The stretch from Salinas UT to Grand Junction is as open as it gets once you come out of the hills and after running over 120 for quite a while, decided to see what top end was.
By this time, it was middle of the night and pitch black. Running along at 155 for a while, I looked out the rear view mirror and saw a trail of sparks that seemed like they were several hundred feet long.
Obviously, it startled me enough that I slowed down thinking something was dragging from the rear but they went away below 100 mph and no odd sounds so I continued on.
My only explanation was that the carbon in either the chambers or entire exhaust system had finally heated to the point of combustion.
The car was probably hitting the roads on bumps at that speed.
08-07-2011, 02:16 PM
#19
Addicted Specialist
Rennlist Member
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"Italian tune up" was back in the day of carbs, and perhaps poorly tuned ones at that, especially WRT richening circuits for cold start. Short trips = buildup ...buildup + time = fouling plugs.
Fastforward to today ...nah! All engine management systems are simply too clean to leave layers of carbon gook (given all is in proper working condition, of course!). You ever look at plugs or the inside of your muffler tips? My 95 has 130K or so on it and the plugs look incredible at change time, and the inside of the muffler tips have nary a coat of gray. And with clogged SAIs, the ports themselves are likely stupidly small from the design get-go (pure speculation on my part). Not to mention my guess is since there is no "regular burnoff" for these ports, they simply clog over time (as opposed to exhaust ports whose size and intended function obviously lend to them staying clear. Some time ago I was privy to a high-miles top end rebuild on a 3L engine. According to the wrench, it didn't really need it, but the owner was doing other stuff. Man did those innards look good, especially the heads. Valve area ...well, still looked pretty-dang good considering the miles (purportedly north of 120K). Cars run cleaner with every iteration of fuel/exhaust management system, and our 993 motronic is no slouch.
Ok, then there's the point that any carbon in the head is pretty dang crusted on there. I seriously doubt normal combustion temps (again, we're assuming all is working correctly) will burn off that crud even if you're sitting at redline for a 200 mile trip ...a-hem, not that anyone would want to! If anything, cruising at high RPM is simply wasting gas and accelating wear on all engine bits: pointless, really. Pro wrenches suggest a regular diet of chemical additive to nix the buildup of carbon. Chemical attack is the approach; Andretti-style driving aint gonna do it. FWIW, I used to use Techron but have long since switched over to Ventil-Sauber. Seems to work really well ...at least as far as I can tell
Edward
Fastforward to today ...nah! All engine management systems are simply too clean to leave layers of carbon gook (given all is in proper working condition, of course!). You ever look at plugs or the inside of your muffler tips? My 95 has 130K or so on it and the plugs look incredible at change time, and the inside of the muffler tips have nary a coat of gray. And with clogged SAIs, the ports themselves are likely stupidly small from the design get-go (pure speculation on my part). Not to mention my guess is since there is no "regular burnoff" for these ports, they simply clog over time (as opposed to exhaust ports whose size and intended function obviously lend to them staying clear. Some time ago I was privy to a high-miles top end rebuild on a 3L engine. According to the wrench, it didn't really need it, but the owner was doing other stuff. Man did those innards look good, especially the heads. Valve area ...well, still looked pretty-dang good considering the miles (purportedly north of 120K). Cars run cleaner with every iteration of fuel/exhaust management system, and our 993 motronic is no slouch.
Ok, then there's the point that any carbon in the head is pretty dang crusted on there. I seriously doubt normal combustion temps (again, we're assuming all is working correctly) will burn off that crud even if you're sitting at redline for a 200 mile trip ...a-hem, not that anyone would want to! If anything, cruising at high RPM is simply wasting gas and accelating wear on all engine bits: pointless, really. Pro wrenches suggest a regular diet of chemical additive to nix the buildup of carbon. Chemical attack is the approach; Andretti-style driving aint gonna do it. FWIW, I used to use Techron but have long since switched over to Ventil-Sauber. Seems to work really well ...at least as far as I can tell
Edward
08-07-2011, 09:34 PM
#20
08-07-2011, 11:30 PM
#22
Race Director
typically the front gets more of the lift, but I don't know about the aerodynamic properties of a tl.
08-08-2011, 11:09 AM
#23
Racer
Thread Starter
I recently read an article from a Porsche shop and they seem to notice that "track cars" have less problems of carbon deposits than "street cars". Could it be that average driving doesn't cut it and high intensity driving on the track does?
08-08-2011, 11:32 AM
#25
anyone ever do seafoam? I did it on my bmw, scariest thing ive ever done! It did work though since there was a lot of white smoke (carbon build up) that came out of the exhaust. Ive been wanting to do it on the 993 but i dont know how to on it.
08-08-2011, 01:45 PM
#26
Rennlist Member
I've never used seafoam, but here's a good article I found encountered when doing some work on my camaro a few years back.
http://ls1tech.com/forums/general-ma...-your-car.html
I actually used some seafoam on the tops of the pistons on my camaro when I had it torn down for heads and cam swap but it was taking too long to scrape everything off. In the end, I used an aluminum safe bristle disc and just barred the engine over until the pistons were at the top and ground the carbon off. Check out the before and after pics. The engine had 60k miles when I tore into it
http://ls1tech.com/forums/general-ma...-your-car.html
I actually used some seafoam on the tops of the pistons on my camaro when I had it torn down for heads and cam swap but it was taking too long to scrape everything off. In the end, I used an aluminum safe bristle disc and just barred the engine over until the pistons were at the top and ground the carbon off. Check out the before and after pics. The engine had 60k miles when I tore into it
08-08-2011, 01:56 PM
#27
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not at high speeds, but if you pull 2nd or 3rd through the rpm range a couple times it will work.
reason: springs, vlaves, cams, all the engine peices are working harder, opening/closing harder, quicker and more often, it will knock some the the carbon build up off and send it out the pipes.
reason: springs, vlaves, cams, all the engine peices are working harder, opening/closing harder, quicker and more often, it will knock some the the carbon build up off and send it out the pipes.
08-08-2011, 02:13 PM
#28
Race Director
I've never used seafoam, but here's a good article I found encountered when doing some work on my camaro a few years back.
http://ls1tech.com/forums/general-ma...-your-car.html
I actually used some seafoam on the tops of the pistons on my camaro when I had it torn down for heads and cam swap but it was taking too long to scrape everything off. In the end, I used an aluminum safe bristle disc and just barred the engine over until the pistons were at the top and ground the carbon off. Check out the before and after pics. The engine had 60k miles when I tore into it
http://ls1tech.com/forums/general-ma...-your-car.html
I actually used some seafoam on the tops of the pistons on my camaro when I had it torn down for heads and cam swap but it was taking too long to scrape everything off. In the end, I used an aluminum safe bristle disc and just barred the engine over until the pistons were at the top and ground the carbon off. Check out the before and after pics. The engine had 60k miles when I tore into it
not at high speeds, but if you pull 2nd or 3rd through the rpm range a couple times it will work.
reason: springs, vlaves, cams, all the engine peices are working harder, opening/closing harder, quicker and more often, it will knock some the the carbon build up off and send it out the pipes.
reason: springs, vlaves, cams, all the engine peices are working harder, opening/closing harder, quicker and more often, it will knock some the the carbon build up off and send it out the pipes.
Opening and closing harder? spring pressure is identical regardless of rpm/load.
quicker/more often...sure, but so what.
A modern car driven normally should not have chunks of carbon to be knocked off. It may have a light coating, but thats about it.
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M. Schneider (03-29-2020)
08-09-2011, 12:09 AM
#29
Rennlist Member
I have an e34 m5 which is used mainly for low rpm commute duty. I can tell you from first hand experience, if I do an Italian tune up for the first time in a while, it spews all kinds of smoke out the exhaust.
Runs after that produce much less smoke for a while.
I've always attributed this to the 185k miles and original valve seals/guides and burning all that crap out of the engine. I'm not sure if it is carbon or not, but the engine feels happier for a while.
Runs after that produce much less smoke for a while.
I've always attributed this to the 185k miles and original valve seals/guides and burning all that crap out of the engine. I'm not sure if it is carbon or not, but the engine feels happier for a while.
08-09-2011, 02:19 AM
#30
Addicted Specialist
Rennlist Member
Rennlist Member
I have an e34 m5 which is used mainly for low rpm commute duty. I can tell you from first hand experience, if I do an Italian tune up for the first time in a while, it spews all kinds of smoke out the exhaust.
Runs after that produce much less smoke for a while.
I've always attributed this to the 185k miles and original valve seals/guides and burning all that crap out of the engine. I'm not sure if it is carbon or not, but the engine feels happier for a while.
Runs after that produce much less smoke for a while.
I've always attributed this to the 185k miles and original valve seals/guides and burning all that crap out of the engine. I'm not sure if it is carbon or not, but the engine feels happier for a while.
Edward