Vanquishing carbon deposits (water injection)
01-28-2003, 02:17 PM
#1
Rennlist Member
Thread Starter
Vanquishing carbon deposits (water injection)
Years ago, I heard tell of a technique for removing carbon from Alfa Romeo motors. It went something like this: pull the air cleaner, start the car, rev it up to about 3,000-4,000 rpm, and then pour a glass of water down its throat about as fast as a person would drink it.
This always fascinated me, so a couple years ago I tried it.
I had a Saab 900 Turbo with about 200k miles. The engine control system had knock sensors. If the system detected detonation during boost, it would (among other things) open the wastegate of the turbo to reduce the boost just enough to make the detonation go away. Over the course of the 110,000 miles I put on the car, the max boost the system would allow seemed to gradually decrease.
A small rubber hose went from the PCV valve to the intake manifold, so I got a jumbo glass of water, disconnected the hose from the PCV valve, revved the motor to about 3,000 and stuck the hose (leading to the intake manifold) into the glass of water. Huge clouds of steam shot from the exhaust, and the car sucked that glass dry in about 10 seconds. <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" />
This procedure seemed to work. On the test drive the max boost was noticeably higher, which I attribute to fewer deposits in the combustion chambers. My brother (who has a normally aspirated Saab 900S with now about 300k miles) tried it too, he noticed a performance increase. His cat also ran hotter for a few days, we think because it was burning off the carbon blown into it.
So the question is, anyone tried this technique on a 911?
I might try it on my 964 if I can find the PCV plumbing, and if it leads to a reasonably symmetric location on the intake system (decent fluid/vapor distribution among the cylinders).
I know 964s have ceramic linings in the heads near the exhaust valves, but I don't think this "water injection" would hurt them, in other words I don't think shock cooling is an issue. After all, they get shock heated every morning when I fire up the motor and head off to work (with ambient temps below freezing, recently) and that does not seem to bother them.
This always fascinated me, so a couple years ago I tried it.
I had a Saab 900 Turbo with about 200k miles. The engine control system had knock sensors. If the system detected detonation during boost, it would (among other things) open the wastegate of the turbo to reduce the boost just enough to make the detonation go away. Over the course of the 110,000 miles I put on the car, the max boost the system would allow seemed to gradually decrease.
A small rubber hose went from the PCV valve to the intake manifold, so I got a jumbo glass of water, disconnected the hose from the PCV valve, revved the motor to about 3,000 and stuck the hose (leading to the intake manifold) into the glass of water. Huge clouds of steam shot from the exhaust, and the car sucked that glass dry in about 10 seconds. <img border="0" alt="[jumper]" title="" src="graemlins/jumper.gif" />
This procedure seemed to work. On the test drive the max boost was noticeably higher, which I attribute to fewer deposits in the combustion chambers. My brother (who has a normally aspirated Saab 900S with now about 300k miles) tried it too, he noticed a performance increase. His cat also ran hotter for a few days, we think because it was burning off the carbon blown into it.
So the question is, anyone tried this technique on a 911?
I might try it on my 964 if I can find the PCV plumbing, and if it leads to a reasonably symmetric location on the intake system (decent fluid/vapor distribution among the cylinders).
I know 964s have ceramic linings in the heads near the exhaust valves, but I don't think this "water injection" would hurt them, in other words I don't think shock cooling is an issue. After all, they get shock heated every morning when I fire up the motor and head off to work (with ambient temps below freezing, recently) and that does not seem to bother them.
01-28-2003, 08:48 PM
#2
I would be extremely careful about how much water you inject at a time. Water does not compress, and if you got too much into the cylinder you would blow the head off (which is one of the reason steam engines have cylinder ***** to allow the water to escape when they have sat for any length of time).
01-29-2003, 05:03 PM
#3
Rennlist Member
Thread Starter
Dsinn,
Good point, thanks for commenting.
In the context I gave I don't think this is an issue.
Consider a 964 motor (3.6 liter displacement, 6-cylinder, 4-stroke) running at 3,000 rpm with a compression ratio of 11:1 and slurping 1 liter of water every 10 seconds, each cylinder's combustion event will get 0.66 milliliters of water.
When the water stays in its liquid (incompressible) form, this raises the combustion ratio one percent to 11.11:1. Insignificant in my view.
I think there would have to be a lot more water before hydrostatic lock or excessive cylinder pressure would harm the engine. Especially with the engine running at mid/high rpm with no load.
Good point, thanks for commenting.
In the context I gave I don't think this is an issue.
Consider a 964 motor (3.6 liter displacement, 6-cylinder, 4-stroke) running at 3,000 rpm with a compression ratio of 11:1 and slurping 1 liter of water every 10 seconds, each cylinder's combustion event will get 0.66 milliliters of water.
When the water stays in its liquid (incompressible) form, this raises the combustion ratio one percent to 11.11:1. Insignificant in my view.
I think there would have to be a lot more water before hydrostatic lock or excessive cylinder pressure would harm the engine. Especially with the engine running at mid/high rpm with no load.
