Carbon buildup in a combustion chamber - how bad is it?

[greymouser7]

i was watching a porting video on YouTube and they mentioned carbon buildup.

I look it up on the web and most references relate to the problems created by direct injection-which I understand.

1. How bad is it?

Is this correct: “You might already be aware that an additional heat buildup of just 30° to 40°F from excessive combustionchamber carbon deposits can cause preignition, resulting in a reduction in fuel economy,”

2. Does it get everywhere? In and around the top ring? Around the valve seal?
Valve seat? Valve guide?

3. Is this not a problem due to other parts of the engine wearing out prior to significant buildup? (not a concern except for racers??)

4. They used to talk about the parrafin in AV gas creating significant carbon build up and aviation combustion engines are subject to 3,000 hour rebuilds unless home built.

5. Does a polished combustion chamber reduce this problem?

6. More likely to occur on iron or aluminum heads/cheap gas or ethanol free fuel??

Extremely curious, thanks for your time!!

 

[RustyRatRod]

Drivers who drive like grandma are usually the ones where carbon buildup is a problem. If you blow it out regularly by dumping the secondaries open or brisk acceleration, you'll probably never have that problem. If you think you might, take a coke can full of water and dribble it down the primaries of the carburetor keeping the RPM up around 2500. That will steam all the carbon off the piston tops and out of the chambers.

 

[Max1196]

Here's a couple of yukies for you. This crap you see is caused by old stale fuel, It will stick the valves in the guides and bend the pushrods.

 

[Slowswinger]

My concern would be enough build up that prevents the gas ring from sealing causing excessive blow by.

 

[MOPAROFFICIAL]

Here's a couple of yukies for you. This crap you see is caused by old stale fuel, It will stick the valves in the guides and bend the pushrods.
View attachment 1715398753 View attachment 1715398754

Most look like that in 5k

 

[greymouser7]

Seafoam help any?

 

[MOPAROFFICIAL]

Seafoam help any?

stock style engine the valve will spin in the field wash will usually keep a good amount of it cleaned the oil that gets down the guy does buildup however on the backside of the valve Heating and cooking on to it along with fuel deposits.
Know where the performance motor the valves don't spend the spring pressures are high in the valve does not rotate you will see buildup on mostly one side.

Carbon takes up space, adds heat, hinders flow....it sucks.
Guides perfect, ring seal perfect, carb tune perfect..you'll barely have any, just a light lil crust patch near the exhaust somewhere after a few thou of full throttle blasting...depends how you drive how long it takes.
Ridding it? Turn it up to 2500 and dump trans fluid down the carb..lol...water is better and won't get the FD called on ya.

 

[yellow rose]

There will always be carbon in the combustion chamber. When you burn fuel and it goes through its (somewhat) orderly decomposition you develop deposits.

You can read the burn patterns and see where there is no fuel in the air (all clean spots on Pistons and combustion chambers is from no fuel in that area...its not from fuel wash as is commonly believed) and looking at those you can correct any porting issues or whatever to correct the issue.

Even alcohol based fuels leave carbon.

The issue is when it becomes excessive deposits. Those can be caused by a crappy tune up, and even crappy fuel.

Slow, late timing, untuned, rich carburation or both will cause excessive deposits.


Edit: When I get the spark plug looking mean (when I like the tuneup) I pull the headers and look in the exhaust ports. The exhaust port adds information to reading spark plugs and piston tops, which are the bottom of the combustion chamber.

 

[Kern Dog]

If you take a coke can full of water and dribble it down the primaries of the carburetor keeping the RPM up around 2500. That will steam all the carbon off the piston tops and out of the chambers.

I understand also that because water cannot compress, it bounces around in the chambers to knock loose some of the deposits.

 

[RustyRatRod]

I understand also that because water cannot compress, it bounces around in the chambers to knock loose some of the deposits.

That may well be true.....which is also the reason for the high idle. Since engines cannot compress liquid, you don't want anything stupid happenin. lol

 

[Kern Dog]

I wonder how much of the crap gets embedded in the mufflers ???

 

[Kern Dog]

I once had a super high mile '84 Chevy truck. After replacing the engine I expected it to have more power. I tried a bunch of things and had no luck UNTIL I pulled the catalytic converter and found the input screen (Looks like a screen on a screen door) was at least half blocked by what was surely burnt oil/carbon/fuel.
I put in a straight pipe in place of the converter...(For testing or course, gotta comply with CA smog laws) With the straight pipe, the truck peeled out for the first time in years!

 

[MopaR&D]

I understand also that because water cannot compress, it bounces around in the chambers to knock loose some of the deposits.

With the engine spinning that fast the water gets atomized as it flows past the throttle valves just like fuel coming out of the boosters. Water obviously doesn't burn but gets hot really quickly and turns to steam from the air/fuel mix burning which kind of "blasts" the carbon off.

If you floor it occasionally while driving the only places carbon will build up much is in the exhaust ports and pipes. It builds up in the exhaust system as the gases cool down and can't carry the carbon all the way out the tailpipe.

 

[jos51700]

Keep it floor-boarded, and carbon build-up will be the least of your problems. I guarantee it.

 

[toolmanmike]

Drivers who drive like grandma are usually the ones where carbon buildup is a problem. If you blow it out regularly by dumping the secondaries open or brisk acceleration, you'll probably never have that problem. If you think you might, take a coke can full of water and dribble it down the primaries of the carburetor keeping the RPM up around 2500. That will steam all the carbon off the piston tops and out of the chambers.

And it works.

 

[Syleng1]

If “water based steam” is not your feel good place then go to Gm dealer. They have in a can (everything magical at GM is can based) a top engine cleaner. One can per 1 V8. Works amazing.

Engine hot and rpm is up to
Like 2500; slowly dump can down throttle slowly. When you get to 1/2 left, can pour rest in to throttles to stall the engine. If big engine- you need to shut key off to kill the engine. Not a huge can mind you like pint.
Then let it sit over night. Next morning start it up and drive it hard. A lot of stuff will come out tail pipes. It cleans everything from chambers, to valves to mufflers and even cats. It may even kill the neighbors cat that sleeps on your hood at night. Anyhow good stuff. But the water method is cheap easy and also works. GM stuff was developed in the 70’s for oil carbon.... a GM that does not leak or burn oil... is out of oil. Lol!

 

[TrailBeast]

i was watching a porting video on YouTube and they mentioned carbon buildup.

I look it up on the web and most references relate to the problems created by direct injection-which I understand.

1. How bad is it?

Is this correct: “You might already be aware that an additional heat buildup of just 30° to 40°F from excessive combustionchamber carbon deposits can cause preignition, resulting in a reduction in fuel economy,”

2. Does it get everywhere? In and around the top ring? Around the valve seal?
Valve seat? Valve guide?

3. Is this not a problem due to other parts of the engine wearing out prior to significant buildup? (not a concern except for racers??)

4. They used to talk about the parrafin in AV gas creating significant carbon build up and aviation combustion engines are subject to 3,000 hour rebuilds unless home built.

5. Does a polished combustion chamber reduce this problem?

6. More likely to occur on iron or aluminum heads/cheap gas or ethanol free fuel??

Extremely curious, thanks for your time!!

To answer your valve question specifically, direct injection is inside the cylinder so it doesn't wash the back side of your valves and they get a buildup.
TB injection and carbed helps wash the valves, and port injection washes them even better do to the fuel spraying directly on the back side of the valves.

As far as buildup everywhere else, the guys have explained that already.
PS, water down the intake works really well but doesn't do squat for the backs of the valves.
Only inside the cylinder when the fuel is ignited.

2. Yes carbon buildup can get everywhere inside the cylinder as low on the piston as the oil rings and both sides of the valves.

3. It really only affect engines where crap fuel is used and/or the engine is babied all the time.

4. ??? No idea.

5. Yes, as polishing gives deposits less to attach to.

6. I would guess head material wouldn't matter much, so both.

 

[adriver]

Great movie with a great running joke about that in it.