carbon build up and flow numbers

[rebelrouser]

I want to ask what you guys think about carbon build up in cylinder heads and its effect on air flow. I know I do a lot of work on engines that people run for several seasons, and I wash the heads just enough to get the oil off and flow them with the carbon still in runners and chambers. I always see an improvement after they are cleaned before doing any valve work or further porting. Do any of you guys use a carbon cleaning product in your race engines? Motorvac and BG products both make a good cleaning system I have used on stock engines. A lot of the newer engines especially those direct injected engines have a lot of carbon issues.

[David Redszus]

I want to ask what you guys think about carbon build up in cylinder heads and its effect on air flow. I know I do a lot of work on engines that people run for several seasons, and I wash the heads just enough to get the oil off and flow them with the carbon still in runners and chambers. I always see an improvement after they are cleaned before doing any valve work or further porting. Do any of you guys use a carbon cleaning product in your race engines? Motorvac and BG products both make a good cleaning system I have used on stock engines. A lot of the newer engines especially those direct injected engines have a lot of carbon issues.

Just to add more crap to your bucket.

Consider the effects of hot carbon deposits in a running engine on air flow. The local heat changes the local air density and viscosity,
and therefore the air mass flow.

[mag2555]

On the Exh side of the motor carbon scale and rust scale can add up to a reduction in flow real fast!
Take a look at this.
Here's the difference in flow from a Exh port that's only some 3.5 inches long.
All I did was use a 80 grit sanding roll to remove the carbon and rust, note in the pictures that I did not add polish anywhere.

If this much of a flow gain comes from just a port 3.5 inches long then think about what can take place in the tubes of a used header!

Flow @ 28"
.050--.100---.200---.300---400---.450---.500---.550---.600---.650
22.4---43.8--89.9---120.2--149.5-156.4--162.3-166.6--167.2
With clean up
22.5--44.2--91.5---128.4--153.5--161.3-167.2-174--177------180

[GARY C]

I want to ask what you guys think about carbon build up in cylinder heads and its effect on air flow. I know I do a lot of work on engines that people run for several seasons, and I wash the heads just enough to get the oil off and flow them with the carbon still in runners and chambers. I always see an improvement after they are cleaned before doing any valve work or further porting. Do any of you guys use a carbon cleaning product in your race engines? Motorvac and BG products both make a good cleaning system I have used on stock engines. A lot of the newer engines especially those direct injected engines have a lot of carbon issues.

Just to add more crap to your bucket.

Consider the effects of hot carbon deposits in a running engine on air flow. The local heat changes the local air density and viscosity,
and therefore the air mass flow.

Does it increase or decrease temp? It seems it would insulate the runner from heat and the texture would help fuel atomization therefore cooling the intake charge.

I think you would have to do a before and after dyno test to find out it's effects.

[MadBill]

Many years ago Smokey related a story about one of his engines mysteriously losing 20 HP during an all-nighter session. They finally realized that somewhere along the way they'd switched headers to a pair that was identical in every way, except for heavy rust deposits in all the tubes of the second set...

[GARY C]

Many years ago Smokey related a story about one of his engines mysteriously losing 20 HP during an all-nighter session. They finally realized that somewhere along the way they'd switched headers to a pair that was identical in every way, except for heavy rust deposits in all the tubes of the second set...

When Lingenfelter was interviewed about his Pro Stock truck development he said that they polished and coated the inside of the primary tube on the step header. I don't remember is exact statement but it was measurable enough to do it.

Intake side may be a different story.

[mag2555]

If you ask me the Intake side reacts like my Exh side test does here, and Exh wise it's likely even far worse as a flow bench can not produce air at near sonic speed!
And yes I know the Intake ports do need texture for wet flow fuel issues.