I wouldn't.... As others have said, this is an old-school trick used frequently in the carburetor days. Ice water, in a spray mister, engine at operating temp. Technically speaking, the resultant thermal shock can shatter the carbon. With the engine running, it simply sends the partials down stream. The catalytic converters today wouldn't like that I'm sure...
I've posted the BG stuff before, and again re-gained about 30ft/lbs of torque after cleaning. (That's saying a lot right there...)
.

And a tad from the BG site
https://www.bgprod.com/blog/fuel-ser...our-customers/
Vince

 

It amazes me how there are more folks looking for performance gains in all the wrong places and no one thinks to this essential thing.
And its more than just power gain, its responsiveness too.
I will do the BG on the next go round. Been doing CRC.
Thanks for the quantifiable figures.

 

Very true especially on the 4.2 SC engine charge coolers, and below the throttle body which I believe get pretty clogged with soft carbon deposits after about 40-50 k miles or even sooner.

 

Not to rag on Q&C, but this did flicker a 'Wow... Interesting!' moment...
DI is perhaps the only time we can now consider 'extrude honing our intakes!

It was a rage years back to have your intakes polished. Everyone dove on the concept of uninterrupted fuel and airflow to the cylinders. Turned out the auto engineers knew what they were doing using a rough cast surface. I forget the term (laminar flow?), but the rough surface created minute vortexes, keeping the fuel suspended in the airflow as it traveled. People started polishing their intake surfaces only to discover that without the vorticies, fuel suddenly clung to the walls and allowed pooling and inconsistent delivery.
Having known this, I set the whole process aside as useless.

But as I'm reminded by Q&C's comment, we no longer have fuel running down our intakes, so smooth airflow via extrude hone is now finally a valid process that may offer gains!
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And another side note to the OP now that he has the intake manifold off, is to consider doing 'Port matching' before reassembly. I've done it on several cars in my past, and you would be shocked at just how far skewed the lineup between the manifold and the head can be.... Worth the time to look at while you're there...

Peace
Vince

(Of course I just noted the new post for the OP... showing he has already reassembled the engine....opps... MyBad)

 

Airflow is not the issue- neither is varnish, the evidence is right in front of our eyes; long before any of those become remotely an issue, the tops of valves is becoming a carbon magnet to where it resembles a port injected engine with 250000 miles.If they could coat those valves with the same film they do the throttle body, they would.
Basically the question is, how do you prevent anything sticking to the valves, and causing loss of performance; one could try a high temp non-stick coating, but if it flaked off you would have a disaster on your hands. Or you could reduce the surface area by micro polishing.

 

Sorry... You missed my point. I am saying that now I have an engine that does 'not' carry fuel through the intake, the issue of wet walls and fuel pooling is out of the picture. Now... after all the years of seeing problems with polishing the intake on normally injected (multi-port, single-port, or carburetor ) engines, extrude hone is now a viable performance enhancement, that's all.

V

 

I had the same thoughts Vince, especially on the lid where the supercharger directly discharges to it was very rough. If I was confident enough about getting the cac's out without damaging anything I was going to smooth that up myself. The manifold to head port was actually a pretty good match.

Performance wise I think there could be pretty good gains by porting/polishing the supercharger, intake manifolds, and lid. It would be nice to polish the ports but for most (like me) they wouldn't want to spend the time to do it in place and certainly wouldn't want to pull the heads for it.