Coating the inside of the intake?

[Dirk37]

As we know extrude honing the intake makes it perfectly smooth on the inside which removes the turbulence layer and helps airflow. What if instead of polishing the metal, the inside was coated with paint or plastidip or something of that nature? Theoretically the surface should be just as smooth as extrude honing.The difficult part would be the actual process of coating it, but I feel like pouring it in and rotating it around and then blowing some air through it to remove the excess would work just fine.

 

[Racer X]

Doing this would also potentially reduce the internal volume of the intake runners, changing it's performance characteristics, nevermind the risk of the oil breaking down the paint and the subsequent ingestion by the engine.

EH, or even acid porting are far better options.

 

[sperold]

You are trying everything else without the benefit of a script, so I don't see why you should stop now.
I know that people paint the interior of the heads to maximize the oil return back to the sump, so there are paints that will work for every application.

 

[Dirk37]

Doing this would also potentially reduce the internal volume of the intake runners, changing it's performance characteristics, nevermind the risk of the oil breaking down the paint and the subsequent ingestion by the engine.

EH, or even acid porting are far better options.

How significant is the volume of the intake runners?

There are several oil resistant paints, one in particular I've used in the past is glyptal. I can tell you from experience that stuff is almost impossible to remove even with acetone, I still have a red spot on my back patio from 3 years ago. As sperold mentioned, people coat the inside of blocks with paint for better oil flow, one of the most popular paints being glyptal so it is definitely oil resistant.

I'm thinking to maintain the volume of the intake runners, I'll acid port it and then paint it internally.

 

[sperold]

It is only in theory that a bigger volume is better in the intake. When it comes to thermodynamics, the obvious isn't obvious at all.

I remember in the old days of ShoShop, they built some tube headers for the exhaust which should have freed up the exhaust and maybe increased volumetric efficiency. When installed, the motors produced less horsepower. And at the time, that was something that was obvious.

As far as paint, whatever the intake is made from, just get a paint for that material. It is in a slightly grimy environment, but as far as I know, it is only air going through it. As far as heat goes, whatever temp range of paint that is suitable for the outside of a motor should be ok for the inside, as most of the time it will be cooler than the outside. You have the minus 20 to consider as well, and the rapid heating to much higher temperatures. Maybe a primer and a finish coat is in order. Talk to a paint guy and get some advice and consider painting an intake on the outside (maybe in a not obvious place) and see how it behaves.

 

[SHOdded]

It is in a slightly grimy environment, but as far as I know, it is only air going through it.

Air & PVC blowby (unless you get a real good catchcan ) ...

How do you coat the insides of the intake evenly? Would seem easier in a shop set up to do that kind of work.

 

[broke1]

It is only in theory that a bigger volume is better in the intake.

That can only be said for some N/A applications. Turbocharged apps will gain hp/tq every time when increasing plenum size/runner volume.

My Escalades NA stroker engine picked up substantial hp with a larger plenum/runner volume with this Holley intake vs a FAST. 20hp/15ft lbs at peak on an engine dyno.

 

[rubydist]

Size of the intake runners does indeed matter significantly, as does length of the runners. What people tend to forget is that air does have mass. The airflow through an intake is not a nice smooth flow, in spite of the fact that magazines like to publish airflow test results.

The air column for each cylinder only flows when the intake valve is open. If the cross section of the intake runner is too small, then there is more pressure drop as the air moves, and less air actually gets into the cylinder. If the cross section is too large, then the air moves more slowly as it takes longer to accelerate the larger mass of air.

The length is important because air is also compressible and if properly tuned for length, the pressure waves can help accelerate the air column into the cylinder. That is why the SHO has primary intake runners that are longer and shorter secondary runners - to take advantage of the pressure wave to fill the cylinder better. If you have ever looked at a torque curve for the stock SHO motor, there are two torque peaks - one before the secondaries open and one after - now you know why. If you run secondaries open all the time, the low rpm torque falls significantly. If you never open the secondaries, the higher rpm torque falls significantly.

OK, so what does all that mean in terms of the op's question? Guys have done extrude hones on intakes and shown performance improvement, mostly at higher rpms. I think that is as much from the smoothening of the intake runners as from the cross section ***********, but I don't know. A good test would be needed to confirm. In any case, I would not be interested in anything that made the cross section area smaller by more than a couple of thousandths of an inch (a thin layer of paint). The thin layer of paint would not even out the casting roughness, so extrude honing or other smoothening would need to be done first, in which case I don't see the point of the paint. A layer of paint thick enough to take out the casting roughness would result in a significant reduction in cross section, which would cause me to rule it out immediately. Remember that the area of a circle is proportional to the square of the diameter, so doubling the diameter gets 4x the area.

sperold's comments about larger exhaust not necessarily being better are only partly relevant - the exhaust side has much more than atmospheric pressure to induce flow, and the reflected pressure waves are even more important, so exhaust tuning is even more challenging, imho.

 

[Slo-Sho]

You can thin out the plasti dip up to a 1:1 ratio with xylene from the hardware store varying the ratio for pour/sprayability...thoughts of the insides of the intake looking as smooth as glass...damn why did I have to see this thread? LOL