Polishing intake runners

[JustJeff]

I'm curious what people think about polishing intakes?

I'm specifically interested in polishing the intake runners on the irons, but also interested about polishing the runners on the LIM and UIM.

I'm in the middle of a rebuild on a JDM S5 13B that is mostly stock. I'm not doing any porting of irons or housings. I had a friend suggest I polish the intake runners on my irons, but to me it seems like the benefits from that would be minimal at best.

I suppose all things being equal polishing wont hurt anything. But I'm all out of those types of bits for my dremel and don't want to spend $40 on bits for little or no gain.

[TitaniumTT]

You don't want to polish the runners at all. Clean them up sure, but I wouldn't go any finer than a 220 sanding wheel.

What should benefit you more than polishing the runners is portmatching EVERYTHING. Elbow to TB, TB to UIM, UIM to LIM, LIM to block.

[JustJeff]

^ Got any links. I understand the idea of port matching but not the procedure.

[sen2two]

Dealing with port matching, porting, shaping, polishing, ect. can be VERY trick.

Paul Yaw did a test on a 12a with a flow bench. One port matched, one stock. The stock one produced better flow and power. And he knows what he's doing. Not guess work.

It's a hit or miss without a dyno or a flow bench. But in saying that, I always port, shape, and mess with my intake manifolds, TB's, ect. If it works cool, if not, I'm not trying to set records... so no big deal.

[TitaniumTT]

You are correct, if you're not testing you're guessing and I did read that "blog" by Paul. However, it has been documented that there are gains to be had on the RE mani with port-matching and honing... so I did it damnit.

[sen2two]

There are plenty of designs online to build a home made flow bench on the cheap. I'm just wondering if its worth the space it will take up if your just doing it for fun. Now if I was competing or trying to break records, I would build one and test my manifolds before I did anything else...

[TitaniumTT]

Links? I've got a spare set of mani's that are bone stock right now that I wouldn't mind testing before and after...

[sen2two]

Did a quick google search and came up with this... I'm sure there's a ton of info here. A bunch of links came up when i searched diy flow bench.

http://www.tractorsport.com/cgi-bin/.../ikonboard.cgi

[NoDOHC]

What is inportant is that the intake runners do not change in cross-sectional area throughout the entire length of the runner. This way the air can maintain a constant velocity. The runner should be slightly larger than the intake port, so that the air is accelerated through the port, resulting in better fuel mix.

I polished my intake runners to 600 grit where dry and 160 grit where wet (after the injectors). If you polish the runner too much where they are wet, you will see a symptom called fuel pooling, which is the fuel forming rivulets on the polished surface. Fuel pooling will make the engine idle very poorly.

160 grit seems to have a small problem with fuel pooling, but nothing next to 600 grit.

My engine will occasionally misfire at low fuel and air flow rates (idle, lightly loaded cruising), but the misfiring is infrequent and barely noticable.

If I were you, I would probably not go past 80 grit past the injectors if you want a good idle.

If you follow the rules of intake porting, there are major gains to be had from it.

EDIT: Here is a thread where this was discussed.
http://www.rotarycarclub.com/rotary_...ead.php?t=8550

[JustJeff]

Thanks for the link I'll read it later tonight

What I have read so far about port matching is regarding piston engines. I'm sure it's the same idea but the lip created by variance between where two runners meet encourages the fuel to start coming out of suspension from the air. In other words the fuel starts sticking to walls of the runner at those points.

What I don't understand yet is how you determine which lips/contact surfaces need matched. Or for that matter how much they are off from each other. With piston engines they talk about simply using a marker through cylinder heads and such.

What I'm assuming I could do is use a light coat of paint or ink, simply bolt the parts together and then pull them apart. But that seems awfully prone to fucking it up. Seems like the amounts they will be off will me millimeters and any wiggle or smudging of the paint/ink will throw the whole measurement off.

I'll be doing engine work today between football games and I'll look over the parts. Hopefully having parts in hand I can figure out answers to my questions.

[vex]

Most people port match to the gaskets. Just sayin'

[RETed]

Yep, use the stock gaskets.
It's the "easiest" method.
Just port both sides to match the gasket dimensions.


-Ted

[JustJeff]

That sounds awfully prone to simply making them wider but not matched much better than the factory did. I'd think having them widen and then constrict back down would equally help pull the fuel out of suspension just as much as an uneven lip. Like NoDOHC posted. Hhmmm but perhaps allow the air to flow "better".

I'll read what NoDOHC linked after lunch and some football.

[TitaniumTT]

Here's how I do it.

Lets say you're matching the UIM to the LIM.

There are a few studs on the LIM so place the gasket over them. There should be little wiggle room but there will be some. If there is enough such that the gasket is interfering with the ports, you need to tape that gasket in place. But do this before you put a few bolts through the upper intake manifold and make sure the same thing doesn't occur.

Once you're satisfied that the gasket is in the right position and tapped off such that it won't move, assembly the sandwich. Take a small 3/32 or 1/16" drill bit and drill through the Upper intake mani, the gasket and into the LIM.

Remove upper intake.

Place drill bit through hole in gasket and into hole in LIM. Mark with whatever what needs to be ported.

Port

Place drill bits through UIM and gasket and mark with whatever what needs to be ported

Port

Clean throughoughly

Place drill bit through UIM, place gasket over drill bits, place gasket, UIM, and bits over LIM until bits fall into previously made holes on LIM.

Bolt UIM to LIM.

Remove drill bits.

PayPal me some form of compensation and go touch yourself repeatedly infront of the mirror while your neighbor watchs.

[NoDOHC]

I think you understand this issue better than most already.

The purpose of port matching is to avoid any steps in the intake runners (where the ports do not match) which impede flow.

There are various factors that can impede flow, one of which is a step in the pipe.

Bad flow results in a loss of power (pressure drop in the intake runners will reduce the pressure in the chamber when the intake port closes, thus decreasing the volumetric efficiency of the engine)

The air must flow at a certain velocity in the pipe in order to acheive a certain flow rate. Losses are related to velocity (slightly greater than the 2nd power). Larger diameter pipe will result in a lower velocity (fewer losses).

The effective diameter is what I call the center portion of the intake runner that is able to carry air (not effected by the boundary layer). The boundary area is determined by surface roughness of the material. Polishing the runners will decrease the boundary layer, increasing the effective diameter of the runner. Bear in mind that increasing the size of the runner has it's own implications.

Larger runners will help high end and hurt low end (due to fuel mixing problems and lack of energy for inertial or resonance tuning).

Please remember that with any intake-injected engine, it is not all about air flow, but fuel mixing and mixture distribution are equally important. On a DI engine, it is only air, so make it flow as well as you can.

On no account should the intake port be larger in cross-sectional area than the runner (unless this is a track-only engine). This will result in a poor low end performance and excessive fuel consumption as some of the fuel will fall out of suspension in the runner as it expands.

If a runner diameter can't be maintained constant, it should decrease area as it goes toward the engine as this will keep the fuel in suspension.

I wish I could explain this simply, maybe Vex can help me out:

Any step in the wall of the pipe disturbs the flow of the air, so does any change in cross-sectional area (as it requires a change in the velocity of the gas). Turns also create losses.

Basically, any time the air changes velocity (magnitude or direction) it requires energy to do so. This energy is absorbed from the incoming air as a pressure drop in the intake runner.

To make a long story short, what you say is true. If you gasket-match the intake manifold to the block without addressing the cross sectional ares of the intake runners or the block, it would probably have been better to have left it alone. If you gasket-match the intake and then make sure that the runners also match the cross-sectional ares of the intake manifold gaskets, you should have a very good flowing engine.

It is completely acceptable to polish the exhaust ports to a mirror-like finish. This will do no harm to the engine. It will have two effects:

Nominally better heat reflection (less exhaust heat absorbed by the inserts).
Slightly louder exhaust note (less sound energy absorbes by the exhaust ports).

Exhaust ports should increase in size as they leave the engine. sharp steps are a no-no, but the gas is expanding and cooling, so it will need more cross-sectional area as it moves away from the port.

My friend who taught me to port always said "If you think bigger is better, leave the exhaust port alone."

I hope this helps. It helped me when it was explained to me.