OK, I'll confess up front. I'm working on a 2.3L I4. But my questions should pertain to all engines. I recently picked up a spare cylinder head with the full intake up to the throttle body to do a port and polish on. Now I've read the standard abrasives instructions for DIY describing leaving the intake somewhat rough but polishing the exhaust runners.

Now, here is the question. The intake I got is quite fouled from what I assume to be residue from the EGR feeding exhaust gases back into the intake. Now the entire intake before the injectors just flows air. SOOOOO......does it make sense to polish the intake up to the injectors or is it just a waste of time and effort??

 

depends what you consider wasteing your time but since its a 2.3 you need all the power you can get.

 

even if its just air flowing through, if you open it up a little it will always help and like fordeverpower said you will need all the power you can find for that motor.

 

I would only polish the area close to the EGR inlet port..to keep the exhaust deposits from building up and keeping the intake runner clean.....therefore more able to dissapate heat.

Keep in mind that the intake runners have to gradually decrease in size as they approach in the intake runner.....with the smallest part of the port being the riser....and smooth the bowls out....create a teardrop shape around the valve guide boss....with the point facing the cyl head to intake mating surfaces.

You still want to bead blast the intake ports (except the EGR area) to help agitate the air coming into the engine....remember the air moves fast and you need as much agitation before the injectors as possible.

gasket match the exhaust ports, smooth and polish.....most of the work will probably need to be done around the valve guide boss...bowls and lower radius.

good luck...let us know how it goes.

 

David Vizard, an engine tuner, did some research on the subject of porting for street engines. One area of study that's been overlooked in the past is reversion.

Short answer; yes you can polish your intake smooth, but it might be best to polish the long side and leave the short side rough to help prevent reversion.

 

I would not worry so much about polishing the ports. Just don't remove any significant amount of meat around them. Intake velocity is important to low-end torque. Velocity drops off with wider ports and intake runners.

 

Intake velocity is important to low-end torque. Velocity drops off with wider ports and intake runners.
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I do agree with this based on the gas laws......aka physics.

which is why I specified this:
Keep in mind that the intake runners have to gradually decrease in size as they approach in the intake runner.....with the smallest part of the port being the riser....

FOr street applications, it isn't always a good idea to port match to the gasket.......leave at least 1mm around the inner of each gasket port opening....juST REMEMBER THAT when porting, the main task is to remove ans smooth factory cast flashing in order to prevent reversion and unwanted turbulence.

As long as the intake ports get progressively smaller as they approach the riser in the cyl head intake port....the velocity will increase....

smaller port = less volume (this means more frequent collisions betwen air molecules.....this means higher pressure thus higher potential velocity.

Open the ports up too much and the amount of air the engine moves won't be sufficient to stimulate higher port velocity until the higher rpms kick in.

Do more research on this.....you are already on the right track with us talking to you about it.

 

Thanks for the advice, Capone.

I wasn't planning on significantly altering the geometry of the intake runners or intake ports. Just matching openings at the gaskets (not to the gaskets but just to each other), cleaning out all casting flaws, etc. I guess having the turbulent airflow before the injectors makes sense so out with the intake polishing.

I think I have Vizard's book (How to build HP?), but only the first one which deals with carbed engines. I definitely wasn't going to polish the intake ports on the head. Again just smoothing the rough edges and port matching. My plan is to go with larger valves and a more agressive cam. When that happens the valve seats will have to be re-ground, un-shrouded and possible new valve guides put in. May shorten the deck some to bump compression closer to 10:1 but I haven't decided. I wouldn't do that if I were to stroke it later on.

Have always been told that the head was the bottle neck on this engine. But is some clean up and detail work all that is needed to release it or are we being too conservative here??

 

Stock ranger,

The ideal setup is to clean up the intake runners, have them bead blasted
in order to help keep the moving air inside the runners agitated. Turbulence can induce reversion and this is bad......

reversion is caused by slowing the intake port velocity where one shouldn't.

This is why I stated to make sure the intake runners start large at the Plenum....and make a gradual transition to a smaller port up until the port riser (just before the lower radius begins the dropoff towards the valve seat)

Alot of the work will need to be done to the area around the valve guide...

I can emails you some pics to help you visualize what needs to be done....and give you ported and untouched port pics for comparison.

ask away before touching the carbide to the metal...

 

seeing as there is only air moveing throug it i would polish the shi_ out of it myslef to make it smoth as a babys botom more air flow the beter it is on carborted or throtle boby motors id leave it rough. besides i know porshe and masadies have smothe intake ports on there EFI motors. hope this helps Andy

 

My 3.8L in my car gained 8rwhp/4rwtq from polishing the the runners completly on the upper and lower intake. Polish them up to a mirror like shine BEFORE the injectors, and a slightly rough finish after the injectors.

 

This is what I'd do. The only qualification to this idea is that I'd look at where the injectors are pointed and leave that area of the port rough to help with fuel atomization. And if there is a pinched in area, such as where the port might curve around a pushrod passage, polish that surface to increase the velocity relative to the rest of the port. That's how Vizard ported to prevent reversion.

The increased surface area of a rough surface and the slight turbulence caused by the roughness will help with the atomization of any fuel that lands there.

 

Do not match the intake and head ports. Even the slightest misalignment will result in lower flow. Always make sure your intake manifold port is smaller then the port in the head and the gasket. The intake does not fit onto the engine precisely in the same way every time since there are clearances around the bolt holes etc. Edelbrock casts their manifold to allow for this variance, I suppose the other manufacturers do also.

A polished runner will have higher friction than a slightly rough finish due to boundary layer flows. The exhaust is polished to hold more heat in the gas and to reduce the buildup of deposits on the surface. The intake manifold "as cast" finish is best for flow. The only thing you need to do is rough grind away any imperfections along casting lines etc.

 

the rough finish that the intakes have from the factoryis great for carborated, With EFI you WANT a smooth shinny surface before the injectors. We have flow tested a stock 3.8L intake with just the casting flash cleaned up on the runners and another one with the runners cleaned up and polished to a nice dull shine. The one with the dull shine outflowed the one with "factory" surface. I've been working with porting intakes and heads for a few years and a polished surface does work better before the injectors on an EFI intake.

 

That test may not have been quite correct somehow, maybe enough material was removed in the polishing process to increase the cross section significantly. The aerodynamics people have done a lot of research in this area.