is it worth the time to polish your runners in the skunk2 intake manny, will it even do anything?

 

are you gonna be doing it yourself and why?
many people rouned their IMs and lost power because they heard that port and polish is good.

it should be done by a pro and tested on a flow bench.
or someone local with experience. but have the car dynoed before and after to see the gains losses and get your money back in case of loss in power...

 

you will prolly get alot of different opinions on the "polishing" question.

heres mine...it doesnt matter if the surface is perfectly smooth or slightly rough (cast). there is a boundary along the walls and the air flows inside of this boundary.

in other words its not gonna hurt to polish it but i doubt it will help either, the air doesnt know the difference.

 

This is true with Injection. The runners are so far away from the injectors that it doesnt matter. The only thing that matters is AIR FLOW.

If you could move the injectors towards the plenum than I would say keep it a little rough so the fuel & air can mix better..

 

yeah i did hear that injectors that spray further back in the runners, should keep the runner cast rough or w/e so it mixes better to polished it dosent. i was just wondering cus just thinking about how friction works on air flow just that tiny bit of cast roughness, id figure would slow the air flow a bit at the walls.

 

I acknowledge that I know nothing specifically about S2s pro intake, but I have to believe these principals would apply to anything. Up until 2006, we used to just CNC mill the port windows and throttle bores in our manifolds and the runner material in between was all hand ported and blended with a "tootsie roll" finish. So it wasn't "polished" but it was smooth with noticeable surface scratches.

Before the investment was made on new 5-axis CNC machines, Jim (Kinsler) wanted to learn about the difference as well. So we did either 4 or 5 manifolds: one hand ported like normal, the other 3 or 4 were identical in every way except they we're CNC'd at another shop, each with different cutting paths and overstep. Since everything we do is CNC'd now, it goes without saying what won, but the most interesting thing was how the overstep in itself affected performance.

We came to the conclusion that the smoother the runner is, the more friction the air has passing through it. Since the air has nowhere to roll as if forms the boundary layer, the boundary layer "thickens" the longer it is. The CNC'd runners had minute dimples and ridges from the cutting path/tool that we concluded gave the air an area to roll as it tumbled down the runner, reducing the boundary layer.

And I can't help but to compare it to the dimples on a golf ball.

Regardless of the science, the hand ported mani made 840 hp vs. the cnc'd mani's 860 hp, and that was enough for us.

I also recall in the early 2000's, a friend of mine was all excited to have his ITR manifold Extrude-honed. It lost HP and he was pissed.

 

Extruding is really only good for FI applications. When things need to be hogged out for more , non directional mass air flow...

 

good **** right there

 

I feel like I should put foot in mouth though because you're beating my customers. dammit.

 

was the op asking about DIY or professional polish anyway he didnt really specify.

 

Its so good to see a companies like Kinsler using CNC machines and putting research into tool paths, stepovers, machine feeds and speeds for making HP,and giving there products the edge over there competition with surface finishes.It took me 3 years playing around to work this out with combustion chamber finishes.

 

i was just intrested in the idea to see what everyone thought. if i would do anything id just do it myself. beleive me i have comfidence in myself that id be able to. all i was looking for is nothing like a smooth shine finish just a lil smoother say running some 280 300 grit sand paper or one of those port polish ***** and use a short bit. but as i am reading the post i am just gonna stick with not doing it. the whole not letting the air roll on its self makes since.

 

Some Pics of my polished GSR manifold.




The gains with manifold change on stock GSR cams.
Most of the gains came in the mid range. Made the car really fun.
Tuned on a Hondata S300 in a P72 ECU with IAB relay.




I'm curious why did the CNC make more power than the hand ported? All the shops I have been in contact with that CNC manifolds reshape the runners with a taper. That speeds up the air and creates more power.
When a shop hand ports they typically don't go to the extremes of reshaping the runners by hand, just making them shiny.
Now a polished CNC’d manifold you'll have the best of both.

OH and my car did make power.

 

I thought polishing was only for exhaust side.. I thought by porting the runners and not polishing it gives a "cyclone" effect which would maximize airflow ?

 

I remember Omni (Steve) saying something a couple years ago that having your intake manifolt ITR style Extrude-honed was typically good for an 8% power increase if I remember correctly. Was it an ITR motor that he lost power on? Was it across the whole power band?

 

good stuff.

On a couple manifolds I have had my hands on i noticed the casting marks and flashing (excess material in the area where 2 mold halves, or dies, meet) were really bad. these would have been parts that came off the mold at the end of a long, hot day, or near the end of the molds life. With these conditions gains would definitely be seen after cleaning up the casting and a slight polishing, but as many people have mentioned, there are things going on at the boundary layer that aren't necessarily common sense.

as a general rule of thumb, when working with mild setups, remove any obstruction but don't change the size or shape
changing the surface finish probably won't make a noticeable difference on most setups

sc at kfi's example showed a 2% increase at the mid 800- hp level, a 2% increase at 200 hp is only 4hp and that is probably being generous.

although i have only taken one fluid dynamics course at school, some of it is applicable to this type of thing. I could see the larger mass of air flow in a boosted setup being the reason that a polish shows gains.
since there is more air pressure and flow the boundary layer is reduced. Since the boundary layer is shorter, the air has less time to accelerate from no movement at the surface of the plenum wall, to the flow velocity in the center area. thus more restriction in the boundary layer requires more force to over come and less force is used in the acceleration of the intake charge into the cylinder.

 

lol

so send me a set of itb's and put your name on my car

 

I didn't notice much of a difference in polishing mine.

 

I think its really cool you can say that. its nice to see someone who's ego doesn't get the best of them



I did a mild clean up on a p75 im that was on a b20b motor for my buddy, I used the cheap 80grit rolls on a die grinder and it turned out pretty good. motor pulls alot better on the top end now. Id say it made a few more whp at least.

 

is this just a myth?

 

I think most of the real engine builders I know polish the runners because that is what customers like to see. they like "shiny" hahah.... but it really does not help performance

 

great post, can't argue with THE GODFATHER of B series