It doesn't help that some people say "port and polish", so people just coming into the idea of engine work hear "port and polish" and think that getting everything all polished up is going to be some big benefit...

IMO polishing *anything* is for show, not go!

I get physically irritated every time I hear "port and polish" to describe portwork.

 

Polishing hurts laminar flow. You'll get less flow with a smooth port wall. Take a look at the science of golf ball dimples to see how this works.

http://www.golfjoy.com/golf_physics/dynamics.asp

 

that's an 80 grit finish. it just photographs nicely

 

The dimples on a golf ball(I don't need to check the link) operate by traping a bubble of air that circulates round and round acting like a ball bearing. Not a knew idea. It' been used in aircraft wings, in both dimples and series of steps. The latter has been used by Fountain power boats in hull design. Dimples have been outlawed on wings and underpanels in F1 racing.

That said. Can you prove that the irregular cast surface of a stock port has the same effect? Every race shop I've been in, no matter what they're racing, smoothes thier ports. If it doesn't offer an improvement, then why is Extrudehone in bussiness?

I've always heard that the rough surface increases the "boundry layer" of the air stream. The layer of air that doesn't move as well because of it's proximity to the surface. It's always there and has to be influenced by the smoothness of the surface.

 

I understand why the rough wall is better for flow on the intake side, is polishing the exhaust still the way to go to, for lack of a better term, 'reflect' exhaust heat?

 

i've never heard of a rougher finish actually improving airflow, rather providing turbulence so the fuel doesn't stick to the wall.

 

Th most obvious answer to that question is because people will pay for it. In business the most important thing is making money. Look at how many ads and claims are out there that we know are bogus. There is always someone who will believe it though. That's the key to making money. It's selling your product and idea to people with claims. How about the tornado? Not saying extrude hone is absolutely terrible as the cast marks are probably worse but it's definitely not optimal. You can use the process to make passages larger. This is an easy way to do it if you need it. Just go back and rough it up a bit. There are some good things about extrude honing.

Alot of race shops also follow the philosophy that bigger is better. This too is wrong. I'm not saying that all race shops are all dumb but I will go so far as to say a majority of them are ignorant to how things really work. There are some very good ones out there though. I can think of a couple of local shops here that follow the bigger is better philosophy and have no clue how things really work. They just make them larger and crank up the boost. They don't know where the gains really came from. When you find a good race shop, they'll take everything into account and can tell you why it works that way and how they came about doing it that way.

The casting marks in a manifold are not uniform. Like Dave I too use 80 grit to finish off my ports and runners but will go no smoother. This is smoother than the irregular cast surface but still not smooth as glass. Polishing is definitely a no no.

 

Fountain is known for his "step hull" which breaks water tension utilzing air which has less friction than water.
However,
pad sanding in boat racing is standerd (I owned an Allison XB2002) but once again it is to break water tension. Guitair Junkies is correct on the fuel application. But today's F.I. eliminates a lot of the carb / runner fuel pooling of the past.

 

i've got a question about the golf ball thing--

does that only work when the ball is rotating, or does it have the same/similar effect if the ball is stationary?

 

Well the affects of the golf ball are from the rotation and the dimples. You will recieve more lift w/ more speed and spin on the ball. Therefore the dimples have more of an effect at higher speeds and spin. This is why it is easier to hit a wedge straight versus a 3 iron. I don't know a ton about physics, but I have made my fair share of money w/ 14 clubs and a white ball.

 

so why would the dimples help port flow if the port isn't spinning?

is it just the little pockets of air that act as bearings between the main flow of air and the port wall?

 

It is all compromises.

Irregularities (like a dimple, casting grain, etc) will trip the flow to turbulent and this WILL help it to cling to the port wall for a short radius bend (like opening edge of port).

The thicker boundry layer can also keep fuel from condensing on the surface and so offer better gas mileage- especially during warm up.

But smooth has its advantages as well as it offers a thinner boundry layer and so more room for actual flow.

If it is all rough there is a thicker boundry layer and so the airflow is actually happening in a smaller cross section. If you take off 1/16th inch of stock irregular surface finish off all the way through porting a manifold smooth you have increased the flow cross section by 16th inch PLUS the difference of the now thinner boundry layer all around the surface.

Since Guitarjunkie likes to port the port runners larger (as do I) he will really like the benifit of porting the manifolds larger to match

It also increases the dynamic affect as the accoustic wave travels with less energy loss on the smoothed surface as well.

Just stick one end of the manifold in water and "flap" the runner w/ stiff 80 grit (off a belt sander). Material comes off VERY quickly w/ the help of water. You can work to finer grits if you want...

 

The fact that it is spinning has nothing to do with it. Spinning actually changes the effective speed over the top and bottom in relation to each other. This is what leads to a ball curving in flight.

 

so if dimpling is a better way to do it, how come i've never seen or heard of it done before? yea, "most" shops/people hog it out and think bigger is better, but surely, SOMEONE has to have done it...

 

Yup it's been done before. The key is to do it in certain locations to try to promote airflow in one direction. In the case of the intake ports, make the inside of the turn much rougher and th outer edge smoother. Go over to nopistons and chat with Lynn Hanover about it.

 

will do.

 

This brings up some interesting discussion. I've wrestled with so many different concepts and ideas when it comes to porting that it makes my head spin. Sometimes I tend towards the "bigger is better" feeling, or the "no, keep it small" feeling, or the "make it smoother than a baby's butt" thing, or whatever. The thing that I find difficult about much of this is the quantifiable, practical, and measurable end-effect of all of this. Sure, with drastic changes like mild to extreme overlap in the case of a bridgeport, the changes are evident the first time the engine starts (if it does, that is). However, on some of these other changes th at still stay within the pale of its size and shape, the effects seem more subtle... atleast, that's what I've found to be true.

Lately I've been toying with the idea of cutting and shaping the primary ports with semi-small port outlets, left only with 60 grit grinding stones and no finishing work. I am curious as to whether or not it will help with low-end and low-loads such as vacuum driving, throttling, gas mileage, etc.

I recently did this on Reese LeBlanc's 20B motor as well as a buddy of mine's 13BREW here a month or so back.

http://bdc.cyberosity.com/v/Assembly...geViewsIndex=1

It's kind of hard to tell, but the secondaries are my usual finished product, but the primaries, while shaped and cut the way I normally do them, are left rough. What do you guys think?

B

 

i think i'd like a reliable, inexpensive way to measure everything. then a couple kegs of coffee, and some "alone" time in my shed. i'd get to the bottom of things and bring the proof to back it up.

i think a lot of the fuel atomisation characteristics are totally negated when guys swap out their primary injectors. the injector has a spray pattern, and if it's not deep enough in there, you're gonna be spraying fuel right onto the walls and it won't matter what finish the ports have. obviously, we all know this, but i work on a lot of cars that have injectors stuck in any way they can where they technically don't leak. injectors, and their placement are a BIG deal!

 

One thing I've noticed is that small things like this don't really seem to do much with forced induction. You can do so many things "wrong" when used for naturally aspirated engines but still have great results with a turbo. I use the term "wrong" very loosely of course. We've seen accounts of bell radiuses on the intake runners in plenums that work great for naturally aspirated engines but then hinder power when used with forced induction.

Brian I'm willing to bet that you won't see any difference power wise. Any changes will probably only be when not under boost when cruising and even then so many things can afect mileage that it may even be hard to prove. Especially on a half bridge engine. When under boost the bigger is better approach isn't neccessarily bad but it can be on a naturally aspirated engine. You probably won't notice anything with that engine.

I think techniques like these would be far more beneficial on a naturally aspirated engine where every little bit of flow makes a difference. Forced induction makes up for much of these techniques.

 

Lynn has plans up for a simple flowbench on No pistons. A flow bench and your smoke machine could be very useful and fun!

For fuel atomisation tests you could convert to a wet flow bench, but truthfully it is not such a big deal with a turbo as the heat of the compressed air charge really helps atomise/evaporate the fuel. It would help save gas during warm up.

Just remember it is only a tool and can be used wrong. I have read on here guys designing exhaust port sleeves on a flowbench for more flow. Great, but the gas leaving the port is still rapidly expanding and a standard flow bench won't account for that. Not to metion designing it so the accoustic reversion wave is reflected away from the port opening.

Part of the fun is figuring out how to flow your ports as close to how they are in the engine as possible (primary opposing 2ndary, rotor as port wall during opening/closing, etc.)

 

I don't have a smoke machine. Do you mean guitarjunkie? I do have a flowbench.

Actually I'm the person with the exhaust sleeves. They work really well. The "small" ones keep the stock exhaust port size but hold that cross section all the way into the header. I love these on n/a engines. It really broadens the powerband with a good set of custom built headers. On turbos they work really well too with extremely fast spool and great top end as a result of a larger a/r housing but you need to be careful about turbo selection. You need an Inconel wheel. There are alot of people on the forum who don't believe anything without actually seeing it (and even then they doubt it most of the time) so I really have no desire to share lots of things for that reason. They can go figure it out on their own instead of me wasting my time trying to convince them which never works anyways. The flowbench does show a nice improvement in flow with the sleeves and the results verify that it does work. The whole point of them is to keep really high exhaust velocity which keeps more energy in the system. You can alter tuning with header length. Steps in headers can be used in some cases to alter the powerband. The size of the pipe after the header collector alters the powerband as well. It's not only the primary length and diameter. Gasses only expand for a very short time. Then they rapidly start to cool and slow down. You can even make the pipe smaller starting at a certain point in the system as you get towards the rear of the car with no bad side effects. When it comes to the sleeves, high velocity is the most important things. The science of expanding gasses of accounted for in the header. It's not that hard and certainly doesn't hurt power anywhere. You just can't use any off the shelf parts with them which makes them more trouble to use. The sleeves are just doing ot properly. If you altered the exhaust port openings on any piston engine to simulate the area and shape changes in a rotary exhaust, the world would laugh at you and power would fall off. Mazda had to do this to dissipate alot of heat though so they made a tradeoff. Go look at the race peripheral port housings. They don't have this same expansion as the street engines. They stay fairly consistent.

I agree that a flowbench is only a tool and any tool an be used wrong. To use a bench properly with rotary intake and exhaust ports, you need to have a rotor crossing the port at several different stages of opening and closing. Piston engines are tested at different stages of "lift". We need to do the rotary equivalent. Too many people only test with no rotor in place with the port wide open. That's the wrong way to do it. This technique leads to people always searching for the highest number. Then you also need to use a velocity probe which is really nothing more than a skinny welding rod with different sized ball bearings on the tip. Insert these into the airflow at different points to watch how flow is affected. The thing that you are really trying to do isn't so much to get the highest flow numbers you can but to fix the problem areas that have turbulence and poor flow. You are trying to even out the flow in the entire system. The total flow number is the last thing I care about, and the thing that should take the least priority in some cases. Getting it all even is what matters most.

The worst "tool" that people seem to misuse is common sense as air doesn't always do what it appears it should do. A flowbench can sometimes leave you scratching your head at the results because common sense just didn't see it happening that way. How many times do we see people gasket match their manifolds? For what? Common sense may tell people that this is a good idea because it is smooth but the reality is that the runner area goes from one size, to larger where the work was performed and then back to smaller. Area changes remove energy from the air. Keep it as consistent as possible. Instead of gasket matching, make the downstream side gasket sized but the upstream side stock. This is a small lip. Not alot and airflow won't even see it as an issue on the way to the engine. This is more beneficial. It'll help stop gas reversion but not returning acoustic pulses. Both of these "gasket matching" techniques can't be seen on a flowbench when flowed normally if the area that was worked on was not the worst flowing part of the system. However flow both of them backwards and you'll see a difference from that lip! You wouldn't know unless you tested it.

When used properly with a little bit of knowledge, a flowbench is a fantastic tool. It is far more helpful than common sense and guessing anyday. When used wrong it is a hinderance but show me any tool this isn't necessarily true for. Use the right tool for the job and use it properly. There is no one thing out there that will give you all the answers.

 

i'm using a cosmo intermediate in my latest engine. other than cleanup, the ports are almost stock size. with the huge runners, that makes the port outlet the smallest link in the chain. i'm hoping the extra velocity will make a difference in both low end and cruise tuning. i also dug out a bit where the injectors spit. i'll be using the rochester injectors as primaries (since they atomise the best), but in doing so, they have a bit wider spray pattern. so i ported a bit of a "bubble" just right around the injector outlet to keep fuel off the walls. all that, combined with the later opening of the primaries, should help improve the fuel economy overall.

and if i'm wrong, i can always open them up later on down the road.

 

i'm at 24/400+ now.

my new goal is 25+mpg, 400whp, on 87 octane

 

If unless you can get the charge colder than Alaska in a blizzard, 87 octane is far too volatile for that kind of power.

B

 

No, I don't remember seeing Rotarygod thread on exhaust sleeves-I will go search for it. I like things that improve spool up .

I was thinking of another thread where they designed exhaust sleeves w/ volume expansion for best laminar flow on the flow bench, but lost power on the dyno.

-edit spelling