Port and Polish?

[audijunky]

This may sound stupid but what does this consist of? I am interested if it can be done yourself (myself). Any one know what actually is done and w/what tools. I generally get the Idea,just wondering how it is actually done. Actually I dont want to open anything up any more (unless it is fairly easy),just want to clean thoroughly and polish exhaust ports.Thanks Steve

[DiverRay]

Steve,
You can use a dremmel tool to clean up the ports. The exhaust should be a mirror finish, and the intake NEEDS TO BE A SATIN FINISH. The intake side needs just a bit of turbulance to help mix the air/fuel.
A good "do it yourself" would be to clean the bumps and polish the exhaust, and then clean the big bumps on the intake. I wouldn't try to "open up" the ports, as you need all 4 to flow the same amount, or you can have problems with the way the engine runs. one other trick is to polish the valves all the way to the face. If you look at the part that opens, the "head side" usually is just a little rough. Drag racers can take .10 of a second off the ET just with a polish on the valves.
Ray

[audijunky]

Thank you for your reply kind sir. Icalled a buddy at a shop and he says it will cost about 500 to port and polish/clean valves. Sound like a good deal?

[trbig]

Hmmmm Ray,

I remember this subject in here before and it seems to me that they said that polishing the exhaust actually DECREASED horsepower. The back-presure was helping it. I am wrong alot of times, but I will do some checking on it.

Tod

[DiverRay]

Tod,
Backpressure can be had in many forms. A small diameter pipe (stock Yamaha) will help keep some pressure, but a large diameter pipe (header) may decrease the pressure. A basic port job will include an almost mirror finish on the exhaust ports, and a satin finish on the intake. This is basic motor building. The exhaust system will then be built for the motor, and the back pressure needs met.
My Kirker 4 into 1 system has small diameter head pipes, 1.38". E Liberty has 1.5" pipes on his MAC 2 into 1 system, and they both run well.
Porting a head helps the engine breath, and produce more HP. The actual porting is almost as much art as science, and it does cost too have a good job done.
Ray

[Goin Commando]

Porting a head helps the engine breath, and produce more HP.

Mostly on the top end of your rev range.

The actual porting is almost as much art as science, and it does cost too have a good job done.

Yes it is and yes it does, just going in with a cutting tool and hoging out the ports any ol way, will only ruin your day. There is a reason that porting costs so much, you really do have to have some kind of a clue before you start messin with the ports.
The term "port and polish" is from two stroke tuning, not really any polishing on a four strokes head. polishing the exhaust ports on your 4 stroke is kind of usless as the carbon will build up in there within a couple of hundred miles anyway. Racers rebuild there motors after every race and the fuel they use is very different, polishing the exhaust ports might be of some benifit to them, but no noticable improvement to us.
I would try and Google some information on this subject before breakin out the power tools.

[Geezer]

You would get more return on your efforts matching up the intake manifolds to the intake ports. Any step there would reduce flow.

Smoothing and polishing the exhaust ports helps reduce cylinder head temp but not by much. The smoother surface also builds up carbon slower and even carboned up, will be smoother and flow a little better. It's still a lot of work for a tiny improvement.

There are new coatings for combustion chambers and ports that are very promising but also very expensive. I'm holding out opinion until I see some dyno test results.

Polishing the valves is another thing that's a lot of work and yields little or no improvement. Back in the 70's one of the bike rags did a test on this and actually lost flow. After that they had to take the head to a pro and have it worked on to get the flow numbers up.

Geezer

[trbig]

Man... I can't find the link I was looking for. Someone had done some port and polishing and had pictures and everything with dyno runs. Anybody else remember the thread I am talking about? I can't find it.

Tod

[MAXIMAN]

Maybe Sensei Dan will chime in here. He has a wealth of info to add.

While it is true that porting a head is very much an art...the science of it comes in the form of a flow bench. Not all artists are equal.

Back pressure in the flow regime of an engine can occur in two place ...pre combustion and post combustion. Post is done via exhaust tuning. Pre is done by welding up the intake ports. This creates higher annular velocity resulting in more power due to more turbulence and better combustion.

A decent acceptable port job can be had without a flw bench. But the fact is you never really know if the flow is exactly. There are some mathematical rule concerning flow regimes in internal combustion 4 strokes. It's basically a ratio of intake to exhaust.

SENSEI! SENSEI! help! I'm getting in over my head!

[Goin Commando]

The smoother surface also builds up carbon slower and even carboned up, will be smoother and flow a little better. It's still a lot of work for a tiny improvement.

On our low compression, low yield engines you would feel this mod about as much as you would feel the difference if you had indexed the plugs.

Btw, thank you for the regulator/rectifier Geezer, it works good.

[81xsproject]

trbig, I think you are thinking of pggg. I know he has ported his heads.

[TADracer]

My $0.02

I guess my two cents on this subject would be as follows,

Match up the intake runners with the manifolds.
Remove little material but maintain a satin finish on the intakes.
Concentrate on the bowl area just above the intake valves.
Smooth the bowl area into the valve seats.
Get a good 3-angle seat grind and lap the valves in.
Polish the exhaust runners smooth.
Exhaust ports kept slightly smaller (maybe 1/16") than the exhaust pipe (if possible).
While everything is apart, check valve spring compression and the valve guides and seals.

This is alot of work and in reality may not produce much of a gain on a street bike. Any gain would be noticed on the top end. Plan on spending a few hours per runner. Also, you take the chance of ruining your head if you do any major grinding. Once good flow characteristics are lost it is nearly impossible to regain them back.

Now, if I were going to do major head work for a real gain I think I might just clean up the intake/exhaust runners alittle and look into milling a few thousanths from the head surface to raise compression ratio up to maybe 10-1. This will raise cylinder pressure and that usually results in more HP. But then you would probably need to use premium gas.

[pggg]

TAD it's factory mass-production that leaves 'rough edges' on all sorts of engine components that can be improved with a lot of extra work that the mass-production costs just don't allow for, from the few XS11 motors I've seen, they all had a mis-match of a few mm's around the inlet/ carb manifold area, whack off the extra few mm's of alloy from the inlet perimeter and you've done what they call a 'clean up' in other words you've matched the inlet ports to the carb boots.

Some rip-off outfits will call it a port-job and hit ya for a few hundred bucks, you can do it yourself with an electric drill fitted with a grind stone. For a 'proper' port-job, it's still a job done with a hand-held die-grinder, it takes the experts a couple of days or more to do, they're experts only because practice makes perfect and they've done it all before. they grind out the stock heads' obstructions and re-shape the bends and curves, they swap from port to port as they go, gradually re-shaping and grinding each port evenly untill done.

It's all checked and measured continuously throughout to ensure the ports are carbon-copies of each other. There's variations for each 'type' from mild street to full on race, a good port job gives a noticible kick of extra power, even without hot cams and big carbs, it's also not true a port job only gives a boost at high revs, the experts will port the head to give extra power right through from idle to redline.

[mro]

TAD it's factory mass-production that leaves 'rough edges' on all sorts of engine components

Just outa curiosity,
has anyone bothered to check out "combustion chamber volume" on an XS.

Just guessing, but 4 or 6cc difference between cylinders could make for maybe 5% compression ratio difference??? Don’t know if it would be noticeable on a stock XS.


mro

[TADracer]

PGGG,
Everything you say is certainly true. Mass production methods are a trade off that usually leaves alot to be desired from a perofrmance standpoint. My comments are made from very limited experience with an XS head. Rather they are more from experience with automotive heads for dragracing (wish I had a dollar for every pound of heads I have screwed up back in my day). What I see is that the XS head is already pretty efficient with short intake runners, a fairly straight through design, hemispherical chambers and no real bumps or nodes in the runners that have to do with water jacket or air pump castings, etc., to upset the airflow. I do not have a flow bench but I suspect the XS head is probably already a fairly good-flowing design and probably has something to do with the high torque that these engines give in stock form.

When I did my head I stuck to most of the steps I listed because they were rleatively easy to do and were fairly reproducible in a home workshop with hand tools. I did notice the mismatch in the intake runners and the manifiolds so I blended those. I also noticed a very, very small step where the intake bowl met the valve seat and I blended that as well. And I figured that since the darn thing was off of the bike I might as well do some checking and tweeking around the valves and freshen up the seats. Did I get kick in the pants performance from this? No I did'nt. What I did find is that even slight tuning seems to have a more noticable effect and that tells me the work was worth the effort.

Without a flow bench, heavy porting is blind trial and error. There is something to be said for a guy (or girl) that has the gumption to get in there and start grinding. Before CNC machines came along that can reproduce shapes that are identical to its neighbor, trial and error was the state of the art. And an art it still is, even with a CNC machine. If you have a bad porting job and a CNC machine, you can make thousands of bad ports. It is just plain fun to get in there with a die grinder and fashion your own. But, since XS heads are not quite as prevelant as say, small block Chevy or Ford heads, it will be a real gamble for the unexperienced to do much more than a clean up (unless you are sitting on a few extra practice heads). Thats why I think on a street machine, less is more. Just a clean up, sort of a 'blueprinting' if you will, to put eveything in order to realize better gains from other mods that are easier to do and are reversable if they dont work..

Cause remember, once you uncan a can of worms...........