High velocity porting....

[cheesie]

it is talked about in the tuning book I have and epoxy resin is used to fill the ports and then grind back to the shape you are after, i personaly would stick to tried and tested tuning on the trx unless the person doing it is a top race team engine builder and knows his shit

[Killerwhale]

Seems as most of you think it´s to big of a job....so now i HAVE to do it!!

[phuk72]

Seems as most of you think it´s to big of a job....so now i HAVE to do it!!

it's not a big job and not neccessarily that hard to do but getting it right is.

Gas flowing is a combination of science and experience. To get proper results you need to spend money and esnure that the flow through out the air / fuel cycle is correct - not just at the head. So to maximise the benefits you need to be thinking about air box, cams, compression, exaust etc.

Not one person I spoke to about tuning the TRX mentioned or suggested this - I have to wonder why? I fully understad the science behind it but maybe it isn't worth it on the TRX?

[Killerwhale]

Seems as most of you think it´s to big of a job....so now i HAVE to do it!!

it's not a big job and not neccessarily that hard to do but getting it right is.

Gas flowing is a combination of science and experience. To get proper results you need to spend money and esnure that the flow through out the air / fuel cycle is correct - not just at the head. So to maximise the benefits you need to be thinking about air box, cams, compression, exaust etc.

Not one person I spoke to about tuning the TRX mentioned or suggested this - I have to wonder why? I fully understad the science behind it but maybe it isn't worth it on the TRX?

Your quite right, but if the results are good at least someone has done a TRX!

[phuk72]

True enough - go for it

[youngy]

I fully understad the science behind it but maybe it isn't worth it on the TRX?

I'd say you're probably right. With a 5 valve head the inlet tracts are pretty small already.

[Quan-Time]

@ steve speed
Ive been busy the past ~2weeks and i totally missed this thread.. heh.

High velocity porting. Its valid to a point. It really depends on how your engine is setup, and how you want it to work and deliver power.

Changing your port velocity should be matched to your throttle body velocity for "optimum" performance, but even then, you need to know where you want your power.
Race bikes tend to be very top end, and "more HP over torque" as they rely on inertia to drive the engine, rather than brute force to pull out of a corner (such as low down torque). high velocity tends to premote more top end, and sacrifice some bottom end.
Think along the lines of tunnel rams / velocity stacks. The R1 yammy has a variable velocity stack so it has great top end (obviously for "we are the most powerful litre bike, woo !" but because they can change the stack height, they can premote quite reasonable mid range aswell. Obviously EFI aids in this achievement.

There are a few things you really want to do BEFORE you start velocity porting.
1: find out where you want your power (you want good low end power ? do your valves and seats, you will get better power), midrange ? clean up your ports, top end squeel ? port for velocity.
2: get your head port mapped. Find out where its flat spots are, how much does your port flow at a max (take your valve out, turn it upside down and put it in, flow, this is your theoretical max flow possible, then flow as normal with the valve the right way, this gives you a % of flow.. say with a valve in, you get 65% of flow at 100% lift (8mm / ~420thou) but you get 30% at 2mm lift (~80thou) which means you have great valve shape, but bad port shape, you can plot on a graph and see how things all work. Decide what section of your port need work.
3: check bias. Is the air going to one side of the port over the other ? balance it out, you would be surprised how much this can help.
4: i can keep going, but im gonna leave it there.

JB weld is fine to throw into your ports to build them up, IF !!! you clean your ports properly and spend quality time preparing. Attention to detail can be a real win here.
Id suggest:
1: CC your ports
2: clean your ports, make sure they are identical CC (within 0.5)
3: build up your ports and follow whatever rule you want (motoman says 65% from memory, i personally disagree, but we wont go into that here)
4: smooth your ports out as evenly as you can, make it all smooth, basically finish them off 95%
5: CC your ports so they are identical again. (the rest of the 5%)
6: balance your carbies before you do this, and check them for balance after, you should be able to attain a ratio of "they were this much out via % according to port CC, but because they even now, my balance should be out by that same % on the other cylinder (give or take a touch).

If you dont know how to CC your ports.. Get a plastic syringe (chemist / vet give em out). Clear piece of perspex or something. With your valves in, put the perspex (with 2 holes in it) covering the inlet, fill it up and count how many CCs of water / fluid you put in. I used a 30cc syringe and some water with food colouring. Because it was the head (same with exhaust port) i CC'd dirty and then cleaned. Carbon takes up 1cc on both heads I discovered.



One hole you put the syringe in, squeeze the fluid in, and air should come out the 2nd hole. I used a wipe of vasoline to seal it so it didnt run everywhere. 32cc for the record

Forgotten the head CC off hand, but ill get it this weekend and show you some port info when i got the chance to map it out on a graph.

Exhaust port is a completely different animal. There is a BULK load of directions to head here. I have my opinion, but again, i wont voice it, because everyone is different.

As for "D" porting, thats just the simple principal of "air travels faster over a flat surface". The velocity of fluid (air, its got fuel in it, thus treated as a fluid) is always zero. Think of it as a tank track. The track on the ground doesnt actually move, its stationary while the vehicle still moves forward. fluid does this in... sorta like "smoke rings" almost.
optimum "flow" or "raw CFM" potential would be divided into 3 parts (im going from memory here, its been a while since i studied the math on it).
you have a big round hole. Now imagine a smoke ring that just fits into it, but make the smoke ring 1/3rd the diameter of the hole thick. Meaning, the smoke ring is thickish. not really thin on the walls.


Ok, please excuse the shitty 10sec MS paint drawing.

BLUE is the fluid moving in the port. The left donut is us looking at the air, like thru a vacuum cleaner tube. Thats how it would be moving. The red is "venturi effect". The empty space "sucks" air in. because the air is spinning, it pulls air in, its how a vacuum cleaner pulls up stuff, but the void. Different size tubes provide different suction.
The pic of the right is a side on view of how it will look. The red being the parts sucking along.
Now theres a few things to take note of here. SMOOTH walls make tiny tank swirls, so the red part in the middle is bigger, as the "smoke rings" will be quite thin. Because its not hard to roll over. Really rough ports make really thick smoke rings, thus less red area.

If your port is too polished (and ive seen mirror finished ports and this happened) the velocity REALLY drops off. Sure you get a good raw CFM value, but the port velocity is quite slow. Grab some really rough sand paper / emery tape, rough up the port, velocity picks right up again and cfm is generally the same (picked up the smallest %)
If its too rough, you get whats called "reversion" in the port. Ever seen a carbie have "blow back" or a really old car that gets spits thru the carbie ? There is too much gunk in the inlet port and its creating so much port swirl that when the valve closes, it gets a push back effect. Think of a bunch of people running thru a door, slam the door closed, the ppl bunch up at the door, and push back, you can see a sort of "mexican wave" of ppl pushing back. The air does the same thing. Corvettes have "TPI" or "tuned port" length. You can calculate your port CC, air velocity, operating RPM, etc, you can calculate how long your runners should be (between your butterfly / carb slide to the back of your valves.
This is going to extreme lengths to suck out a 1/4 of a poofteenth HP, but its good for economy (so im told, i havnt seen anything to support that). Concidering most pro racing leagues have fuel / inlet restrictions, i guess there is merit in it, but its a bit beyond me honestly.

Summary is this:
Velocity porting is good, providing you setup properly. Also, take note to polish in the direction the fluid is moving. So when you want to sand, use "in and out" motion rather than "side to side" or a rotary pad. It premotes cfm and velocity. Side to side makes WAY too much swirl, and your velocity seems really good, but the dyno will prove otherwise.

enjoy. (sorry for the long winded reply)

[Killerwhale]

Well, it´s these kinda "articles" that should be in a sticky workshop thread!!

....i´l have to take a vacation to read thru it!!

[steve speed]

wow quan time thats fooking marvelous just got got back from hot and sunny Cyprus and started to read your post ,,,i think iam going to have to read it about six times to get it in my head ........... very very interesting ps iam still not sticking owt in my inlets

[HansJ]

OK, Pandora's box has been opened

As stated, there are probably as many opinions as there are tuners.

JBWeld or similar will stick, as long as the surface is cleaned well, and the mixing is done correctly. My engine has (although sometime I wonder) definitely had longer service intervals than 6 hours Like KW says, it's very common among the Swedish tuners to do. The guy who does my engine has used epoxy (don't think it's JBWeld though) for years, and only had a few cases where the glue went away. And even in this case, it won't be a disaster, the "glue" he uses will be smashed to powder and flushed through the exhaust long before it hurts the engine internals.

I agree with most of what QT says, but I was a bit surprised to read that higher speeds would increase top end power? What I've been told is the opposite, narrower ports will reduce top revs, but the fill factor in the head will be greater on lower revs? Flowing is really complex, especially as one has to take valve opening/closing into the equation... And I am not so convinced by the sanding direction either, but like I wrote, there are many opinions

Personally, this is not a job I'd carry out myself, theory is one thing, practice and experience is a completely different beer... It takes more than a couple of tries to get the feeling for what works and what not. And deciding withthe butt dyno is not enough...

But if You decide to go ahead and do it, instead of CCing the ports You could take it one step further and use one of those kits for making a "willy" copy for Your girlfriend, and instead use it to make a copy of the port, then it's much easier to see the form of the ports and to compare them (and it's possible to use them for calculating volume as well.)

[HansJ]

This gives You an idea what KW talks about. Granted, plastic isn't everything, it all depends on the goal with the flowing. In this case driveability has been emphasized over extra HPs on top.

[Killerwhale]

This gives You an idea what KW talks about. Granted, plastic isn't everything, it all depends on the goal with the flowing. In this case driveability has been emphasized over extra HPs on top.

Yup, fekkin´ great job...just can´t wait for your numbers!!

[phuk72]

Yep - my motor was flowed and ported to work with the Kent cams. Midrange was the goal

[kenmore]

What are you talking about?

One wonders how many of you would attempt to do what you are talking about?

I thought that this was a place to discuss real world issues about TRX850 Yamahas.

I used to enjoy the topics

Tell me to feck off if you like, but remember that sites like these are driven by ordinary every day people that enjoy the cameraderie of other owners and real world topics regarding their bikes.

Make it real,it's not a competition is it?

Anyone can pick up a book and expound on a subject, but in my world it's real world experience that counts.

Anyway,adios for now.

Hope that I have not offended anyone that contributed to this topic, but its a very technical discussion that most people would find threatining if they did not have a basic understanding of engines.

[youngy]

One wonders how many of you would attempt to do what you are talking about?

I thought that this was a place to discuss real world issues about TRX850 Yamahas.

That KW is attempting it makes it worth discussing.

Define real world issues, then we all know what is, and is not, acceptable subject matter.

Maybe admin can limit the forums to tyres, oil, mirrors and changing spark plugs?