Yamaha TRX850 Enthusiasts Forum

Well. Life is weird isnt it ? Just when you think you have time to do stuff, your thrown 3 curve balls in a row and then get hit by a spanner fair and square in the noggin.. *sigh*.

Made some time to go into the shed tonight. My last setup had a leak which was screwing with things.. Nothing drastic, but yer. I noticed it. My setup isnt pretty, but its what i quickly whacked together the other day mainly because of time restraints. It works, but as you can see, its.. err.. ugly. Doesnt effect readings, but yer. Ill make a proper adapter at some stage.. Its on the bottom of a LONG list of "to do".

Stock TRX850 cam is 8mm lift. The "kent cam" is 8.4mm from what i remember (someone correct me please) i tested up to just shy of 9mm. In 0.25mm increments.

OK. Should be fairly much explanatory, but ill break it down.
FPS = feet per second. Put a piece of confetti in the air, its how far it will move. IE: its the velocity of the air in the port. Higher is better, to some extent. Low movement means its not getting into the cylinder fast enough.
CFM = Cubic feet per minute. How much volume of air is getting in. More is better. always. (well, theres an exception to that rule too, but lets not go there)
Depression = The relative "power" of the air. How much ability it has to suck something.. Think strong vacuum VS weak vacuum.

With that said.. Im sure you can see that CFM tends to drop off a bit at top end.. Ive gone to almost 9mm, and the trend continues. Id expect total plateau around 10.5mm, or possibly 11mm at the outside. But its dropping fast, so my guess is 10.5mm.
Velocity tends to spike a bit. Partly due to internal turbulence, or possibly me not holding the velocity probe at EXACTLY the same spot every time.. But it was fairly consistent. It was in the middle port, just before the valve stem, in the middle of the runner. Each side was yielding faster FPS, but thats to be expected because of the port shape.

From ~6.00mm and up, FPS is about the same. It also SCREAMED as it was doing it. Its literally tearing the air apart. Its something i really need to fix. The port is just not able to ingest that amount of air with that port shape. It will do it, but it wont like it.

I have some RADICAL designs planned. Time will tell if they end up good or bad. Ill document with pics and stuff later on.. But i got the next 2 days off providing i leave my phone turned off and turn the stereo up in the shed so i cant hear the missus or the kid yelling at me.

OK.. Now for some other stuff.. Dunno how many people know this, but the inside of your chamber also effects flow. Its to do with swirl. Theres LOADS of ways of measuring this. Ive chosen the cheats method because of time restraints, but its inherently messy. But it gives a good idea of whats happening. Saying that, the stuff i used is too powdery.. Its good that its drying almost instantly, but its not getting a chance to stick to anything. Im able to wipe it off the inside of my bench, its like powder, its sticking to the head, but its very weak.. I need something more "inky". Much like dy-mark. It doesnt matter if the air moves it about thats partly what i WANT it to do.
Get a drop of water on a piece of paper,, now blow it with a straw.. all around.. Notice the nice lines it draws ? if you have someone else blow with a straw the same time, you get a TOTALLY different pattern, and different air pressure also does the same.. With a "inky" or slightly more liquid medium, this will happen and really show the path of where the air is actually going.
These were taken at 0.5mm lift increments, the last one is 8mm to show nothing else was happening.
The air was moving fast enough that it wasnt sticking.. So yer.. Ill need to retest with something better so i can see whats happening.
The method is to spray about 2 feet away, not directly at the port, but sort of "let the port pull the paint out of the air".. So that way it has a more natural path.


Not much happening.. Its only really dribbling air in anyway.

starting to see it get into the cracks. This is natural.

OK.. starting to see a defined line between the exhaust ports. Also seeing some bias on the bottom of one of the inlet valves. That inlet valve was usually SLOWER FPS than the other side, only by a touch.

Probably could have sprayed more. But yo ucan see it pooling around that exhaust valve, and it wants to break over.. Needed more time to reveal exactly what it wanted.

You can see it going from one exhaust valve to the other clearly, and then down and around to an inlet. This indicates a clockwise swirl. Its quite large, sometimes swirls are the size of a fingernail.

Its stopped swirling and wanting to break to the cyl side, between the exhaust ports. The swirl is going clockwise from one exhaust to the other, but its instantly going BACK and up at about 45deg.. You can see a heavy line drawn. On the cylinder wall at the 3 oclock position, you can see its got a line that is starting to carry on clockwise again.. Its like its comming off that lower exhaust valve, smashing against the cyl wall, and then swirling again. You can almost see the splatter mark.

Again, not really heavy enough. But you can see quite a collection on the lower inlet valve. Maybe its got a bias to that area ?

Velo's fairly much taken over here. Its got some signs, but nothing new, and velo is really starting to boogie now.. Paint is getting a chance to stick to anything.

I can see its still swirling clockwise some what.

Nothing new to report.. This is 8mm lift. I used a fair amount of paint as you can see. But when its comming out of the valves, its moving too fast.. once it slows down its able to stick as you can see by the layer of blue dusting on everything.

Well, thats about it for the moment. Hopefully i have something new to report in the next day or two, but no promises. Hope you all learnt something and if anyone has any questions or querys on anything, ask away ill answer to the best of my knowledge. (right or wrong, who knows !!)

Interesting as always!

But a few Qs:

You're pushing air in, or pulling?
Isn't the "piston" shape, i.e. the shape of what's been beneath the cylinder head crucial?
The volume below the cylinder head is also differing during the "real" intake phase, how does this affect your conclusions?

Maybe you could explain a bit more in detail how you performed this test?

Kent specs are 8.43 with 8.28 valve lift.

VERY intereseting stuff Quan-Time.
I`m wondering,have you thought of using a dye penetrant and a developer?

yer that was one of my thoughts. I used dymark aerosol can, but its very dry. Id like that dymark staining ink, and put it in a hand spray bottle. Would only require one squirt, that stuff gets EVERYWHERE. Ill have to experiment and find something good..
Also note: old toothbrush is great for cleaning the chamber out. With a clean rag to dry. That and a quick shot of the air compressor to make sure its good to go.

HansJ wrote:8<
Kent specs are 8.43 with 8.28 valve lift.

Is the lift with standard cam 8 mm?
I'd like to know because I screwed something up

yup, 8.00mm exactly.

Cheers. I discovered in the meantime that it's easy to measure though.

Well, time for an update.

I roughly modified my inlet port and have started work on it. And by "roughly" i mean "i was very rough with it".
If you compare the flowchart at the top with this one, you will notice quite a few things.

Lowend lift is MUCH more linear and progressive, theres no flat spot. Some people WANT that flat spot, and i can work on that later. Much of low end lift is purely about the valve angles and shapes rather than port design. So anything from about 1.5mm and less isnt really using the port as such.

Mid (3mm - 6mm) sees quite a marked improvement, it does obviously start to drop off much earlier than id want, but we can see CFM is up, not by a huge amount, but velo (FPS) is really startin to move.

High end (6mm - 9mm) starts to come on song for velo, but its fairly flat. I dont thing 10mm would yield any more volume (CFM) which means im restricting too much which i was honestly HOPING to do. This means that i can grind away rather than having to add back in. Make my life much easier at this stage.
Velo is really starting to help here, id suspect i can get it over 330fps which would be nice. Just need to find out where the exact restriction for CFM is then i can work around it to keep velo up, maybe even increase it if im lucky.

Id really like to see 225 or 250cfm at around 350fps at top end, but im not sure thats possible without another huge revision to what im doing. Ill have a play over the next few weeks and see how i go.
For the record, as it stands this head is good for over 110hp.

Questions / comments welcome obviously.

Quan-Time wrote:Questions / comments welcome obviously.

Holy poop. 110bhp from a TRX. Where do I sign?

think 110hp is good ? wait till you hear what im aiming for

The stock port also had a HUGE whistle / tearing sound. It SCREAMED at above 5mm lift. Its still loud, but noticeably quiter. Its one of the benefits. Also, the final "exhaust note" will change quite substantially. Sad, but not sure if it will be better or worse, but i like how it sounds now...

Quan-Time wrote:think 110hp is good ? wait till you hear what im aiming for

The stock port also had a HUGE whistle / tearing sound. It SCREAMED at above 5mm lift. Its still loud, but noticeably quiter. Its one of the benefits. Also, the final "exhaust note" will change quite substantially. Sad, but not sure if it will be better or worse, but i like how it sounds now...

When my head was ported i got areally noticable "sonic boom" on the exhausts (exhaust ports welded)

got a pic of how yours was done ? Im expecting a "D" port with the floor being raised slightly.. Who did your work ?

I have pics of my welded exhaust, but you won't see them until you explain my questions above...

Seriously, i do understand the basic concepts, and figured that much that the piston/lower part of combustion chamber is not really in play when inlet valves are open, but would still like to understand better what you're doing and what corners are cut for drawing the conclusions? And it's pure curiousity, i am not on the "hunt" nor in any sense a pro or even an amateur... Just want to learn!

HansJ wrote: You're pushing air in, or pulling?

Pulling for inlet, pushing for exhaust. My flowbench works in 2 directions.

HansJ wrote: Isn't the "piston" shape, i.e. the shape of what's been beneath the cylinder head crucial?

Yes. Piston shape has an.. "impact" on flow characteristics. A good "rule" to follow is, 1.5x cylinder diameter as the simulated stroke. That means dont just have the head open. Lets say the piston diameter is 100mm, that means you want about 150mm of cylinder for the test run. its not perfect, but it does give you a very good ball park / idea of how things willl swirl.
Understand that the cylinder is under VACUUM, so yes there is a piston in the way. Its not a perfectly linear vacuum, but its reasonably close to being linear. People have been flowing heads in this manor for almost 40 years now. If a better system comes along, im sure everyone would use it. But the 1.5x rule seems to help. Theres other things you can do to help and be more consistent, but for someone chasing 2hp and not 0.2hp, its perfect. Incidentally, thats 0.2hp on a 700hp engine. Thats how fussy, and consistent they can do it.

HansJ wrote: The volume below the cylinder head is also differing during the "real" intake phase, how does this affect your conclusions?

Refer to my above point. "clean" air will also be DIFFERENT to air with something in it, such as fuel. Its why many of the BIG players in cylinder head development are using "wetflow" to work on the chamber shape. Its not perfect, but gives you a fairly good representation.

HansJ wrote: Maybe you could explain a bit more in detail how you performed this test?

What part are you refering to ? Im using a flowbench to get my results. Its a digital manometer which can repeat results quite easy. This is a pic of TDM900 throttles which I flowed.


Does that let me see your welded up port ? Im just interested in how other ppl do things. Obviously theres more than one way to skin a cat, but its surprising how people who are 10,000km apart come to the same conclusion / port design. So yer.. linky me up !!

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EDIT
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OK.. you wanna learn ? ok.. It takes ~2cfm of air to produce 1hp, fuel dependent. If you use "charge motion" porting, ie: try to match your resonating freq to your cam, you can get MORE filling than you would normally, which means more power. Your inlet area (total valve size) should be approx 58% of your cyl diameter. Your exhaust port you want to chase FPS (velocity) NOT CFM. You want that air to do some serious boogie. Most people make the mistake of OPENING their port when actally if you close it up, you get more benefit. "Air" flows faster over a flat surface, rather than a curved surface. You want some down draft on your inlet, but its dependent on your port config, we have 3v so that makes it a bitch. Incidentally, the "Break-point" of "air" is 11deg. Which means if you have a radius of MORE than 11deg per diameter, the air seriously screws up and looses momentum. That means DONT bent a tube back on itself, you want to create a "horse shoe" size rather than a really sharp bend. If you create a too sharp a bend, you can get problems.. Ive seen carb's do a burn back. They spit fuel out, and that was on a brand new port. Only cos the fool who did it was .. he was a fool. When a port starts "backing up" you did something wrong. Backing up is when you flow your port, and at a higher lift, its DECREASING cfm or fps, much like a dip in the power curve. Always flow to a lift which is GREATER than what you will run the cam, its why i go 9mm. If you get backing up at a higher lift, the engine WILL see that effect and give you a HUGE flat spot. So you need to sort that out quickly.

What else do you want to learn ? flow basics, port design, flow method, some maths,.. gimmie some direction and ill walk you thru it. Contact me in PM if you want some REALLY interesting stuff to chew on.

PM sent

And later I'll probably follow up with some questions of more common interest.