F5's 300 head mod thread
 

Well I might as well start a new thread for this, there have been a couple before but not with quantitative figures that I have seen.

Clearly if this gets beyond you there are plenty of tuners that will take your money for their well earned development time & expertise machining stuff.

This is my take doing it myself using fairly simple well trodden paths. I've done this a heap of times on small cc roadrace bikes and the odd larger roadbike & dirtbike. The principles are the same although the application requires a different approach for best results. -read: roadrace application lots of revs, lower MSV, top end power over acceleration.

Anyhoo this is a playbike to me, not a racebike. one of the big considerations is being able to kick it over in snotty trails & I'm 5'8". The advantage here is there is a compression hole drilled above the exhaust port to reduce the compression ratio, but it is only ~4mm so while it will help at kicking speeds it shouldn't have much affect at high rpm. If you were going to Motard this you'd block it up.

That & the easy compression ratio is why the 300 is as easy to kick over as the 200. I intend to keep the comm the same to retain the same level of ease. That said. maybe I'll be a little greedy and crank it 1/2 a ratio & see how it goes, I can easily pull a bit more out if needs be. Easier than putting metal back in.

OK to start with here are a couple of pics & I'll add how I got there next post. You can see the mandrel which screws into the spark plug hole. It needs to be flat/straight to be worth while.

OK my bike is an '07 EC300. The principles will remain the same, but I can't tell you where other models may have altered in spec.

3 years ago I bought it & I fired a new piston in it 2 ago. I sadly onl get to ride this bike once a month on average. When I measured it I was a bit surprised, but its taken me till now to do something about it as time has been tight & racebikes take priority over perfectly serviceable playbikes.

Compression ratio was about 12.5:1, which is easy on a 300, esp a square one at 72/72 (maybe new ones grew 0.5 with a quick google). The squish clearance was a mammoth 2mm.

Squish areas have long been used to reduce risk of detonation by creating a thin boundary layer of cool gas that doesn't burn & promotes good cooling to the piston from the cool head.

Also by reducing the spark lead (Length the flame has to travel from the sparkplug) and thus combustion time. As a point the piston is not driven down by an explosion, the spark ignites & burns the fuel to increase the pressure; Boyles law in a fixed volume, except the fixed volume, has a piston on one side that is pushed to create a bigger volume, reducing pressure as it does so.

On top of that it increases the MSV but I'll get to that later.

Any space in the squish is a lost batch of combustible gas. Of course you need to have some space as the clearance gets used up at high revs. But as long as it never touches, you're sweet.

Manufacturers always leave this gap huge so if they get a batch of long rods, tall pistons & short barrels, there is still a gap. However if you just shave the head to reduce this to a decent gap the compression ratio always seems to go too high, so its a bit of a faff.

The queer thing is my bike had a 4*(degree) difference between the piston & the head squish area. This increases the area of unburnt gas which the flame can't effectively get to and decreases the pressure that the mixture is squished & squirted into the burning part of the chamber.

As the piston squishes the last bit of area of a mixture (that has sparked a few degrees earlier) & flame is propagating, increasing pressure, the mixture burn efficiency can be affected by the turbulence smashing the fuel into smaller particles supposedly increasing surface area, though I struggle with that, but helping mix the gas for sure. Anyhoo the speed that this mixture is squirted out of the squish area can be calculated & is called the Maximum squish velocity. the idea is that a certain MSV will suit your application, ours being dirtbike type power at comparatively low revs.

There is software to calculate this, however some uber tuners have started to poopoo this as it ignores the fact that the volume in this squish area decreases as the engine revs higher so the numbers are false. Either way the numbers give a reasonable indication of where you should head. People moved to Mota and then to EngMod, but I can't be with the $400 & considerable time investment to learn to drive it rather than monkey enter some data & get peanuts results.

This aside a dirtbike running somewhere around 50% of chamber area to squish area with a close gap & reasonable compression should be in the ballpark so I might not give a rats. I've lost my sw on this PC so I'll try find it at home & give it a bash for giggles.

Back to my bike; so I found the squish went from 2mm at the outside edge to 3mm at the chamber edge. The squish area seemed to be 13*(degrees). The piston measured 9* hence the wedge shaped space.

I was going to reduce the gap down to 1mm (safe as houses on the 300, I run my 50 at 0.5mm, but it has less mass to stretch/displace). Mail order Tuners probably add a tickle of extra clearance as they can't trust that an owner will have measured the squish properly (esp hard when it is wedge shaped), or that they will do it again when they rebuild the bike.

But I decided to flatten the squish area out to a almost parallel shape. Having a closing shape is a no-no so I got the squish cut to 10*. Yep I paid someone $50 to do it as I mounted it on my 1940s? lathe & decided there was too much movement to create a flat surface. Well I got scared.

I wanted a 3.3mm step from the chamber to the sealing surface to get the gap right (it was 2.4 before, heck maybe I'll be conservative & it will end up 1.1mm, but the chamber was 0.05 off left to right). Anyhoo, once the squish was at 10* (leaving a little at the inside as a starting point) there was only a slither of the original step showing shown by the anodising visible (see outside picture 2). Then cut it down a bit to achieve where I want to be. Note to self, I'll have to ovalise the head stay mounts a little now I think of it.

So that's where I'm at. 1mm is about 4cc so 1.7mm cut is more like 7cc from the original 25.7ish which will take me to ~17:1 which is clearly waay high.

Next step is to shave some from the chamber to reduce the ratio down to <13:1, but I'll bolt it on first to check the clearance to be sure. I have a curved cutter to remove material & as it isn't a seal bearing surface my lathe will be well accurate enough. I can remove area from the chamber area or I can encroach into the squish area to make the chamber diameter wider. This would reduce the MSV if that was desired. roadrace bikes typically have much smaller squish areas for this reason.

As I take cuts out I will then have to place the head back on the bike & remeasure the volume with the piston at TDC. Its a bit boring but it is free & better than watching some renovating program on TV. I'll prop the bike up so the engine is level & lightly grease/wipe the piston & lock at TDC with some chain grips on the flywheel (the magnets like to move it off TDC). I'll then use some fork oil in a burette http://glscience.com/Lab%20tools/burette.htm available from an online lab supply place for very little for a plastic one.

I fill the spark hole till 2 threads up from bottom to account for spark plug internal shape. I perform this a few times till I get consistent measurements, it takes a while to get your technique in. Head off & wipe between trials.


The end result I hope will be a better running bike that carburettes better at lower revs & is working more efficiently. Did wonders for my 200.

Oh yeah I never bother with compression tool readings. They are convenient, but hopelessly inaccurate on a 2 stroke as they can be affected by oil flicked up from the crank. As an example when I did my 200 I used a meter between modifications. As the compression got pretty high there was little or the wrong way numbers when I had removed material & had a psi higher reading. Rubbish even on my fair quality German guage.

I'm racing this weekend so maybe next week I'll get this dusted ready for first ride that sunday.

Alright, I'm ready to declare (F5) is to head mods what Jake is to jetting! Great write up ... more pics as the project progresses please.

:oWell I still have to end up with a quantifiable improvement yet.

Surely with this much dikn round I should end up with 200hp more power, 10mpg better mileage, longer floating wheelies & of course get more chicks.


. . .actually I don't want to get more chicks, the wife would complain & besides I ran over an eel in a shallow puddle once & I still feel guilty about it.

Great write up F5. I think I find all the cc'ing and measuring of the trapped volume good too, but don't have the access to machines or knowledge to use them to make it happen.

Having recently had my 2013 250 head setup, I can confirm, the newer ones still run around 3 degrees difference between the piston and head. On my 2010 S3 head we left it as is. On the new one had the band recut to match the dome.

Well had a few min spare to put the head on the barrel & measure squish. 1mm at the cylinder wall & 1.1ish at the chamber which is pretty much exactly where I wanted to be & its the same the back as the front which is an improvement over stock.

Here it now waits forlornly in my Sheldon c/w old style tool holder for everyone to laugh at, but it still works fine for this sort of stuff. The hand cut head tool is pretty small as I made it for doing heads of 40-50mm dia. A bigger one would be easier but my tool holder ain't that big. I'll just take a few cuts and work carefully with blending radius's.

I had a quick play with some old TSR sw & calculated the head currently in the 40s which with a suggestion to stay within 15-25m/s range is pretty high, so first thing I'll do is take off the inner anodised section which should take my squished area from 56% down to 50 & lower that substantially.


I'll need to remove a fair bit of material but I'll do it in a few steps & measure cause even though that is tedious, its easier than putting material back in.


I've taken the head stays off to slot them a bit more than std to account for about 2mm of movement down.

Just a couple of snaps, bike held so cylinder vertical with some straps & front wheel on stand. Excuse filthy bike.

Flywheel held still at TDC, easy as had a weight to grab, but carefully can put on flywheel itself. Won't stay at TDC by itself, the magnets pull it around.

Burette down spark hole with bright torch so you can see it actually coming up lug hole. I use 2 turns from bottom to account for plug inner recess. Take your time to practice technique. I've done this a few times but it takes me a while to get my eye in.

ok here we are after 5 cuts & measures. I should have taken some more heavy cuts at the start, but as I said; harder to put metal back on. Good thing I'm not charging myself for this.

This leaves me with 24.0cc measured on the bike so full stroke compression ratio of 13.3:1. This is still higher than my target but it got to my self imposed midnight curfew (any later in the garage & the wife starts to consider coming down to see I'm not trapped under a bike or anything).

I could run it like this on decent gas, but kickstarting might get slightly harder & it might take me another 3 years to get around to taking some more out.

I think I'll pull another cut & get to 13 or just under tonight. I ran a bit of sand paper in it but it cut quite nicely from the tool.

Pic 2(edit snafu, pic 1) shows how much metal has been removed. Its quite a bit, but simple math & measurement says we chopped out about a 2mm donut of space from the outer edges of the cylinder, it will take more out of a smaller circumferenced area to replace it.

You may note the un-radiused edge on the squishband edge. Conventional tuning wisdom tells us to remove that, but advice from the research of the uber tuners debunks that practice.

I might make a template (a finger of kneedit pushed into the chamber left to right & sectioned in 1/2) so I can do a friends one with little measuring if it turns out all right.

Keep up the good work! Love all your spares clipped/zipped around the bike chasis.

Ha, yeah lost a gear lever a while back so had to complete a loop in 3rd which was tedious, fortunately no killer hills. Hence, a gear & brake, clutch lever. Split link, the tube in front of PV cover is a looped 4' length of gas tube. Black thing at top of pic is small bicycle pump tied to rad hose. All items very light.

That's great work. Here's a question though - from your previous work with 2T engines does the shape of the chamber (taller shoulders to achieve volume) make much difference in how the engine will idle? Rev? Torque?

I'm getting excited to fire up the lathe and have a go first at cutting a mandrel and then at modifying a head.

Most of my work has been on high rpm roadrace bikes so the power you want is a good spread before & past peak power to cope with gear changes without falling from power. We try to make the chamber real shallow. There has been a trend to toroidal shapes which are more bathtub, skinny squish areas & with flat top pistons even moving the sparkplug closer to the piston so it is protruding from the chamber ceiling. Makes measuring volume like I've done problematic.

Dirtbikes, esp Enduro/trail bikes you want a considerably wider spread. To be honest I don't know whether the same extreme shallow shape would help or hinder. What I do know is that the squish area is larger so the chamber will naturally be taller anyway. The most influence will be in the effect of the squish area. Get that working properly & you should be ahead of the game. I think this will have some reasonable effect at lower revs, lower throttle position & idle. But there should be less gas wasted in an unburning area. this should mean more power.

The std chamber is a bit odd in that it has a flat section by the spark plug. I think the reason they have such an angle on the squish area is to stave off detonation as uncertain which fuel the customer will use (who reads the manual huh?).

Anyhoo, I made another cut & that ended up as 13.1:1 & I decided to call it a night, slapped it back together & ready to ride sunday. Hopefully it is worth the effort, proof in the pudding & all.

F5's head mods
 

First off thank you for sharing your knowledge. I am a rookie when it comes to rebuilding modern 2 strokes but I enjoy tinkering with machine tools. I was re-reading your first post and I am confused about the 4mm hole above the exhaust port you were describing. Is this stock or something you have added? I don't remember ever seeing a hole in any pictures I have seen. Also, I always assumed that the top of the piston was flat. Is it actually domed? You said that there was a 4 degree difference between the piston and the squish band. I am just trying to picture this in my head. I am also wondering how wide the squish band is from the outside edge of the cylinder to where the dome starts? Once again, thanks for sharing!

Knowledge
 

Ok, I found the technical article and the excellent diagram of the squish band shape by RB. It's all starting to make sense now, like I said , I'm a rookie. Now I want to go home and check my squish. I love this forum!

That hole is on the 300 cylinder only, it is supposed to be a compression 'release' to aid kickstarting. From what I have read you want that hole there when kickstarting a 300. I have no experience with it, just what I've read on it

So, just for the fun of it, where in the stroke do you start your displaced volume calculation?

Is it full stroke, so BDC? When you close the exhaust port? When you pass the compression bleed hole (on the 300)?

Full stroke. That's what matters when specifying a com safe for the gas you will use. When the engine is running the pipe is pushing mixture back in when in its range. when out of range the effective compression will alter, but the power valve is moving changing that point so so called 'trapped ratio' is a moving target anyway.

If people still argue point out that foul strokes stated compression ratio never mention when the cam opens or closes the valve. Why should the position of the hole - side of bore vs top of head make a difference. ;)

The hole in the 300 (wasn't one in my 200, haven't pulled apart a 250) helps kickstarting as it does lower the compression ratio as the engine is turning over so slowly & cycle not started yet.


Actually I hadn't read that tech article (or at least might have skimmed it many years ago). It is well written & his picture looks quite a bit like my end result, but tiny picture. He also seems to have polished the heck out of it which looks nice. I don't agree with everything he says, but not enough to argue. $75US is a very fair price to pay (about $400nz kidding, -actually our exchange rate is much better, about $95NZ) is a good deal for that existing development. Cost more in freight & time for me & I like doing things myself, but if yer stateside it would make good sense, he's not being greedy.

No comp bleed on the 250's.

Well I'm impressed. At first I was wondering if the bike was just running great but it was what I love about a big bore 2 stroke. Maybe I've made noi change and I'm just making it up as I've done some work. As I went on I realised it had woken up at low revs and low throttle positions. It's much like my old GG trials bike.

So after a loop (37km), I swap bikes with my mate, also a 07 EC300. The difference is stark. I find myself blapping. We change back. He's impressed, more bottom end and sound different he sez. Mine feels like it's burning more cleanly.

Fuel consumption is identical though.

Might have to experiment with mainjet. Feels altered in requirements but not sure which way. Not getting on it for long today. Also idle is lowered to the point it will stall. Must try altering idle jet but it feels so perfect off bottom I'm not inclined to mess with it.

I machined my squish yesterday down to 1.2-1.4 (measured with blue tac so only so accurate!), I was running 0.5mm base gasket before, I've just bumped up to 1.5mm base gasket (to get ports to line with piston flush) and reduced the squish. The difference to the bottom end is insane, far more powerful (counter intuitive considering raising the exhaust port etc benefits higher revs more), BUT, I have actually lost a bit of top end (I did machine out for same cc in head), this has lead me to believe that perhaps before I had jetted rich to compensate for the bad squish (I was running 2.6mm), and now it is corrected, the jetting is too rich. This would bring me to a 175 main jet which is in line with a fair few people's bikes (I would go out and mess around with it now, but I am hungover and it's pissing it down outside :p, fair weather much lol!), would be interesting to know if you found the same with jetting?

Yeah I'm running a 178 & have been meaning to try a 175, but just a bit lazy on that front. Once you get to a ride you ride a loop & then either go out for another loop, or have lunch. The bike is dirty & you are tired, about then people say, ok lets do another loop.

. . .so do I get out the tools & perform carbadectimy in the dust? Nah, just ride. Actually we were on the grass under the shade of a line of trees (summer here), but still couldn't be arsed. Actually I'd not packed my jets come to think of it.

This morning I was thinking it may be easier to find an old 18" tyre & throw it o the dyno I have access to.

The latest 2013 that TSP setup the head on, and then tuned on the Dyno ended up with 40 NEDJ#3 (or NECJ#3) and 168 main and was sufficiently rich off the bottom end. Thats on a PWK AS2 38mm with leak jet.

On my 2013 250 I'm at 175 main and think I could probably drop one more yet.

RE:
"I've just bumped up to 1.5mm base gasket (to get ports to line with piston flush) and reduced the squish. The difference to the bottom end is insane, far more powerful (counter intuitive considering raising the exhaust port etc benefits higher revs more)"
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this gets me excited to find out what this would do to my ec 200!
but if this turns out bad for me, there aren't that many ec 200 to find a second hand head if i f*ck up... or if i want to make it undone... you can only take so much off the head right?

Hannes.

You can always buy the S3 head with removable inserts. I took 2.2mm off my head with no worries whatsoever.



I put a 174 main jet in today (tried 172), they both feel roughly the same, 178 is definitely too rich as when you whack it wide open in neutral it 4 strokes and smokes like hell. I have gained a lot of low, mid and upper mid range power, but the bike feels flat on top (this is on the road, not the track), is this just the nature of the beast or is something killing my power?

So have you checked the volume at TDC on the bike to be super double sure? What compression are you running? & on what fuel?

wow, is that on a 300 Jakobi? That's the needle i'm using, but i'm at 175 MJ and pretty happy - tho this will prob change with the newly machined head.

obviously ~45:1 and ultimate 98?

I'm not sure who's bike that was that Dave was setting up, what the final squish or compression ratio was that it ended up at either. It was definitely a 300 though. I'm sure the post is on DBW somewhere but he has confirmed it on the phone for me too.

Mine is a 250 with 45:1 Amsoil and BP 98RON. Yep!

Edit: Found the post and quoting the man

"I recently did a 13 gasser 300, removed the high comp s3 head, installed the stock head again with corrected squish clearance, angle and comp ratio and made way more power everywhere. The main thing was that on the dyno I was able to drop the main from a 178 to a 165 and it ran brilliantly. Just pulled it down after 3 fairly hard hours and there's no signs of overheating or running lean. The rest of the specs were 40 pilot (runs rich down low, starts without choke, could get away with a 38) and necj needle #3 clip.

I'm not sure I'd try these on a stock head but it seems the gassers can take similar jetting to the KTM's when set up. Ill post up if this bike needs to be richened up in the future."

Thanks Jake for that.
Very interesting setup. Where did you find that info? Would love to read more.


Sent from my iPhone using Tapatalk

There is not a whole lot more to read. Just a jetting thread on another forum where Dave chimed in as he'd just set one up on his dyno.

Now also keep in mind thats on Australian fuels and for some reason I have noticed we typically end up a bit leaner than US. The mods he has done are probably very similar as what F5 has done. Cut the band back to reduce the angle, reduce the squish clearance, and then open up the chamber to correct the volume. I'd ask Dave to chime in here in the thread but he's been seriously busy with work. Its hard enough getting a few messages back and forwards on the phone. Its also on the newer designed cylinder with the G stamped into the side of it.

ooh, interermisting,

I've found a hole in my Keihin jet range below 178 & above 165. I might just have to cash up & buy those jets & find an old tyre & dyno it.

38 on the Pilot? I've got a 40 but atm I've got idle wound in all way so I was going to try pulling the slide down so less influenced by start of needle, but I thought a 42 would have been the direction to compensate. I'm on a CEL (or was it CCL?).

Thats all on the newer AS2 carb with the shallow bowl F5. Seems to like much leaner jetting in general. They have a newer model AS2 on the 2012/2013 from what I can see too. My new bike has a leak jet. I have a pic of it somewhere but can't recall what number it is. The NEDx/NECx needles also supply a decent amount of fuel towards wot. They taper right down like a toothpick, where comparitively the N3xx needles are much thicker towards the pointy end.

Even with the two engines I have setup very similar in terms of base gasket and head mods, the port layout is different, the way they run is a little different too (same jetting specs, both running in sunshine mode). Slight differences in carb, different airbox, different silencers.

Local shop sez they run most older on 175 on our gas, worth a try buying a 175 and 172 at least. Then try pilots and se if I can get idle up again.

thinking about this, i bet that bike was running the stock Q stealth

Its very possible.

What I have noticed with these engines is that its quite hard to get a main too rich to the point that the throttle just breaks up and burbles. I've had my bike do it with no main jet, and at 180 it felt fluffy up top (not crisp), but I imagine it would take quite a bit to get it blubbering away on the main.

I wouldn't be surprised if we could all drop quite a few mains to make peak power and max overrev, but honestly, how often do we spend at WOT, do we need the max, and is it worth sacrificing the safety buffer of richness?

Certainly I spend little time tapped out. The only time I'm wanting is sometimes up a slight to moderate hill and I want to get a boogie on and whapping throttle wide, it's got a bit flatter than it was due to different fueling requirements now.

put a 168 in mine, insane.

Mine does have a 175 I just found (must update my notes). Oh well I'll buy next 2 sizes down & trial when I have a mo. (its an 07).

Does have a 40 pilot with airscrew wound out 2 turns so I may try a 38 & try get a higher idle with idle screw out a bit further so I'm not ont eh needle at all. Not sure if there is enough straight section on my needle or if I'm into taper but I think I had to drop the needle to run best so I could well be in taper.

Only drama is getting it hot to test it out where as most trails we set up & go for a long loop.

I found the jump from 178 to 172 only have me more mid range. I was almost disheartened then put a 168 in and scared myself to death!

40 pilot, air screw 1.5 out. cek 3rd clip, 168 main

Well ordered my missing jets. Will see if can get a skip bound tyre for dyno.