S3 Race 250 Port Matched Cylinder and Head

[Jakobi]

I would say that's been more than just a little lean

Come on MrBlah How about you put some effort into it. Lets keep this thread informative. I'm not disagreeing with you, but I wouldn't mind hearing your reasoning behind your comment. Maybe that way everyone can learn something from it.

 

[MrBlah]

you should post a good picture of the inside of that piston

 

[Jakobi]

Definite hot spot in the middle of the piston dome which is undebatable. Caused by a lean run at some point in the 85hrs. I am in no way denying this. It has seen so many different needles in so many different positions.

The rest is a very light caramel colour. No heavy carbon deposits internally or white flaking/chipping. No damage to the piston edges around the ring lands. No sign of detonation on the piston dome.

 

[(F5)]

. . . If anything I now think the measurements I did on the 300 were wrong as they were my first attempt and the maths shows that it should have been closer to 24.12cc instead of 23cc. This gives an uncorrected CR of 13.11:1. What a learning curve these last 2 days have been!

so 13.1 is close to the 12.6 or 12.7 I measured in my 300, easily within tolerances of whatever gaskets they throw in at random. Pretty high for a such a big slug that could be run on any old pump gas.

But 16:1 is mental. Why would they make it so small? Looking up a chart that really is methanol numbers.

 

[(F5)]

Gee I wouldn't lose any sleep over a dark spot on the bottom of the piston. - If it was grey - then I'd get worried.

 

[Jakobi]

so 13.1 is close to the 12.6 or 12.7 I measured in my 300, easily within tolerances of whatever gaskets they throw in at random. Pretty high for a such a big slug that could be run on any old pump gas.

But 16:1 is mental. Why would they make it so small? Looking up a chart that really is methanol numbers.

My thoughts too. Out of curiosity I grabbed the silver insert and cc'd it aswell. Same same figures.

With the 300 I can confirm both the stock chamber volume and s3 chamber volumes are the same. I obviously don't have a stock 250 head to cc but following the trend you'd imagine it would be the same as well. I wonder if this means that all the 250's run high CR's straight from the factory? Using the same volumes and a 3mm squish height (epicly huge) the CR would still come to 14:1 with a 19.12cc trapped volume.

It feels like somethings not quite right with these numbers. I wonder if the people at S3 have made a mistake on the 250 chamber volumes?

 

[(F5)]

yeah seems like a lack of understanding to run squish clearances you could stand up in. But heck how can I criticise people who make their own engine parts? Must be a 'back story'.

PS dmcca pops up in another forum from time to time, so I have heard of him.

 

[Jakobi]

A 'back story'??

Not being critical of anyone here, just putting my thoughts down. I can't really think of any pure bolt on head that would work for all situations without offering multiple inserts (different volumes) and a way to adjust for squish dependant on the base gasket stack. Any way you look at it there's still work involved to come to the right answer, so its never as simple as bolt it on and go.

I'm certain that Dave will have a record of the stock 250 chamber volume so will be able to fill that void for us.

While probing your knowledge F5, what CR would you be looking at to achieve my goals? Premium pump gas (95RON) minimum, although I always run 98. Looking at a soft yet torquey and tractable bottom which builds into a strong mid - top with good over rev. Not a real MX kind of hit, but enough to let me know its still a 2T.

 

[dmcca]

I just did many runs ccing the red head insert using a piece of glass some grase and some metho filing in the plug hole. Came out to 17.5cc and I believe all the head inserts are the same volume.

Deck height was calculated from the squish measurement 2.05mm, and I used a dome calculator (http://www.monolithic.com/stories/dome-calculator) to work out the volume based on a dome height of 3.8mm. All cubic mm were then converted to ml.

Combustion chamber vol = 17.5cc
Deck height volume = 7.27cc
Dome volume = 8.77cc

Trapped volume = (Combustion chamber vol + Deck height volume) - Dome volume

I was wowed to see the figure come out to 16cc. Maybe my measurements weren't so sketchy after all. In any case that gives us a really high CR. Imagine what it would be like if I dropped 1mm of base gaskets.

If anything I now think the measurements I did on the 300 were wrong as they were my first attempt and the maths shows that it should have been closer to 24.12cc instead of 23cc. This gives an uncorrected CR of 13.11:1. What a learning curve these last 2 days have been!

Hi jake, check the dome vol... Should be 6.5-7cc for a 250 domed piston from memory. Pretty sure I got 17.6cc for the last GG250 head I measured. I'll get back to you tomorrow to confirm. If your dome vol was closer to 6.5cc then you'd end up with a CCR of around 15:1 which is about what I got last time... They seem to set up their 250s and 300s very differently.

 

[Jakobi]

Dave, I just used a calculator (listed above) to calculate it based on a 66.4mm diameter and a height of 3.8mm

Double checked my work and I used 'Oblate Dome Calc' instead of 'Sphere' ...Oops - The later gives me a dome value of 6.6ml. This would bring trapped volume to 18.17cc and CR 14.7:1.

The strange thing is that using the 'Oblate dome calc' not only gets the calc close to what I measured for the 250, but for the 300 too! I think I must have measured them both incorrectly (or not spotted the line at the bottom of the plugs correctly). On my notes I had jotted down values for what I thought was the bottom of the spark plug gap and the top. There appeared to be a 5ml difference. Today I just measured and there is only 2.5cc of thread so working backwards from the full I get..

Measured 300: 28 - 2.5 = 25.5 Mathematically 26.4
Measured 250: 21 - 2.5 = 18.5 Mathematically 18.17

On the 300 I made the noob mistake of drawing to a line and filling right in instead of dropping to another measured mark so may have added an extra cc or two through the tip of the syringe which would bring it back into spec with the maths. I think the angle of the engine must have been trapping some air when I thought the fluid was touching the spark plug. Ie touching 1 side but not the other.

If I could have my time again I'd spend more time and effort to get it 100% right. Hindsight is wonderful.

Thanks Dave.

 

[GMP]

Unless this is for your own personal education and interest, which is cool, your putting more effort into this than is neccessary. If you set the head up for max compression on your fuel source, and min squish accross the band, it will be good and you can move on. It will grunt off the bottom fine and rev out as well. No reason to switch heads unless you have a cheap race gas source and can squeak out a little more compression for more low end, but you had a 300 for that. The 250 will be all you need and then some. Set it up and ride it. It won't hit too hard with that big 2K-3.

 

[Jakobi]

Unless this is for your own personal education and interest, which is cool, your putting more effort into this than is neccessary. If you set the head up for max compression on your fuel source, and min squish accross the band, it will be good and you can move on. It will grunt off the bottom fine and rev out as well. No reason to switch heads unless you have a cheap race gas source and can squeak out a little more compression for more low end, but you had a 300 for that. The 250 will be all you need and then some. Set it up and ride it. It won't hit too hard with that big 2K-3.

Spot on Glenn. All this babble is all for my own interest in the subject. Technically all I had to do was take a squish measurement and send the head to Dave and he'd take care of the rest. I just have an inquisitive mind and like to know the whats and whys behind things. I also find it much easier to learn if I can report my findings and be told if I'm on the right track or not. Like just now I realised that I can't accurately estimate the dome volume with a calculator and that there are a few methods to measuring that aswell.

I guess by putting it on here I am keeping a record for myself, and possibly providing a source for anyone else who is interested in going a bit deeper. I will be having the 300 head set up properly down the track as well so by identifying all my muck ups and things I missed this time around I will be educated on how to do a better job. Ramble ramble ramble..

I went through it with jetting, i'm going through it with the engines, just wait until I get a taste for suspension. Haha!

 

[dmcca]

PS dmcca pops up in another forum from time to time, so I have heard of him.

ha, only to ask stupid questions then hide again in the presence of greatness

 

[(F5)]

Hey with Frits & Wob onboard it is a unique opportunity.

Jakobi, by 'Back story', which is a new phrase I'm trying out, . .. clearly to bad effect, I meant that S3 may have had a reason for making them like that assuming that the customer would make an error somewhere or didn't want to remove base gaskets, who knows?

For compression ratios vs gas I use TSR list, but pretty much same as Bell.

 

[Jakobi]

I'm picking up what you're putting down. With any luck Dave will have received the parts by now (or will some time today).

In the mean time the bike has been seeing some new parts here and there and getting its lube on. Its all coming together quite nicely.

 

[dmcca]

So i got the cylidner on Friday arvo... just had a chance to map it out this morning and compare it to the last stock '11 EC250 i worked on...

Some obvious things about the S3 cylidner...
- it is the exact same basic cylidner as a stock unit, obviously cast from the same batch as the standard cylidners, it just has S3's logo on the side.
- its had some extra work done to the ports over the stock unit and the finish on the ports is MUCH better than the last stock one i had (which was terrible)
- the aux EX ports have been widened
- Main Ex port has been widened and raised to match the timing of the aux EX ports (stock is staggered with Main Ex lower)
- Main and Aux transfers have been widened
- Boost port has not been touched

All pretty standard stuff aimed at more top end power, most likely at the expense of bottom (as to be expected)...

I ran it through the sim software and got the following graph...

BLACK is the S3 cylidner with a 1.3mm base gasket stack
RED is the S3 cylidner with a 0.5mm base gasket stack
GREEN is the stock EC250 cylidner with a 0.5mm base gasket stack (how the last stock bike that i worked on was set up from the factory)

So the S3 produces significantly more power up top than the stocker due to the larger ports, but you pay the price in reduced bottom end. When i did the last one i faced the same issue and decided to leave the 0.5mm base gasket stack in order to retain some bottom... it was pretty much a half way measure and the final results were very very similar to the RED line on this graph (that person had asked for an increase in top end without a drop in bottom if possible).

So Jake the choice is yours...

- run a 1.3mm base gasket stack and have the port floor flush with the piston at BDC (remembering its only there for a fraction of a second)... this will give the strongest top end but less bottom/mid and the head will have to be shaved 0.8mm to get squish clearance to 1.25mm (current SQ with the 1.3 gasket stack is 2.05mm)

OR

- run a 0.5mm base gasket stack and have the piston a bit above the port floor at BDC (remembering its above the port floor for the rest of the crank rotation anyway)... this will give less up top but keep more down low. The head wont need to be shaved because the cylidner is 0.8mm lower (dome volume will need to be sorted out still though, yet to do the calcs on that)

Of course you can run anything else between 1.3 and 0.5 if you want and its intuitively obvious how the power will be affected.

Aside from the drop in bottom end power the real issue is how important is is to have the piston flush with the port floor at BDC anyway?? In my opinion (and there are many others way more qualified to answer this) the port floor issue is the lesser of two evils... for normal trail riding id rather retain some bottom/mid and live with the fact that my port floors arent flush for the ~0.0001 of a second they otherwise would be at 8000rpm.


Another issue with the EC250 is that the fact that the powervalve snaps open very fast causing a drop in the mid range with the larger exhaust port... if you could keep the same opening start point (about 4500) but extend the opening period out to 7000+ rpm (currently fully open by ~6000) it would work better with the bigger ports... this is obvious in this graph how the GREEN line doesnt drop at all at 6500 but the other two do... its timed to work with the smaller stock ports.

Plenty of food for thought.

 

[Jakobi]

I'm happy to hear a few other opinions over the next 24hrs. Love the discussion that goes with. The obvious answer I think is the red line though. It takes half of the work out of the equation for you Dave. Leaves the head stock enough that it would still accept the other 2 inserts if I ever decide to sell it, and the slight decrease in peak power over a relatively small rpm is moved and spread to boost a 4000rpm area through the mid range.

I don't want to sacrifice the top end, but thats all wishful thinking. For the riding I do the mid to top is where I like the power to be. I can only ever hold it open for about 2 seconds before I'm backing off anyway.

Others opinions welcome. Yours too Dave!

 

[Jakobi]

Dave,

While I've got you here. My 300 is about the same same in regards to measurements with the stock squish measuring 1.9 - 1.95mm when I pulled it down. Would dropping to a single 0.5mm gasket be the go for that too. Obviously I'd have to get you to correct the volume for me. I also have the stock 300 head here that I'd be willing to send you if you wanted to go getting all experimental and trying some new things.

 

[NSE.ONE]

Great read guys.

Dave is the man. You'll be very happy jake.

Decided im keeping my EURO after last weekends disapointment on the RMX.
Back to the Gassers, only took me 6 months to work it out.

 

[dmcca]

The obvious answer I think is the red line though. It takes half of the work out of the equation for you Dave.

Dont worry about the work, its more important to set it up the way you want... and maybe i was a bit pushy with my opinion before, id forgot that youre keeping the 300 cylidner as well so theres always the option of setting up the 250 as the top end screamer and setting up the 300 as the torque monster for when you feel like riding different animals. I guess what i was pushing for was setting it up as an allround bike, but maybe thats not the point here. Its not like running the 1.3mm gasket stack will be bad, its just going to be more of an MX style delivery compared to the enduro delivery of the stock EC.

Ill get back to you about the 300 specs... have to look at my notes first.