S3 Race 250 Port Matched Cylinder and Head

[dmcca]

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.

What happened on the RMX Col?

 

[Jakobi]

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.

You haven't pushed anywhere Dave. Its just a tough choice because part of me wants the screamer, but the other more realistic part of me knows that my riding doesn't let me scream everywhere and that I would benefit more from a greater spread of power. The 250 is going to feel more revvy than the 300 which ever way we set it up, and if its not got enough zappo I'll probably be looking at a 2k2 ignition with a fww to bring it to life.

The basic engine characteristics I was looking for was soft off the bottom with a crisp snappy mid mid to top pull. IMO the red curve gives the best of both worlds.

Everyone else chime in already!

Welcome back Col No real nibbles selling the Euro?

 

[Jakobi]

Well doesn't look like too many people have much to say on the matter.

I've had a good nights sleep and a day to sit and ponder and I think I'll go with the red configuration. Few reasons why I justified this.

1) Less work for all involved.
2) Retains head as stock to still accept other inserts at a later date (not that I will use them.
3) If I'm not happy (which I doubt) its easier to send it back and have the extra material machined off than it is to try and add it back on.
4) Graphically it still shows a good rush in power from 6500rpm, and significant gains over stock into the top end.
5) Leaves me with a spare gasket or two.
6) It will probably add extra preload to the powervalve actuator arm which wasn't 100% tensioned. It was against the stop but not a lot of preload.
7) I spend more time with the revs between 4500rpm - 8000rpm than I do at 8500.

Basically I feel that this will provide the best results all around. While a top end screamer is fun, its not neccessarily the best choice for the conditions I ride.

Anyone got a 2k2 they want to move? Anyone with EC250 jetting specs they want to share?

 

[NSE.ONE]

My preference was to have strong smooth power all the way through the range.
It sort of feels weak compared to my mates 6 Day but its just cause its so smooth. Theres nothing in it in a straight line drag.
Be stuffed if i can ride a 300 on the pipe all day.
Id go the red curve setup Jake, its more real world suited.

Yeah 1 nibble in 6 months. Its sitting in my mates shop all nice and pretty so im getting her back. I really missed it everytime i rode anyway so its like getting back a long lost friend.

Dave, RMX was good but too heavy and has some weird EFI/Clutch issues. Tried a few things and couldnt get it working in the ST that i mainly ride. Fire trails it was a hoot and easily the best handling bike ive owned (Dirtworks revalved), but the flame out thing pissed me off.

That and im still just an ol 2T head
(Sorry Back on Topic)

 

[lonetree]

So where is the "red" setup going to put your piston above the exhaust port at BDC? about .7mm above? interesting, considering a .5mm base gasket., correct me if im wrong.
I think you'll find the 250 heaps more zingie top end compared to the 300 anyways.
Dunno, but i love mine, cant wait to get back onit after the head mods....

 

[Jakobi]

Right on Col. I'm reminded how much I enjoy my gasser every time I ride it. Its just been resprung front and back, had a motosportz damper fitted. Ohlins TTX carts up front and when its all done it'll have some of Daves handy head work to complete the 300 to 250cc conversion. I can only see it all making a good thing better!

Lonetree. I know you have a 250 and a 300 so I value your opinions on the two setups. By running a single 0.5mm gasket it will put the piston 0.8mm above the port at BDC. The 300 was running too much squish (1.95mm) with the piston flush using a 1.3mm gasket stack so it was set up to favour the top end. I never really found it too much to handle but did find it hard to use the power anywhere near its potential. I'm just hoping the 250 pulls a bit faster through the rev range. Ie I'd want something I feel like I'm feeding more throttle to achieve the same goals. The 300 feels like I hardly show it any throttle until the track opens up some, then its a weapon! Considering ST is what I enjoy most I'd like a bike that I can keep singing some more between the trees. Its not about pace, but all about the experience.

Dave. When you read this feel free to let me know and go ahead with setting the bike up as per the red line. 0.5mm gasket, 1.25mm squish. Whatever CR you deem best.

 

[(F5)]

Just a point to remember comparing gasket thicknesses; They compress. So a like a 1.3 when all screwed down will lose 0.1, 0.2, so you have to measure the effect on the metal bits once you've added or removed the gasket.

It would be interesting to know what the diff in the 300 to 250 porting was. Bearing that they seem to run the same carb & pipe, riding the 250, I find it too aggressive for me, whereas the 300 is a pussycat. . .well unless you leave the throttle on too long, & then it bites.

so what are you going to end up with as a squish clearance? & what comp ratio?

 

[Jakobi]

Just a point to remember comparing gasket thicknesses; They compress. So a like a 1.3 when all screwed down will lose 0.1, 0.2, so you have to measure the effect on the metal bits once you've added or removed the gasket.

It would be interesting to know what the diff in the 300 to 250 porting was. Bearing that they seem to run the same carb & pipe, riding the 250, I find it too aggressive for me, whereas the 300 is a pussycat. . .well unless you leave the throttle on too long, & then it bites.

so what are you going to end up with as a squish clearance? & what comp ratio?

F5, When I took the measurements for the squish samples I used the same 0.5mm gaskets from when I pulled the 300 top end off so they had been compressed, and a fresh 0.3mm as the old one tore. Shouldn't be too much difference once the new gaskets are torqued up after the work. I do however see how the difference wil vary the data on the graph. Dave was going to set the squish at 1.25mm I believe, not sure what CR he's aiming for.

As for the 250 vs 300 Sims, he should be able to run that for us (please Dave) as he has all the info from when he did NSE.ONEs bike. I'll be able to give a ride report once its all back together.

 

[Jakobi]

EC300 Graph

Here is the last graph that Dave did up for Cols 2010 EC300 Euro

The Black line is the stock engine, in this case 2.5mm squish, 11.9:1 comp, 1.3mm base gasket stack, piston level with port floors at bdc

The Red line is the cylinder dropped by 0.7mm to give a squish of 1.8mm, no further changes other than what occurs by dropping cylinder.... comp increases, exh duration drops, transfer duration drops

The Green line is the cylindner dropped by 1mm to give a squish of 1.5mm, no other changes.

The Blue line is dropping cylinder a bit but then doing some basic mods to the exhaust port to bring the top end power back... best of both worlds... better bottom without the loss on top. You can take this much further to get better top end if you want.

 

[Jakobi]

And another regarding the 300. It would be nice to see them all overlayed on one graph though.

BLACK line is stock engine

RED line is 1.6mm squish, 13.2:1 compression, done by machining head only
cause Jakobi asked for it

GREEN line is cylinder dropped by 0.7mm to give squish of 1.8mm, same as red line in first graph

BLUE line is same as blue line in first graph... cylinder lowered but then exhaust raised a bit


Doing the squish by machining the head shows a small gain everywhere without a loss of top end

 

[dmcca]

Hi guys, I'll do the 250/300 graph combo as soon as I can, but I'm hardly at home again until the weekend, gotta earn some money, so it could be a few days, sorry.

I'll try to dig out the porting specs for each, but basically the 300 is set up for low down and looks easy to get more top from without losing much bottom end, while the 250 is already biased towards top so trying to get more comes at a cost. Pretty much what you'd expect from any 250/300 comparison I guess.

I'll be back with more info soon...

 

[(F5)]

. . . , but basically the 300 is set up for low down and looks easy to get more top from without losing much bottom end, while the 250 is already biased towards top so trying to get more comes at a cost. . . ...

Oh well at least that is how they feel to ride.

 

[(F5)]

F5, When I took the measurements for the squish samples I used the same 0.5mm gaskets from when I pulled the 300 top end off so they had been compressed, and a fresh 0.3mm as the old one tore. Shouldn't be too much difference once the new gaskets are torqued up after the work. . .

Sure, figured you had the barrel done up. I was meaning Lonetree seemed to be doing addition using measurements of gaskets in free air vs bolted down measurements of piston position. - At least I think that is what was being suggested, I didn't draw a picture & get the calculator out.

Mainly because I'm lazy.

I find that is a policy that has served me well. And will continue to serve. Unless it seems like too much effort at the time, or I just can't be bothered.

 

[Jakobi]

Still picking up what you're putting down F5

Looking at that data you can see that both bikes start off very similar, however the 300 remains very linear building through the mid into the top. The 250 has less power between 4500 - 7200rpm where it catches up and then pulls hard into the top. From the data I should retain the same low end torque or grunt, tame out the lower power on the pipe (making it more usable), and then have the top end pull more aggressively. All in all what I was aiming for. Thats all in theory of course!

 

[lonetree]

Sure, figured you had the barrel done up. I was meaning Lonetree seemed to be doing addition using measurements of gaskets in free air vs bolted down measurements of piston position. - At least I think that is what was being suggested, I didn't draw a picture & get the calculator out.

Mainly because I'm lazy.

I find that is a policy that has served me well. And will continue to serve. Unless it seems like too much effort at the time, or I just can't be bothered.

na, i was bolting mine up before mesuring, and its just easier to identify the base gaskets by approximate sizes rather than actual mesured compressed sizes...
its just interesting to compare how different even the cylinders are between bikes.....

 

[(F5)]

ahh, I thought you were doing arithmetic using gaskets removed from original posted measurements.

But they're Spanish & I think variation between different engines can be classified as Character? Well, if they were roadbikes it would be.

 

[dmcca]

Finished the head and sent it off to jake yesterday, thought I'd post up some pics...

Designing the new profile on mastercam...

Cutting it on the cnc mill...

The finished product... Letf the squish band and gasket surface alone, just machined extra volume into the dome... Kept the standard roof height, just made it flatter and wider... Old head vol was 17.5cc new head vol 21cc, when the cyl is dropped by 0.8mm it'll give 1.25mm squish, 2 degree difference between the piston and squish band and approx 14:1 CR.

Also jake I noticed in your calculations of trapped volume you were correct up until the point where you subtracted the volume of the plug hole... It's closer to 2.5cc not 5cc, so your volume of 21cc to the top of the plug hole becomes ~18.5cc to the bottom which is about 14.5:1 CR. so the new head will be slighty lower comp than the std black insert but the better squish action will more than make up for it plus it should rev out a touch better too with lower comp.

 

[Jakobi]

Finished the head and sent it off to jake yesterday, thought I'd post up some pics...

The finished product... Letf the squish band and gasket surface alone, just machined extra volume into the dome... Kept the standard roof height, just made it flatter and wider... Old head vol was 17.5cc new head vol 21cc, when the cyl is dropped by 0.8mm it'll give 1.25mm squish, 2 degree difference between the piston and squish band and approx 14:1 CR.

Also jake I noticed in your calculations of trapped volume you were correct up until the point where you subtracted the volume of the plug hole... It's closer to 2.5cc not 5cc, so your volume of 21cc to the top of the plug hole becomes ~18.5cc to the bottom which is about 14.5:1 CR. so the new head will be slighty lower comp than the std black insert but the better squish action will more than make up for it plus it should rev out a touch better too with lower comp.

Very nice work Dave!

I had identified the spark plug hole measurement and worked back. See post #50 at the bottom of page 5. Great to have you confirm it though. Also just double crunched some numbers for giggles.

Stock S3 Black Insert. 1.3mm gasket stack. Trapped Volume 18.5cc. CR 14.5:1
Stock S3 Black Insert. 0.5mm gasket stack. Trapped Volume 15.7cc. CR 16.8:1
Daves Modified S3. 0.5mm gaket stack. Trapped Volume 19.2cc. CR 14:1

 

[Jakobi]

Just out of curiosity, what would be the dangers of running a single 0.3mm gasket with this set up? That would then bring the trapped volume back to 18.5cc and the CR to 14.5:1 with a squish of 0.95mm. Too tight on the squish? Too risky? Would the port timing destroy the top end? Any chance you could plot that on to a graph too? Also if you get the chance Dave, would still love to see the differences in 250 vs 300 on the same graph. No rush though.

 

[Simmo737]

This post is starting to compete with Brent's posts as the reality show enthrall of the year, hurry up and ride it...... Actually don't hurry, the suspense is just awesome!