S3 Race 250 Port Matched Cylinder and Head

[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]

Originally Posted by 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.

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]

Originally Posted by (F5)

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]

Originally Posted by Jakobi

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.