Pinittowinit
New member
I have a 2010 ec300. Can I put a 200 top end and space up the cylinder to account for the longer stroke of the 300's rod
300 to a 200
- Thread starter Pinittowinit
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Jakobi
Super Moderator
They share the same rod, but the 200 has a different crank/offset so as you've already identified, the stroke will be different. I'm not sure if the cylinder will bolt up directly (need someone to check the studs/transfers etc). You may need to modify the PV arm to reach if you had a spacer made up. After all that you'd end up with an undersquare engine which favours bottom to mid power.
Not sure what effect the CDI etc would have or where you'd end up jetting wise. You'd also have to consider the port timing, as even if the jug bolts straight on, the ports could be all out of place in relation to the piston.
Not sure what effect the CDI etc would have or where you'd end up jetting wise. You'd also have to consider the port timing, as even if the jug bolts straight on, the ports could be all out of place in relation to the piston.
Pinittowinit
New member
What do you mean by under squared? The port timing I thought about. I guess at that point it's easier to change the crank.
Jakobi
Super Moderator
Google - http://www.thenakedscientists.com/forum/index.php?topic=34958.0
Basic summary, undersquare = longer stroke than bore, square = same stroke and bore measurement, oversquare = shorter stroke than bore. You can a certain capacity engine in a few different ways depending on what you want to achieve. Pro's and Con's with all.
I believe once you get to the crank end of things then you start dealing with variances in the engine cases etc as well and might as well just source an entire 200 engine.
Basic summary, undersquare = longer stroke than bore, square = same stroke and bore measurement, oversquare = shorter stroke than bore. You can a certain capacity engine in a few different ways depending on what you want to achieve. Pro's and Con's with all.
I believe once you get to the crank end of things then you start dealing with variances in the engine cases etc as well and might as well just source an entire 200 engine.
Pinittowinit
New member
Wow thanks for the link. I never knew that stuff. Under squared is exactly what I'm looking for in this case. So how would I go about measuring the port timing? Well before I get ahead of myself guess I should see if the barrel fits.
Jakobi
Super Moderator
Now you're really getting into things, and well out of my depth..
http://www.macdizzy.com/cyl_primer.htm
If you already have the two cylinders I'd simply start by comparing them to eachother. Particularly the heights from the top if the cyl down to the depts that the ports both start and finish.
http://www.macdizzy.com/cyl_primer.htm
If you already have the two cylinders I'd simply start by comparing them to eachother. Particularly the heights from the top if the cyl down to the depts that the ports both start and finish.
Zman
Platinum Level Site Supporter
Just for fun I set a 250 top end on a 200 bottom end. As I recall the piston was about 1.5mm to 2mm low in the bore. So all things being equal you should either raise the cylinder and or cut the part of the head that goes into the cylinder.
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pscook
Platinum Level Site Supporter
The piston doesn't go flush with the top of the cylinder on the 300, I suspect that the same can be said of the 250 as well. It looks proper, how about dropping on the head and measuring squish?
Zman
Platinum Level Site Supporter
I do understand that the head protrudes into the cylinder. In order to get a reasonable squish I would have had to cut the head mounting surface or cylinder base about 1.5 to 2mm. I did not look at port timing when I did it, but I can say there were no or interference or clearance issues with the assembly. I did this over last winter while we were rebuilding a 200 engine and unfortunately I lost my notes on the exact measurement.
Jakobi
Super Moderator
Cheers Zman. Going with the 250 jug on a 200 bottom end 'over square', as you said you'd need to machine from the cylinder. It would be important where you take it from in terms of port timing though, and also I'm not sure but I think you'd likely be up for the price of a replate on top after doing such work.
Going the other way is probably easier as in you can have a spacer machined up to lift the cylinder, as long as the ports are where they need to be.
Going the other way is probably easier as in you can have a spacer machined up to lift the cylinder, as long as the ports are where they need to be.
pscook
Platinum Level Site Supporter
I would guess the exhaust port would be well below the top of the piston at BDC, so you would want to raise the roof of the exhaust port a bit. Unless you want killer grunt, but I don't know if that can be achieved with such an over-square engine. Maybe the exhaust valve could be timed to help with top end, I don't know. I'm not smart enough for that math.
I would be looking at the smallest piston possible on the longest stroke for a myriad of reasons, mostly for grunt. But you would have pretty much no top-end, I would think.
I would be looking at the smallest piston possible on the longest stroke for a myriad of reasons, mostly for grunt. But you would have pretty much no top-end, I would think.
Pinittowinit
New member
Ok the 300 bore and stroke is 72mmx72mm
The 200 is 62.5mmx65
If you raised the cylinder 7mm that should make the stroke the same. So 62.5x72. Then of course is the exhaust ports. But as it sits like that it should have loads of bottom to mid and fall in its face on the top correct?
The 200 is 62.5mmx65
If you raised the cylinder 7mm that should make the stroke the same. So 62.5x72. Then of course is the exhaust ports. But as it sits like that it should have loads of bottom to mid and fall in its face on the top correct?
Pinittowinit
New member
I'll be the test dummy if anyone has a 200 cylinder and piston.
Pinittowinit
New member
So the 200 crank will drop in a 250-300 bottom end?
