Dax 40mm stroke vs Dax 38mm stroke

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mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
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Central Area of Texas
Theon said:
With a stroke of 40mm and a piston of 47mm, it's still a short stroke motor.
The 38mm stroke motors we get in OZ from Ebay are rubbish. So I have not had a 38mm stroke motor that will match the well balanced 40mm stroke cranks I have, and gave all my 38mm stroke cranks away.
With a KTM pipe, I back off at 10500 RPM with a 40mm stroke, and have three 40mm stroke motors that have all shown those revs, I see no need to drop back to a 38mm stroke. And doubt that I could even find a 38mm stroke crank here in OZ (given what I've seen so far) that would rev as well as the 40mm cranks? But it sounds as though you guys get better ones?
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The GT5 engine I bought used from YesImLDS has a good balance, I was honestly surprised at howgood it is, Im sure I could see a slight bit of wobble in the counterweights when I would rotate the crank and that worried me, but when I got it fired up the first thing I noticed was how smooth it is, I cigured the issue would come when I revved the engine good and wouldn't ya know it actually gets smoother as it revs up....

Im gonna set this thing up as close as possible to ow I've had a ouple of my 40mm stroke engines set up so I can get an honest comparison so that I will know if this engine is capable of performing like they did with same exhaust, same head, same carb which will likely be a SHA Dellorto clone/RT carb since all my engines have always had better low to mid pull with the RT carb compared to the NT or N Speed carb.

Im very happy with the balance of this GT5 but Im not satisfied with the power of it currently even though its doing 40+mph with a 41T on a 26" wheel, I want to see better mid range grunt and 3-4mph top speed increase and then Ill be happy.
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
cannonball2 said:
That calcs to 9000rpm. That aint bad!
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yeah it does really wind up nice.

I may end up with a 38 or 36T if the exhaust, carb and head change boosts the mid range power a little.

I may not swap the jug on it if these changes get me where I want to be with it.

Im actuall6 happy with 40mph as long as it isnt sluggish getting there.
 
YesImLDS

YesImLDS

Member
Jun 29, 2013
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Columbia, Missouri
Map I had that bottom end at 45mph on a 36T it didn't seem to struggle too much in the low end. I guess I had my expansion chamber for some low-mid to mid-high range. The thing would start to fly after 20!
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
YesImLDS said:
Map I had that bottom end at 45mph on a 36T it didn't seem to struggle too much in the low end. I guess I had my expansion chamber for some low-mid to mid-high range. The thing would start to fly after 20!
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yes it does pick up good after about 20mph, just a little weaker than my 40mm stroke engines on 5he inclines around here.

Not a dog by any means, just a little less grunt and probably more to do with the external devices than the engine itself.

Im gonna tinker with it and I feel like I will be able to get it where I want it to be and if I cant make much improvement over what it is now it will still be an excelle t runner just as it is since it will easily cruise at 40mph on the flat.
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
allen standley said:
Jus curious Map, what your weight?
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Well, from one Allen to another Allen I weigh about 213-215lbs dressed depending on the time of day I weigh...lol!

I fall into the 5'10" 215lb country boy catagory so I know that having my bikes dragging me around at 45mph is purdy good compared to what some of the buck40 and buck50 peoples arw getting done.

Im not a heavy weight by any means but Im not a super lite weight either kinda in the middle I guess.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
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memphis Tn
All this talking about the "balanced" 40mm strokers finally made me get off my duff and find the right parts to get my GenV back up.
I used that weird black jug that was giving me fits on all my 38mm bottoms and it fits the 40mm GenV bottom like it grew there.
I ported this one quite a bit more aggressively than the jug on my current Pig mill(which is doing GREAT btw) so I figure it should be substantially more powerful on top.
What baffles me is why I have it in the first place.
The ONLY 40mm strokers I own are the GenV and a recent customer trade (which both had jugs) so I have no idea how I came up with a spare jug since I have only ever ordered ONE and that is accounted for (broken)
Yet this jug fits the GenV AND the bikeberry 40mm perfectly, and NONE of my other bottoms. So where the heck did it come from?!?
Oh well.
I have too many dolls underfoot after a frame poor winter.
Weird.
Pics.
The wider 40mm rod bearing from the GenV vs the 38mm's

Now THAT is what I wanted to see...

Exhaust

Ported intake compared to wide port 40mm billet intake manifold

Don't worry, I won't be using the crappy stock cast head...still have to trim the piston skirt too before buttoning it up.
 
maniac57

maniac57

Old, Fat, and still faster than you
Oct 8, 2011
4,484
22
0
memphis Tn
I can't figure out those weird marks on the exhaust flange either...
looks almost like machining damage, but the jug had some run time from the dirty exhaust port so I'm doubtful it would have run without leaking before I cleaned it up. And this kinda looks like it might be vibration related or from a pipe hit that was run while damaged...
Seems to me had it been on a customer motor, I would know about it. I work on a lot of motors, but I don't work on so many I would forget rebuilding a 40mm stroker and having a jug left over....
I'm happy but baffled.
 
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