Dax 40mm stroke vs Dax 38mm stroke

[mapbike]

I've not had a 38mm stroke motor that compares to a 40mm. Extra CC's +extra stroke both = more power, I have three 40mm stroke motors that will do over 10k.
I'm not convinced.

Im not convinced either Theon, I have a "half breed" 38mm stroke short rod on one bike and now the 38mm/114mm rod on the latest build, Im very disappointed in how the half breeds balance is and the performance is lacking considerably compared to the GT5 or especially my 40mm stroke dax lowers.

The GT5 long rod engine is very low vibration and the higher it revs the smoother it actually gets, it doesnt have the low to midrange grunt that my 40mm stroke engine do but it does rev nicely from mid to top rpms, it will do 41-42mph on the flat currently with a 41T sprocket on the rear and the way it runs Im not sure it will pull a 36T well, it does wind up good but it just lacks some torque and the light inclines have a bigger and quicker affect on speed than I experience on my 40mm stroke, honestly I think a lot of these issues are related to the jug I put on the GT5, it has smaller lower transfers that aren't but maybe 75% open when piston is at BDC, the transfers are also the cat eye looking ones and my plan is to clean up one of my rectangular transfer jugs, shave the deck to get squish and compression better and then see what it attitude is, Im thinking restrictive transfers and port timing may be the reason the GT5 is so rev limited right now and I plan to put a different head on it also.

Ill have a much better clue to how it is gonna do once I have it set up more comparable to my 40mm stroke engine set ups.

 

[YesImLDS]

I've been wondering where yo bought the GT5 geometry engine I got from you, which ebay seller did you get it from? if you dont mind me asking.

It was Rose326a I believe. Imagine my surprise when I got a 40mm stroke motor from the same seller... Was expecting a gt5, but I guess I never really asked any questions.

 

[mapbike]

It was Rose326a I believe. Imagine my surprise when I got a 40mm stroke motor from the same seller... Was expecting a gt5, but I guess I never really asked any questions.

yeah that is odd to get a 40mm stroke engine from them, I know maniac57 has bought a pile of engines from rose326a and had excellent luck with them, I had heard that their engines were all GT5 type engines and thats why I never ordered one from them since I have a bunch of parts collected for the 40mm stroke engines.

I will have to say that the overall balan e of the lower I got from you is better than I expected, its a good running engine, it needs some changes made though to getit to perform as good as I would like, I'll be working on that before to long because I like to get a tad more grunt out of this one if I can.

I use a jug on this one that would have been better suited for a 40mm stroke engine, I shaved the deck down to bump compression up, but the transfers just aren't right for good power in the uper rpms I dont think, oh well time will tell once I do some more tinkering with it, Im just wanting to gain 3-5 more mph and help the mid rpm pull a little if I can, Im sure a better exhaust would make a difference also but Im gonna do my work on it only changing jug and possibly head to begin with and then I may start messing with exhaust if Im not where I want to be.

 

[YesImLDS]

Should be a good one map. I remember seeing that the transfer ports on the bottom end were pretty good for being untouched. Also I took out my newest build and opened it up and for some reason I am at the same point I was with the 36T. Must be the new exhaust. Might need to be a little bit more free flowing like you mentioned. The snake pipe hasn't been touched internally, so I am thinking of drilling some holes like you mentioned. Surprisingly it's a bit louder than my SBP exhaust was. Before I installed it I made sure to get rid of the extra welds that were sticking through on the header of the snake pipe because there was a ton in there. Could just be the day too. The motor has some new piston rings in it so I am sure those are still settling in. Might take the plug out and check tuning as well.

Moral of my newest builds motor... I am not really happy with this PK80!

 

[maniac57]

yeah that is odd to get a 40mm stroke engine from them, I know maniac57 has bought a pile of engines from rose326a and had excellent luck with them, I had heard that their engines were all GT5 type engines and thats why I never ordered one from them since I have a bunch of parts collected for the 40mm stroke engines.

I will have to say that the overall balan e of the lower I got from you is better than I expected, its a good running engine, it needs some changes made though to getit to perform as good as I would like, I'll be working on that before to long because I like to get a tad more grunt out of this one if I can.

I use a jug on this one that would have been better suited for a 40mm stroke engine, I shaved the deck down to bump compression up, but the transfers just aren't right for good power in the uper rpms I dont think, oh well time will tell once I do some more tinkering with it, Im just wanting to gain 3-5 more mph and help the mid rpm pull a little if I can, Im sure a better exhaust would make a difference also but Im gonna do my work on it only changing jug and possibly head to begin with and then I may start messing with exhaust if Im not where I want to be.

What really surprised me was finding a zl rod 40mm stroke crank in the customer trade in motor bought from BIKEBERRY of all places!
Bikeberry usually has crap. This REALLY shocked me as I did not know there WAS a 40mm crank with bolt on counterweights.
This just illustrates the simple fact: 99.9% of vendors NEVER SEE THE ENGINES THEY SHIP. They simply drop ship from a wharehouse and you get whatever the factory has in the box the day it ships. Even rose326 has NO idea what they are sending you. They are simply sending from the current batch. The nice thing about rose is that they seem to be getting better quality motors lately that the first few I ordered. The last four or five kits have been every bit as nice as the GenV "balanced" 40mm engine I bought from MBR out in Cali.
Overall, it's hard to beat rose for quality vs price.
Unless I'm building specifically for high rpm power, I will stick with rose and mod it myself.
(Just for information, my GenV is sitting under the bench. I have the parts to get it up again, but feel no need. My current ported mill is doing just fine. It feels no different to me vibration-wise over the "balanced" GenV so I'll worry about it later. Maybe.)

 

[YesImLDS]

What really surprised me was finding a zl rod 40mm stroke crank in the customer trade in motor bought from BIKEBERRY of all places!
Bikeberry usually has crap. This REALLY shocked me as I did not know there WAS a 40mm crank with bolt on counterweights.
This just illustrates the simple fact: 99.9% of vendors NEVER SEE THE ENGINES THEY SHIP. They simply drop ship from a wharehouse and you get whatever the factory has in the box the day it ships. Even rose326 has NO idea what they are sending you. They are simply sending from the current batch. The nice thing about rose is that they seem to be getting better quality motors lately that the first few I ordered. The last four or five kits have been every bit as nice as the GenV "balanced" 40mm engine I bought from MBR out in Cali.
Overall, it's hard to beat rose for quality vs price.
Unless I'm building specifically for high rpm power, I will stick with rose and mod it myself.
(Just for information, my GenV is sitting under the bench. I have the parts to get it up again, but feel no need. My current ported mill is doing just fine. It feels no different to me vibration-wise over the "balanced" GenV so I'll worry about it later. Maybe.)

I wish I could say the same about my experiences in quality. First engine was gt5 and it was in good shape. Newest is a PK80, which while it works perfectly, it has a nasty cast spot on the crank which really bothers me.

 

[maniac57]

That's simple lazy chinese machining. They true the OD in a lathe and since this will not affect anything, they just left it like that. A few more cranks on the lathe feed and it would have been gone. They probably use a go-no go gauge and once it fits, they are done machining.

Appearance issue only. Won't affect running.

 

[YesImLDS]

That's simple lazy chinese machining. They true the OD in a lathe and since this will not affect anything, they just left it like that. A few more cranks on the lathe feed and it would have been gone. They probably use a go-no go gauge and once it fits, they are done machining.

Appearance issue only. Won't affect running.

Yeah I know it won't effect the running of the engine I was just saying that quality hasn't increased in these motors as much as we would like them to have.

 

[mapbike]

the engines with the Z-L rods are old stock stuff I think.

most all of the newer engines are coming with the copper washer color rods with holes drilled for oiling instead of the scalloped edges.

 

[YesImLDS]

Well this engine isn't brand new by any means. I bought when I still lived in Illinois last year. Could be it was some old stock. Need to stop fiddling around with it and just get the 38mm dax lower running!

 

[maniac57]

Yeah I know it won't effect the running of the engine I was just saying that quality hasn't increased in these motors as much as we would like them to have.

I disagree. The internals may not be any better assembled or machined, but the basic parts are slightly better quality lately compared to the first few kits I bought from Rose.
Better ports, better solid cranks (even if poorly machined, still better than the bolt on counterweights) and better sparkplug wire and boot assembly.
Small differences, yes. But better is better when price is the same.

 

[YesImLDS]

I disagree. The internals may not be any better assembled or machined, but the basic parts are slightly better quality lately compared to the first few kits I bought from Rose.
Better ports, better solid cranks (even if poorly machined, still better than the bolt on counterweights) and better sparkplug wire and boot assembly.
Small differences, yes. But better is better when price is the same.

Well I haven't really kept up with the differences other than the internal of the engines, I agree with you on the updated CDI's and other components. I guess you are right. I must have just got a crappy cast crank! Wonder if the CDI offers any real performance gains over the original one which I am running. Still need to compare what I got to the HD lightning CDI I have in the spare room.

 

[maniac57]

Honestly, your crank is no big deal considering...Appearance flaws are super common inside chinadolls. I'll bet I've seen inside somewhere around 2-400 chinadolls since I discovered them and I cannot remember a single engine that did not have something inside it that made me want to slap the "machinist" hack that did it. The cases are ALWAYS machined a bit off center during the casting clean-up and prep when they cut for crank clearance.
Not because the case is bad, just because whoever is cutting them cannot do proper machine set-up or is using a HORRIBLY built jig. I think it's a jig since ALL of them are done wrong and even a random chance should give us ONE done right....
As long as they get the big stuff good enough, I'm not going to quit buying them.
I've seen bent cranks, mismatched crank halves, mismatched case halves, Huge casting flaws, missing gaskets, big end rod pins off center or crooked from improper crank assembly, bearings crooked, pistons in backwards, broken rings from assembly, nuts and bolts in the crankcase, missing rod bearings, the list just goes on and on.
Your defect does not affect operation.
Count your blessings! Lol!

 

[YesImLDS]

Motor has probably 35 miles on it and with the lightened top end I can't really complain. Just was showing what my motor has from the factory.

 

[maniac57]

I feel you. It drive me crazy too.
So MUCH wasted potential....

 

[Theon]

Better balance will give more top end potential regardless of stroke being 38 or 40mm.
Good port timing and well balanced crank is the most likely reason that gt5 got 45MPH.
with correct port timing and balanced crank a 40mm stroke motor will also do 45.
And will likely have better low and Mid at the same time, that's my view.

 

[YesImLDS]

Better balance will give more top end potential regardless of stroke being 38 or 40mm.
Good port timing and well balanced crank is the most likely reason that gt5 got 45MPH.
with correct port timing and balanced crank a 40mm stroke motor will also do 45.
And will likely have better low and Mid at the same time, that's my view.

Stroker motors which are basically stock motors that have a bigger crank in them are known to not rev as high as the stock configuration.

http://en.wikipedia.org/wiki/Stroker_kit

On top of this I agree with you on a corrected motor with a balanced crank will be able to rev and do 45 no problem. The thing is that on my GT5 I had untouched port timing while my PK80 has corrected and cleaned ports with the stock crank untouched as well as the untouched crank on the gt5. While I will agree with you the 40mm has better low end because strokers make more torque low down, but the shorter strokes make more power up top and continue to rev higher. This is why F1 cars have huge bores (almost 4 inches) and really short strokes (around 1.5 inches) so they can rev to 20k rpm. I am just saying from my experience with the two different motors in stock configuration and modified configuration the GT5 was always able to rev higher. The GT5 had 12 holes drilled in the piston and was a couple grams lighter than the stock, the PK80 has 12 holes, ramps, and cut skirts and weighs 65 grams without rings and still can't rev as high. It might destroy the GT5 in acceleration, but the GT5 will always pass with a higher top speed.

Also here is the information on F1 cars and there bore and stroke.
http://www.enginelabs.com/news/high-revving-thrills-formula-1-engines-at-20000-rpm/

 

[mapbike]

Better balance will give more top end potential regardless of stroke being 38 or 40mm.
Good port timing and well balanced crank is the most likely reason that gt5 got 45MPH.
with correct port timing and balanced crank a 40mm stroke motor will also do 45.
And will likely have better low and Mid at the same time, that's my view.

i hear ya, good balanced rotating assembly increases rpm potential and ability with these engines, I have one 40mm stroke that would maintain 46-47mph on the flat before I put a different exhaust on it to quiet it down a little and now it does 43-44mph solidly on the flat as long as Im not bucking a head wind, this is with tunning a 34T rear sprocket, NT speed carb, 6cc Fred Head and my own unscientific port cleaning and piston ramping, I think with a better exhaust and a slightly larger carb this bike would probably do 50mph or maybe a little more, I have had one that I GPS'd 52mph on, it had more mods done to it but I ran it a bit lean and racked the piston, and took the tension out of the rings, jug is still fine but at those rpms I was turning running a 24" wheel and a 30T sprocket it just leaned out to much and I ran it WOT for to far and hurt it bad on the third or forth high speed run, Im thinking the 100:1 Opti2 just wasnt enough lu ri ation at those rpms for that long, I know others who race their bikes that have said the Opti2 is great but they've also had issues when running very high rpms for extended distances with it mixed at 100:1.

One guy told me it should be run at 50:1 in those condition and then it will do a good job.

I honestly want to get thsi GT5 engi e to hit 45mph on the flat running the 41T sprocket if I can, but I dont know if I have the porting skills to get all of it good enough to do it with the 41T, I think I can get there fairly easy with a 36T since Im getting 41-42mph with the 41T now.

Im gonna put the KX65 chamber on it, and put my Puch Hi Hi 70cc head on it along with a cleaned up jug I have that has larger transfers and I,m gonna shave it down to get a good tight squish and optimal compression.

If this dont get it done I'll be disapointed for sure.

 

[Theon]

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?

 

[YesImLDS]

I had no problems with mine and I also bought one for a friend who would cruise with me. When I bought the PK80 after my GT5's self-destruct I couldn't keep up with him and had to have more mods to be able to beat his stock with a crappy aftermarket exhaust. All I am saying mathematically speaking the GT5 will be able to rev higher, now a beefed up anything motor should be able to rev high as well. From a stock stand point the GT5 will rev higher. Now if you mod both a PK80 and GT5 the PK80 will be able to beat the GT5 for a little while, but the GT5 will always be able to catch up in the high end, and we are talking with the same mods. PK80 is basically a stroked out GT5 which gives it a little more displacement (3.5cc) that's where that extra low down comes from, but because you have a larger turning radius with the crank it won't turn around as fast as the GT5 cranks would if you know what I mean. The GT5 crank (38mm) has a perimeter when spinning of 238.76mm while the PK80's crank (40mm) has a perimeter of 251.33mm. Now I just have a high school education, but that 13mm is ~5% so if you want to go from a crude method of thinking. In the same conditions with same mods etc etc and you hit 10k rpm with a PK80 you should be able to hit 10.5k with a GT5 engine.