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# Thread: Bikes Labelled 78 cc are not 78 but 88cc or rather 90cc bikes

1. ## Bikes Labelled 78 cc are not 78 but 88cc or rather 90cc bikes

hi
today i opened my engine of dhoom yd 70 to solve the mystery of its bore and stroke size .. eventually calculate its true displacement in cc.
the results were stunning
i used vernier calliper to do this experiment
the bore came out to be 46.8 mm or rather say 47mm
and the stroke calculation was a bit tricky as the piston was not flat it had a lot of surfaces and that was giving different values at differnt points.

however if calculated from the place of higer posion on piston the stroke was 50mm... and this depth is not from the top face of cylinder rather from the point whre the piston reaches at its TDC ..

Now using formula foir cc calculation
cc= bore^2*stroke*.7854 [bore and stroke r in cm]
cc=4.7^2*5.0*.7854
cc=86.7cc

now despite being an 88cc their top speed is 80 mostly on flat road.. mostly ..and what i have noted is that they have very hard time in climbing whareas honda cd 70 has also got 80 as top speed and its climbing ability is awsome..

so where is the bottle neck in these CHondas...?

2. yd dhoom is Chinese bike not original parts or workman ship of Yamaha Japan, so no comparison with Honda CD70
However Junoon is original bike of Yamaha So you may see the difference its best in 100 cc category.

3. Originally Posted by asjdsm
hi

Now using formula for cc calculation
cc= bore^2*stroke*.7854 [bore and stroke r in cm]
cc=4.7^2*5.0*.7854
cc=86.7cc

whats this .7854??

4. pi/4
the equation is size in cc= bore *bore*stroke*pi/4 [ or pi/4 is constant = .7854]
for instance for honda cd 70
cc=4.7*4.7*4.15*.7854
cc=72cc

5. Why we are not promoting the bikes which are made in Pakistan .... and about climbing its not the bike its the rider ... if you r a good rider you can climb with 50cc or if you r not you can't even take the 125cc bike on country side rods .... and for your kind information i have beaten the Honda cd 70 with the loaded weight of 80kg where i am using Habib with the loaded weight of 130 kg ... so it snot the bike its the rider

6. ^^ o bhai ya 70cc motorcycles hain koi Fighter Jets nahi jin ka lia experienced pilot chaiya...
i have tested 3 honda cd 70 and almost half a dozen chondas till this date in murree and that is y i am saying this fact..

7. So we don't even want to promote the Pakistani Made Bikes ... Then we never have the names like Harley Davidson , Boss Hoss known as American Muscle Bikes .. ok we made JF17 Thunder with the Help of China so what do you said its also the GF17 (Girl Friend of F17) ... Fine Fine Fine .... and i am not against the Honda or other International Brand .. but we should also respect the Local Brands..

8. and sir jee where u get this eqauation from??

9. Originally Posted by h3llzang3l
So we don't even want to promote the Pakistani Made Bikes ... Then we never have the names like Harley Davidson , Boss Hoss known as American Muscle Bikes .. ok we made JF17 Thunder with the Help of China so what do you said its also the GF17 (Girl Friend of F17) ... Fine Fine Fine .... and i am not against the Honda or other International Brand .. but we should also respect the Local Brands..
bhai la tho li ha so called pakistani bike,, ab our kaisa promote karoun,,,?
the bold text is not said by me don't put words into others mouth,, for the use of word chonda ,, google it ,, or just wiki it,,,,u will come to know,, and for the word GF 17 .. thats is ur own creation not mine.,,

or here is the wiki refrence to the entry chonda
http://en.wikipedia.org/wiki/Chonda

@cursedd
knowledge of basic geometry in enough to calculate the volume of cylinder,,oh if have studied integration it will also give u the exact equation,,google for more info
calculate displacement for single cylinder engine in cc

10. ohh so its application of integration..then this equation thing is really to do a thing with me..coz nowadays em' learning integral calculus. inshallah will understand this!

11. its double integral in cylinderical cordinates in Calculus 3,,

12. ohkk.. i'll get to learn it when i'll learn the surface integral and now em studying line integral.

13. @asjdsm
Bhai meet me and i'll let u test ride my hero rf 70 2011.No alterations whatsoever and bike climb's like a 125.Tested on the roads of peer sohawa.It all depends on the setting.This is the term that mechanics use and even i dnt understand.My mechanic took abt 2k for this setting i wached him do it.He was meddling a lot with carb and tappet settings that's all i can tell u.

14. i can do carb settings,,and they matter a lot,,i say a lot.. now i m not free but when i get some time to visit mmurree i will adjust the carb and share those tips/tricks with u ppl,,

regarding tappets settings i will have to check them,, but again the only setting done to tappets is its clearance..
after tuning u could easily reverse engineer his settings .. just check what the clearance is and also what the carb is set to.. i.e. what number of jets r placed and how is the placement of needle in the grooves..

also dear can u tell me what are the main and pilot jets of ur hero carb ? is it the one labelled pz22 ? i have purchased one replica of this carb it has jets but not labelled can u help me by telling me what are the primary and secondary jets..

15. @asjdsm
Yes i remember him talking about jets or something.He said that older model's i.e 2010 2009 etc had jet size 72 i think and my bike had a built in jet of size 75.Anyway's what he was saying that new model has bigger carb jet's.Regarding ur question i will ask my mechanic and answer u soon.

16. Originally Posted by outlaw92
@asjdsm
Bhai meet me and i'll let u test ride my hero rf 70 2011.No alterations whatsoever and bike climb's like a 125.Tested on the roads of peer sohawa.It all depends on the setting.This is the term that mechanics use and even i dnt understand.My mechanic took abt 2k for this setting i wached him do it.He was meddling a lot with carb and tappet settings that's all i can tell u.
like a 125? no way man there is a hell lot of difference in engines of 70 &125,
regarding 2k, i think he cheated u coz car tuning costs RS 500 maximum

17. @umer009
As long as i'm satisfied with the performance of my bike i dnt think he cheated me and i think the way my bike is performing right now 2k is definitely worth it.Ur right tuning costs 500 max par mein nay tuning nai karai thi aur bhi kaafi kaam karaya tha eg alignment wheel balancing etc etc...

18. @umer009
No matter what you do u cant reach the performance of 125 but like asjdsm i go a lot to murree peer sohawa and other hilly areas and bike climb's very very easily almost the same result as 125.

19. to get u an idea , an engine overhaul for 70 cc costs 1500 of labour maximum
anyways its ur bike and as long as ur satisfied its ok , good luck

20. hahaha guys if u alter ur piston and valve also than also u cant reach at the performance of 125cc.cause thr iz not only change in size piston ,carb,valve,weight,spockets , are too differ....chchchchc......i think k agr aisa hota to company b 2k 70cc k upr lga k kehti lo g 125 hazir hai janaab

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