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Post by kkzxxx on Sept 20, 2018 12:23:11 GMT -5
I recently bought two a9 cams, first one I installed on a 50cc motor, the second one I installed on a 72cc and I have to say that there was no noticible gain, I would now say its a useless upgrade. Also tried a head with bigger valves on the 72cc, it brought the CR down, which made it slower, 50cc head was much better. Maybe 50mm and larger bores gain something but not 72cc it seems.
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Post by Sir Scoots-A-Lot on Sept 20, 2018 18:29:30 GMT -5
I have done quite a bit of reading on A9 cams, obsessively trying to decide whether to BBK my engine or to be happy with stock and see how many miles I can get out of the well used setup I bought and ride a lot. I found evidence from people on this forum and other forums and over a decade's worth of people talking about performance vs stock and A9 cams has kind of scared me a little...BECAUSE it seems that there are at least 3 different "A9" cams out there. that is to say 3 different makers making cams with the "A9" stamp , yet they all have apparently according to other users different profiles! There was a guy on here recently who I can't remember his name but I read his post about building with a guy who owns a machine shop and the thread says there were 2-3 different kinds of A9 cams! This thread, scootdawg.proboards.com/thread/4798/gy6-cams-a10-a11-a12 ,from over 10 years ago, purports that A9 cams have about a 40% greater lift than stock! to be fair I'm not sure if they were talking about a 150cc or 50cc A9 cam or if the two are in proportion to each other based on cc size and vs stock cams. On that thread 90GTVERT warned people against the aggresive A9 cams people were finding (way back then)....so Im not sure if the A9 of today is different than that of a decade ago, Im not sure if it's safe, I'm kind of sure there are significantly different versions of A9 cams on the market today...So I can't make up my mind whether to get one, was planning on it not only to gain a lil more power, maybbe a couple mph but was hoping it would lower compression and be easier on my heavily used 'n' abused electric starter...but with people in different forums at different times reporting vastly different findings and Ratdog on here sayin lift is less and I think he said timing is retarded>?? or maybe it's just me that's retarded? I just don't know. I'll have to get back to you all on this one. may leave out a new cam and head for now and just try a BBK cylinder/piston with high flow intake, try to derestrict my exhaust and jet my carb. what do y'all think>? PEACE!
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Post by hackinhondas on Sept 23, 2018 10:53:53 GMT -5
Sorry if this the wrong place to post this reply but i can longer restrain the impulse, I wonder if the people who are reporting a lack of gains with the cam's are missing out due to not utilizing the greater/longer lift.if your current setup is already tuned well and the valves are already allowing all of the fuel/air into the chamber the cam is just creating a bigger opening for the same volume of combustibles. I am but a humble electrician by trade so if I have misunderstood something feel free to correct me.
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 23, 2018 11:22:11 GMT -5
The main reason I made this post was to let people know the the “A9” cams are NOT high preformance cams! They do not have more duration. They do not have greater lift. They do not have less clearence at TDC on the intake stroke. In effect, they are a whole lot like a stock cam with slightly different lobe timieing
And, yes, they are different. Orginal, I thought it was like a lot of Chinese stuff, that they were all the same with different names. Now I know that is not the case. But I don’t understand why the stock cam has the greatest lift of all the cams I have tested. If you look at the cam stats for these engines, they are way milder then other small displacement single overhead cam two valve engines.
Yet we have had many report a preformance increese with these cams. Of course I have seen reports that claim a preformance increese by switching to the “racking” ignition parts too, and I think everyone knows those are of no value
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 23, 2018 11:34:49 GMT -5
Hackenhondas, I’m not sure I understand what you are saying. Is it your impression that you can only get “so much” in the combustion cycle and more is wasted? Real preformance cams open the valve sooner and often wider to pack a LOT more fuel/air into the cylinder. This effects mostly the higher RPMs. It’s a time issue. First it takes time to get the air fuel mixture moving. Then the vale is only open a very short time to let fuel in. As your RPMs go up, that time becomes shorter. This is why a mild cam for , say a lawn mower engine, has a very pointy looking cam, and real preformance cams have an oval look. The big disadvantage of preformance cams is that they tend to not run well at low RPMs do the two A9 cams look anything like the the preformance cam for a different engine? I’m talking about the shape of the lobes
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Post by hackinhondas on Sept 23, 2018 11:48:52 GMT -5
Hackenhondas, I’m not sure I understand what you are saying. Is it your impression that you can only get “so much” in the combustion cycle and more is wasted? Real preformance cams open the valve sooner and often wider to pack a LOT more fuel/air into the cylinder. This effects mostly the higher RPMs. It’s a time issue. First it takes time to get the air fuel mixture moving. Then the vale is only open a very short time to let fuel in. As your RPMs go up, that time becomes shorter. This is why a mild cam for , say a lawn mower engine, has a very pointy looking cam, and real preformance cams have an oval look. The big disadvantage of preformance cams is that they tend to not run well at low RPMs I was trying to say that with an "upgraded" cam your trying to allow more AF into chamber, but if the carb (or other limiting factors) doesnt allow more AF into the circuit it's a wasted mod
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ratdog
Scoot Enthusiast
Posts: 342
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Post by ratdog on Sept 23, 2018 12:09:05 GMT -5
Well if say we only have a 18 mm carb on these little scoots, at 8500 rpm, the preformance cam will give you a small but measurable increese in preformance, but you are correct that if I want to get everything out of that cam, I need to get a bigger carb and move the RPMs up to 9500 or more
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