Can you clever guys help me clear up some of these questions please
Stock 'busa lobe centres are Ex 100 In 105 right?
What's the proper way to measure opening and closing times to figure out overlap? Actual point of opening is difficult to measure (and closing is worse) so do I use x amount of lift? What's the standard?
What is stock cam timing overlap on the 'busa?
If I wanted to cause the engine to "hang on to power" in the upper ranges (even if it means sacrificing mid-range) without swapping cams at all, which cam would I move and why (or is it not possible by altering cam timing)?
Mostly hypothetical questions since I don't have a N/A 'busa but I'm trying to get this cam timing thing straight in my head . Thanks for any replies.
Let's get the terminology down first .
The exhaust being on 100 is the centerline in relation to the crankshaft degree's of rotation . The intake on 105 is the same = intake centerline 105 . Remember , the 4 stroke engine spins the camshafts at half the speed of the crankshaft .
With the cams set like that the actual lobe centers are 102.5 . Saying lobe center separation and intake or exhaust centerlines are two different . If the cams are set at 108 in - 108 ex .. both the in and ex centerlines are on 108 and so are the actual lobe centers . If the intake is set on 100 centerline and the exhaust is on 108 , the lobe separation angle will then be 104 .
When you advance an intake cam , the opening number becomes larger . If the valve is opening at 42 degrees before TDC and you advance it 2 degree's it will then open at 44 BTDC . The valve will also then close earlier after TDC by the same 2 degrees making for a lower numerical number . 104 down to 102 as example .
On the other hand when the exhaust cam is changed to open earlier it raises the numerical number ,unlike the intake . Advance the exhaust cam or valve opening and the number will change from 104 to 106 , again as example .
Once you establish an exact valve early opening lift , figuring valve overlap is easy . That can be at .050 lift , .070 lift , ect but it needs be with exact lash settings when using low low lift and barely onto the lobe ramp. Just add the intake opening number to the exhaust closing number and you've got it .
Giving an engine more overlap always tends to lessen the low rpm power due to the loss of cylinder pressure at lower rpm's but adding overlap via means of cam timing only will not always be the ticket for best top end power .
Taking the Yoshimura Stage 1 cams with the valve opening and closing events taken at 1mm valve lift you will see the overlap can be increased , lessened at different settings . Larger overlap numbers will make for less than optimum low power due to exhaust needs and factoring in some possible/probable intake charge reversion and dillution .
Yosh cams set per the Yosh cam card :
102 in-105 ex = 30 degree's of overlap
105 - 102 = 30
102 - 102 = 33
105 - 103 = 29
102 - 103 = 32
105 - 105 = 27
105 - 104 = 28
102 - 104 = 31
100 - 103 = 34
100 - 104 = 33
106 - 103 = 28
Anytime a cam needs moved more than say 5 degree's , another cam profile is most likely in order .
In my view , changing exhaust cams and their centerlines do more to change the power curves of the Hayabusa engine than the intake cams do generally, but factor in running single pattern style cam choices " same duration in and ex " any number of other cam combinations makes the case for one on one look at what centerlines and separation angles to choose based upon the combination of performance parts and intended usage . Cams with a 14 - 20 degree spread of duration between intake and exhaust are working well at anywhere from 103 - 106 to 106 -108 . The Busa seems to like a 3 degree spread from intake to exhaust most cases . But again much depends on the combination of other parts and intended usage .
When you look at Yoshimuras HP chart of the Stage 1 cams set on 102-105 on the stock bore piped Busa the graph chases the stock cams on a line near perfectly until it finally makes the aprox 10hp gain only after 9200 RPM . Those cams have a 14 degree spread vs the stock cams 20 degree spread between intake and exhaust . Many that put those cams in at 105-105 speak of the engine being soft down low after install but with the intake on 102 , no power is lost over stack cams and timing .
As for you question about the stock cams , the exhaust cam is small allowing just a certain amount of movement before one gets the exhaust valve closing too close after TDC . That cam has 214 duration @ 1mm lift vs the little Yosh cams 230 duration @ 1mm lift . The Yosh ex cam closes at 10 degree's . Carefull of getting around 105 or higher with the stock ex cam . Suzuki wanted those cams in at 106/103 . For whatever reason most check at 105/100-99 .