Megacycle cam for 750 twins

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LV750

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Hello community,

I?m right in the middle of puting together an engine for my twin-racer. At the moment I?m thinking about what cam I should use. I?ll stick to 750 ccm because of reglement issues but the head is portet and the compression ratio will be ca. 10,5:1. Has anyone of you guys ever used this



megacycle cam? Any experiences?

Cheers,
Eric
 
Hi, I have no experience of that cam but the numbers look a bit doubtful to me.  It looks to be all lift and not much duration, in fact more lift than valves in a standard bore size can use effectively.  I suggest you have a look at the Laverda profiles on Laverdamania and do some comparisons, I think one of the SFC profiles might work better for you.  But then, I don't race 750's and there are others on here who do ...
 
As Nick says, do a bit of camparing before you commit and hopefully find someone who has used it.
In my SF2 racer I use a 6C cam with 10.5 compression. I have 90deg motor but it works well with a 2into1 exhaust from a local formula and quite small 36mm headers for gasflow. It is tractable enough even in the wet but pulls very strong from just over 4 to 8000rpm.
Whatever you fit make sure you can adjust the timing to get it as desired. Phil T has a system on the Laverdamania site. I used a simple system where I don't run the key through the sprocket and have slotted the flanges. From memory I run about 6deg advanced cam timing from factory spec, again for better tractability. You end up in a playoff between depth of valve pockets etc. with cam timing.
A mate has a lumpier cam he got from I think Michael Moore. However his 90deg motor has firing 90deg apart with a long long rest cycle so I cannot compare it to mine (270/450 firing).
Squish, exhaust system, inlet length, compression ratio and timing all will affect how good your cam "works".
The factory spec I have here for the 6C is Inlet 62/88, exh 87/67. A long way off what you have there.
 
Compare apples with apples....284deg @ .040in is a lot of duration - what is the lift figure the OE cam is quoted at ?

I've used a lot of megacycle grinds in quite a few different motors over the years and never struck a bad one.
Though not in a Laverda yet.

When I was building a race 1200 for a local a couple of years back I looked at what was available in the factory race profiles.
I was not impressed....very old school - plenty of duration, not a lot of lift , tight lobe centers.
Even out here i can get good springs which let you use plenty of lift.
I finished up selecting a profile from the local Cam grinder's library.

If flow maxes out at say .460in valve lift, the idea is to get it up there pronto and keep it above that point for as long as you can.
area under the lift curve is key.
 
Hi Eric

Mindful of the fact that manufacturers don't stick to a standard set of parameters for defining cam timing - some use 0.050" open, some use the opening point with recommended valve clearance, Megacycle are obviously using 1mm, some just leave you to guess - I had a bit of a dig this afternoon and found my cam profile graphs which I have to assume are based on the opening point.  Reading off at 1mm open, the 6C cam has 278 degrees of duration both inlet and exhaust; 11mm inlet lift and 10mm exhaust lift.  It also opens and closes pretty fast to give a good area - the useful bit as Greg says - but is known to need good springs!  100/100 look like fairly standard lobe centres, the 6C appears to run 8 to 10 degrees advanced from this.

I run 5C cams, the 6C is clearly more racy, though.  But even manufacturers' figures are not gospel, I measured the lift of my 5C exhaust cams and found significantly more lift than my data states.  The Megacycle cam may work well, it might even be what Michael Moore used.

Would be interested to hear how the motor turns out.
 
Hi Eric - I used a 6/C cam in all my racing twins - but I also reduced the radius on the followers - mainly to reduce duration a bit and get a slightly different rate of lift - motors ( Both 750cc & 870cc) have good low end power - the reduced radius also helps reduce wear as the original flatter rocker profile isn't so kind to cam when it 1st lifts. Speaking of rockers - the originals have only about 2 thou of hard chrome - I had mine refaced with 6thou of chrome - HTh - Phil T
 
megacycle measures at .040" lift with zero valve clearance

from their catalog
lift, duration, lobe center:

585-x4  RACE PROFILE.
.446" 284? 100? 42 btc/62 abc .006"
.448" 284" 100? 62 bbc/42 atc .008"

585-x8 6-C reproduction.
.440" 282? 101? 40 btc/62 abc .006"
.406" 283? 101.5? 63 bbc/40 atc .008"

585-x9 5-C reproduction.
.437" 272? 103? 33 btc/59 abc .006"
.364" 272? 104? 60 bbc/32 atc .008"

stock  For your reference.
.384" 254? 102? 27 btc/47 abc .006"
.374" 259? 100.5? 50 bbc/29 atc .008"

the 585 is the make and model identifier
the X number is the order in which masters were created and stored
so the x4 is an older design before they had good copies of the 5C and 6C to make masters

michael moore's grind is x10

cheers,
scott
 
Thank you all for your help and comments! I think I will first try a 5C or 6C depending what I can get. I prefered a 6C but a friend of mine told me about the megacycle cam - this was the reason to ask you for more information.

If anyone of you wants to sell a 6 or 5C cam please drop me a note. It?s also possible to swap it with other parts. I have a more or less complete SF2 in parts and I want to keep only the engine.

Cheers,
Eric
 
I had a 5C in the head when Jim Dour at Megacycle borrowed it to measure for the new cam.  He didn't sound very enthusiastic about the 5C grind.

Scott needs to get the racer going so he can report on how the cam works.  :)

cheers,
Michael
 
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