Degreeing Mega Cycle Cams

[Chris58]

So Ive been working away at building the vtr.... Again

I've begun assembling the heads. I have fitted 1mm OS intake valves with some porting in the throat area, stiffer high lift valve springs, new buckets and stage 2 Mega Cycle cams.

Is it such a bad idea to leave the timing in the stock position? Does anyone know a good place to start when it comes to:
Intake btdc opening, abdc closing
exhaust bbdc opening, atdc closing
amount of overlap

The comp ratio is 12:1 if that has any relevance

Any advise on this subject is greatly appreciated

Chris

[Stephan]

Post the cams informations - duration, valve lift, and then we can assume some starting point. I did this way with my cams 256 deg duration and 10,3 mm lift.

For sure factory timing is applicable just to oem cams.

[Chris58]

Post the cams informations - duration, valve lift, and then we can assume some starting point. I did this way with my cams 256 deg duration and 10,3 mm lift.

For sure factory timing is applicable just to oem cams.

They dont give much info about them, this is all I have.

my cams are the ones with 272deg and 280deg

[Stephan]

Thats enough, i will post some suggestion tomorrow when I get to pc with my data.

[Stephan]

Let be honest and say I cannot give advice which is 100% correct. I know that oem and stg1 cams operate somewhere between 20-26 BTDC and 50-55 BBDC.Your cams are quite extreme, duration is even longer than Moriwaki stg2 cams, and the closest I found were info on Kent cams and Webcam cams.

Another point is that you must check piston to valve clearance after cams assembly, minimum for IN is 1.2mm, EX is 1.5mm. With this valve lift, unknown cams and timing, you work can be busted very easily.

So here is my suggestion, but again, I cannot guarantee it will work and I don´t exactly know what am I doing here ... You can download excel file and play a little, just change the BTDC and BBDC numbers

https://uloz.to/!FDzL8KwHNNES/cams-timing-xlsx switch to EN language in top right

[Chris58]

Let be honest and say I cannot give advice which is 100% correct. I know that oem and stg1 cams operate somewhere between 20-26 BTDC and 50-55 BBDC.Your cams are quite extreme, duration is even longer than Moriwaki stg2 cams, and the closest I found were info on Kent cams and Webcam cams.

Another point is that you must check piston to valve clearance after cams assembly, minimum for IN is 1.2mm, EX is 1.5mm. With this valve lift, unknown cams and timing, you work can be busted very easily.

So here is my suggestion, but again, I cannot guarantee it will work and I don´t exactly know what am I doing here ... You can download excel file and play a little, just change the BTDC and BBDC numbers

https://uloz.to/!FDzL8KwHNNES/cams-timing-xlsx switch to EN language in top right

Thanks ! that is great. They do seem quite extreme.. I will definatly be carefully checking the pistonto valve clearance . Could it be that the durarion is longer because they measured it from 40thou instead of the standard 50thou?

[Stephan]

Not sure, i consider 0.04 (1 mm) as standard.

Maybe ask Mega cycle what is their thought, they should know a bit more ...

[Chris58]

I was doing a bit of reading on the subject and it seems that many different aftermarket cam manufactures measure from 0.050" lift but oem are from 0.040" (1mm)

I would imagine that everywhere besides Canada and the USA uses 1mm as standard... for some reason we seem to be stuck on using imperial units

After a bit of playing around with that calculator as well as some others this is what Ive come up with to try:

[Stephan]

at least if both, stock and mega cycles are measured at 1mm valve lift, you see the real difference between specs.

I found specs for Aprilia race cams, close to yours. See the link https://www.kentcams.com/part/APR03?man ... &engine=63

My corrected suggestion would be 30/70/66/26 with valve overlap 56.

I wonder how it will perform, because I expect you will struggle with air volume and correct afr. At least open airbox and fuel pump will be needed. This is uncharted territory.

[Chris58]

at least if both, stock and mega cycles are measured at 1mm valve lift, you see the real difference between specs.

I found specs for Aprilia race cams, close to yours. See the link https://www.kentcams.com/part/APR03?man ... &engine=63

My corrected suggestion would be 30/70/66/26 with valve overlap 56.

I wonder how it will perform, because I expect you will struggle with air volume and correct afr. At least open airbox and fuel pump will be needed. This is uncharted territory.e

your suggestion is close to what Ive come up with, Maybe better with a bit less overlap.

I have removed the filter plate in the airbox, covered the snorkle , and cut a square in the top of the lid for the filter element. I also raised the tank slighty and removed the foam from the bottom of the tank.
the airbox volume is now almost double and breathes freely.

I may fit a fuel pump. Ive never had a problem with fuel supply before, but I could see that being a possible issue now.... as you say, Its uncharted territory

[Martinz]

May I ask How the cams look ? Have they got any marking on them at all, or any stamps ?

The reason I ask is I was led to believe I have Mega cycle cams, but upon inspection, have found no markings or any form of identification.
cheers

[Chris58]

May I ask How the cams look ? Have they got any marking on them at all, or any stamps ?

The reason I ask is I was led to believe I have Mega cycle cams, but upon inspection, have found no markings or any form of identification.
cheers

They do use the stock core, but there should be markings stamped on the sprocket end showing the part number. You should be able to see that one cam has a different profile than the other, and some of the bearing caps had to be filed for the lobes to clear.

Chris

[Martinz]

Thanks thats great information. Did you have to remove the cam sprockets in order to view these stamps ?

Thanks again,

[Chris58]

Thanks thats great information. Did you have to remove the cam sprockets in order to view these stamps ?

Thanks again,

The stamps are visible with the sprockets on... they are off in the picture because I received the cams without sprockets.

[Martinz]

Thanks thats great information. Did you have to remove the cam sprockets in order to view these stamps ?

Thanks again,

The stamps are visible with the sprockets on... they are off in the picture because I received the cams without sprockets.

Cheers for the info mate. Im gonna whip the sprockets off anyway.....just to be sure...