Intake valve closing angle

Posted By: Viol8r

Intake valve closing angle - 07/17/09 10:02 PM

http://www.lunatipower.com/Product.aspx?id=1580

I understand that when you are using the closing angle number to compute dynamic compression you add +15�. According this cam its 43�abdc + 15�= 58�

Can someone confirm this for me?

Posted By: 64Post

Re: Intake valve closing angle - 07/17/09 11:37 PM

Answered in Race forum... I think.

Posted By: goldmember

Re: Intake valve closing angle - 07/17/09 11:52 PM

The program is flawed. Adding 15 degrees to the closing @.050 is useless. Most cams are asymetrical further throwing a wrench in the works. Don't waste too much time,just use the correct compression for the availible fuel,cam sensibly and have fun.

Posted By: 64Post

Re: Intake valve closing angle - 07/18/09 01:46 AM

Quote:

The program is flawed. Adding 15 degrees to the closing @.050 is useless. Most cams are asymetrical further throwing a wrench in the works. Don't waste too much time,just use the correct compression for the availible fuel,cam sensibly and have fun.

I may be having a brain fart, but I gotta disagree. I think the 15* figure is far from exact, but I wouldn't call it useless -- just very general -- and better than nothing. Ramp speed and the clearance ramp also plays a part. If you wanted exact, that would involve "graphing" the cam lobe from .050" back down to the original lash value/base circle. If Comp categorically stated that they grind a 6* clearance ramp on all their solid cams, the window could be narrowed further.

IMO, intake velocity @ .050" is marginal. An intake open @ .050" with 160-180 psi of cylinder pressure is an issue as pressure continues to bleed off until the valve is closed. There is definitely pressure to be lost by the additional .050" closing event. The question is, how much?

I also disagree that most cams are asymmetrical.

Flame suit on...

Posted By: goldmember

Re: Intake valve closing angle - 07/18/09 01:56 AM

"far from exact" and "useless" are one and the same. Why bother to measure the exact comp ratio? Why do anything if you dont' want to do it right? By far the majority of automotive cams are asymetrical. How much offset a design has is known by the designer and anyone that wants to figure it out,a degree wheel and dial indicater can get you the info,but a camdoctor is far faster. Using the timing numbers @.050 and adding a fixed number is useless,better than nothing,but only by a bit.The cam in question has approx 8degrees of offset,so a little math and you should get what you want.Lot's of factors more important,but more work or experience required.

Posted By: Dodgem

Re: Intake valve closing angle - 07/18/09 03:22 PM

Well knowing the exact static compression is a must and knowing the cranking compression is real usefull in picking a cam that will allow the fuel you want to run. or the fuel you want to run and what cam.
I have a 272 deg @ .050 cam 10.5 to 1 static compression and it had 155 average cranking compression at install of 106 advanced the cam to 102 and it has 165 average which is still way short of what 94 pump gas will allow.
This program says 172 lbs so close as my two highs are 170 other 6 are right at 160
put 0 in for boost and it's @.050 been close on all motors I've dealt with.
http://www.rbracing-rsr.com/comprAdvHD.htm
I'm in the process of bumping my compression and my target is 190 to 195 for the highs and the ring seal probably not as good on the rest so 180 will have to do till I pull motor and have it torque plated and re honed.
I think most builders now like to aim at a max cranking compression of 185 for 93 octane!!

Posted By: Dodgem

Re: Intake valve closing angle - 07/18/09 03:25 PM

put boost at 0 and altitude is best to have altitude on day of test (not density altitude) cheap weather stations will give altitude pretty close