retarded cam question
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
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From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
retarded cam question
OK so I am playing with DD2K and cams recently.
Why is it that the farther apart the in duration the intake and exhaust lobes are the more the volumetric efficency?
for example. if I have a 206/212 duration it is lower than say a 188/250 duration cam. Why?
Why is it that the farther apart the in duration the intake and exhaust lobes are the more the volumetric efficency?
for example. if I have a 206/212 duration it is lower than say a 188/250 duration cam. Why?
Drifting
Joined: Oct 2000
Posts: 1,825
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From: Shawano WI
In the particular case that you mentioned, the exhaust valve would be open so long that the intake charge would enter the cylinder and exit the exhaust valve right away. That would cause your VE to be very high but not in a useful way. You have to look at much more data than just one output to understand if the data is useful or not. DD is a useful tool for very mild motors but the more "radical" the combination the less reliable the data is. DD (and any other engine simulation package) still goes by the asumption that "bigger is better" as far as producing big HP numbers even though real world experience tells us that "bigger" is far less important than "correct combination".
Thread Starter
Team Owner
Joined: Apr 2002
Posts: 62,198
Likes: 1
From: All humans are vermin in the eyes of Guru VA
Cruise-In IV Veteran
Cruise-In V Veteran
I am aware of the correct combo theory. it applies in less radical cases. like 212/218 versus 206/224.
I was just using extreme cases to illustrate a point.
I was just using extreme cases to illustrate a point.
Race Director
Joined: Nov 2000
Posts: 16,416
Likes: 1
From: NC,USA
Theres a thread about Lobe seperation in Engine Mods that goes in to this a little...
Something about reverberation of exhaust gases into the intake... the farther apart the lobes are, the less overlap you have... overlap causes the exhaust to go up the intake, or the intake charge to go out the exhaust.
The guys overthere explained it better than I'm capable of understanding!
Something about reverberation of exhaust gases into the intake... the farther apart the lobes are, the less overlap you have... overlap causes the exhaust to go up the intake, or the intake charge to go out the exhaust.
The guys overthere explained it better than I'm capable of understanding!
