Twin cam

[Leny Mason]

Hi, I know there is some smart cam people here, if we advance the intake cam 4 degrees what  should this do runs hotter to spool up faster, and what does advancing of retarding the exhaust  cam just trying to understand how twin cams work thanks. Leny Mason

[blykins]

Leny, look at it this way:  you are dynamically changing the lobe separation. 

In a single cam engine, we order the cams with a specific lobe separation and it's fixed.  You can only change the ICL and you do that with advancing/retarding the camshaft. 

In a twin camshaft engine, with one cam working the intake valves and the other cam working the exhaust valves, you set the lobe separation dynamically by advancing/retarding each cam. 

So you degree the intake cam, put it where you want, degree the exhaust cam, put it where you want, then LSA = (ICL+ECL)/2

Now, how you manipulate each cam will depend on what you want to accomplish, what size engine, the application, etc.  There is no real set of rules or results, just like there are no real sets of rules or results for a single cam engine. 

[chris401]

Hi, I know there is some smart cam people here, if we advance the intake cam 4 degrees what  should this do runs hotter to spool up faster, and what does advancing of retarding the exhaust  cam just trying to understand how twin cams work thanks. Leny Mason

The Honda guys like the idea of sticking an Acura head on there car. I have worked on two of such modified engines but can't remember the specs. One of the owners was telling me  4-6° advance on the intake and 6-8° rerard on the exhaust. I do not know where that puts the dynamic compression but it suposed to give the car best of both worlds. Could be curved with larger cams I suppose.


Some VVT systems use oil pressure to keep the intake advanced under cruise and low rpms and default to retard under high rpms(seems the Triton engines for one). Other systems use oil pressure to force the intake cam retard under high rpm.