I am studying up to figure out the drilling of the cams for a 3.5 swap. From the FAQ thread, the picture shows the new dowel hole to be drilled slightly offset from the small pin hole. (as drilled by Tilley I assume)




I have been comparing, it appears that the new dowel ought to be exactly in line with the small dowel hole. I have set the cams side by side and they appear to be the same. When you line up the notch on the VQ30 intake sprocket with the 3.5 vtc small dowel, the timing marks on the sprockets exactly ine up which would lead me to believe that they should be in the same spot.

Is there something I am not seeing?


intake cams: VQ30, VQ35, JWT VQ35





intake sprockets: VQ35 vtc, VQ30






Has anyone else studied this? And please don't tell me just send them to Tilley for drilling, I want to make sure I understand it first before I just let someone else do it which may or may not be exactly correct.

 

Maybe the cams were made like that to advance the timing a tad bit That could be why its slightly offset to the small dowel hole on the stock 35 cam.

 

Just send them to Tilley for drilling...

 

The scary thought is how much was it advanced or retarded? Just ghetto drilling a new dowel pin location is a scary thought to me. What happens if its off by 1.2xxx degree from the optimal location? I hope they are not "eye-ball" drilled

From my studies on the FSMs between both engines, it looks like it shouldn't be off centered.

 

I remember comparing the position of the cam lobes to my 3.0 cams after I received my 3.5 cams back from Tilley, and when you line up the the dowel hole with on the 3.0 cam, the newly drilled dowel hole (which is off centered a bit) is a dead on match with the 3.0 dowel hole.

 

96Sleeper, wouldnt comparing the other cams to the JWT 3.5 cam in your first pic be irrelevant? Because arent the JWT cams made to be advanced 2 degrees, meaning the lobes would be slightly at a different angle?

 

It is in the pic for reference. They are advanced 2 degrees, and you can't tell it with the naked eye which is scary for the sake of drilling the other cams. If the other dowel hole looks to be off that badly, how much is it?

 

The small hole in the VQ35 cam references the cam in the fully retarded position. If you use that hole for positioning the timing gear, then the intake cams will open late and close late, and there will be only 2 deg of valve overlap. This is good for idling and low-mid rpm performance, but power will suffer greatly at higher rpm. The VTC advances the intake cam a total of 30 crank deg (15 cam deg) as rpm builds up. If you drill the cams with this much advance, torque will suffer. So a compromise has to be made that won't limit torque too much while delivering acceptably good power.

 

I was thinking since the cams are advanced, that the reference would be advanced. Basically the cams are high rpm cams, and the vtc's retard them for low and mid rpm use? or the other way around? I was assuming the small dowel hole was the cams advanced position since the cams are high rpm cams, and they were retarded.

Having JWT VQ35 cams actually complicates this alot more, since they are made for even more high rpm power. I could potentially have no torque at all. I wonder if Tilley is just splitting the difference and going with 7.5 degrees of cam rotation from the small dowel?

The crank (and cams) rotate clockwise right (from the cam end)? So the cams in the first picture are drilled slightly retarted from the small dowel right? That would be backwards from what you are saying.

I have thought about this so long I am starting to get messed up. Set me straight.

 

Yes, everything rotates clockwise.

Think of the timing gear with the timing chain assembled and the timing marks lined up. Now you want to advance cam timing, which means rotating the cam clockwise relative to the timing gear (holding the gear and everything else fixed). That puts the new hole at a CCW position relative to the old hole, just like Tilley did.

The FSM says that the VTC advances the cam relative to the position at idle. The amount of cam advance depends on load and rpm.

 

Ah, thanks, I understand. So its basically pick your powerband. I guess with the JWT cams I will split the difference, since they make more top end anyway. Thanks for the help, I really appreciate it.

 

Stephen Max, did you drill Dubbya's cams or did you have Tilley do them?

 

I sent them to Tilley for drilling.

 

so depending on where you drill the intake cam if you choose to do it yourself.u can kinda have a onetime adjustable cam gear?

 

So drilling the hole allows one to choose the cam position. I still wouldn't trust some guy to eyeball a hole on a $1,200 set of camshafts.

 

Me neither. Tilley made a template for precise location of the hole.

 

[QUOTE=Stephen Max]Me neither, but then again, what is the exact location of the hole for max area under the power curve (or max torque or maxpower)? Nobody knows. Tilley made a template so that both cams are drilled in the same place, at least.