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dialling in cams (vernier gear)

5K views 8 replies 7 participants last post by  Soxx 
#1 ·
We hear a lot of talk about improving performance with various aftermarket cams. I wonder how much extra performance could be obtained by simply dialling in existing cams to tdc of the valve openings. Just some food for thought. As previously mentioned, manufacturers simply dont have the resources to do this at the factory. Shane
 
#3 ·
I spent a lot of time dialing in my DEV3HL and tried a numer of settings from 0.010", 0.020", 0.035", 0.050" lift at the cam ATDC. It was an interesting excercise and I can see how you could explain those really good freak cars you see out there. Particularly some of the AU XR6's non VCT engine cars that do really seem to go well with stock cams.

All cams will respond a little differently but with the DEV3HL at .010" it lost all low end and mid range was flat but it kicked in very hard around 3500 and wanted to rev right to the rev limiter with a big rush. set at 0.050" the low end was the same as stock the mid range quite beefy and it wanted to rev to redline and pulled well to the rev limiter. At the 0.035" the cam spec recommended setting it was a good compromise and the best setting with no noticeable on cam feel at 3500 and a rush to the rev limiter.

Overall the idle, low end and mid range response changed the most in response to cam timing with the 4000-5500 range all feeling pretty similar.
 
#6 ·
madmelon said:
So how do u "dial in" a cam? what does it involve? Who does it in sydney? (do u need a dyno?)
Anyone one can do it.
You need to know how to use a clock, find 'true' TDC, and either know the cam specs and what the cam grinder suggests as the right position, or spend an hour or so on a dyno.

It is fiddly to do it properly and accurately.

If you have know idea what I just said above, then don't bother attempting it yourself.

Rick.
 
#9 ·
How to dial in a cam.

First thing we need to establish is whether the harmonic balancer is showing true TDC, as it is quite common for the outer ring to slip with age.
There are several methods for finding TDC, but this is probably the easiest way for a beginner.
Screw a bolt into number 1 spark plug hole with the end of it protruding (say) 10mm down the bore.
Wind the engine over by hand (gently) until the piston hits the bolt. Make a mark on the harmonic balancer at the TDC indicator. Now wind the engine over backwards until the piston hits the bolt again. Make another mark on the harmonic balancer. Now, the point exactly between the 2 marks you just made on the balancer is true TDC, make another 3rd mark, this may be on top of the mark which is already in the balancer. Simple.

Now that we have found TDC we can move onto adjusting the cam.

You will need a dial indicator for this, and you also need to know (from the cam grinder) the 'lift @ TDC' figure, which might be (say) 0.040".

You will need to set up the clock so it measures the movement of number 1 intake valve, this is very critical and accuracy is important here.
Adjust the clock so it reads zero when the valve is closed, slowly wind over the engine by hand until you reach TDC. The valve should have started opening and you will have a reading of 0.030" to 0.050" depending on how close the cam is set up to ideal.
If it's perfect straight away, you don't need to go any further.
If it's out by more than 0.001" either way, you will need to move the cam either by the use of the your newly fitted vernier gear.

That's about it for now, I may have missed some minor details as I'm just trying to remember all of this from the top of my head, so if anyone can fill in the gaps, go right ahead.

If you also have any questions, fire away.

Rick.
 
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