Cam Timing Turbo App

[Ben's Z]

With the gracious help of "Z Greek" Andy I was able to find if my cam was advanced or retarded last night.  He instructed me to start out with the cam gear on Hole 2 and then proceed with his instruction on setting the valves at zero lash and turning the engine over.  Here is what I came up with. (It should be noted Andy said run it in hole 2 based off of these results be he also confessed his knowledge of forced induction and cam timing was limited)

 

I had lash of .017 ex and .024 intake at TDC on the combustion stroke.  He said with some chain stretch after break in I should be good.  I did find TDC on #1 with a dial indicator before the head was put on. 

 

Thanks.

[Ben's Z]

Let me be blunt.  Does a turbo motor run better with an advanced or retarded cam?

[skirkland1980]

It depends on your exhaust air ratio. I run mine at the stock #2 mark I use a .82ar turbo. Boost hits hard about 4k.

 

 

 

[TimZ]

Let me be blunt.  Does a turbo motor run better with an advanced or retarded cam?

There is no correct way to answer this.  

 

What do you consider "better"?  _Very_ generally speaking retarding the cam moves your torque peak a bit higher in the rev range, advancing it moves it lower.  Which is better depends on what you want - higher torque peak generally means more power, but less response on the bottom end.  You also need to match your turbo sizing.

 

Also, maybe I'm not very smart, but I'm having trouble understanding the significance of your lash measurements with respect to your cam timing.  How is that supposed to work?

Edited January 29, 2013 by TimZ

[Ben's Z]

There is no correct way to answer this.  

 

What do you consider "better"?  _Very_ generally speaking retarding the cam moves your torque peak a bit higher in the rev range, advancing it moves it lower.  Which is better depends on what you want - higher torque peak generally means more power, but less response on the bottom end.  You also need to match your turbo sizing.

 

Also, maybe I'm not very smart, but I'm having trouble understanding the significance of your lash measurements with respect to your cam timing.  How is that supposed to work?

 

I won't try to explain it, but here is what Z Greek sent me. 

 

Here is a quick way to set your cam at "split overlap," or "straight up"

1. Put the cam in "hole number 2" Set the engine to exactly TDC on the compression stroke for cylinder number one. Intake and exhaust lobes should be pointing at about 10 and 2. Hopefully you verified TDC before you put the head on, if not you will have to rely on factory timing marks which could be off a degree or two, hopefully not more.

2. Set the valves to zero lash on number one.

3 Roll the engine around one full revolution to TDC on the exhaust stroke for cylinder number one.

4. Back off the adjusters until you have zero lash again.

5. Roll the engine back around to TDC compression for cyl. number 1.

6. Measure the amount of lash now at the intake and exhaust valves, this measurement tells you how much the valves were open at overlap (to get actual valve lift, you would need to multiply the number by the rocker ratio, but we don't care about that right now. We are only interested in comparing the relative opening of the intake and exhaust valves) If the intake has more lash, that means it was further open at overlap, and the cam was advanced. If the intake has less lash than the exhaust, that means the cam is retarded. Move the cam one direction or the other, and try again. Try to get the lash as close to equal as possible, a little avanced is OK, the chain will stretch in the first few thousand miles and naturally retard cam timing.

If you do not have enough adjustment using the 3 factory holes available, you will need to create a means for further adjustment. I use off-set bushings designed for Chevy V8's. All you need to do is drill out the middle hole in the cam sprocket to the OD of the off-set bushing, and your in business.

[NewZed]

Might be in one of your other threads, but it's not clear what cam you're using.  Turbo cam or NA?  If it's the turbo grind, why not run the stock factory spec.?

[Ben's Z]

Might be in one of your other threads, but it's not clear what cam you're using.  Turbo cam or NA?  If it's the turbo grind, why not run the stock factory spec.?

Running the NA cam that came out of my car. (77) Tony D thought the NA cams have little more lung on the top end.

[Xnke]

If you are running a stock cam, with stock timing components, then run a new timing set and the cam in hole #1.

[Tony D]

There is a difference between 'thought' being opinion, and restating facts.

It was not my opinion, it was a repeating of stock cam testing on the dyno and observing power peaks.

 

People blame the turbo, and the cam on the "L28 not revving like an L24"---showing a TOTAL ignorance of internal combustion engines.

This is largely dictated by the cam profile, plain and simple.

 

Put an L24 cam in an L28, it revs like an L24.

Put it in an L28ET, and the power peak changes from the designed 53-5500, to what the N/A L24 peak is...

 

As I also stated, and which many here already know: if you choose a "cam" for an engine, don't waste your time on a STOCK GRIND for anything more than a CORE from Isky...

 

That's what "Tony's Thoughts" are on the Cam Subject.

[Ben's Z]

There is a difference between 'thought' being opinion, and restating facts.

It was not my opinion, it was a repeating of stock cam testing on the dyno and observing power peaks.

 

People blame the turbo, and the cam on the "L28 not revving like an L24"---showing a TOTAL ignorance of internal combustion engines.

This is largely dictated by the cam profile, plain and simple.

 

Put an L24 cam in an L28, it revs like an L24.

Put it in an L28ET, and the power peak changes from the designed 53-5500, to what the N/A L24 peak is...

 

As I also stated, and which many here already know: if you choose a "cam" for an engine, don't waste your time on a STOCK GRIND for anything more than a CORE from Isky...

 

That's what "Tony's Thoughts" are on the Cam Subject.

At least you answered my original question about which cam sprocket hole to use....    I'd also question using an aggresive turbo cam with using the stock ECU, like I intend for the near term. 

[Tony D]

No such thing by definition, the opening events on a Turbo Cam minimise overlap, and generally concentrate on lift to accomplish breathing improvements. Within reason those ramp rates that remain stable return good idle vacuum characteristics... Which in turn are OEM ECU friendly.

 

Understand if you get "aggressive" like JeffP you are not going with an unported head. In fact, the dynamics of the assembly of an UNPORTED head dictate restricted lift since opening the valve further than your peak head flow point just wastes ramp and beats up your springs.

 

On an UNPORTED head, you can only get so "aggressive"... Now if you got a head to flow 220cfm at 550" lift you could make prodigious turbo power with a cam optimised with different ramps to get that cam to 550 and add boost. It could literally be a stock cam, yet you double or even triple horsepower and still have a 5500 power peak.

 

Mess with duration and get aggressive and you end you with a turbo cam that idles at 900, barely makes 10" of vacuum so your vacuum bullfrog croaks continuously to keep the leaking HVAC Controls working, and has a power peak somewhere north of 7400 and a power potential over 763RWHP, but that is another conversation altogether...