How much variation in factory cam timing adjustment?

[mike100]

I have driven or ridden in about half a dozen ZR-1's and everyone of them had a different personality and seemed to have different torque characteristics. Some were real soft down low and fairly "top-endy". My car has a great grunt at 4000 rpm but is a little flat on the top, and the car I drove last Saturday had normal to good mid range and super great top end and it was still on factory 91 manifolds (Erik-YZPilot's 91). Erik's car has the same timing curve as mine seeing as how I made the chip for it so pretty much all things being pretty equal with a similar home grown plenum and inj housing port job, same chip, same weight, same car, etc...

I'm seriously considering degreeing the cams on my car to make it run better. This is of course assuming that there are gains to be realized there. I'm very much thinking that this is the silver bullet to Permagrin and the intangible difference and the mysterious reason some cars have the extended torque peak/cylinder pressure and others are just 'ok'.

I'm remember reading this is easiest with the engine removed?

btw, I think I'm going to keep this car assuming I can keep it smogged in this state. If I can get it to run like Erick's I would drive it a lot more often.

[Dynomite]

I would say impossible to do with engine in car But you are welcome to give it a try and let us know how it works out for you. You have to somehow install two mechanical chain tensioners and Cam Covers removal with engine in car is no fun.

Of several 90's I have checked, none required Camshaft Timing as my LT5 engine In Car Inspection of Timing was within 1.5 degrees for each Camshaft.

Checking your Camshaft Timing Engine IN Car Checking Camshaft Timing Engine In Car
You have to remove Cam Covers engine in car...then set up to determine or assume the current TDC timing Marks on the Harmonic Balancer are correct.
You can get close without pins in front camshaft retainers just by using a flashlight observing the pin hole in the camshaft journals alignment with the holes in the camshaft front retainers. If you want to make sure of the TDC marks on the Harmonic Balancer, you can install a dial gauge to determine when piston #1 is TDC to determine TDC easy enough engine in car and can then mark harmonic balancer and use degree tab bracket easy enough engine in car. The Tab has marks 25 deg Before and 5 deg After TDC (A total of 30 deg). You can use the marks on the Timing Tab to mark your Harmonic Balancer. Mark 110 deg BTDC by rotating the Harmonic Balancer 3 complete Tabs (90 deg) + 20 deg Counter Clockwise and mark. Mark 114 deg ATDC by rotating the Harmonic Balancer Clockwise 3 complete Tabs (90 deg) + 24 deg and mark.

See Item #2 Camshaft Timing



You can check by rotating engine (with chain tensioners still keeping chains tight) by visual inspection in pinning holes which can be done engine in car easily. If you mess around too long especially reversing the rotation of the crankshaft, the Timing Chains will loose their hydraulic chain tensioner tension.

I set the pins in the Venier Plate slot such that the camshaft sprockets are rotated against the half moon on the camshaft (clockwise looking at front of engine) which prevents additional movement of sprockets on camshaft under any conditions. This is within 1.6 degrees of where I want the timing. See item #5c and #7a of LT5 Camshaft Timing Additional Tricks



CAMSHAFT TIMING USING DEGREE WHEEL
Camshaft timing TIPS
Dial gage holder TIPS
LT5 Camshaft Specifications and Camshaft Timing Tricks
Tech Info - LT5 Summary of Camshaft Timing from Start to Finish
Tech Info - LT5 Timing Diagrams
Tech Info - LT5 Camshaft Timing and Timing Chain Calculations
Setting/Installing the Chain Tensioners and Timing Chain Tricks
Camshaft timing optimum deg
Cam timing
First attempt at camshaft timing

[Scrrem]

I just had the cams timed on my new motor and the first step is to pin the motor as they do at the factory to set the timing. We then set up the degree wheel and a dial indicator and the drivers side intake cam was retarded almost 7 degrees!! The other three cams were not as bad, only 2-3 degrees out. I can kind of see why GM is resisting releasing any dyno sheets if the #'s can vary this much.
Rich

[mike100]

Originally Posted by Scrrem

I just had the cams timed on my new motor and the first step is to pin the motor as they do at the factory to set the timing. We then set up the degree wheel and a dial indicator and the drivers side intake cam was retarded almost 7 degrees!! The other three cams were not as bad, only 2-3 degrees out. I can kind of see why GM is resisting releasing any dyno sheets if the #'s can vary this much.
Rich

Did you ever drive that engine in a car first or did you buy the engine separately? Wanted to know what your before and after was either on a dyno or seat-of-the-pants wise.

[Demps]

I agree they all have their own personality. Others can comment on specifics of what gives what. Here's what I found on a '93.

Cam factory...pinned/degree'd
Rt Intake 110.5...112p/114
Rt exhaust 110...113p/110
Lt intake 115.5...111.5p/114
Lt exhaust 110...112p/110.5

I didn't drive car hard before as it had a stuck lifter.

Ted

[Paul Workman]

FWIW, Mike, Marc Haibeck said he did one in place with the help of a video camera. But, he also said he wouldn't do it that way again, given the choice: easier to take the motor out!

Timing is specific to the performance characteristics. To that topic, Marc Haibeck published a paper on cam timing which addresses FAQs. However, the short story is there is considerable "gold" in that thar cam timing!!! (See article from Haibeck website).

Also, it requires new cam bolts each time the phasing/timing is changed as they're torqued to stretch.

[Scrrem]

Originally Posted by mike100

Did you ever drive that engine in a car first or did you buy the engine separately? Wanted to know what your before and after was either on a dyno or seat-of-the-pants wise.

No, this was a second engine that I purchased to build and just going to swap motors.
Rich

[mike100]

Would there be any reason to keep the exhaust lobe center at 114 degrees as per the original early engine specs or maybe split the difference and put it at 112 deg?

(I'm leaning to use the 114/110 since it is well known to add area under the curve).

[Dynomite]

Originally Posted by mike100

Would there be any reason to keep the exhaust lobe center at 114 degrees as per the original early engine specs or maybe split the difference and put it at 112 deg?

(I'm leaning to use the 114/110 since it is well known to add area under the curve).

Marc Haibeck suggests to have a broad torque and power range (3000 to 7000 rpm) use Intake 114 ATDC and Exhaust 110 BTDC. 114/114 is nice when trying to tame idle roughness out of a cammed engine.

I notice the factory cam timing specs may be different on a 90-92 versus a 93? I see on one diagram that the 90-92 are set at I114 and E114. I assumed that is factory engine with the pinned settings.

I also notice that the single flats on a 91' camshaft/vernier plate have a play of up to 6 degrees (crankshaft degees). I think 93's have double flats with the play cut in half or 3 degrees (crankshaft degrees).

1. Timing Chain Effective Lengths.

The crankshaft rotates clockwise looking at front of engine. The Timing Chain Tensioners are located on the bottom (passenger side) chain before Camshaft Sprockets and on the top (drivers side) chain before Camshaft Sprockets. The chain between and after the Camshaft Sprockets returning to the timing chain Idler Sprocket is normally relatively tight. That section of the Timing Chain remains relatively tight as long as the crankshaft is rotated in a normal direction and as long as cams do not push back (lifters pushing the camshafts clockwise). Timing chain Effective Lengths are related directly to timing chain tightness and Timing Chain paths as directed by the Timing Chain Guides (That path changes with Timing Chain Guide wear).


a. Chain Tension different with engine running as compared to the Camshaft Timing Process.
If the Timing Chains are tighter during engine running with hydraulic lifters pressurized the Exhaust camshafts may be advanced a degree and the Intake camshafts may be retarded by a degree. For Exhaust camshafts at 110 deg BTDC may actually advance to 111 deg BTDC. The Intake Camshafts at 114 deg ATDC may actually retard to 113 deg ATDC.

b. Fixed Timing Chain Guide wear.
As the Fixed Timing Chain Guides wear the chain returning to the Idler Sprocket between the Camshaft Sprockets and Idler Sprocket decreases in effective length Advancing the Intake Camshafts and retarding the Exhaust camshafts. The Exhaust Camshaft may retard from 110 deg BTDC to 109 deg BTDC. The Intake Camshafts may Advance from 114 deg ATDC to 115 deg ATDC.


Tech Info - LT5 Timing Diagrams



See Item #4 Camshaft Timing

What you want is equal lifter depression before and after max lifter depression noting the crankshaft rotation degrees (degree wheel set up on front of crankshaft pully) before and after max lift set up on (No. 6 cylinder passsenger side and No. 1 cylinder drivers side). For Intake example you might see equal lifter depression at 104 deg ATDC and 124 deg ATDC and splitting the difference would be 114 deg ATDC. You do the equal lifter depression "trick" because it is almost impossible to see max lifter depression using a dial gauge within say 5 deg either way as the cam lobe rotates over the flat.

Marc Haibeck suggests positioning the cam at .010" before top of lift and .010" after top of lift point where .001" change in lift is about 1 degree of cam rotation.

If you want to make sure of the TDC marks on the Harmonic Balancer, you can install a dial gauge to determine when piston #1 is TDC to determine TDC easy enough engine in car and can then mark harmonic balancer and use degree tab bracket easy enough engine in car. The Tab has marks 25 deg Before and 5 deg After TDC (A total of 30 deg). You can use the marks on the Timing Tab to mark your Harmonic Balancer. Mark 110 deg BTDC by rotating the Harmonic Balancer 3 complete Tabs (90 deg) + 20 deg Counter Clockwise and mark. Mark 114 deg ATDC by rotating the Harmonic Balancer Clockwise 3 complete Tabs (90 deg) + 24 deg and mark.

See Item #2 Camshaft Timing