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

[A26B]

Originally Posted by 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.

As Paul stated, it is critical to use new cam bolts. I'm just going to clarify that this only applies to the OEM cam bolts. A few years back, we (Jerry's Gaskets) had ARP manufacture a new cam bolt that is made from higher tensile billet steel, that does not require torque to yield installation. When properly installed, these special bolts can be reused.

[LGAFF]

8K+ miles on my Jerrys cam bolts, no issues......they were torqued and reset twice

[mike100]

Originally Posted by LGAFF

8K+ miles on my Jerrys cam bolts, no issues......they were torqued and reset twice

Good to know... I will also be looking at the mysterious front of oil pan seapage (or maybe the front seal) and would be a good time to take care of all of it with an order to Jerry.