Chevy LS, Verifying Timing

[DaveMcLain]

A few weeks ago I put together a Chevy LS engine for a customer and I've been wondering how builders verify the ignition timing on this type of engine. There are no timing marks on the balancer and it can go on the crank in any position. Timing is controlled by the computer using the reluctor wheel on the crank and a sensor that sticks into the block but how accurate is all of that really?

[sanfordandson]

A few weeks ago I put together a Chevy LS engine for a customer and I've been wondering how builders verify the ignition timing on this type of engine. There are no timing marks on the balancer and it can go on the crank in any position. Timing is controlled by the computer using the reluctor wheel on the crank and a sensor that sticks into the block but how accurate is all of that really?

You answered your own question...you don't. same way you do it on all computer controlled ignition engines. Been that way for decades.

[In-Tech]

I'm on my phone so I'll make a reply on how I do my LS engines in the morn.

[needforspeed66gt]

Like was said, you don't - you have to assume that the accuracy of the cam, timing set, and crank reluctor is good enough to get the job done...and in the end, the absolute number doesn't really matter other than for comparison purposes with other tuning situations, whatever timing creates the best safe power is the number you use.

[Dragsinger]

With most computer controller timing, a scan tool will show live data and ignition timing is one of the items displayed.

If it is important [or just curious] you could bolt on some type of pointer, find TDC on the damper, mark it, and apply an MSD timing tape to the damper.

[EthylCat]

[quote="DaveMcLain"]A few weeks ago I put together a Chevy LS engine for a customer and I've been wondering how builders verify the ignition timing on this type of engine. There are no timing marks on the balancer and it can go on the crank in any position. Timing is controlled by the computer using the reluctor wheel on the crank and a sensor that sticks into the block but how accurate is all of that really?[/quote]

I have always relied on the scan tool data. It may have been off a little at times but I just give it what it wants and go.

An important thing to remember is that if you changed the pcm or the crank reluctor you have to do a crank relearn to make timing as accurate as possible.

[DaveMcLain]

I'm really quite surprised that somebody doesn't make a tool that can verify the position of the reluctor wheel and crank sensor with the piston at TDC relying on the accuracy of the block machine work without a way to double check seems a little hokey.

[In-Tech]

I'm really quite surprised that somebody doesn't make a tool that can verify the position of the reluctor wheel and crank sensor with the piston at TDC relying on the accuracy of the block machine work without a way to double check seems a little hokey.

Goodson makes one and is the one I use and I verified my tool on several OEM cranks. TDC is leading edge of 14th tooth CCW from the missing teeth on a 58x crank. As stated, key the crank, use an ati damper, make a pointer, verify timing. If using an OEM computer it's rarely anything to worry about. Aftermarket ecu...no guarantees.

Dave, I feel ya, the first LS I built I had the same concern so I took all the necessary precautions to verify and be able to alter the ecu settings if needed. Otherwise as stated by a couple others...you get what you get.......NOT good enough for me considering I use a "window" to listen for detonation and that's a small amount of degrees(example numbers would be 50 BTDC to 15 ATDC only on the compression stroke of THAT firing cylinder the knock sensor/ecu is listening to) so I want my numbers "on the money". Anything outside of the "window" is discarded as engine noise.

[3pedals]

I verified TDC, marked and pinned the balancer, and checked it with a light, like any other spark engine

[dirtracr5]

I use a "window" to listen for detonation and that's a small amount of degrees(example numbers would be 50 BTDC to 15 ATDC only on the compression stroke of THAT firing cylinder the knock sensor/ecu is listening to) so I want my numbers "on the money". Anything outside of the "window" is discarded as engine noise.

what are the OEM paramater for detecting engine knock and how do they differ from your parameters? Wondering how OEM can detect knock without "verifying ignition timing"??

[In-Tech]

This will take me some time to prepare an answer with screen shots. This is an OEM computer, Delphi Mefi 4 is what I will show examples of. I will reply when I can, hopefully it will shed some light.

[jake197000]

any ls that makes power should have the balancer pinned.

[LSP]

I marked the damper/pulley with a silver, and marked the timing cover with a black sharpie.

I think Patterson makes a bolt on pointer IIRC.

[peejay]

Dave, I feel ya, the first LS I built I had the same concern so I took all the necessary precautions to verify and be able to alter the ecu settings if needed. Otherwise as stated by a couple others...you get what you get.......NOT good enough for me considering I use a "window" to listen for detonation and that's a small amount of degrees(example numbers would be 50 BTDC to 15 ATDC only on the compression stroke of THAT firing cylinder the knock sensor/ecu is listening to) so I want my numbers "on the money". Anything outside of the "window" is discarded as engine noise.

Why is this a major concern? You trust your ECU to be timing-accurate to a tenth of a degree but you can't trust it to be accurate within a 65 degree window?

If you know your way around a 2-channel scope and have known-good patterns, you can verify that the crank wheel hasn't shifted relative to the camshaft by scoping those two sensors. I've never seen one shifted, although I have seen that a 300,000mi timing chain can be a whopping two degrees retarded...

[In-Tech]

Yes on the scope. I apologize, what's clear in my head sometimes doesn't come out right once typed. I'm busy on the dyno today and Monday but will try to make it clearer with screen shots of software and such for others not familiar with ls crank/cam wheels. I totally trust an OEM GM cal to have everything correct as far as crank/cam settings. What I was eluding to was how I don't trust the aftermarket to be correct and I verify and adjust if needed. Also when I receive a sample base cal as a starting point I like to verify everything. Starting from scratch with all 0's in the fields as in these screen shots can be tough

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