LT1 Crank Reference Angle - need some help

[97bowtie]

I have a '93 Z28 with a 396in LT1 and a FAST B2B setup. The heads are off the car right now so I can find TDC pretty easily. I want to take this opportunity to mark the harmonic balancer and get my crank reference angle and timing dead on.

How are you LT1 guys doing this? What's the easiest way to find the exact horizontal center of the harmonic balancer and what are you marking the balancer with? Are you painting a stripe on it, grinding a line it? Also, what are you using for a timing pointer? If anyone has any pics of their setup or can describe exactly what I need to do to get this thing right, I'd really appreciate it.

Also, what's the best way to find TDC? I can rotate the crank and visually see when the piston 'appears' to be at TDC but I'm afraid that's not very accurate. Is there some type of tool/guage I should use to find TDC?

Thanks.

 

[Quick86GN]

Fab a pointer somewhere you can see with a timing light, Make or buy a piston stop that bolts to the deck, Rotate motor buy hand until piston contacts stop and mark balancer, rotate oppsite direction mark balancer, split the difference and you have TDC. Almost all the LT-1s I have tuned with FAST units the offset angle is 0-1 deg.

 

[ijames]

Is your balancer keyed to the crank? If not, it will walk around whenver it feels like moving and your timing marks will be useless shortly after you crank it up the first time .

 

[97bowtie]

Is your balancer keyed to the crank? If not, it will walk around whenver it feels like moving and your timing marks will be useless shortly after you crank it up the first time .

The balancer isn't keyed. My hope is that I can look at the timing and adjust the crank reference angle right when I start it up. Or, can I just look at the timing while cranking the motor, not with it actually running? Once I find the crank reference angle, there really isn't any reason to look at the timing with a light again.

I mounted a timing pointer and marked the balancer at #1 TDC. I just want to make sure I have this straight. If I command 30* of timing in the ECM, I should adjust the timing light until I see the mark on the balancer line up with the pointer. If I have to advance the timing light to 34*, does this mean the crank reference angle is 4*, or would advancing the timing light to 26* mean the crank reference angle is 4*? I'm thinking if the timing light is set to 34* to match the ECM's commanded 30* that the crank reference angle is 4. Any input is appreciated.

 

[InjectConnect]

Is your balancer keyed to the crank? If not, it will walk around whenver it feels like moving and your timing marks will be useless shortly after you crank it up the first time .

The balancer won't move unless you are using a supercharger. To adjust look at commanded timing and it should agree on the balancer if not change the crank ref angle.

 

[ijames]

A friend who used to have an Impala SS checked and marked his balancer in about 6 places over 3 months. No nitrous, no supercharger, just ported aluminum heads, the GM hot cam, and slp headers. He was having optispark issues and using a timing light to help diagnose it, but each time he wanted to check things he had to pull the #1 plug and remark the balancer. I'm sure you will be okay just cranking it and idling, but past that I wouldn't trust it .

 

[Quick86GN]

A friend who used to have an Impala SS checked and marked his balancer in about 6 places over 3 months. No nitrous, no supercharger, just ported aluminum heads, the GM hot cam, and slp headers. He was having optispark issues and using a timing light to help diagnose it, but each time he wanted to check things he had to pull the #1 plug and remark the balancer. I'm sure you will be okay just cranking it and idling, but past that I wouldn't trust it .

Your friend was having more than an opti-spark problem, That balancer hub is a press fit with a center bolt with 70 + ftlb torque. If it is moving it is a problem. Having said that on all the LT-1 performance builds I always key the crank and hub. Than degree the balancer for TDC

 

[97bowtie]

Thanks for the help guys.

So, I was wiring up the knock sensor and when I tapped into the "12V" source wire from the FAST ECM, I was only seeing ~ .06 volts on this wire, and the battery was measuring ~ 6.5 volts (car has been sitting for 6 months). This is with the key in the 'run' position. Should I be seeing 12V on this wire (L3 on the FAST box), or will it only read 12V when the car is running?

 

[Craig Smith]

That's not a source wire, it needs to be connected to a 12 volt source for the box to turn on.

 

[97bowtie]

That's not a source wire, it needs to be connected to a 12 volt source for the box to turn on.

When I said 'source wire', I meant source wire that powers the factory PCM (I believe that's what that wire powers)...the wire coming FROM the FAST box. The FAST box turns on, I'm trying to get a 12V IGN switched source to the knock module.

 

[97bowtie]

Is J3 the correct wire to hook the knock module to? I need a 12V ignition switched source.

 

[Craig Smith]

There are no 12 volt sources from the FAST unit. If you need power for an external device it must come from somewhere else in the car.

All the 12 volt connections on the FAST are gazintas. No comzoutas.

And the signal wire from the knock module should go to pin H1.

 

[97bowtie]

There are no 12 volt sources from the FAST unit. If you need power for an external device it must come from somewhere else in the car.

All the 12 volt connections on the FAST are gazintas. No comzoutas.

And the signal wire from the knock module should go to pin H1.

OK, then it's the 12V wire that feeds the FAST box. I have power there now...I'm embarassed to say this, but I had the volt meter on the wrong setting...the .06V I was seeing was actually 6V...same as the battery was reading. :redface:

 

[HighPSI]

All the 12 volt connections on the FAST are gazintas. No comzoutas.

Craig,
You never cease to amaze me with your technical knowledge j/k

 

[Craig Smith]

Convince my wife that I know something!

 

[norbs]

Did you change your email Address Craig? Have a few questions for you thanks.

 

[Craig Smith]

You can email or PM me here now, I updated my settings.

 

[97bowtie]

Well, got the car running and checked the crank reference angle. I'm not sure if I did this correctly, but I came up with a crank reference angle of 18. I did this by hooking the timing light up to the #1 plug wire, setting the timing on the timing light to 30 degrees, commanded 30 degrees of timing in the FAST ECU, then adjusted the crank reference angle until they matched.

Was I supposed to set the timing light to 30* advance to match the commanded timing or leave it at zero?

 

[Craig Smith]

Something is wrong...

Rather than going strictly by the commanded timing value, make sure that a sensor in the FAST unit called Spark (BTDC) has a number that matches your timing light. In addition to the programmed value in the spark table, there are some other things the FAST does that could make the actual commanded timing value different than what is programmed in the spark table.

Try a different timing light. Not likely to produce different results, but generally an easy test to accomplish. Just to make sure you aren't chasing non-existent engine problem.

Would it be possible to verify that the timing pointer is in the correct location?

Is it possible that the balancer has already spun?

The reason that I am asking all this is that 18 degrees is a long way off of what should work on an LT-1. As mentioned in previous posts it should be very close to zero.

 

[Quick86GN]

Make sure there is no idle spark.