How much can reference angle be moved?

[summit]

I am running a Buick based Fast system on my other car and have had to fabricate the crank and cam sensors. The way the crank sensor had to be made there is no adjustability on it and I had to guesstimate where to locate. I'm pretty sure it is within 5 degrees either way. The only way to get the timing dead on is to move the crank reference angle in the software from the Buick setting of 10 degrees. How much room do I have to play with before something else gets affected? I got the motor fired up and it runs well so it is somewhere close, but I have not zeroed the timing yet. 5 degrees can be a big deal on a turbo motor.

Long story short--where does the 10 degrees reference angle come from?

Greg Kring

 

[TurboTR]

Greg, think I can help here. Since the stock Buick crank ref angle is 10 deg, the FAST Buick system is a predictive spark system. Which means it is designed for ref pulses to occur AFTER any spark would ever occur. So in essence, you can move the ref angle around some down below the minimum timing that you would ever see. If say your minimum timing is 15 deg BTDC, the ref pulses (and corresponding crank ref angle setting) must occur somewhere less than that, but should not be too far less than. You could get fancy and cheat the tables and angle and such and make it all work if need be, to some degree. Or consider moving the crank interrupter wheel too if need be. Where is your ref pulse occuring now, roughly?

TurboTR

 

[summit]

I used an old degree wheel to clock the sensor location and mock it up on the engine stand. It is very close to 10 degrees. even I can eyeball within 5 degrees. My minimum timing I should ever see would be about 20 degrees at full boost pump gas situations. If I had to set the reference angle to 15 degrees would that 5 degrees left over be enough room? I could cheat the trigger wheel, but the timing marks are on it and I would have to remark it and slot the mounting holes to do it. which also involves removing the balancer to get to the wheel, and removing the radiator to get to the balancer. Sounds like I should have no trouble just moving the reference angle a degree or two in the software.

 

[TurboTR]

Yes, 5 deg cushion should work fine. When I tested mine on a bench it would get spark down to within ~ 1-2 deg of the actual ref angle if I recall.

TurboTR

 

[bruce]

Originally posted by summit
I am running a Buick based Fast system on my other car and have had to fabricate the crank and cam sensors. The way the crank sensor had to be made there is no adjustability on it and I had to guesstimate where to locate. I'm pretty sure it is within 5 degrees either way. The only way to get the timing dead on is to move the crank reference angle in the software from the Buick setting of 10 degrees. How much room do I have to play with before something else gets affected? I got the motor fired up and it runs well so it is somewhere close, but I have not zeroed the timing yet. 5 degrees can be a big deal on a turbo motor.

Long story short--where does the 10 degrees reference angle come from?

Greg Kring

The 10d is for being able to start the enigne, before the ecm takes command of timing, over from the ignition module, in the oem application.

When you have it all bolted together, then 0 out all the timing tables, and see what you *10d* reference actually is. Or what should be 10d, with no other advance. FWIW, in the oem TR code the reference angle is 70d.

Being 5d off initially, can lead to a motor that *windmills* when really cold, or can be hard to crank over on a hot soak restart.

 

[TurboTR]

Yes that's a good point if you still use the stock CCCI module and bypass. One way around that is to hard wire the bypass to the coil module, but then you must have the FAST set correctly for a cranking timing value (like 10 deg) Is how I have mine at least, because I had to give up the bypass to run the nitrous control.

If your ref angle comes in at 15 deg, it might/probably still work ok for cranking if you use the stock bypass and coil module setup.

The 70 deg ref angle would just be the other (leading) (depending on the polarity of it all) edge of the crank interrupter wheel, 60 deg + 10 In that case it's a delayed spark approach of course

TurboTR

 

[summit]

Thanks Bruce-that's what I was worried about.

Todd--Is that a hardware issue to get the Fast to default to 10 degrees? Something I need to send the box in for? Details please.

Greg Kring

 

[TurboTR]

Well if the real ref angle is 15 deg, you can't get the actual timing to occur below that in this case. Unless you can fudge the maps and such somehow; have not thought about it enough.

In my case, the ref angle is still 10 deg. The bypass is hardwired to "always on EST". The spark map in the FAST is set to 10 deg in the column that the engine cranks in.

I suspect that cranking at 15 deg should probably still work ok if need be.

TurboTR