sytyguy
Moderated User
I often get customers calling/PM'ing and asking about the differences between the GM factory EPROMs and the revisions. So, instead of responding to each individual one, I decided to outline the differences in a post. I realized that I had actually written this up a few years ago, but it was buried in a For Sale post, so I thought I'd post it where it belongs:
Here are the differences between then 4 common SyTy chips:
AYBM - First production Syclone chip.
AYBN - Improved Syclone chip.
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Improvements over AYBM:
- Improved idle quality (via PS Stall settings)
- Rewritten F77 to provide leaner low boost AFRs (for better spool up)
- Rewritten F71 to provide delayed WG opening (for better spool up)
- Minor changes in F70 to prevent too much boost at low rpm (WOT in 4th)
- Various changes to WG control scalars (to provide better boost control)
- Lowered Overboost fuel cut (to prevent too much allowed boost, corresponds with above improved control)
- Rewritten F3 for much less timing at higher boost (to improve control, prevent overboost, and avoid detonation: a common killer of early engines)
- Rewritten F1 for much more mid-range (improved spool up and fuel economy) and full WOT advance (GM felt it better to have more static timing in F1 and have it pulled out by F3 dependent on temp/boost)
- Removed unneeded CEL flag (41) and enabled two needed ones (31 & 33)
- Improved cold start and hot start via various scalar changes
- Minor CL improvements via scalar changes
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
BBZA - First production Typhoon chip (IIRC).
----------------------------------------------
Improvements over AYBN:
- Rewritten F18 for lower idle in gear
- Modified F70 for lower commanded boost at 100% (to allow more overboost "padding" and reduce overall boost = reduced detonation/engine failure)
- Modified stoich crosscount threshold (from .500 to .350 - to, IMO, achieve leaner AFRs across the board for emissions and fuel economy - either that or a coding error)
- Added a little more retard at idle (to improve idle quality and crank time)
- Modified TCC lockup characteristics from 35mph-60mph (to allow converter to lock under more throttle)
- Lowered RPM scalar for ESC retard cut-on (from 1800 to 750 - to allow ECM to see low rpm KR)
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
BBZB - Improved Typhoon chip.
----------------------------------------------
Improvements over BBZA:
- Modified stoich crosscount threshold (from .350 back to .500 - when the expected improvements didn't pan out - or to repair coding error)
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
So as you can see, the BBZB chip is the most refined chip for SyTys released by GM. Is it perfect? Nope. Is it better than it's predecessors? Yep.
Here are the differences between then 4 common SyTy chips:
AYBM - First production Syclone chip.
AYBN - Improved Syclone chip.
----------------------------------------------
Improvements over AYBM:
- Improved idle quality (via PS Stall settings)
- Rewritten F77 to provide leaner low boost AFRs (for better spool up)
- Rewritten F71 to provide delayed WG opening (for better spool up)
- Minor changes in F70 to prevent too much boost at low rpm (WOT in 4th)
- Various changes to WG control scalars (to provide better boost control)
- Lowered Overboost fuel cut (to prevent too much allowed boost, corresponds with above improved control)
- Rewritten F3 for much less timing at higher boost (to improve control, prevent overboost, and avoid detonation: a common killer of early engines)
- Rewritten F1 for much more mid-range (improved spool up and fuel economy) and full WOT advance (GM felt it better to have more static timing in F1 and have it pulled out by F3 dependent on temp/boost)
- Removed unneeded CEL flag (41) and enabled two needed ones (31 & 33)
- Improved cold start and hot start via various scalar changes
- Minor CL improvements via scalar changes
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
BBZA - First production Typhoon chip (IIRC).
----------------------------------------------
Improvements over AYBN:
- Rewritten F18 for lower idle in gear
- Modified F70 for lower commanded boost at 100% (to allow more overboost "padding" and reduce overall boost = reduced detonation/engine failure)
- Modified stoich crosscount threshold (from .500 to .350 - to, IMO, achieve leaner AFRs across the board for emissions and fuel economy - either that or a coding error)
- Added a little more retard at idle (to improve idle quality and crank time)
- Modified TCC lockup characteristics from 35mph-60mph (to allow converter to lock under more throttle)
- Lowered RPM scalar for ESC retard cut-on (from 1800 to 750 - to allow ECM to see low rpm KR)
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
BBZB - Improved Typhoon chip.
----------------------------------------------
Improvements over BBZA:
- Modified stoich crosscount threshold (from .350 back to .500 - when the expected improvements didn't pan out - or to repair coding error)
- Necessary hex changes for revision (date code, seq code, prom ID, and checksum)
So as you can see, the BBZB chip is the most refined chip for SyTys released by GM. Is it perfect? Nope. Is it better than it's predecessors? Yep.
