Q about supercharging an 89
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Joined: Oct 2004
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SUPERCHARGING The C4
Hi Flood,
Most, if not all, your questions are addressed in my "C4 Semi-White Paper" available by e-mailing me at: Greg@BlowerWorks.net.
The L98 and the LT1, 1985 thru 1993, use e-proms that can be erased under a UV light and then 're-burned' with a new program. The 1994 thru 1996 LT1/LT4 use e squared flash memory that can be reprogrammed on board with a laptop utilizing such programs as LT1 Edit. Obviously the older Vettes are painfully slow to do by today's standards.
That said let's look at the L98. Without re-writing my paper here I'll just briefly address the major issues.
1. In-tank fuel pump must be upgraded regarless of whether the kit includes an in-line pump or not. See my fuel pump graphs in another post and you'll understand why.
2. Stock L98's 'poop-out' at 4800 rpm and thus the stock ignition up to 6 or 7 pounds of boost is OK. However plugs must be changed to a colder heat range. I use Champion 7401.
3. The ECM goes to open loop past about 50% throttle opening and defaults to one set of fuel curves. The stock injector pulse width falls off with increasing RPM, the opposite of what you want if supercharged. My kits all include new e-proms that tailor the fuel curve to a centrifugal supercharger. Unlike turbo's or positive displacement blowers there is one boost pressure for any given RPM provided you don't change the blower pulley. Match that boost to a new fuel pump, sometimes FMU, sometimes injector change, water/alcohol injection and you come up with a formula for a new e-prom. After hundreds and hundreds of trial & error combinations you get it right for each 'set-up'. That's why my C4 sales catalog has recipe's for power. Follow the recipe and most of the time you get a good cake - LOL
4. The ECM spark curve must be tailored much like above for fuel. Other people's supercharging kits do not include new e-proms, therefore they give you an ignition unit with adjustable boost retard: a compromise at best.
All of the above is good for 8-10 pounds of boost pressure. Anything above that you really need replace the ECM for best results and do your own custom tuning. Also you really do not want to go above 6-7 pounds with stock 'cast' pistons. One little ping and the piston cracks. Those pistons will handle more boost if you don't detonate but few people make it to 10 or 12 pounds without experiencing detonation for one reason or another.
Hope this 'short' reply helps you out Flood - regards Greg.
Most, if not all, your questions are addressed in my "C4 Semi-White Paper" available by e-mailing me at: Greg@BlowerWorks.net.
The L98 and the LT1, 1985 thru 1993, use e-proms that can be erased under a UV light and then 're-burned' with a new program. The 1994 thru 1996 LT1/LT4 use e squared flash memory that can be reprogrammed on board with a laptop utilizing such programs as LT1 Edit. Obviously the older Vettes are painfully slow to do by today's standards.
That said let's look at the L98. Without re-writing my paper here I'll just briefly address the major issues.
1. In-tank fuel pump must be upgraded regarless of whether the kit includes an in-line pump or not. See my fuel pump graphs in another post and you'll understand why.
2. Stock L98's 'poop-out' at 4800 rpm and thus the stock ignition up to 6 or 7 pounds of boost is OK. However plugs must be changed to a colder heat range. I use Champion 7401.
3. The ECM goes to open loop past about 50% throttle opening and defaults to one set of fuel curves. The stock injector pulse width falls off with increasing RPM, the opposite of what you want if supercharged. My kits all include new e-proms that tailor the fuel curve to a centrifugal supercharger. Unlike turbo's or positive displacement blowers there is one boost pressure for any given RPM provided you don't change the blower pulley. Match that boost to a new fuel pump, sometimes FMU, sometimes injector change, water/alcohol injection and you come up with a formula for a new e-prom. After hundreds and hundreds of trial & error combinations you get it right for each 'set-up'. That's why my C4 sales catalog has recipe's for power. Follow the recipe and most of the time you get a good cake - LOL
4. The ECM spark curve must be tailored much like above for fuel. Other people's supercharging kits do not include new e-proms, therefore they give you an ignition unit with adjustable boost retard: a compromise at best.
All of the above is good for 8-10 pounds of boost pressure. Anything above that you really need replace the ECM for best results and do your own custom tuning. Also you really do not want to go above 6-7 pounds with stock 'cast' pistons. One little ping and the piston cracks. Those pistons will handle more boost if you don't detonate but few people make it to 10 or 12 pounds without experiencing detonation for one reason or another.
Hope this 'short' reply helps you out Flood - regards Greg.
