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You guys who have permanent or occasional midrange leanness/ richness need to read the article on DTR explaining exactly why some CFI4 800's had that awful lean midrange/ detonation...it is posted by date in my tech articles on 2/21/10.
The lack of precision of the Polaris engine's exhaust valve opening/ closing is very likely the culprit. During moderate acceleration when the valves open at the proper time, the airflow IS REDUCED along with factory programmed fuel flow. The article explains it and shows the actual airflow CFM and fuel flow lb/hr at that point measured on my Superflow engine dyno. What happens to many stock CFI4 800s is there's insufficient energy to lift the valves when the ECU closes the valve solenoid and the AIRFLOW INCREASES just as the ECU base map reduces fuel causing deto-producing lean misfire. When the valves finally open all is good. But that half-second delay in opening (sometimes one will open properly, and the other will open a second later--sort of like a drunk's eyes when waking up in the morning) will drive the stockers crazy, and add to that a few pounds of boost pressure and you can see why some people find it impossible to perfectly and consistently tune ALL fuel controllers regardless of who makes them. The first stock CFI4 800s suffered from early valve closing when backing off from full throttle to high speed cruise. Then, we saw just the opposite effect--airflow would drop prematurely and the engine would go into a rich misfire that we fixed by reducing fuel flow in that area by 25% or more! The "Stoutner" PCV maps on my website fixed that. Click on the icon to download one so you can see what we went through to make those run well. Crazy stuff, but that's why I sold 1000 power commanders mostly to CFI4 800 owners who nominated me for the Nobel Peace Prize for fixing their lean/ detonating midrange and adding 10 HP on top end to boot.
One fix would be to put a set of Gus Bohne's blow-through carbs on the engine--what? Ebay my throttle bodies? Heresy! Those 1960's era carbs are great because when the airflow goes up, you get more fuel automatically. So if the mag valve stays closed and the airflow unexpectedly increases on that side, you get more fuel on that side. Every time. Even a nice closed loop EFI system like Pinnacle's can't completely fix that since it measures the average of the two cylinders.
But since there's not much room for a set of Gus' 44 roundslides, how about just fixing the exhaust valves so they are fixed in, say, the half open position? Then you would have absolutely fixed airflow rise from idle to full bore with no awful varying dips and rises to try to deal with. And it's even possible the the reduced exhaust port timing would increase power and reduce BSAC, boost for boost. Back in the early days of Aerocharger, we made way more power out of lower exhaust port engines so maybe a partially closed ex valve could help everywhere. But since that lower exhaust port will increase corrected compression ratio, caution must be used at WOT.
Someone needs to try locking their valves and tuning like that. Blaine Small was talking about getting a group of flusterated (combining the words frustrated and flustered) of turbo Dragon 800 owners to chip in on a dyno session for him to find a spot-on tune for the PCV. I've done lots of boosted sleds and bikes with PCV's and they are a simple, great way to tune for boost. But if that airflow rise is not perfectly predictable, then it's an impossible situation. I suggested to Blaine to just try locking his valves in some position and see what happens. That's better than driving 500 miles to DTR for a tune.
Who'll be the first to try that?
The lack of precision of the Polaris engine's exhaust valve opening/ closing is very likely the culprit. During moderate acceleration when the valves open at the proper time, the airflow IS REDUCED along with factory programmed fuel flow. The article explains it and shows the actual airflow CFM and fuel flow lb/hr at that point measured on my Superflow engine dyno. What happens to many stock CFI4 800s is there's insufficient energy to lift the valves when the ECU closes the valve solenoid and the AIRFLOW INCREASES just as the ECU base map reduces fuel causing deto-producing lean misfire. When the valves finally open all is good. But that half-second delay in opening (sometimes one will open properly, and the other will open a second later--sort of like a drunk's eyes when waking up in the morning) will drive the stockers crazy, and add to that a few pounds of boost pressure and you can see why some people find it impossible to perfectly and consistently tune ALL fuel controllers regardless of who makes them. The first stock CFI4 800s suffered from early valve closing when backing off from full throttle to high speed cruise. Then, we saw just the opposite effect--airflow would drop prematurely and the engine would go into a rich misfire that we fixed by reducing fuel flow in that area by 25% or more! The "Stoutner" PCV maps on my website fixed that. Click on the icon to download one so you can see what we went through to make those run well. Crazy stuff, but that's why I sold 1000 power commanders mostly to CFI4 800 owners who nominated me for the Nobel Peace Prize for fixing their lean/ detonating midrange and adding 10 HP on top end to boot.
One fix would be to put a set of Gus Bohne's blow-through carbs on the engine--what? Ebay my throttle bodies? Heresy! Those 1960's era carbs are great because when the airflow goes up, you get more fuel automatically. So if the mag valve stays closed and the airflow unexpectedly increases on that side, you get more fuel on that side. Every time. Even a nice closed loop EFI system like Pinnacle's can't completely fix that since it measures the average of the two cylinders.
But since there's not much room for a set of Gus' 44 roundslides, how about just fixing the exhaust valves so they are fixed in, say, the half open position? Then you would have absolutely fixed airflow rise from idle to full bore with no awful varying dips and rises to try to deal with. And it's even possible the the reduced exhaust port timing would increase power and reduce BSAC, boost for boost. Back in the early days of Aerocharger, we made way more power out of lower exhaust port engines so maybe a partially closed ex valve could help everywhere. But since that lower exhaust port will increase corrected compression ratio, caution must be used at WOT.
Someone needs to try locking their valves and tuning like that. Blaine Small was talking about getting a group of flusterated (combining the words frustrated and flustered) of turbo Dragon 800 owners to chip in on a dyno session for him to find a spot-on tune for the PCV. I've done lots of boosted sleds and bikes with PCV's and they are a simple, great way to tune for boost. But if that airflow rise is not perfectly predictable, then it's an impossible situation. I suggested to Blaine to just try locking his valves in some position and see what happens. That's better than driving 500 miles to DTR for a tune.
Who'll be the first to try that?
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