GSMnow
New Member
- Messages
- 165
- Location
- Santa Clarita, CA USA
Just a little clarification. I have programmed a few EFI systems with alot of data logging so this is fact.
Given a normal constant pressure (over manifold) fuel pressure regulator, the highest duty cycle will occur at the horsepower peak. That is the rpm when the greatest amount of air is flowing requiring the greatest amount of fuel per second.
On the other hand, the torque peak will require the greatest pulse width. The torque peak is where the engine is breathing the greatest amount of air for each revolution. This is also the rpm point that will produce the highest cylinder pressure and will likely be where pinging will occur. This can sometimes make it neccesary to increase the fuel flow a little more to be safe.
To make the math a little easier, the injectors should make 400 hp at 100% duty. So if you have a motor that can make 300 hp at 6000 rpm, it would only need about 75% duty cycle up there (about 7.5 ms of on time) with the stock 251 cc injectors. But if this same motor makes 320 lb ft at just 3000 rpm (this figures out to only 180 hp) the duty cycle is then just 46% but that is a pulse width of 9.14 ms.
The rough rule of thumb is that you can feed 2 horsepower for every pound/hour of fuel injector. CC/MIN is very close to 10 * lb/hr. This still works out to 400 hp on a set of 8 251 cc/min injectors, but that is well over the recomended 80% duty cycle you should shoot for when designing a system. My turboed 22RE was running 4 550 cc/min injectors to nearly 90% duty cycle. That is feeding about 1980 cc/min which would theoretically be 396 hp. This resulted in a 12:1 a/f ratio at a bit over 300 hp at the crank. Thanks to a crappy 2 valve head and turbo exhaust restriction, the BSFC is abit low on that motor. The same injectors feeding a Mitsu Eclipse 2.0L turbo motor would be more like 360 hp at the crank and a serious non turbo motor with a tuned intake and exhaust system would have to make close to 400 hp to use that much fuel. I figure the 1UZFE with the "economy" F head design should be at least as good of a BSFC as the turbo Mitsu motor.
Gary M.
Given a normal constant pressure (over manifold) fuel pressure regulator, the highest duty cycle will occur at the horsepower peak. That is the rpm when the greatest amount of air is flowing requiring the greatest amount of fuel per second.
On the other hand, the torque peak will require the greatest pulse width. The torque peak is where the engine is breathing the greatest amount of air for each revolution. This is also the rpm point that will produce the highest cylinder pressure and will likely be where pinging will occur. This can sometimes make it neccesary to increase the fuel flow a little more to be safe.
To make the math a little easier, the injectors should make 400 hp at 100% duty. So if you have a motor that can make 300 hp at 6000 rpm, it would only need about 75% duty cycle up there (about 7.5 ms of on time) with the stock 251 cc injectors. But if this same motor makes 320 lb ft at just 3000 rpm (this figures out to only 180 hp) the duty cycle is then just 46% but that is a pulse width of 9.14 ms.
The rough rule of thumb is that you can feed 2 horsepower for every pound/hour of fuel injector. CC/MIN is very close to 10 * lb/hr. This still works out to 400 hp on a set of 8 251 cc/min injectors, but that is well over the recomended 80% duty cycle you should shoot for when designing a system. My turboed 22RE was running 4 550 cc/min injectors to nearly 90% duty cycle. That is feeding about 1980 cc/min which would theoretically be 396 hp. This resulted in a 12:1 a/f ratio at a bit over 300 hp at the crank. Thanks to a crappy 2 valve head and turbo exhaust restriction, the BSFC is abit low on that motor. The same injectors feeding a Mitsu Eclipse 2.0L turbo motor would be more like 360 hp at the crank and a serious non turbo motor with a tuned intake and exhaust system would have to make close to 400 hp to use that much fuel. I figure the 1UZFE with the "economy" F head design should be at least as good of a BSFC as the turbo Mitsu motor.
Gary M.