VE vs Psi
Thread Starter
Joined: Jun 2002
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From: Colorado
VE vs Psi Which is more important and/or produces more power in a FI application:
Higher VE by more cam duration
or
Higher Psi of boost by less cam duration
TIA
Higher VE by more cam duration
or
Higher Psi of boost by less cam duration
TIA
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From: orlando, florida
I always thought that with psi comes VE. When running boost arent you running over 100% VE? On another note from what i`ve read it seem most FI applications like a cam with low to mid duration218-226, Lift in the .570 range and a LSA of 114 or higher for moderate boost levels 8-12psi
Thread Starter
Joined: Jun 2002
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From: Colorado
By keeping the intake valve open longer, the VE will increase because more air is allowed in( even if it is over 100% ). Also if the intake valve is allowed to remain open longer, less psi is allowed to build up in the intake manifold and thus produces less psi of boost.
On the flip side, if the intake valve is remains open for a shorter duration, then less air can flow into the cylinder. And if the intake valve has a short duration, then obviously more psi of boost can build up in intake manifold.
I guess my question is; Is it better to have more air enter the cylinder because of the extra duration or to be pushed in by the extra pressure build up in the intake manifold?
On the flip side, if the intake valve is remains open for a shorter duration, then less air can flow into the cylinder. And if the intake valve has a short duration, then obviously more psi of boost can build up in intake manifold.
I guess my question is; Is it better to have more air enter the cylinder because of the extra duration or to be pushed in by the extra pressure build up in the intake manifold?
airflow makes power, pressure makes heat. If your blower/turbo is not maxed out by pushing in as it can flow, then you want to do whatever will help that engine flow the air. Then you can boost up even more to move even more air 
Thread Starter
Joined: Jun 2002
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From: Colorado
Originally Posted by Ryan23silverado
airflow makes power, pressure makes heat.
This is a point that alot of people get confused.
It is a fundamental law of engine physics: A specific build will ALWAYS flow the same VOLUME of air.
With that being said, a supercharger, turbo, is never going to change the VE of the engine. The only thing that forced induction does is change the DENSITY of the air that is being ingested by the motor. The motor is still ingesting the same VOLUME of air.
Which is more important, VE or PSI? Its a tossup. PSI, once you have the system is 10x easier to increase, while most changes to your motor will only produce marginal changes in VE.
Good Luck
It is a fundamental law of engine physics: A specific build will ALWAYS flow the same VOLUME of air.
With that being said, a supercharger, turbo, is never going to change the VE of the engine. The only thing that forced induction does is change the DENSITY of the air that is being ingested by the motor. The motor is still ingesting the same VOLUME of air.
Which is more important, VE or PSI? Its a tossup. PSI, once you have the system is 10x easier to increase, while most changes to your motor will only produce marginal changes in VE.
Good Luck
Thread Starter
Joined: Jun 2002
Posts: 4,281
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From: Colorado
Originally Posted by NoGo
Which is more important, VE or PSI? Its a tossup. PSI, once you have the system is 10x easier to increase, while most changes to your motor will only produce marginal changes in VE.
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i figure we 'traded' running my baby cam for maybe 1.5 psi of boost to make the same numbers.. follow me?
small cam = 775 with 16psi
big cam probably would = 775 on 15 or 14
figure yea it adds little more heat but obviously at my power level still in a safe range
.. and it sounds stock some dont go for the rumpity rump barely idling non emmissions passing ticket encouraging thing... some do.
i really dont think cams make a hill of beans.. octane permitting.. not on our engines.. not yet..
small cam = 775 with 16psi
big cam probably would = 775 on 15 or 14
figure yea it adds little more heat but obviously at my power level still in a safe range
.. and it sounds stock
some dont go for the rumpity rump barely idling non emmissions passing ticket encouraging thing... some do.i really dont think cams make a hill of beans.. octane permitting.. not on our engines.. not yet..
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From: Jersey boy
another thing to consider is that with more overlap and more charge being blown out the tailpipe, you are still driving the turbo/supercharger just as hard which creats some(i dont know how much)parasitic loss to turn the blower but ends up being wasted through the tailpipe.
just something to ponder.
just something to ponder.
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I think when answering these sorts of questions you have to ask another. What breaks first when you push the motor? If its due to torque then you should increase VE at higher RPM to make power but if its due to the engine over reving then making more boost at a lower RPM will be better get more power.
So what breaks when these motors are pushed? Ignoring detonation which is another problem in itself. I don't know, I don't own an LS1 motor yet.
So what breaks when these motors are pushed? Ignoring detonation which is another problem in itself. I don't know, I don't own an LS1 motor yet.
It depends on what kind of power level we are talking about.
Forced induction on a stock block it is usually a ringland or the #7 piston that is the first to go. Both of these failures can usually be attributed to a poor forced induction tune/method of operation.
Forced induction on a stock block it is usually a ringland or the #7 piston that is the first to go. Both of these failures can usually be attributed to a poor forced induction tune/method of operation.