EVO manipulation for torque output is bullshit.
07-23-2010, 04:34 PM
#1
EVO manipulation for torque output is bullshit. OR I guess I could have titled it Power stroke gains vs Pumping loss..
Within a given range the effect of EVO on torque production is virtually zero. I understand the idea of delaying EVO to make more use of the power stroke. However at the bottom of the power stroke, the cooling gases are providing exponentially less force on the piston. Because the gas is slowing down, it is less likely to want to go out of the exhaust valve on it's own. So it is more likely to be stealing power after bottom dead center by putting a force on the piston travelling up ie: creating more pumping loss. So in effect it is a trade off. What you MAY lose in the power stroke, you also gain back by lessening the pumping loss. I just get tired of people using EVO when speccing cams to talk about torque. They read it in a book somewhere and are regurgitating it.
For instance I had a couple better known head and cam guys tell me I was going to have exhaust reversion and power/torque loss everywhere with the cam I was discussing with them. It's a 234/246 110+3 cam. I guess what maybe they didn't do was look at the valve events and see where the actual changes were being made vs what they were offering (mainly EVO). How does a 346 with massaged 241's and a bad typhoon intake make 450/420 rwhp/tq if the valve events are so bad?
/rant off I guess!
Within a given range the effect of EVO on torque production is virtually zero. I understand the idea of delaying EVO to make more use of the power stroke. However at the bottom of the power stroke, the cooling gases are providing exponentially less force on the piston. Because the gas is slowing down, it is less likely to want to go out of the exhaust valve on it's own. So it is more likely to be stealing power after bottom dead center by putting a force on the piston travelling up ie: creating more pumping loss. So in effect it is a trade off. What you MAY lose in the power stroke, you also gain back by lessening the pumping loss. I just get tired of people using EVO when speccing cams to talk about torque. They read it in a book somewhere and are regurgitating it.
For instance I had a couple better known head and cam guys tell me I was going to have exhaust reversion and power/torque loss everywhere with the cam I was discussing with them. It's a 234/246 110+3 cam. I guess what maybe they didn't do was look at the valve events and see where the actual changes were being made vs what they were offering (mainly EVO). How does a 346 with massaged 241's and a bad typhoon intake make 450/420 rwhp/tq if the valve events are so bad?
/rant off I guess!
07-29-2010, 02:25 AM
#2
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Nice rant, but BS is such a strong term.
I'd have to agree with your points for the most part. It really depends on the
motor with respect to EVO. Using a high duration cam on a short stroke motor
is cutting into that range you're talking about.
There is some great discussion with a few cam designers on Speed Talk if
you're interested. Just search for EVO, or Valve Timing in the Advanced
forum.
I'd have to agree with your points for the most part. It really depends on the
motor with respect to EVO. Using a high duration cam on a short stroke motor
is cutting into that range you're talking about.
There is some great discussion with a few cam designers on Speed Talk if
you're interested. Just search for EVO, or Valve Timing in the Advanced
forum.
