Intake valve closing point: Boost vs N/A?
06-18-2012, 06:47 PM
#1
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Intake valve closing point: Boost vs N/A? I have a general understanding of it for N/A motors but boost is a whole new world to me. Is a later ICV better for boost or do you want to keep it around the same as if it were an N/A motor?
If anyone wants to know my goals they are either a 347 or 383 with AFR 225s and 15 psi from an A&A ysi kit. Compression ratio will be how ever much can be ran on 91 pump gas with no meth. I would rather not have to rely on meth but may add it in the future for insurance.
If anyone wants to know my goals they are either a 347 or 383 with AFR 225s and 15 psi from an A&A ysi kit. Compression ratio will be how ever much can be ran on 91 pump gas with no meth. I would rather not have to rely on meth but may add it in the future for insurance.
06-19-2012, 09:07 PM
#3
In my opinion, it actually depends on the TYPE of boost. Before you wonder if I've lost my mind, consider this.
A centrifugal blower lacks midrange boost, so I might go with a earlier IVC than a N/A engine, to help crutch the midrange torque and help flatten the torque curve. As the centrifugal blower builds boost, it's going to make good top end horsepower, so there's no need to go with a later IVC.
A positive displacement blower makes a ton of midrange torque, but tends to lack top end horsepower. In which case I'll close the intake valve up to 5 degrees later than normal. For example, on the Redline Motorsports ZL1 Camaro I went with a IVC past 50 degrees, which I would never do on a LS3 head on a 6.2, average IVC on that application is about 45 degrees for me.
A centrifugal blower lacks midrange boost, so I might go with a earlier IVC than a N/A engine, to help crutch the midrange torque and help flatten the torque curve. As the centrifugal blower builds boost, it's going to make good top end horsepower, so there's no need to go with a later IVC.
A positive displacement blower makes a ton of midrange torque, but tends to lack top end horsepower. In which case I'll close the intake valve up to 5 degrees later than normal. For example, on the Redline Motorsports ZL1 Camaro I went with a IVC past 50 degrees, which I would never do on a LS3 head on a 6.2, average IVC on that application is about 45 degrees for me.
