Head Flow vs. Velocity
Originally Posted by Nickn20
you guys talk about TQ at 2-4k what does that really matter with racing where the rpms never drop below 4500 rpm? for a street car, yes 2-4k TQ is fun, make your tires spin, etc in the end in a straight line race who is gonna win a car that makes more TQ 2-4k or a car that makes more over 4k? just curious...........
this is provided both cars are setup properly for their power band.
this is provided both cars are setup properly for their power band.
Chris
TECH Fanatic
Joined: Mar 2003
Posts: 1,112
Likes: 0
From: Dallas
Originally Posted by rotarnomore
Most races that I have witnessed are won at the starting line and the next 60 or so feet. The time difference in the beginning takes a lot of HP to beat down the track.
Chris
Chris
My learnings on older Pontiac and Chevy heads were that port velocity wins over mass volume in most if not all applications. Jim Butler Performance in Tn. was a fast growing Pontiac head porter in the early 90's when Edelbrock heads were just to be released.
Jim used the "biger isn't always better" theory while porting and developed some of the best performing cast iron heads. The challenge was limited casting removal areas before breaking into water jackets, pushrod holes and tops of rort runners.
Jim managed to utilize valve seat/bowl blending and refined runnuer shapes to achieve awesome low lift flow numbes and respectable full lift numbers.
Then working with camshaft manfaturer Ultradyne devloped coplimentary cams with improved duration numbers at the .200" lift area.
These packages of well ported heads/cams with a nice dual plane hi rise intake manifold and properly matched header tubes made and still make some of the best quarter mile and street Pontiac motors built.
My point: history is repeating itself with the LS1. Big lift/duration cams, huge runner - high flow and dyno numbers and wild intake manifolds are produced first. Then after research and development takes a more "real world" look at applications, port velocity, volumetric efficiency and conservetive combos take over.
Jim used the "biger isn't always better" theory while porting and developed some of the best performing cast iron heads. The challenge was limited casting removal areas before breaking into water jackets, pushrod holes and tops of rort runners.
Jim managed to utilize valve seat/bowl blending and refined runnuer shapes to achieve awesome low lift flow numbes and respectable full lift numbers.
Then working with camshaft manfaturer Ultradyne devloped coplimentary cams with improved duration numbers at the .200" lift area.
These packages of well ported heads/cams with a nice dual plane hi rise intake manifold and properly matched header tubes made and still make some of the best quarter mile and street Pontiac motors built.
My point: history is repeating itself with the LS1. Big lift/duration cams, huge runner - high flow and dyno numbers and wild intake manifolds are produced first. Then after research and development takes a more "real world" look at applications, port velocity, volumetric efficiency and conservetive combos take over.
Originally Posted by kumar75150
Most people I know launch their car at 5000rpm or higher at the track.
Chris
Thread Starter
Launching!
Joined: Feb 2004
Posts: 271
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From: California
That article is great. I had a ZX7R and might see why he would reduce port volume to increase the velocity...my bike used to pull hard past 16,000RPM... my ZX2R had the RPM limiter at 21,000RPM!
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
On The Tree
Joined: Jul 2003
Posts: 166
Likes: 0
From: San Jose, CA
Originally Posted by c5blkvette
That article is great. I had a ZX7R and might see why he would reduce port volume to increase the velocity...my bike used to pull hard past 16,000RPM... my ZX2R had the RPM limiter at 21,000RPM!
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
But, what that article also pointed out was why you lose power at lower RPMs when you lower velocity too much. Basically, because the piston isn't moving fast enough to get ahead of the intake charge and create a vacuum to cover the time when the piston hits 180 degrees and the valve is still open... when the piston starts moving back UP is pushes air out of the intake valve, and those GREAT high-flow ports also show how they flow IN REVERSE.
Staging Lane
Joined: Jan 2005
Posts: 89
Likes: 0
Originally Posted by c5blkvette
That article is great. I had a ZX7R and might see why he would reduce port volume to increase the velocity...my bike used to pull hard past 16,000RPM... my ZX2R had the RPM limiter at 21,000RPM!
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
It also confirms what Tony was saying. From the section on intake charging:
" This is the time when the piston has passed the bottom of it's stroke, and begun to move up. Because of the charge momentum created by the intake suction phase, lots of fuel and air mixture is still rushing down the intake tract to fill the cylinder. This phenomenon increases with the engine speed, to the point that a progressively higher percentage of the cylinder filling occurs after the piston is no longer physically "sucking" the charge in. Because of this, it's necessary to extend the intake phase way past the physical 180 degree intake stroke. On average, the valves don’t completely close until the piston has moved up about 55 degrees past the bottom of it's 180 degree stroke !! "
It would explain why a higher velocity (and not volume) would really start to help at high RPM... and why the high velocity / lower flowing heads would perform well in real world racing applications.
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