Intake runner length?
11-26-2007, 01:09 AM
#1
Three Wheelin'
Thread Starter
Intake runner length?
Ok I have done a search and not come up with a straight answer on this. Here is my question;
Supposedly shorter runner intakes (i.e. the SFR and Lindsey Racing intakes) create less torque.
WHY ?
If a larger volume of air is getting into the cylinder, why would the length of the runner matter for torque once the intake valve closes?
IPSC
Supposedly shorter runner intakes (i.e. the SFR and Lindsey Racing intakes) create less torque.
WHY ?
If a larger volume of air is getting into the cylinder, why would the length of the runner matter for torque once the intake valve closes?
IPSC
11-26-2007, 05:54 PM
#2
Drifting
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short runners may show a little less torque off boost but will show more on boost . every hot turbo. OEM thing has short runners I would imagine the runner dimensions of the the turbo are taken strait from the NA car which they are engineered for
11-26-2007, 11:31 PM
#3
Race Car
Ok I have done a search and not come up with a straight answer on this. Here is my question;
Supposedly shorter runner intakes (i.e. the SFR and Lindsey Racing intakes) create less torque.
WHY ?
If a larger volume of air is getting into the cylinder, why would the length of the runner matter for torque once the intake valve closes?
IPSC
Supposedly shorter runner intakes (i.e. the SFR and Lindsey Racing intakes) create less torque.
WHY ?
If a larger volume of air is getting into the cylinder, why would the length of the runner matter for torque once the intake valve closes?
IPSC
Ultimately, an intake runner is only optimal for medium-narrow rpm bands.
T
11-26-2007, 11:47 PM
#4
Three Wheelin'
Thread Starter
So there is an oscillation of the charge air going on inside the intake?
My belief was that there was a constant pressure inside the intake applied by the turbo on boost and that when the intake valve opened, X amount of air was forced into the cylinder until the valve closed.
So in the case of the 951 intake with it's twisty long runners these were optimized for what power band?
IPSC
My belief was that there was a constant pressure inside the intake applied by the turbo on boost and that when the intake valve opened, X amount of air was forced into the cylinder until the valve closed.
So in the case of the 951 intake with it's twisty long runners these were optimized for what power band?
IPSC
11-27-2007, 12:50 AM
#7
Nordschleife Master
Here's my understanding of runner length and resonance tuning...
Long runners = bottom end torque
Short runners = top end power
But it's all about the setup as a whole, how the system functions together.
If you tune the exhaust for top end, the intake for bottom end and the turbo to pick up the mid-range...you could end up with a nice, broad power band that doesn't make an incredible amount of PEAK horsepower.
If you tune all 3 for top end, you'll make great peak power with a weak bottom end. You can run into some funny business with resonance though...so it's not quite as simple as it sounds. Unequal length runners on the intake side is another way to widen the powerband, without going through the expense and complications of a variable intake runner length intake.
In the end...resonance tuning plays a much bigger part in designing an n/a engine than it does a turbo one...since the turbo overshadows the effects.
Long runners = bottom end torque
Short runners = top end power
But it's all about the setup as a whole, how the system functions together.
If you tune the exhaust for top end, the intake for bottom end and the turbo to pick up the mid-range...you could end up with a nice, broad power band that doesn't make an incredible amount of PEAK horsepower.
If you tune all 3 for top end, you'll make great peak power with a weak bottom end. You can run into some funny business with resonance though...so it's not quite as simple as it sounds. Unequal length runners on the intake side is another way to widen the powerband, without going through the expense and complications of a variable intake runner length intake.
In the end...resonance tuning plays a much bigger part in designing an n/a engine than it does a turbo one...since the turbo overshadows the effects.
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11-27-2007, 02:12 AM
#8
Drifting
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Also fluid density changes in a forced induction motor thus changing the rate of pressure oscellation. Not to mention a ton of ther factors when dealing with different density fluids.
11-27-2007, 02:32 AM
#9
Race Car
velocity.
Chris, I think what is meant is the plenum volume.
On boost the relavance is not as great, but at low rpms and low boost the torque is definately better with a longer runner similiar to stock. However at high rpms the larger plenum allows for a more balanced intake flow which obviously creates a more consistand temp between cylinders.
At least this is what I have seen with the nitro coupe setups.
Chris, I think what is meant is the plenum volume.
On boost the relavance is not as great, but at low rpms and low boost the torque is definately better with a longer runner similiar to stock. However at high rpms the larger plenum allows for a more balanced intake flow which obviously creates a more consistand temp between cylinders.
At least this is what I have seen with the nitro coupe setups.
