This is topic runners on cobra lower intake in forum Tech Talk at Northern California Ford Owners  .


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Posted by imbroken (Member # 165) on :
 
any of you have any suggestions where to cut the runners for most power n/a? any suggestions? the intake is pretty well ported right now my main concern is the runners

thanks!
 
Posted by PunkINa5.SLOW (Member # 10) on :
 
Matt,
It would depend on where you want your "more" power at. Up high in the RPM band or down low? Want the torque curve to look nice?

For example a stock intake on a SEFI 5.0L is a pretty good piece at making the car "feel" fast cause it keeps decent velocity and has tuned runners to provide the most top end power it can without sacrificing low end.

When you go to an intake with more runner length (like say a Cobra intake) you see maybe more peak power but the power that is given up down low is never fully recovered by having just the higher peak power.

OR the heads just simply wont keep up with the intake and velocity goes down.

So be careful when playing with runner length.
 
Posted by 93PONY (Member # 60) on :
 
Basically, the shorter the runner, the more upper RPM torque you get...or HP, if that's what you like.

My take on it:
As the intake valve closes it sends an air pulse backwards, up through the intake, then incounters the incoming air & starts back towards the intake valve. Pulse reversion I think it's called. At certain RPM's it reaches the intake valve just as it's opening & causes an increase in torque output do to the increased velocity. The longer the runner, the longer it takes to make the trip.
So, a shorter runner would be good for a kick in high RPM power when the valve is opening faster.
A longer runner would be benificial for low-end torque were the intake valve is opening slower.

So, the real trick is figuring out were you want the added torque & cutting the runner to match.

Good luck!
 
Posted by imbroken (Member # 165) on :
 
anyone else who has shortened their runners on an n/a car?

also to make up for the low end torque i could just advance timing down low yeah?
 
Posted by Greenandsilver (Member # 1371) on :
 
quote:
Originally posted by 93PONY:
Basically, the shorter the runner, the more upper RPM torque you get...or HP, if that's what you like.

My take on it:
As the intake valve closes it sends an air pulse backwards, up through the intake, then incounters the incoming air & starts back towards the intake valve. Pulse reversion I think it's called. At certain RPM's it reaches the intake valve just as it's opening & causes an increase in torque output do to the increased velocity. The longer the runner, the longer it takes to make the trip.
So, a shorter runner would be good for a kick in high RPM power when the valve is opening faster.
A longer runner would be benificial for low-end torque were the intake valve is opening slower.

So, the real trick is figuring out were you want the added torque & cutting the runner to match.

Good luck!
Sounds like it would be extremely hard but usefull to find the perfect balance!
 




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