Velocity stacks

philbrads

Club Member
I have started doing some home mechanics on my 73 240z. I am running a stock l24 with Weber 40s. After removing the air filters I noticed that the carbs do not have any air horns. After reading lots on velocity stacks I am thinking that they are necessary but I am struggling to find information on whether they are necessary, and if so, what size air horns I should fit if any. I do not have good mechanical knowledge and so I would really appreciate any advise on this subject. I do want to increase power in time but at present I just want to just get the best performance with what I have. Torque being a priority over bhp. I have a cannon manifold if this makes a difference in what size air horns I should fit.

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jonbills

Membership Secretary
Site Administrator
I'm pretty sure the engine works better with them.
Mine are about 50mm tall. I think the idea is that longer ones are better for low rpm and shorter ones for higher rpm. Whichever ones you get, you need good clearance to your air filter cover.
 

SteveK

Forum User
DCOE Webers are designed to use stacks, aside from managing the airflow they help keep the choke/venturi in place (part of stack slides into carb mouth, see shoulder and lower section in picture) Bolt on stacks dont have this lower section. Short stacks bump the power up the rev range, longer stacks bump the torque up lower down at the expense of power up top.

s-l300.jpg
IMG_20160909_180227.thumb.jpg.06be751f936ca0b8a1a012bbd231c6f9.jpg
 
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philbrads

Club Member
I'm pretty sure the engine works better with them.
Mine are about 50mm tall. I think the idea is that longer ones are better for low rpm and shorter ones for higher rpm. Whichever ones you get, you need good clearance to your air filter cover.
Thanks for the info jonbills, are you running a stock set up? I have 90mm deep air filters, so will 40mm be enough clearance do you think if 50mm stacks are suitable for my set up?
 

philbrads

Club Member
DCOE Webers are designed to use stacks, aside from managing the airflow they help keep the choke/venturi in place (part of stack slides into carb mouth, see shoulder and lower section in picture) Bolt on stacks dont have this lower section. Short stacks bump the power up the rev range, longer stacks bump the torque up lower down at the expense of power up top.

s-l300.jpg
IMG_20160909_180227.thumb.jpg.06be751f936ca0b8a1a012bbd231c6f9.jpg
Any recommendations for stacks such as those in your post? from what I have read the curvature of the stack is important
 

jonbills

Membership Secretary
Site Administrator
Thanks for the info jonbills, are you running a stock set up? I have 90mm deep air filters, so will 40mm be enough clearance do you think if 50mm stacks are suitable for my set up?
I have an airbox and cold air induction. There's certainly no more than 40mm clearance from the airbox so I'm sure that sort of size would run well on yours.
I haven't done any comparisons with other lengths though.
 
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