Velocity Stacks?

[w3wilkes]

Do these fit the 4 screw roundtop SU's on an early '71 240Z?

http://aptfast.com/showitem.aspx?id=102637&name=Ram Pipe Full Radius HS2 1.5" Tall&

[w3wilkes]

Next question... From all I've been able to glean from my friend google the Hitachi 3 and 4 screw round tops are HS style SU's. Looking at different listings for velocity stacks there are several HSn listings, HS2, HS4, HS6 and HS8! I can't find anywhere that lists what the HSn is for the Hitachi 4 screw round top SU's. Would any of you 240Z 4 screw SU experts know what the HS number is? Or if the Hitachi's even fit this HSn nomenclature? 

[w3wilkes]

And now for 1 more question... What is the height of the velocity stack (referred to as Air horn) in the stock air filter back plate for the 4 screw carbs?

Edited May 29, 2018 by w3wilkes

[w3wilkes]

Hopefully someone will find all this info useable. The HJG46W-4 is the carburetor for the 71 Z. This carburetor along with all 240z / 260Z's is listed as having a bore of 1.811in (46mm), this must be at the throttle valve plate as I used my micrometer and measure 43mm at the carburetor inlet. It does appear from this diagram that the throat? is widened on the intake manifold side of the venture. None of this info really helps to answer any of my questions in this thread. Hopefully someone with the stock air cleaner can measure the height of the integrated velocity stacks and post in this thread.

Who knew it would be this hard to figure out which stacks would be compatible with these SU's beyond what's available through MSA!

[NVZEE]

Stack height looks to be about 40mm or 1.57” from the carb mounting surface to the rim of the stack.

[w3wilkes]

11 minutes ago, NVZEE said:

Stack height looks to be about 40mm or 1.57” from the carb mounting surface to the rim of the stack.

Thanks! I'd guess Datsun came up with this height for best overall power/performance.

[NVZEE]

Relating to stack length, this Toyota comparison was interesting. There’s other data out there but this was butt-dyno impressions as well as real-dyno numbers.

 

[w3wilkes]

Great video! Looks like with about any air filter (I have the single ITG) that we're limited to a 40 to 50mm stack. Would be nice to see this same test done with a 240Z.

[240260280]

One way to get low end torque.

 

[240260280]

[torynich]

240260280, I keep seeing those pictures of norms mod but I can't find a write-up on it anywhere. Does anyone have more info on it?

[NVZEE]

You find Norm in or referenced in several zcar.com threads on this topic:

http://www.zcar.com/forum/10-70-83-tech-discussion-forum/118695-su-air-horns-velocity-stacks.html