everyone that has built a custom intake for the L6

[JustinOlson]

Thats very nice. Does it have internal velocity stacks or atleast some grinding work to give a nice radius transition from the plenum to runner?

 

Justin

[OlderThanMe]

You can't weld aluminium to steel with any traditional process. There are some new processes that can do it though. That is just sheet aluminium welded to cast aluminium.

[mario_82_ZXT]

Also, in a L manifold, isn't one of the major bottlenecks the runner diameter?

So... I don't recommend doing something like that on a stock Datsun intake...

 

 

I'd go with the Q45 TB if possible.

Mario

[Guest ZFury]

Why wouldnt it? It uses the same TPS, all you would have to change is the throttle linkage.

[Shadytrixta1]

The runners are gasket matched.I was thinking that manifold, custom runners, and Q45 throttle body.And since he works with me it will cost me supplies and a little for his time.

[Guest ZFury]

ah'...

[robtpt]

I'm a grad student in mechanical engineering and I've spent a lot of time looking at flow visualizations in water and wind tunnels, so I'll give you my thoughts. I have no experience designing intake manifolds, though, so take anything I say with a grain of salt. It seems to me the two biggest problems are the protruding velocity stacks and the abrupt expansion right after the inlet. Pipe flow will tend to separate and go turbulent when there is a large area expansion, like there is at your inlet. Also, the protruding velocity stacks are bound to cause separation and turbulence. I don't know if it is common in this type of EFI intake, but I would think it would be a lot better to have the face of the velocity stacks flush with the surface of the intake manifold rather than protruding into it.

[JustinOlson]

Actually, it may be counter intuative why a protruding velocity stack works the way it does. It actually ends up pulling cleaner air out of the boundry layer around the edge of the plenum which improves performance. I've personally seen good gains by going to a properly designed tappered velocity stack(which in its self helps turn turbulent air from the plenum into nice laminar airflow) that protrudes from the plenum around an inch. The prime example of this are Full-Race/Hypertune inlet manifolds for the supra:

 

 

[veritech-z]

Looking at that supra manifold, the actual round area of the plenum doesn't start until above the opening of the velocity stack. Wouldn't that make it act pretty much as if the stack were flush? I've been unsure of the logic behind this theory since the first time I've heard it, so I'm always up for a good explanation.

[robtpt]

JustinOlson and veritech-z,

 

I think you both have valid points. I can understand how the protruding velocity stacks could be helpful. However, I do think veritech-z is correct about the fact that the velocity stacks don't protrude into the main part of the flow. They just sort of stick up in the boundary layer. I've been thinking about suggestions as to what might help the OP redesign, and I have the following thoughts:

1. He should add a length of pipe to the inlet of his model. The fluid dynamics of air being sucked into that hole are going to be VERY different if it's just a hole or if it's a length of pipe running into the intake manifold. Even a short length of pipe would be helpful.

2. An abrupt edge at the inlet may be better than the taper. The flow will definitely separate either way, but at least an abrupt edge will keep the separation point fixed for all flow conditions.

3. I would also play around with the amount the velocity stacks protrude. I accept your explanation of their benefit 100%, but if they protrude TOO much they will definitely disturb the flow.

[turbobluestreak]

guys I've got a new flowtest to post with great results, I'll post it tonight. Oh and the stacks are in it this time.

 

 

 

 

 

 

tbs

[turbobluestreak]

ok here it is my fixed flow

 

http://www.needmoreboost.com/turbobluestreak/fixed-flow.avi

 

 

 

 

 

tbs

[b__sosick]

that little pocket near the first runner could be fixed with just a piece of sheet metal couldn't it? just to make it smooth between the entrance of the manifold and the first runner. just a thought.

 

 

edit: or maybe thats beneficial? j/w

[alexideways]

When I was younger, I had a Rabbit with a 2.0L 16 valve engine fed by twin mikkuni's and a G60 blower, for it to work correctly (or so i tought at the time)

I had built some kind of a header but for the intake. The filter was hooked to a big 3" pipe that seperated into 4 smaller pipes, my question here is would'nt it solve all those turbulance problems to have your TB hooked in the same way with all the runners facing the TB? It sure worked for my little bunny.

[Guest hegan1956]

Has anyone looked at using a dual plenum and dual TB's? Using the valve opening to draw the charge in as in a tuned system? It would be similar to headers but in the reverse. That way it might stop the reversion problem because one valve opening isn't sucking the charge back out into the plenum body. Maybe even set it up on 3 TB with the TB at a much smaller size and connect them with a reversion tube to equalize the fuel and vacuum charges. This might also enhance the low speed charge characteristics and add low end torque. I know on my 280 I could use all the low end torque I could muster. Just a thought since we are looking at fabricating a complete from scratch system. I am more interested in non-turbo intakes so my idea may be inappropriate for turbo systems.

[veritech-z]

Might as well just do the triple dual throttle bodies on a converted carb manifold at that point, right?

[AnTmanS130T]

How much do you think that manifold will cost Cody? Let me know, I may be interested.

[ezzzzzzz]

The abrupt opening into the plenum is causing the immediate turbulance IMHO. It's the same reason we get so much exhaust intrusion into our S30's at speed. Why not taper the opening into the plenum like a reversed velocity stack assuming there is enough material to allow this? Maybe a couple of thin strips could be added horizonally just behind the throttle body to provide more control of airflow entering the plenum?

[robtpt]

The recirculation at the inlet is basically unavoidable. Whether you taper it or not, the area expansion is too great and the flow will separate. The best solution is to match the area of the manifold to the area of the inlet pipe as closely as possible. This will result in smaller recirculation regions. Look at the flow visualization on the stock manifold that was posted earlier as a good example of that. With as large of an area expansion as there is in this manifold, the taper could actually be worse than the step. When the flow separates and creates a recirculation region, the air flowing back towards the inlet sees a converging duct and is actually accelerated back out of the manifold. You can also see that quite clearly in the flow visualization that was posted earlier. While the step is an imperfect solution, it does at least prevent the back flow since the air in the recirculation zone can't make back out past that step.

[ezzzzzzz]

I stand corrected.