Building a custom UIM, thoughts wanted!
01-20-09, 08:59 AM
#29
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01-20-09, 03:01 PM
#30
506 RWHP 12A..
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I do have stacks inside the plenum. They slip into the "tube" part of the UIM and are welded to the plenum side. The box itself is detachable, so i can play around with different setups if this doesnt get me the desired results.
01-20-09, 04:50 PM
#31
The problem with raised velocity stacks inside a plenum are seen when ordinary bell mouth flares are used. His have the radius continuing a full 270 degrees which really help airflow out. Although you wouldn't think something as simple as whether the radius is 270 degrees, or 180 degrees would matter, it actually does from a flow standpoint.
01-22-09, 07:45 AM
#34
It's tried and true testing. If you want an example of it look at some of the custom intake manifolds that are made for EVO VIII's. Yeah, they make more power than stock but why go through all the work to make something that doesn't have high efficiency. Just because it made power on the dyno doesn't mean it busts the consensus...
01-23-09, 08:19 PM
#36
What I do think is a waste of time and effort is gasket matching and other small things that people do to stock manifolds. They typically "increase flow" in the areas that aren't the restriction and then justify it by saying "every little bit helps". That only applies to helping the worst area though. If you improve an area that already meets your flow requirements while something else is more restrictive, you've done nothing so no every little bit does not always help.
When I was running my S5 TII LIM to 3rd gen UIM with all the pinning/matching/porting/polishing naturally aspirated I was seeing as high as 3psi boost in the ~5,000rpm range on data logs. For reference, the stock '86 6-port system didn't quite make 2psi boost max.
01-26-09, 01:27 PM
#37
Since you changed to an entirely different upper manifold, you can't say with any certainty that any one thing is what did it. That of course would be guessing!
FWIW: I have more flowbench experience than almost anyone here. Sadly my flowbench went the way of the dodo about 2 years ago.
FWIW: I have more flowbench experience than almost anyone here. Sadly my flowbench went the way of the dodo about 2 years ago.
01-26-09, 06:46 PM
#38
It's tried and true testing. If you want an example of it look at some of the custom intake manifolds that are made for EVO VIII's. Yeah, they make more power than stock but why go through all the work to make something that doesn't have high efficiency. Just because it made power on the dyno doesn't mean it busts the consensus...
-J
01-26-09, 07:57 PM
#39
I fully realize your point, but i am not talking about the evo's mani nor am saying "this" is more efficient than "that". And I fully understand what rotarygod is saying as well..... But the fact of the matter is, it is NOT true accross the board. There is a broad range in-between flush/reassessed runners and 6" velocity stacks in the manifold. And what is "efficiency" in intake manifold design in your mind?
-J
-J
Simply put, raised velocity stacks in forced induction engines cause turbulence. Without velocity stacks (in a forced induction engine) you're allowing the air to accelerate to a high velocity yielding better combustion (with proper port timing). The more you fill the combustion chamber the more power you make! I'm not going to fight anyone over anything. I'm peaceful and appreciate everyone sharing. I learn something from everyone's setup I see.
As long as were on the topic maybe we should talk about runner lengths. The runner length controls the amount of air that actually gets into the chamber during the intake cycle when NOT under boost. Higher speed engines (road racers) will associate gains from shorter intake runners. If you want mid range torque you'll benefit from longer runners. Turbo applications generally find the best results with long runners. Long runners provide a flat torque curve at low speeds, while the almighty turbo keeps the top end strong.
Rotary God is correct about the radius of the runner. I'm very particular so I use machined velocity stacks to it's always perfect. Each runner's ID is going to determine each runners radius. I played with a couple relative figures to each and found my magic number. What's yours?
01-26-09, 10:12 PM
#40
The interesting thing about the inlet shape of velocity stacks is that to the casual observer it may seem they are equal in flow based purely on looks. However one may work well and the other won't. Air doesn't always do what you think it will and just because something looks like it flows good doesn't mean it does. The opposite of that is sometimes true as well.
The exhaust ports on a 13B are a prime example of this. A 1/8" radius on the exhaust port actually flows more air than a larger 1/4" radius which goes completely against what one would think happens. That's not true everywhere though. Just on those exhaust ports.
The entrance of each intake runner is also the same way. Not from the standpoint of inlet radius size so much as shape. There are actually different kinds of inlets. Some are simple radiuses and others are bell mouths. There's a difference between each. There's even a difference between the radius sizes as well as how far around in degrees the radiuses extend from the opening. There's some good info on the web about it.
The exhaust ports on a 13B are a prime example of this. A 1/8" radius on the exhaust port actually flows more air than a larger 1/4" radius which goes completely against what one would think happens. That's not true everywhere though. Just on those exhaust ports.
The entrance of each intake runner is also the same way. Not from the standpoint of inlet radius size so much as shape. There are actually different kinds of inlets. Some are simple radiuses and others are bell mouths. There's a difference between each. There's even a difference between the radius sizes as well as how far around in degrees the radiuses extend from the opening. There's some good info on the web about it.
01-29-09, 11:13 PM
#41
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we did lots of flowbench testing on different intakes....we tried all kinds of differnent radius and lost flow with a bell mouth on our intake. We used putty to rework a ton of different radius and finally got to one that is flush with the backing plate. It just rolls into the intake track from that point. It produced a VERY substantial increase in cfm.
01-30-09, 01:24 AM
#42
we did lots of flowbench testing on different intakes....we tried all kinds of differnent radius and lost flow with a bell mouth on our intake. We used putty to rework a ton of different radius and finally got to one that is flush with the backing plate. It just rolls into the intake track from that point. It produced a VERY substantial increase in cfm.
-J
01-30-09, 11:31 AM
#43
we did lots of flowbench testing on different intakes....we tried all kinds of differnent radius and lost flow with a bell mouth on our intake. We used putty to rework a ton of different radius and finally got to one that is flush with the backing plate. It just rolls into the intake track from that point. It produced a VERY substantial increase in cfm.
Thank you!
