Manifold with internal velocity stacks away from the interior walls bad on boost?

[RoadWarrior222]

99%? Not sure about that, especially since the radius matters (a small radius might not help much at all) and also I think if its on the floor it may not work as well fo ras many conditions (RPM, velocity, etc)...

But for forced induction, the height may matter less...

Well, some while back I did the math for what radius curves would give fully laminar flow at typical intake velocities, and it was around 4 inches, so optimal would be a bit far off what fits in an intake...

Also, as I alluded to above, what works for one, may not work for many, the flow is across them, they're not in free air, and they're not being fed from in front, so #1 gets to breathe good, but look at the cross section of the intake path from the POV of #2 #3 #4, there's all sorts of junk in the way, flow is gonna be all messed up and significantly slower at #4 than #1... so while you get the theoretical best velocity at #1, the rest might not be close. The only argument for it is the runner length increase, but you could have that and a flat sided tube that wasn't as turbulent or obstructed for the other cylinders..

Anyhoo, I suspect useful radii to start at about 1/4" and I suspect that a "3 angle valve job" radii would get a large chunk over square end, each refinement to a perfect curve gaining less and less as you go on.

IF you've got one intake, one box, such as in an airfilter box, sure do the raised one, even a square end pipe does better raised off the back surface there, but that's when you've got end on flow and only one of them...

IMO 3% flow improvement into each cylinder with a quickly assembled eyeball ground radius on the entries would be better than the complex arrangement where it's likely to go 4% 3% 2% 1% because of the side on profile of the trumpets disrupting the airflow to subsequent cylinders.

Also, I bet there's a lot of intakes you could achieve this effect on with a flexible bar hone, going up from the motor side and letting it splay at the top of the runner. You'd have to peer down the intake side with a flashlight to see what you're doing and it would take some finesse with tool speed and position, but you could get the edges off.

[shackwrrr]

http://josephrinek.com/intakemanifold.html

Here is a site I found showing the flow with no velocity stacks. Looks like the angled runners, and angled TB did a lot too. Fluid dynamics is really interesting subject for me, I've been looking at designs for my r/t intake


http://www.google.com/search?hl=en&safe=off&gl=us&biw=320&bih=259&tbm=is ch&sa=1&q=cosworth+intake+manifold&oq=coswor+intak e&aq=1l&aqi=g-l2&aql=&gs_l=mobile-gws-serp.1.1.0i13l2.206702l231173l0l237392l27l23l7l0l0 l1l388l2150l0j10j2j1l13l0.frgbld.&mvs=0#p=0


If you look at cosworth intakes you'll notice that that the throttle body comes in below the intake runners. This promotes complete filling on the Plenum, and compared to the flow diagrams from the other link the air doesn't rush in and bounce off of the runners. I'd like to see a flow model of a cosworth intake.

[RoadWarrior222]

Yus very interesting...

It looks kinda like a 4 port log type mani would benefit from having the log plenum extended or the TB spaced off it... if you look at "FT Flow Plot; 0* TB Angle" ... I'd eyeball/rule of thumb that at space your TB from the first runner as far as between first and last runner.

Though the general thing I take from that is... "Logs suck for 8cyl"

Though another point you might take from that is, "don't space your runners further apart than necessary" ... so if you stick protruding stacks on and spaced them out, you might have a large flow imbalance, depending on how your TB was "aimed" in 2 of the cyl vs the other two (near two, far two or middle two)

---------- Post added at 09:22 AM ---------- Previous post was at 09:15 AM ----------

BTW... if you ported the entrance from the TB there it would change things, like if the closest runner was starved, you could radius the bottom side of the entry and it would help it turn in more, if it was the furthest runner, then radiusing the top side would help throw it over there.

[RoadWarrior222]

Another thing that makes me want to do is try angled TB spacer plates, "aimed" with the axis of the TB pointing at the "middle" runner.

though I'm trying to brain out whether you should regard 3.0 runners as coming straight off the bottom of the plenum, or whether really they're acting more like they're planted in it at an angle...

Also makes me think that you have to clock the TB plate right or you starve the central runners at part throttle...

Though I'm wondering about the plots there, if he flowed all runners at once or not, because that never happens, so "more optimum" angled ones won't steal from less optimal ones, unless they're just opening while the less optimum one is at full flow, then they'll strangle it off a bit.

[RoadWarrior222]

... and I'm thinking again...

It's probably okay on a 4 cyl to optimise flow for cylinders 2 and 3, as long as you have enough intake to get ram effect... because 1 and 4 will fill at slightly higher pressure due to ram effect from hard flow on 2 and 3....

on the 3.0 ... can't do that in the plenum... but it fires 123456 ... and then you suddenly realise, doh asymmetrical cams, and no wonder it seems to work better than you'd think it should....

[fishcleaner]

Velocity stacks have to work better than nothing, I was going to put them in my intake but I was in a "better done than right" position, I did taper from 2" dia. to the port and think that helped, good throttle response even with the tune being off and a 65mm throttle body. Look for Aluminum Drinking Tumblers for a cheap velocity stack

http://futuresantiques.dreamhosters....61619_edited-1

[BadAssPerformance]

Neat link Ian... The picture showing the straight in TB and #1 starving compared to #4 is probably also true with the raised velocity stacks but I would say to a lesser level.

[turbovanman²]

Neat link Ian... The picture showing the straight in TB and #1 starving compared to #4 is probably also true with the raised velocity stacks but I would say to a lesser level.

I would guess the stacks probably would help alot. Neat link for sure.

[chilort]

The CFD is neat but many of us still run a curved neck into the intake (I didn't even read the Google thing, so maybe it covers these issues: TL: DL - too long, didn't link). This is going to have a substantial effect as well I would imagine. Where's an F1 engineer when you need one?

[Ondonti]

Read that page about digital flowbenching before but I consider the results worthless since runners spend most of the time closed. This means your plenum is a "bank" of pressure that simply needs to feed each cylinder as the intake valve opens and the vacuum of the cylinder makes a withdrawal from the bank.

What you want is cylinders spaced as far apart as possible to prevent charge robbing and you do not want the walls of your plenum near the edge of your runners and especially not have one runner closer to walls then another (why you should never end your plenum until after the last runner).

DRC posted pictures of a manifold they built recently and while it incorporates optimized angles for runners, the manifold will not have any charge robbing problems.

Velocity stacks? Well tapered runners work amazingly and a bellmouth is great. The only point of extending your runners into the plenum would be an attempt to optimize your performance at a certain RPM but unless you have done the math its probably going to perform worse then a velocity stack welded to the floor thanks to the interruption the beginning runners provide for the rest.

side note: The whole idea of tapering down the end of your plenum strikes me as silly. That assumes your turbo is unable to completely pressurize your plenum and that somehow there is a rush of air constantly flowing from TB to cylinder and "aiming" that air overrides the reality of CLOSED intake valves and cam timing...If air is just waiting in the plenum for the valve to open, why would you taper anything? All that does is give that cylinder less air to draw from compared to the other cylinders. Charge robbing.


There is a better thread somewhere that shows the only design to provide equal flow for these crappy digital flowbenches and its a "double plenum." Double plenum is a normal plenum with a slot in the side and a small plenum attached to that slot. One look at a double plenum and you might reconsider the worth of these flow programs. There might be some college teams running this stuff on their cars.

[RoadWarrior222]

That's half what I'm thinking when I'm thinking about modding a 3.0 plenum by not removing the divider completely, but by cutting it down... the other part of it is flipping flow circulation started by the last cylinder to draw on the opposite bank, into opposite handed rotation for the next cylinder to draw, instead of them fighting each other. Maintain energy. But, shouldn't contribute much to charge robbing, (Well not as much as smoothed plenum) because it makes the path longer.