Yes, I agree losing some of those wonderful tools at university is very disturbing! I don't think you can do much about Catia unless you are lucky enough to get a job at a company that pays $thousands per year for the liscense. However, a low cost, DIY flow bench is quite possible and can have very precise results. Normally, I would assume it would be a tool you would keep for life but with the ICE being legislated out of existence an amp/volt meter may become your go-to tool!

Go here for a great forum on all things pertaining to DIY flow bench technology.

 

I have been a member of that forum for many years and all of the people that post there are very good people.
Tom Vaught

 

Hey question for you guys, I've got an Offy Competition intake manifold for an AMC 258 and I did some measuring on it today. The runners are only about 4" long, and the CSA is in the 1.95" area. Is there any reason I should consider this a sane intake manifold for anything but spinning an engine like that up to 8K? The production intakes are admittedly on the long side with the runners being about 7.75" which seems to be a lot saner to me. I would be operating off the 4th harmonic I suspect and from what I've understood about it that's not really optimal for well tuned power. The runner in the head is about 2.5" (distance from center of valve stem to intake flange.)

 

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WOW.......43 pages and counting (I read every post)! There's certainly a lot of very impressive information presented in this thread! Kudos to all those willing to share their knowledge and experience ~ especially to Tom Vaught for guiding & encouraging the participants. I was actually surprised that the thread hadn't been closed and that I'm still able to post to it, lol. I certainly can't add any wisdom to that which has already been presented, BUT.......I have a few questions.

It seems that the general consensus for constructing/designing a manifold with consistent/uniform distribution is: Direct the charge air against a flat plenum wall that's opposite the individual runners, at which point it loses energy/velocity and disperses evenly to those runners.

Among the prime examples is apparently the Ford GT-40 intake, designed by Mr. Vaught's workmate during his tenure at FoMoCo.......AND some of the designs put forth in this very thread, wherein charge air is introduced from below and (again) slammed into a flat surface ~ in this case the roof of a tunnel-ram plenum ~ yielding (hopefully) the same consistent/uniform distribution to the runners on the opposite side.

My questions (mainly for boosted apps):

1) Are there any flow-enhancing (turbulence-diminishing) "trumpets"/velocity stacks used at the entrance to the runners inside the plenum of the GT-40 intake? OR.......are those 8 runner entrances simply radiused?
2) Same question for the bottom-entry flat-roof tunnel-ram intakes.......¿velocity stacks at the entrances of the individual runners ~ or just radiused entries?
3) If "YES" to velocity stacks.......how far/high past the plenum floor should they typically extend, AND how close/far are the ends from the flat plenum wall or roof?
4) With regard to the tube(s) feeding the air slamming into those flat-walled plenums......how much STRAIGHT length is needed, prior to discharging into the plenum, to prevent the air from being biased towards the same plenum end as the outside radius of the feed tube? (think: typical "carb hat", where the air is primarily discharged out the backside) OR, is it simply a matter of using a sufficiently-large tube to slow the velocity &/or one that widens/"ovals" where it joins the plenum (like the GT-40)?

■ TIA for your anticipated response(s)!

 

My questions (mainly for boosted apps):

1) Are there any flow-enhancing (turbulence-diminishing) "trumpets"/velocity stacks used at the entrance to the runners inside the plenum of the GT-40 intake? OR.......are those 8 runner entrances simply radiused?
Answer: Radiused


2) Same question for the bottom-entry flat-roof tunnel-ram intakes.......¿velocity stacks at the entrances of the individual runners ~ or just radiused entries?
Answer: Radiused

) If "YES" to velocity stacks.......how far/high past the plenum floor should they typically extend, AND how close/far are the ends from the flat plenum wall or roof?

On my intake I made the inlet portion of the intake a longer length to lower the rpm tuning for a street application, the radius acted like velocity stacks on the mechanical Port Injection intake and the plenum was a known and tested plenum shape with a forward throttle body (105mm) entry. I will at some point do a Bottom Feed intake design and tune for best distribution
using spacers to raise/lower the roof height as required.

4) With regard to the tube(s) feeding the air slamming into those flat-walled plenums......how much STRAIGHT length is needed, prior to discharging into the plenum, to prevent the air from being biased towards the same plenum end as the outside radius of the feed tube? (think: typical "carb hat", where the air is primarily discharged out the backside) OR, is it simply a matter of using a sufficiently-large tube to slow the velocity &/or one that widens/"ovals" where it joins the plenum (like the GT-40)?

Intake package plays into the answer here. If the throttle body is 105mm then the "elbow"
only needs to be 105 + the wall thickness. Tubing is based on an outside diameter.

The Bottom Feed intakes work very well on distribution as there is little velocity after the crash into the plenum roof. There is no throttle blade effect sending air the the rear of the intake vs air distributionbeing supplied evenly to all 8 runner inlets.

Tom Vaught

 

THANX for your response, Tom ~ However, I wasn't questioning distribution of the charge air AFTER hitting the flat roof of a bottom-entry tunnel-ram plenum.....I understand that principle. I was referring to the air hugging the outside radius of the bottom "feed tube", thus causing it to impact the plenum's flat roof closer to the rear (assuming a front feed) ......similar to the way air exits a typical poor-distribution carb hat: Namely, outta the "backside", opposite the inlet. <shrug>

As for the GT-40 intake that your workmate developed.......did it merely have radiused entries at the inlet mouths of the 8 tubing runners? OR, velocity stacks? Also......where the large feed tube enters the plenum, does the end extend past the floor? AND, if so, is there a velocity stack/trumpet at the end? I'm just a poor old man and I can't afford to buy one and cut it open, lol. THANX again!

 

From my research/testing roughly 5x the diameter of straight tubing is necessary to allow time for the air in the tube to re-distribute evenly after a 90 degree bend.

 

THANX for your input, 93! Based upon that finding ~ I can understand why you used multiple/smaller "under-plenum" feed tubes......since a single 3" to 4" diameter tube would need a 15" to 20" straight section after the bend <eek> to avoid a "rearward discharge" into the plenum. Obviously, there's not enough room in the valley to do that.

I've got a turbocharged "old-school" Lima/Pinto four-banger in an '87 Ranger, for which I'd like to fabricate an intake similar to the GT40 version that Tom's workmate designed at Ford. Soooo......I'm still curious what the inside of its' plenum looks like. I ASSume that the inlet "mouths" of the 8 individual runners are merely radiused where the air enters from within the plenum. BUT.....what about the larger pipe that feeds from the TB? I'm wondering if it extends inward, past the plenum "floor" (side wall)? AND ~ if so ~ whether or not it's bell-mouthed? <shrug>

 

Yes, exactly the reason I did that.

I ran a Twin Turbo setup on a 93 Cobra years ago, same intake design as the GT40.
We ran into issues with airflow distribution when on-motor, but I never did any testing with boost. On motor we cut back the middle runners (edelbrock EFI intake for SBF) next to the main TB feed 1.5", then the next runner wall 1", and the farthest .5" creating a 'V' shape plenum in an effort to help the air turn to feed the cylinders.
With the Boosted Cobra I cut 2" of runner out to make the plenum larger and runners shorter. IMO the plenum was still too small for the application. An overly large plenum will help airflow distribution, as will runners with total volume larger than the cylinder fill.

As for a bell mouth feeding the plenum, I don't think it's necessary as the air flowing thru it will be traveling at 110+MPH.

 

I have seen a few 5.0 "bread box" upper intake lately mostly as a nostalgia thing. For most mild cars I assume loss of low end is not worth the pick up at the top. How is the distribution on those where they are side entry into an open plenum and short runners.

I saw one that was clearly a 5.0 Truck intake the the top cut off and a box welded to the last 2" or so of the upper.

Hopefully I don't kill it anytime soon but when my turbo SBE 5.0 dies I will more than likely be looking at 5.8 vs LS. I don't have the budget for an aftermarket block. There is no good junk yard 5.8 intake. How would cutting the top off a 5.8 truck intake and adding a box work?

 

The Gen1 Ford 3.5L Ecoboost intake is a bread box style with front inlet. Shorter runners than you'd expect too.
Fuel distribution in the OE tune is VERY bias to the rear cylinders, as much as 13% in factory stock form.

 

THANX for your feedback, gentlemen! I must admit, however, that my curiosity about the bottom-feed tunnel ram is/was strictly "intellectual" ~ since my main focus is the optimum manifold design for my turbocharged 2.3 (Lima)-powered '87 Ranger, whose typical factory EFI intake style is pictured below.

Unlike most of Ford's OE V6 & V8 manifolds, which have a common plenum, all of the EFI intakes designed for the various single & dual-plug Lima engines ('83-'98) have an east/west TB located above the v/cov (as shown), with subsequent intake paths that are divided into 4 individual runners immediately thereafter.

OTOH ~ Virtually all of the really-fast (7 to 9-sec 1/4 mile) Lima-powered cars rely on plenum-style intakes (example = https://www.dragzine.com/features/c...fred-houses-7-second-thunderbird-turbo-coupe/ ). BUT.......despite his amazing 7-oh-second elapsed times, I doubt that Fred's front-entry manifold has equal distribution - DUNNO!

Soooo.......I'm more inclined to fab something similar to the GT-40 style intake, with a slightly-larger plenum (approx 2x cid). Unfortunately, I don't have access to CFD or flow-bench analysis to optimize my imaginary design ~ BUT......I have my trusty eBay anemometer and Stihl leaf blower, lol.

85553091L by TurboRay posted Dec 21, 2022 at 12:52 PM

 

The Technical Specialist" for the intake manifold work several years ago had a very broad view of intake manifold design. "Hurry up and get something built so I can go back to sleep" seemed to be his philosophy for intake manifold design, (my opinion), so the 13% scatter on the intake you described is not surprising at all from your testing.

I tried to get the design to with-in 3% for all of the runners, as did my old Intake Tech Specialist.
The new Tech Specialist as mentioned had a different philosophy.
I did test the "slot design" feed channel concept and it still packed the air up in the slotted passage and fed more of it to the rear cylinders.

Tom V.

 

For shits and giggles........below is an intake y'all might find interesting (not mine):

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This design will over-feed the center cylinders.
We see this issue from the side-feed 96-04 Intake manifolds (both GT and Cobra). Airflow comes thru the TB at 110+MPH (at high density vs all motor), the bulk of the mass of air will not spread out but continue to go straight into the center runners.

 

.
THANX again, for your insight, 93! Unfortunately, the builder/creator of that engine (destined for a "slingshot" dragster) died from cancer before it ever ran. What you say makes sense, however, since the high-velocity incoming air would most likely hug the outside wall of that plenum w/o a whollotta "spreading" to the end cyls.

Can I ASSume that the distribution might be improved by installing a couple of outwardly-angled fins on the inside of that curved plenum wall to assist in "spreading" the charge air to the end cyls? I envision such fins standing proud from the wall about 1 to 1-1/2 inches.

Doing so would not require cutting the plenum open. External "cuts" could be made on that curved wall and the fins slid into the kerfs ~ then welded from the outside. Smokey Yunick implemented that same strategy to improve distribution on the SBC intake "logs" of his 209cid Indy car engine back in the '70s & '80s.

That Indy car had two turbos & two 4bbl Holleys in "draw-thru" configuration. He claimed, "about 1000hp" (nearly 5hp/ci <eek>) in a May 1991 Circle Track Magazine article about reverse-rotation cranks (pics included). His cranks were also 180° "flat" cranks, as used in Ford's latest "Voodoo" Coyote engines.

 

Hard to get accurate with angling fins IMO.
For a manifold design like that I'd likely go for an air to water intercooler core in the plenum that has a pressure drop of a few PSI (tight fin density like the Garrett cores) to force a more even distribution of air. Possibly even block air going thru the middle of the core in line with the TB to force the air to the ends of the plenum before the core. I'd go for a larger core than the HP the engine would be producing, like the Garrett 1000HP core (5"x5"x12") for an 800HP application.

 

You're probably right, 93 ~ THANX again for your input! I can only GUESS that "his" (RIP, Curtis Hensley) original thought was that the large-ish plenum would slow the incoming air charge sufficiently for "self-distribution", lol. As for intercooling......it wasn't intended, due to the latent heat of vaporization of the methanol he was gonna use.

Perhaps a centrally-located flat baffle that traversed approx 1/3 of the plenum's width ~ for the incoming air to "bang off of" (as discussed previously in this thread) would cause it to disperse evenly around the edges and promote better distribution? It would be easy to install (without disassembly), using the method I previously described. DUNNO!

 

The manifolds designed and built by Marcella Intakes are very nice pieces but in some cases will not package like the old GT-40 intakes, (under the factory hood).

The slotted bottom feed intakes from Audi) for sure did not have even distribution.
Lots of testing was done on that design (as used in a on a 4 cylinder engine.
One runner was removed).

In all cased the air packed up in the rear of the slotted intake plenum.

Tom V.

A old video for you to watch 4.6L Ford Twin Turbo Engine.
It had a bottom feed intake manifold and ran in the 7.80s years ago with a 4.6L TT engine.
I suspect that few on the Turbo Board will approach that accomplishment with that size engine
and intake design.

 

Like to hear your thoughts on a "box" upper for a ford gt40 lower. We've all heard the downs ford bread box for the fox which was a popular "upgrade" for 302. it seemed to be more popular amongst the forced induction setups. There where a few others back in the day. I own a small machine shop and am a welder/fabricator by hobby so making something like this wouldnt be to bad. My combo is a 1994 ford lightning. SBE 351w, trickflow heads 11R heads, small trickflow cam, ported gt40 intake and S476sxe turbo. I leave it about 12psi. I'm thinking about ditching the stock gt40 tubular upper and making my own "bread box" open to thoughts on this. Attached is some photos of what i have come up with so far. upper will most likely be 1/4" plate/sheet/box welded construction and the bottom will be a machined billet. Reasoning behind this is the gt40 upper is a known flow restriction. matched with a small cam and this thing make gobs of low end torque and dies off at like 5k. I'd like to shift the powerband up a little to move to torque curve up to be easier on the stock bottom end while not falling off so early.

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