If you could find the info/picures/link that would be great as real date would tell us how to proceed. The slot is only about 3/8" wide on the Audi intake but that is still too much area to control the air distribution (in my testing).

Tom Vaught

 

Do you mean just on the Audi engines or others that you've tested as well?

 

Still cant find the bloody thread but i did find the images on my old computer so here they are, sorry theres no info to be had with it but this at least explains what i was on about, if someone can tell me how to embiggen the images so theyre somewhat useful that would be great.

slotted

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holey

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Are the saved images larger than that? If so, you may have linked to the thumbnail instead of the actual file.

I saw a very, very similar thread on one of the major Nissan car forums. It may have been Nico Club or Hybrid Z, I don't recall. Anyway, one the members was interested in building his own billet intake and investigated the dual plenum idea. He, too, did CFD sims and found the slot to still bias flow toward the rear. He added straighteners/diverters/whatever along the length of the slot and I seem to recall that it helped a lot, which seems like a variation on the hole idea. I just saw the thread a few days ago and now I can't find it again. I think it was a turbocharged 280ZX inline six.

Slotted:
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Straighteners:
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It looks like the simulation may have been done with all the ports open, so take that for what it's worth.

This was a commercially-available intake made by HKS for the same engine.
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I love reading the detailed points and knowledge that is in this thread. So my hat is off to anyone who can build their own intake manifold !!

I stumbled across these 2 videos earlier this week and thought you all would enjoy them.
Looks like NRE has perfected their manifold especially when they got all the major features built into the piece !!

 

Found it, which was no mean feat given my 64kb/s connection and the size of the thread coupled with the fact the thread topic isnt actually descriptive of what i was looking for.

 

Well I am glad that my data was not the only one that said the slot did not work.

We never burned up cylinders but we watch that stuff very closely and stop if we see an issue.

I think the divider fins might have some merit.

Tom Vaught

 

Facinating stuff, guys.

 

OK i don't get it out of everything I've found on custom intakes. the two points everyone seems to agree on is too, run velocity stacks of some sort and to make sure the entrance is off the plenum floor, and that for boosted engines the throttle body at one end of a straight plenum will cause un even cylinder feeding. but then you see an intake like Nelson racings intake and am somewhat shocked to see the port entrances on the plenum floor, and a plenum design that isn't much diffrent then a throttle body at the end of a tube, and to top it off I'm pretty positive the plenum volume is nowhere even near 100% of the displacement of most of the engines its going on.(let me make it clear i love his work i just am curious how his intake really works compared to other designs) so now that my Audi design bubble is burst. i thought i remember reading in a post here along time ago. that you had more success pointing the throttle body away from the intake ports than trying to direct them evenly so that the flow goes right into the port entrances as far as even cylinder feeding is concerned. i got in a debate with a friend on the subject and he seems to think he would make more horsepower by having the throttle body faced directly over the ports, because it would provide for more direct undisturbed flow path and higher port speed and better stuffing of the cylinder. my argument is that in the ideal intake you would have as little airspeed as possible in the plenum. so that when the intake valve opens it can draw as much air as possible because its less disturbed. i want to make sure i have it right. also is there a basic rule of thumb for how high to set the velocity stacks off the plenum floor and how all other plenum walls should be at a min. distance from the entrance? Also what thickness of aluminum and what grade do you guys think is a minimum for the plenum walls on a motor that may see 35Lbs of boost?

 

Awesome read. After reading all of this it leads me to think that the B Headed manifold that MMR is selling will not feed all the runners equally. Been thinking about building my own for the B Heads using the IMRC deletes they sell for the flanges,looks like what they did.

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We ("The Builder" and I "The try it and see if it actually works" guy built a big round plenum "tube" one time EFI intake manifold. 5 inch or 6" diameter tube, I forget. We wanted to have injectors in the runners and more injectors adding fuel to each runner right in the center at the top of the plenum.

Have that big injector fire that fuel right into the port!!!

So we build the thing and try it out and most of the fuel is in the back runners and the front runners are lean. The velocity of the air going thru the throttle body was still high enough to push the fuel past the runner opening (even at 60 psi injector pressure) so the fuel never made it across the plenum to get into the runners. We welded up the manifold in that area and put the injectors back on the runners.

So you have to be really careful with front entry throttle body intakes as far as fuel distribution goes, if you are adding fuel and find the rear is rich and the front is lean.

Tom Vaught

 

Never underestimate the weight of air

 

No Kidding!

Tom Vaught

This Intake even though it is not EFI is very nice.

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Been thinking about designs on this. I realize you'd pick some heat up, but how come someone doesn't stick the plenum area into the "V?" If you had say a 350 CID engine getting it up to 2X the volume would become a lot easier that way. You're talking about something roughly 3 gallons in size at that point, or 5 gallons in size if you do 3X the volume. Sure it's big, but not "that" big. You'd want a valley tray of some sort with some insulation between the pan and the oil I would suspect, but that's not too ground breaking.

 

That would certainly be doable on an engine that doesn't have strengthening ribs going across the valley area. That's the only thing that kept me from exploring that very idea, but it was to mount the coil pack in the valley.

 

An interesting idea that came to mind. Some of the intake designs discussed use a separated plenum with elongated holes or slots connecting the chambers, or vanes, or more simple holes in an attempt to even out pressures to the intake runners.
What hasn't been brought up yet is the use of an air filter positioned in the middle of a large plenum, and how the air filter is used to diffuse pressure differentials within the plenum, above and below the air filter. An idea I saw is popular in the open wheel forms of racing.

 

Re: Don
The first thing that comes to mind is sucking filter element into the engine. The plenum likely sees a higher pressure differential, as well as increased pressure fluctuations (pulsing) when compared to a pre-turbo (or pre-throttle body for natasp), so I'd expect more tensile/ fatigue related wear and tear on the filtering medium. I've never seen such a setup so take this with a grain of salt.

However, using the same "use a slot/ filter to create a pressure differential between two plenums" (to help with equalization) philosophy, I'd like to propose using an intercooler core to achieve the same effect. I vaguely remember some OEM's doing something of the sort (VAG w/ Audi & Bugatti?). Anybody here tried this before?

Re: Slot separators being effectively useless
Regarding the slot separator, I would expect the slot to become more useful in helping cylinder distribution as flowrates (and manifold pressure) increases. That said, I can't shake the feeling that adding a flow restriction to create better distribution is akin to throwing out the baby to get rid of the bathwater.

Another possible solution
Last but not least has anybody tried the "exhaust manifold as an intake" setup yet? I think Mike Moran did one, and there was a red ~'66 mustang that got a bit of magazine coverage, but in my **opinion**, their runner lengths were too long (16" or longer by eyeball guesstimation). The sharp edges in the merge collector (now being used in reverse) don't seem like they would hurt, and the bundle-of-snakes may help with packaging. Throw in a Burns stainless megaphone between the merge collectors and the throttle body and you've got a tuneable plenum size. Any body have any thoughts or experience with this kind of setup?


Regards,
Kurt Betton

 

I like the intercooler core as a diffuser idea. I have seen it done. I would only worry about a liquid intercooler springing a leak. Maybe use a core that could be quickly serviced when it became necessary.
F1 style racing has been using a filter in their intake system to diffuse inlet air just over the inlet bells to the runners. It would be worth studying to see if a durable system is available for a turbocharged application. It would have to be a fire resistant element, in my case. Every once in awhile, I'll get an intake backfire on startup with the methanol.

 

Here's Moran's setup.

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Regarding the I/C in the intake. Isn't that pretty much exactly what Ford did on the blown Cobra engines? Just instead of having the blower on top, you're just talking about having another plenum there.

 

Looks like a bitch to perform a valve adjustment, or check the plugs. On a motor like that, I'm sure you're going to want to do both on a regular basis.