Flow concerns regarding intake Plenums

[Worstenemy453]

I'm just curious because I see the phrase come up more and more these days of how aftermarket Plenums are better because they flow more than stock

What is this obsession with better flowing plenums. There was a thread saying stock obs plenums flowed around 250ish and stock SD flowed like 500ish. I think the unit was cfm per minute but can't remember. But regardless I highly doubt the heads are flowing anywhere close to 200 on a 7.3 in stock form so what's the big deal about trying to create a bigger bottle neck into the heads.

Now if there is something I am missing please educate me. I am not trying to bash aftermarket plenums or anything. I just want to create a constructive informative thread regarding thoughts on this possible issue.

 

[purpleheart350]

I would like to know as well. Just to add to it and see what people say;

With more air flowing, even though the heads flow "200" or so, wouldnt it give it more oxygen which will give a better burn which in turn give a little more power? So in thinking yes it "could" be worth it

 

[Worstenemy453]

The heads would need to be benched to be a perfect discussion. I feel like in a perfect scenario have a little more air in than the heads can flow wont hurt so you don't "run out" but I feel like trying to double it and what not is money better spent elsewhere

 

[Curtis@Vision Diesel]

Very good thread! Thanks for posting thing, hopefully someone chimes in that has flowed a stock head and can show some real numbers

 

[jkidd_39]

The new set of billet plenums that everyone is looking at.. (Can't link them)

Hopefully they become a sponsor over here soon..

I spoke with the owner and they were not designed for improved flow. The big thing is that they hold up to high pressure and have an o-ring for better sealing. And much easier to install.

Do they flow better? Perhaps.. but without head porting you are not going to see huge gains..

 

[Charles]

The volume flow rate is really a non-issue. Most of these engines are probably only consuming on the order of 3xx CFM. The area for improvement probably lies in plenum volume in terms of dampening fluctuations with successive intake valve opening and closing events and ensuring each cylinder gets a fair shake.

Increased plenum volume is where I would look. That and strength/seal.

 

[Ron's Power Stroke]

you have posted that before..that's why I think Beans are worth the $$..there not only funnel shaped to the end of the heads..the inlet is also a little bigger then stock...i didnt sink 5k to get more air and fuel just to step back a little by saving on a $200 part.I'm not going to mod on a budget....i want every thing to balance out for long life...
I'm still not sold on the oring..I guess (i never worked on one) the 6.0 & 6.4 have them..and im sure the 6.0 is not a good example.. but i got rid of my fuel bowl..feed lines and now turbo just to get away from leaking orings that get hard and not seal or just plain rot away from being parked long period of times...ill bet if you could find a 94 sitting in the scrap yard them glued on plenums will still be air tight...

 

[Breaking Habits]

Good thread Kyle. Subscribed

 

[Hotrodtractor]

Plenum volume is key in a lot of aspects of performance that we care about. Flow rate is also important, but only in the respect that we want to limit our flow restrictions to the valves if at all possible (hard in some circumstances on the 7.3 because of the intake runner design).

 

[Worstenemy453]

I definitely understand volume, running out of air that flows at 200 cfm is definitely worse then having plenty of air at 200 cfm.

I have just seen a lot about flowing better and wonder why it seems a lot of emphasis on it.

I know a good reason to upgrade is the make the area where the boot goes more stable so you can clamp a boot tighter.

I know i started this conversation in another thread but i figure it might deserve its own thread.

EDIT: I am not saying dont upgrade plenums, because even if flow isnt a concern they obviously have there pluses, i just want to see more of the other pluses talked about and want to see why flow alone seems to be the selling point.

I wouldnt mind seeing dyno results with a stock head/stock plenum, stock head/upgraded plenum, ported head/stock plenum and a ported head/upgraded plenum. Would be nice for consumers to see some dyno numbers too with the different designs of plenums.

 

[Big Bore]

The billet plenums have a couple advantages other than flow, mainly they allow serious clamping pressure for high boost situations that would crush stockers, and they allow e99 and OBS guys to upgrade intake size. I know there are inserts but IMO that creates a restriction. I think the bigger intakes also complement a cam and flowed heads.

 

[Old OutLaw]

I think it boils down to : Do you want it "Hard" to get 300 CFM in there? or "Easy" to get 300 CFM in there....... if it's easy , you will have less restriction, but more volume at the same pressure ?...... I don't know, but the engineers went to 3 inch plenums on the later 7.3's for a reason I figger......

 

[OSCS]

If volume is such an issue with these and there is "gain" to be had with volumized plenums than why does WOP run completely flat plenums on there drag truck? Turbo charged engines are pressurized we are forcing air into the manifold not pulling it. IMHO I don't think it makes one bit of a difference. I bought the ones you cant talk about with the magical o rings over beans.. If the o ring idea happens to be a bust I'll throw some good ole RTV in its place and call it George.

 

[Powerstroked162]

If volume is such an issue with these and there is "gain" to be had with volumized plenums than why does WOP run completely flat plenums on there drag truck? Turbo charged engines are pressurized we are forcing air into the manifold not pulling it. IMHO I don't think it makes one bit of a difference. I bought the ones you cant talk about with the magical o rings over beans.. If the o ring idea happens to be a bust I'll throw some good ole RTV in its place and call it George.

There's no difference between the two designs in performance. You'll be fine

 

[squeak12]

There is definitely gains to be had by tuning the intake through runner length versus plenum volume, but I don't have any clue what the relative gain would be. Also, the tuning will only be applicable to a single RPM value. Yes, you are forcing the air in, but when the valves open, choked flow occurs which will send pressure waves back into the system. Pretty much what Charles mentioned. Tuning this, simply involves manipulating the length of the system to optimize this phenomena at a given RPM. I think it is more of an advantage on non forced induction engines, but I imagine it still helps on forced induction, but as mentioned earlier, I'm not sure of how much.

If you are truly interested in reading more do some google searching on helmholtz resonator/resonance and choked flow through valves.

http://www.brighthub.com/engineering/mechanical/articles/84316.aspx

 

[Worstenemy453]

If volume is such an issue with these and there is "gain" to be had with volumized plenums than why does WOP run completely flat plenums on there drag truck? Turbo charged engines are pressurized we are forcing air into the manifold not pulling it. IMHO I don't think it makes one bit of a difference. I bought the ones you cant talk about with the magical o rings over beans.. If the o ring idea happens to be a bust I'll throw some good ole RTV in its place and call it George.

There's no difference between the two designs in performance. You'll be fine

This is why i started this thread. I feel the same way but i wanted to have a logical discussion about it and get more input.

 

[Woodnthings]

I'm still not sold on the oring..I guess (i never worked on one) the 6.0 & 6.4 have them..and im sure the 6.0 is not a good example.. but i got rid of my fuel bowl..feed lines and now turbo just to get away from leaking orings that get hard and not seal or just plain rot away from being parked long period of times...ill bet if you could find a 94 sitting in the scrap yard them glued on plenums will still be air tight...

Fluorocarbon (Viton®) o-rings have an unlimited shelf life. The materials used in fabricating o-rings varies and that can lead to them lasting or not. If you are worried about them degrading you should also worry about the ones in the pedestal and turbo flanges. Those are standard AS568 Viton o-rings and they can fail too. Any seal has the opportunity to degrade over time, even the RTV That is used to seal the OEM or aftermarket plenums can and does breakdown over time. I was pretty shocked at how easy my plenums were to remove with very little surface cleaning required on the head when I installed billet plenums.

O-rings are normally used anywhere there is a machined part interface where the part fits as close to perfect as it can. RTV is normally used where you have inferior part interface, like the OEM plenums, oil pans and such. Stamped steel does not provide the near perfect surface that machined parts do. Neither does cast aluminum unless it is machined afterwards. That is the biggest reason that o-rings can be used in this application over RTV that makes a mess. If you are a die-hard RTV fan, you could always remove the o-ring and then the o-ring groove machined into the plenum would make a nice channel for the RTV to squeeze into making a good seal too.

 

[CSIPSD]

I installed the reinforcing inserts about 2 years ago or more... Run T bolts without springs and crank them down tight. Never blown a boot there, only at the turbo and thats at over 50psi...

Dont see a need to change something thats not broken.

 

[PatriotHauling]

Plenum

I don't see the argument here. Upgrading your plenum size isnt going to make more air go into the heads. Your turbo pushes air. The air HAS to go somewhere. Unless the air reaches a restriction so great that it can overcome the force of exhaust gasses compressing the incoming air, then no air will stall until it gets to the head and then the valves. The only difference I see in the plenum designs (stock vs larger) is the pressure at which the air enters the head.

Example: flow 300cfm through a 1" diameter tube. It will flow at X psi. Flow the same 300cfm air through 2" diameter tube and it will flow at X/2 psi. No less air flowed, only at a different pressure between two points.

That's not to say I don't like the Riffraff plenums (I assume there are others, just haven't looked), I just don't think flow has anything to do with it. Just like how changing your rear diff oil to synthetic will improve MPGs.. To me the pluses of these aftermarket products is looks, quality, and strength.


Sent from my iPhone

 

[OSCS]

There's no difference between the two designs in performance. You'll be fine

Lets try and follow along here.... That's exactly what I just said in my original post..

Fact of the matter is that our stock heads flow like crap. Before anyone goes about making flow gains with different plenums, the heads need to be addressed first