Hey guys.

This summer, I wanted to experiment with a TPI plenum to see if I could get any gains out of the stock plenum.

Basically, I see two main flaws with the TPI design, in terms of high RPM power:

1: Runner length. 25+" is the total distance air has to travel before it gets into the combustion chamber, and the runners do not help with this. It's a real pitfall with upper RPMs. A simple way to deal with this is to get a set of SLP, Accel, or Edelbrock runners. I won't be touching on this issue for now.

2: The fact that once air enters the plenum, it has to make a direct 90 degree turn in order to enter the runner. There is no "guiding in" of the air, and this harsh angle greatly disrupts airflow in my opinion. I think that most of the airflow relies on the plenum to first become pressurized, and since that air has nowhere to go but left or right, it finally makes up its mind and makes that sharp turn. This disruption causes a bottle neck in the airflow process, causing the engine to choke at higher RPMS.

I have an idea for problem #2, and I have made a mockup in PTC Pro/Desktop, an engineering modeling program that I acquired from my college. This is strictly a model so I could visualize it, so no measurements are to the T, the runner entries aren't offset, and some flaws need to be banged out. I basically would just like input for now, and ideas on how to optimize this idea. When I finish up school (in a week or so), I will look into this more accurately and more in depth.









The main problem I see now, is an imbalance of airflow to the front runners. As it stands, the first two runners could get anywhere from 25-40% of the airflow coming from each throttle body hole, starving the rear runners. I also realize that the runners are grouped in pairs, so the design for the scoops would have to be thought out with some finesse. Maybe I can have one scoop for each set of runners. I think this design would be more ideal.

I would go about the process of adding the fins, by picking up a spare plenum from a junkyard and cutting it along the back, sides, and front into two halves, and opening it like a sandwich. I would then measure out and fab up the fins and weld them into place, and maybe applying some RTV to the top so that it makes a nice seal when the top goes back on. The seams would then be welded back up. I understand that I would be losing about 1/16th of material where the cut was made, so I would probably take some off of the top and bottom of the runner holes while I had the plenum apart to get a round shape again.

I think that with some testing, and combined with a set of SLP runners, this design has the potential to make some extra horsepower.



Let me know what you guys think, or what you would like to see me experiment with. I'm just a college engineer on a budget looking to put his engineering expertise into action.

 

Nice idea. I like the concept. However, I have to agree about the front runners recieving more airflow than the rears. Perhaps if there was a way to stagger the fins inside the plenum. Another thought is since the runners are paired up (and some runners are siamesed), there could be less fins. About modifying the fins, my thinking is that the front set of fins be smaller/shorter in the front. Another idea is to increase the plenum area which it looks like you give up by taking up the area in the rear. My 2 pennies.

 

Good thoughts, but you need to analyze a bit further. Your diagrams depict a system that might assist airflow a bit at peak RPM, but would likely be a penalty at lower RPM. The "fins" or "directors" installed in the plenum actually create a series of "mini-plenumus" between each pair of fins within the entire plenum. The reversion impulses that are normally allowed to dissipate within the plenum would be directed toward the throttle body. I'm not certain how that would affect airflow intoe each runner, but I suspect it would not be good, especially for the rear pairs of runners since the effects may be somewhat additive. In effect, the concept simply reduces the total plenum volume and lengthens the runners even more.

At peak RPM, the flow to the rearmost runners may be obstructed a bit, and actually cause a rich condition in the rear two holes. That may be counteracted a bit by altering the design of the foils, but care would have to be taken to keep them all the same efective length otherwise the net runner/tract lengths woudl be different for each pair of cylinders. That would create other problems at various RPMs.

But don't stop there. Experimentation and revisiting the concepts used in the intake are what will yield some improvements. The idea may have merit if it is tweaked to resolve some of the potential issues.

This is what I was describing:

 

Cool idea. If you're worried about air restriction then I say just fab up 8 throttle bodies- one for each cylinder! Haha.

 

That is almost exactly how I pictured the staggering in my head, you are dead on there. I think the reversion pulses you are describing that would come towards the throttle body would be essentially jammed further back into the rear of the plenum, and not even make it close to the throttle body, but I see what you are saying.

As for paying for low rpm power, doesnt every aftermarket intake do this to an extent anyhow? You lose somewhere along the lines of 30tq or hp...or maybe both at low rpms with the HSR if memory serves correct.


That would be bitchin'. It'd be like trip-deuces, but better...octa-sings...lol.

 

I think besides the reversion issues Vader brought up, you are going to find your peaks going don the rpm band. I think you are going to find that mod is going to just increase effective runner length.

On top of that, the TPI plenum is on the small side and you are, as Vader mentioned, making 8 little plenums fed by a tiny main plenum now.

Then there will be the turbulance issue as it's being fed by a dual bore throttle body rather than a monoblade. I would think on opening up the front and converting over to a mustang monoblade throttle body. That would give you a bit more main plenum volume and lessen the turbulance issue.

But, as mentioned, you won't know any of that for sure until you test.

 

I think your theory #2 is a bit flawed.

Think of it this way - an exhaust header doesn't quite flow well backwards. Bell mouth intakes with a nice size open plenum would flow much better, when air flow is being drawn in by pulses. Your design would still have lot of air turning back in from the rear, creating a flow separation on those walls you put in, effectively reducing the size of the inlet.

If I were making something from the factory setup, I'd:
A) Cut off the flange on the top of the runners
B) Bell mouth each runner
C) Make a large two piece plenum that sandwichs the runners with a rubber seal (on the round part, not the bells, let the bells stick inside the plenum).
D) Attach TB and IAT to a convenient locations.

 

Woot for fin pwnage Vader. Thats kinda what i imagined and then i saw it... apparently a a good number here of us think alike.

Having that plenuum big and hollow is the best way it can be. That large area is gonna fill to its maximum pressure (still a vacuum if ur n/a) and serve as one large volume feeding all those runners. The eddy currents will adjust themselvs inside the open space as the pressure drops in front of each runner to keep each runner with its highest possible pressure. When the air flows within the intake, in and open area, its gonna stack and manuver the most efficient way possible. Reducing the airs ability to move is not likely to help anything unless it removes some kind of reverb taht creates a high veloctiy turbulent flow or something else crazy(which happens but its difficult to detect sometimes without sophisticated stuff).
Like said before, focus on the runners and throttle body inlets.
Remeber that you cant use more volume than your cam in heads will permit you to get in there.
If you have a short duration motor, reducing runner diameter to increase airvelocity might be worth some power.
With a long duration you might be able to up the diameter to increase air volume. Without flow bench numbers for your cylinder head and cam profile computations it would be really hard to tune your intake runner size for your setup.
Increasing the volume of the plenuum would provide a larger volume of peak presure air and might be worth some torque under acceleration.

 

Looks like your trying to reinvent the wheel. Lingenfelter already did this and obviously learned shortening the runners and increasing plenum volume was the best solution for tpi.

 

Yeah, I understand that, but like I said, this was just an idea and I wanted to get some input before I actually tested it. I figured this wouldnt work too well based on the fact that companies such as GM, Accel, TPIS, Holley, would have implemented this if it worked.

 

well, whether or not it is feasible, it still makes for an interesting discussion. if you're worried about the front tubes getting more air, make the front "wings" protrude shorter than the rear "wings"

 

It is a very interesting idea, and out of the box, and for that I like it. But I think that the downfall of the TPI's asmhatic problems in the high rpmp's is simply the runner length. I just gutted out my plenum by taking out the two walls just inside the TB holes, and then the walls infront of each runner port. Also you can take out the divider in the runner ports on the plenum. This is really the extent of what you can do for the TPI PLENUM, you can get runners, manifold etc.

 

Maybe I'll toy with this idea, maybe not. Who knows, I can keep the plenum until I get to the dyno and try it out. It would be interesting to see what happens.

 

In reality the holes on the side of the plenum are staggered and not directly across from each other. You would have to make your own runners to make them even. Like was posted above I believe the best solution is to make one big plenum including most of the runners. That is in fact what 3 of us have already done. This cuts done on the turbulance of the 90 degree turn as there is now one big chamber. Do a search on siamese runners to see what others have done. I like your thinking.

 

Yeah, I already explained that, this was strictly a mockup because I dont have a plenum to get measurements from at my fingertips at the moment.


Thank you though.

 

....you have to remember one thing. The front holes/runners don't really get any more air than the rears. You're talking vaccum. Each cylinder is trying to pull air in. The large, open plenum is where it gets the air, not just the TB. The TB simply allows the air into the plenum, more air/fuel = more rpm.
- I would go with the larger plenum, shorter runner idea myself. That is where the TPI "problem" lies.