TPI question

[Mathius]

I have a question about the TPI injection manifold. I'm trying to understand the air flow. Some day I would like to fab my own plenum, even if its for no other reason than making my car unique. But I digress...

If I look at the design... the air comes in the front of the plenum, and then goes through a series of chambers leading to the runners, which funnels the air down into the lower manifold and into the heads.



But it seems to me that if the air is coming in the front, then naturally the rear cylinders are going to get less air. (5-8).

Is this somehow compensated somewhere else, or does it just not matter if you get even airflow across the inlet chambers on the heads? Or have I just got it all wrong?

Mathius

[GetMore]

IIRC, there are not a series of chambers, the plenum is wide open.
I believe there is a slight decrease in pressure available at the rear of the plenum, but not much.
Something else to keep in mind is that as teh air flows over the front runners it will decrease pressure to them due to the venturi effect.

There is a lot going on in a plenum!

The ram air effect is something else to take into account. When an intake valve opens it decreases the pressure in the intake, and therefore the other runners. Now air comes in from the throttle body to "refill" the plenum. Then the intake valve closes, causing an increase in pressure in the plenum. If the plenum and runners are tuned properly this increase corresponds with the opening of another intake valve, and coupled with the inertia of the air flowing in through the throttle body, it will force more air into the cylinder than the piston is pulling in.
All of this helps feed each runner approximately the same amount of air.

It is easy enough to make your own plenum, but to make it work at peak efficiency takes a lot of calculation. (I need to find out how to do that as well.)

[Dust87ss]

Drop an email to [email protected] and I'll email you a .pdf that I found somewhere explaining how an intake is tuned.

[Mathius]

IIRC, there are not a series of chambers, the plenum is wide open.
I believe there is a slight decrease in pressure available at the rear of the plenum, but not much.
Something else to keep in mind is that as teh air flows over the front runners it will decrease pressure to them due to the venturi effect.

There is a lot going on in a plenum!

The ram air effect is something else to take into account. When an intake valve opens it decreases the pressure in the intake, and therefore the other runners. Now air comes in from the throttle body to "refill" the plenum. Then the intake valve closes, causing an increase in pressure in the plenum. If the plenum and runners are tuned properly this increase corresponds with the opening of another intake valve, and coupled with the inertia of the air flowing in through the throttle body, it will force more air into the cylinder than the piston is pulling in.
All of this helps feed each runner approximately the same amount of air.

It is easy enough to make your own plenum, but to make it work at peak efficiency takes a lot of calculation. (I need to find out how to do that as well.)

Yeah, the fabrication side seems simple, it's the design that I know next to little about. Also, for some odd reason getting the injectors in the right location seems intimidating to me for some odd reason.

I'm an apprentice tinner and a lot of home HVAC duct uses the same plenum theory you mentioned, just a big box with lines coming off of it. I don't know if I'll ever learn the different ways to make the most efficient airflow method, or if that's a specialization of the trade, but I'm trying to apply a little of what I know in hopes that it helps.

Mathius

[vetteoz]

I have a question about the TPI injection manifold. I'm trying to understand the air flow. Some day I would like to fab my own plenum, even if its for no other reason than making my car unique.

If you are modding for performance then the plenum is the least of your worries.
Stock TPI is rev restricted based on the size of the runners; they can not move enough air to support revs.Will rev to 5500 but peak power at 4500.
That is why the aftermarket has big tube runners and big port bases.
For all out performance the Mini ram has 3 1/2"runners v the 9" of the TPI.
However the TPI (stock or modified ) will out torque anything down low.
The LT1 with better heads and short runner intake made 55Hp more than a L98 but less torque.