The new SuperChevy has a BOATLOAD of information on TPI engines / intakes. What cars came with which intakes, plenums, runners, rails, injectors and regulators. I found it EXTREMELY informative, specially seeings how I'm still new in the injection world. What I found interesting was the following, keeping in mind that the zz4 motor in my camaro has the stock TPI and starts falling on its face around 4500RPM.

"As an example, single-plane Edelbrock Victor Jr. style intake manifold which is the standard bearer on a hopped up small block has a runner length of approximately 6". In contrast, a TPI has a nearly 25" long runner. Engine RPM and thus horsepower is limited with a stock length TPI because the air path is too long to fill the cylinders at high engine speeds. When this occurs the VE of the engine drops off and so does power."

Now, with this in mind... aren't SLP and most other aftermarket runners, larger? (ie. ported) Thus, making it even HARDER to fill the runners at higher engine speeds, yet most of you guys are getting noticeable power increase with just new runners and a plenum!

This article was about the Holley Stealth Ram intake.

So, does anyone agree with this? As nice as a setup as the Stealth Ram intake would be, it's quite pricey and I'd like to figure out a way to get this motor to breathe over 4500, the motor pulls hard, and I know it has plenty of potential up to 6K. Any suggestions as to what else I might be able to do to get this thing to rev higher, (keeping it injected).
Sorry about the long post.

 

Remember, larger diameter runners will flow more air. Yes, the runners are long and restrictive, but if you increase the size of the "hose", you'll get more air through it. Think of a 10 foot long garden hose and a 10 foot long firehose. Which one flows better? Once you understand that example, you'll have your answer.

The reason a TPI falls over "dead" at 4500 or so RPM is a combination of runner length and diameter. You simply can't move enough air through that system. At idle a motor only fills the cylinders, say, 10%, at peak torque it may be 80% or more (up to about 105 to 110% on a well tuned race motor). So, at low rpm, the intake works great, it is only a problem as rpm and therefore airflow increases. The reason a TPI makes great torque is that it fills the cylinders very well at "mid rpm". The reason for this is...another hose comparison.

When you have water running out of a hose, the more water you move, the faster it goes. It has inertia. If you have a hose turned on full blast and pinch the hose off quickly, the last water out of that hose keeps going at "high speed". The airflow in a TPI system does much the same thing. Since it is near it's flow capacity at medium rpm, the air velocity is very high. This air keeps filling the cylinder even as the piston may be coming back up the bore. Just before the pressure in the cylinder is great enough to begin to push air out of the bore, the valve closes. This traps "extra" air in the cylinder which burns "extra" fuel. This makes "extra" torque. The penalty is that after a certain velocity, airflow in an intake tapers off. In a TPI system this is about 4500 to 5000 rpm. So, the only way to increase flow is to make "more room" for air. This is what a large runner setup does. It will trade velocity (and torque) for flow at high rpm. Remember, there is no free lunch.

For reference, LT1 cars have a runner length of about 3-5 inches (I can't remember the exact spec right now, but I'm sure someone will post it soon) and LS1 cars have a runner length of about 9 inches.

Have fun!

 

WOW...he knows his stuff!!!

 

ok, i was misunderstanding the article, from what I got.. i thought the runners had SO MUCH room for air, that at high RPMs the motor had trouble filling the runners, therefore bogging the motor, whereas its the opposite? It wants more room for air?

 

Correct. It needs more cross sectional room. It needs to be larger in diameter. It is not the volume, but the shape of the runner that is the "problem", it is thin and long, instead of short and fat. Just like the difference in the size of the hoses, the runners are different as well.

The TPI is like a fat man running down the street, breathing through a drinking straw. You just can't get enough air through that small tube.

 

I feel much smarter after reading this thread.

This is some good stuff.

Nick

 

There is another article in Camaro Performers about TPI that also gives a lot of info. I was just wondering how much more HP that the Holley StealthRam will produce. Any info will help.

 

In the article I read, the bolt on produced 53hp and 64-ft lbs. over the STOCK TPI. @ 5600RPM (beyond the stocker's potential) the Stealth Ram showed a 98HP jump!

The motor that was used was a 355, with a GM hotcam, high flow aftermarket runners on the stock TPI along with 1 5/8" headers and catback system.

 

the indentifying tpi article is a recycled one from fastlanes. here's the original article.

choosing a tpi

they just changed the opening paragrah.

 

i just picked it up today. havent read it yet i can only read while in the bathroom. i spend 45 mins in the bathroom so i read. lmao sorry for the ifno but its my library

 

The "Tuned" part of 'Tuned Port Injection' is designed to capture whats known as the second harmonic pressure wave as it travels down the runner towards the intake valve at high speed. The inertial force actually mildy 'supercharges' the engine at its sweet spot in the RPM band. At peak torque, this pressure wave arrives just as the intake valve begins to open. VE is highest at peak torque, so the TPI engines are very efficient but only in a narrow RPM band. Fortunately, this narrow RPM band happens to be where our cars spend the majority of their time operating at, which makes the TPI cars a lot of fun in the low and midrange. As Trackbird mentioned, however, as RPM's rise above the resonant tuning of the TPI intake (past 4800RPM) there simply is not enough time to properly fill the cylinders due to the long runner length.

Effective runner length from plenum to intake valve:

TPI: 21.5"

LT1: 5"

LS1: 14"

I remember when I bought my L98 GTA, and during the test drive off a used car lot I simply could not get over how much rubber the thing would slap down. It would burn right into 2nd gear on the upshift (left in 'D') which frankly shocked the crap out of me. I thought the car had some mods done to it, but I've since learned its completely stock. That tire burning ability comes courtesy of our TPI induction.

The TPI intake would have worked fantastic in a truck application.

 

Your right about that.. i didnt realize i can get the plenum and manifold for a mere $300. I was looking at the kit for EVERYTHING!! Which leads me to my next question.. can i use the stock fuel rail?.. or can i use the fuel rail out of an LT1 motor so that the regulator is on the opposite side, and i think those regulators are adjustable too no? Correct me if im wrong.

 

Which is exactly why I'm building a mild TPI 350 for my Jeep.