Sorry if it has been asked a million times over to death... I know i should search but... Really... what is the main Difference between a 350TPI and TBI... HP... TQ... mileage?... How is one better than the other, and vise versa how is one worse then the other...?

This area confuses me abit... Thanks!

 

TBI - Throttle Body Injection. Basically a "wet" flow set-up like carb. Uses injectors in the throttle body above the throttle blades.

TPI - Tuned Port Injection. A "dry" flow set-up in that the fuel is injected right at the intake port entry into the head, rather than flowing through the intake track with the air. The air intake runners to each port are "tuned" so that the pulses arrive at the intake valve as the valve opens, creating a ram effect into the cylinder. The factory tuned the runner length to provide good torque with the effect of limiting the effective RPM powerband of the system.

TBI is less expensive to produce, was used as the "entry level" V8 system to meet both the EPA emissions requirement and CAFE fuel economy requirements. TPI is also clean burning and reasonably fuel efficient, but was used on engines that made more power and therefore wasn't quite as efficient.

The TBI concept was used by Holley and others to make a stand-alone electronic fuel injection conversion system, so it's not fundamentally "bad". But, neither the factory nor aftermarket optimized the factory TBI system for performance.

 

So if Im wanting good performance, get a TPI 350 than?

 

Are you looking for a car, or do you have one already?

 

WOW what a load of crap.

If the TBI had the head flow or the cam of the TPI it would eat it alive. TBI is just a Carb with fuel injectors and can produce just as much HP as TPI and have a much higher redline. As for stock the 305 TBI has a boat anchor for a top end that leave it choking at 4400 but if you took the TPI set up off and replaced it with a TBI intake and TB it would be faster and produce more power through out the rpm range.

The bigest difference between TBI and TPI is that it is significantly cheaper to hip 400hp with a TBI setup than it is for a TPI. Also I will say the TPI has the TBI beat on one thing and that is that its really pretty and complicated sorta like a supermodel but most of those don't know how to cook but atleast you have a looker.

I don't hate it but I think it is over rated because of the sabotage that was done against the TBI and the V6. If GM had given the TBI and V6 a respectable set of heads and a intake that can flow worth a damn it would be a different story. With people finding the 2.8/3.1 making 170+ hp and the TBI making around 300hp with minimal work. If you like the looks and have the money and want to go with some boost it will be far easier with the TPI than to deal with tuning the TBI.

 

Really? What part?

I didn't get into head and cam differences because the question was about the differences between TBI and TPI, not the differences between LO3 and LB9/L98. Those differences (heads, cam, exhaust) are pretty thoroughly discussed here on the Board. Since the follow-up question broadened the topic, then we could go further into the differences - but a would accomplish the same thing.

I also thought I was pretty clear that the TBI system was not optimized for performance by the factory. Even so, a dry EFI system has definite advantages over a wet system; perhaps not peak HP if each is optimized, but certainly over a broader RPM range. As for which is cheaper to get power out of, a TPI Holley/Weiand Stealth Ram is cheaper than aftermarket base/runners, and will out-do both the base/runner upgrade and TBI.

 

Like the nerd in school that studies all the time. I took up this hobby about 2 years ago and spend about 20 hours a week studying various aspects of the automotive industry.

Just what is the difference in TBI and TPI? five7kid said it correct to a point. TBI does exist on top of the intake manifold. Similar to a Carb. the air is atomized and enters the intake manifold where it is drown into the the cylinders by the downward stroke of the crank. A very good system- much better than carb. The reason for being better is the computer controlled aspect. The downside is that you can’t simply tighten a few screws to dump more fuel and air. Being computer controlled it is more difficult to make it perform without tuning ability. The TBI system is very efficient vrs. carb.

What makes the TPI better? It is very simple. Five7kid said and is correct that the injector is placed directly in the intake port so the fuel is dumped into the cylinder directly when the valve opens. This is correct. five7kid went wrong at the point of why this is important. Simply dumping the fuel into the cylinder doesn’t explain why it is better. Instead lets think about this for a minute. Fuel itself is not flammable. So dumping fuel into the cylinder does nothing for burning the fuel. Fuel vapors are however. As a result the fuel is dumped back into the intake runner enough to mix with air or to atomize and become flammable. The only engine that dumps fuel into the cylinder directly is the diesel engine. The fuel in a diesel engine is not ignited by spark but rather compression of the the fuel.

So what does make TPI better? Simply consistency. Because the fuel is delivered into each intake runner; each cylinder is delivered an equal about of fuel. Therefore engine load is spread equally to each cylinder. Making the engine a much more efficient and powerful engine.

In a TBI setup (Which I have); the fuel is delivered to a central chamber of the intake manifold and is distributed to the cylinders by suction which is inconsistent. in a complete crank turn- 4 cylinders might have put out greater power than the remaining 4.

Hope this makes sense.

Resource used for this answer: Motor Automotive Technology Third Edition. ASE Certified Text Book.

 

Thanks for the info. And I wasn't trying to start a war *hides* I was just curious the differences and what not.

I have a car im looking at that has a 305, and was wanting to at some point do a 350 conversion. I'm not asking how to do one, I've read afew things on that. I was just curious the fundimental differences of the TPI and TBI, and yea I want it to go fast. I was basically gonna look for a TPI but I've read alot of people using the TBI and was just curious like I said. and Im not for sure but from how it was stated above, the TPI would get abit better mileage cuz it's more even than just dumping it. Though when I start putting go fast parts on it that probably won't really matter.

But I got the answers I was looking for, so Thanks people! BE HAPPY, MERRY HOLIDAYS!

 

If this is true, please explain how my father and I took a stock 1992 Camaro RS with the 305 TBI engine, and a 2.75" stock L98 cat-back, and made 158 RWHP and 220 RWTQ. Then we swapped the TBI intake and computer to a stock TPI intake and computer, and made 178 RWHP and 290 RWTQ. The heads and cam were the stock TBI parts.

TBI will eat TPI alive? I dont think so. For one, you're limited to 2 injectors, which is barely enough for 300 horsepower, let alone 400.

Lastly, there are a hell of a lot more 350 TPI engines running 12's on this board. There are very few 350 TBI engines running even 13's.

 

Running in the 12's is much more than simply an induction concern. I agree that TPI is better than TBI with all parts being equal. However don't sell TBI short- Our cars was not he only, first, or last to use TBI. It does lack a great deal in performance in our cars. The principle of TBI is very open and you can do alot with it. Total horsepower is a culmination of many things. The induction vehicle on top of the motor is simply a fuel source. A very important factor- but simply one of many factors. Friction robs your motor of horsepower much more than the the induction does. What about weight! Running in the 12s takes much more than a simple TBI to TPI swap.

 

That isn't what I said.

And, again, I wasn't getting into the nitty-gritty details of how the systems work, just the basics.

Give it a break, people. The OP asked a simple question, and you're trying to give him a rocket science answer.