TPI vs EFI

[THORIN]

I was in a thread about getting better millage. Someone said they installed a TPI (tuned port injection) someone an EFI (electrnic fuel injection). I didn't want to steal the thread so here goes with a seperate one. What is the difference between the two and if I were to put one or the other on my 76 with a 350 220 hp engine, which one would be more likely to increase my gas milage? Just to clarify millage isn't the only reason I want to get rid of the carburator. I have tried to look up the answer in other places; but I need a simple easy to understand explanation. Thanks.

 

[JohnZ]

Lots of semantics involved with that definition. TPI (Tuned Port Injection), which was used on Corvettes from '85-up, had a central plenum with a front air intake through a throttle body, individual air runners to each intake port, and an electronic injector in each port, spraying at the back side of each intake valve. The plenum and port runners were "dry", as they only handled air.

Other Chevy products of the era used TBI (Throttle Body Injection), which essentially substituted a pair of electronic injectors in a throttle body for the carburetor, and the injectors sprayed fuel into the incoming air charge, which then traveled through a conventional intake manifold to get to the intake ports - the inside of the manifold was "wet", as it had both fuel and air going through it. The '82 and '84 Corvette used this system, with two throttle bodies ("Cross-Fire Injection").

Technically, both types are "EFI" (Electronic Fuel Injection), although the TBI system was regarded as "a poor man's fuel injection system", as it mixed air and fuel at the air intake and thus still suffered from the same kind of mixture distribution and varying charge density issues (due to the "wet" intake) as a carbureted car.

 

[LT4man]

Several different vendors manufacture EFI systems which you can bolt on to your Vette. Holley & Accel come to mind. I believe Edelbrock also makes a system.

The systems are expensive but I believe the benefits far outweigh the cost.

Ease of cold start-up, smoother idling, more responsive & better mileage due to better fuel atomization are just some that come to mind.

Bling effect is also very high!

I have seen some of these set-ups in person and they do work as advertised.

SAVE THE

 

[KANE]

I was in a thread about getting better millage. Someone said they installed a TPI (tuned port injection) someone an EFI (electrnic fuel injection). I didn't want to steal the thread so here goes with a seperate one. What is the difference between the two and if I were to put one or the other on my 76 with a 350 220 hp engine, which one would be more likely to increase my gas milage? Just to clarify millage isn't the only reason I want to get rid of the carburator. I have tried to look up the answer in other places; but I need a simple easy to understand explanation. Thanks.

Like apples are fruits, TPI is an EFI.

I have TPI-

This is TBI- specifically, the Crossfire Fuel Injection system...

More common GM TBI-

They all have pluses such as the ease of start-up, more precise fuel metering capabilities under various atmospheric, and more consistent operations under temperature changes.


I began tuning and modifying EFI 14 years ago. It is more expensive in the beginning, but its reliability and ease of maintenance once it is set up and initially tuned outweighs the cost. I also do all my own work (sans burning chips). If you do the work yourself the coast is simply parts. However, you can easily double that figure if someone else does the work.

I prefer TPI to carbs, but I am also a minority on this.

Swapping to EFI isn't rocket science... it is really simple.... provided you educate yourself and learn about how it works! If you go in blind you'll fail. You need to make the effort to research the swap.

Below is a great link to one of the best books that explains GM EFI

http://books.google.com/books?id=9w...tune+and+modify+gm&source=gbs_summary_s&cad=0


This one is okay... the process maps for EFI troubleshooting are the best-

This one is a great resource for part numbers- fuel rails, intakes, runners, plenums, etc

 

[THORIN]

Thanks for all the imput, that helps to clarify things. But is one system considered better than the other. I would imagine that the TBI would be better; but alson more expensive to purchase and install.

 

[KANE]

Thanks for all the input, that helps to clarify things. But is one system considered better than the other. I would imagine that the TBI would be better; but also more expensive to purchase and install.

I think for all out performance, then a dry runner system like TPI, Stealth Ram, Mini Ram, Super Ram, converted LT1 intake or any other port fuel injection system that utilizes an injector for each cylinder is the way to go. However- the cost is much, much higher for one of these systems. Typically, these cost around $2k or so and then you'd still need various parts to be complete. Granted, I have built TPI systems for almost half that- but it takes a significant amount of scavenging through the internet, ebay, and various parts suppliers to do it for the $1,300 or so that I've come up with.

Moving on... TBI is great for a daily driver or if nostalgia is an issue. Typically, a TBI system can hide under a carburetor bonnet and look more or less like the OEM carb it is replacing. GM did use TBI for 82/84. These systems produce a lot of torque and the seat-of-the-pants ride is fabulous. It does have limitations to RPM and maximum horsepower.

All in all, I'd say that bone stock TPI is better than TBI in terms of potential- but it may not be as flexible as after market TBIs like Holley or as advanced as Edelbrock port fuel injection. A GM TBI is almost a take-off part from what you can get at a salvage yard and can be acquired for less money.

Below is the Holley Commander 950 system. As you can see, it looks like a carb but has 4 injectors and comes the with just about every conceivable part you'd need to go from start to finish- including tuning software. The kit costs around $1,600 though

So, there you have it.

GM TBI is the cheapest swap followed by some after market systems (low end to mid range cost) and then by GM TPI and then by after market port EFI systems.

Whatever you chose... don't overestimate the purpose against the cost. In other words, don't spend more than you need for what you want to accomplish.

Here is what I'd consider-

• If you want to drag race or road race a highly competitive car with EFI... then go with an after market system like the Edelbrock Pro-Flow XT. You need a motor that makes between 350hp+ to really support this type of expense.
• If you want to install it yourself and don't want to have to rush out and buy additional parts, then go with a stand-alone after market TBI. These systems are good for 200-400hp.
• If you like a challenge, don't mind making frequent trips to the parts store, then custom install a GM TPI or or mid-range port fuel injection system. These are for systems that are between 200-400hp.