[longhorn_669]

I was wondering what the difference is bettween a tuned port injection and a throttle body.

[ahowudoin]

Tune port has 8 injectors and tbi looks like a carb and has 2 injectors.

[ClarkRU]

TBI came on some of the 305 camaros. Pretty weak setup. TPI came on 305s and 350s and came in HP ranging from 220-245.

Howudoin nailed the description, but here's some pictures


This is the TPI




A TBI will look similar to this with the air cleaner removed.

[duckthetruck]

didnt the late model 454 trucks have TBI????

[JimM]

Lots of vehicles used TBI back then. There was a 1 barrel version used on many small 4 cylinder cars, and a 2 2bbl versions used on many large and small V8's and V6's.

Currently, Holley sells lots of TBI stuff. you can retrofit the commander 950 controller, and even the wide band O2 option, to GM TBI cars. They also have a 670 cfm 2 barrel throttle body that is a bolt on on any car or truck that came with TBI.

They also have a 4 BBL retrofit system in 700 and 900 cfm versions, out the door brand new for about $1400 complete with everything but fuel lines.

One big but not really important difference is port injection system such as TPI are high pressure, 50-90 psi, while TBI systems are only 14 psi.

The other big difference is that TBI injects the fuel at the throttle body, above the throttle plate. The manifold is still "wet" and is subject to all the same mixture atomization and distribution issues that a carb'd setup could have.

Port injection systems inject the fuel right at each intake port in the head. The manifold flows only air, and mixture distribution is as good as the injectors. "Flow tested" injectors are available in the fatermarket to ensure proper mixture distribution.

As far as electronics and sensors, they are the same.

Due mostly to budget, I will soon be fitting my car with a holley commander 950 900 cfm 4 bbl tpi. I've found one used and good at a price I can afford.

I'm going to get this discussion moved to the efi forum.