TBI conversion
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
TBI or TPI conversion is very similar. Both can use stock accessories, both require adding electric fuel pump, computer, wiring, oxygen sensor, etc. With TPI units as inexpensive as they are these days, I see no reason to go TBI. However, if you want to go this direction, I suggest a TBI unit from a van. The early ones (around '90) have an almost stand alone harness and the ECM is under the seat so you have a decently long harness. Same ECM for 305 and 350 but you would want a 350 PROM to be closer for a fuel map. Pretty much a bolt-on expect all TBI are centerbolt head style so you have to slot the holes for early heads. TPI on the other hand, if you use a Vette intake, have the correct bolt pattern. Again, with the cost of the parts, I can't see why you would choose TBI over TPI. Either way if you have a 78-82 I would use an 82 sending unit in the tank with the appropriate pump for TPI or TBI. Paragon is reproducing them now I believe.
Melting Slicks
Joined: Jun 2005
Posts: 2,938
Likes: 2
From: Arkansas
1. TPI costs a little more to set-up, your dealing with 8 injectors (9 if you have cold start) versus just two with TBI.
2. TPI is a little harder to troubleshoot, especially if you have vacuum leaks and a faulty injector. You can look right into the throttle body of a TBI system and visually see if the injector is working....you can't with TPI.
3. TBI accepts the stock air cleaner and can look factory to the unsuspecting eye.
4. TPI looks cooler, but your pretty much limited to a K&N air filter that bolts on the throttle body and get's pretty noisy. And if you do a 1989 or earlier with mass flow....it get's a little more complicated.
They both have their advantages
Having done TPI already, if I were to do another car....especially old muscle and wanted something really reliable and easy to mess with, I would go TBI.
2. TPI is a little harder to troubleshoot, especially if you have vacuum leaks and a faulty injector. You can look right into the throttle body of a TBI system and visually see if the injector is working....you can't with TPI.
3. TBI accepts the stock air cleaner and can look factory to the unsuspecting eye.
4. TPI looks cooler, but your pretty much limited to a K&N air filter that bolts on the throttle body and get's pretty noisy. And if you do a 1989 or earlier with mass flow....it get's a little more complicated.
They both have their advantages
Having done TPI already, if I were to do another car....especially old muscle and wanted something really reliable and easy to mess with, I would go TBI.
Le Mans Master
Joined: Aug 2003
Posts: 7,720
Likes: 12
From: Chattanooga TN
1. TPI costs a little more to set-up, your dealing with 8 injectors (9 if you have cold start) versus just two with TBI.
How so? Harness is about the same price especially if you use an F-body TPI harness or make one from a '90-91 3.1 Corsica or Cavalier and add 2 injector leads. I would set it up speed density, especially on a stock bottom end. Now I will grant you that TBI dos not have VATS so you will need a custom PROM for TPI, but you would need one anyway if you get rid of EGR or canister purge.
2. TPI is a little harder to troubleshoot, especially if you have vacuum leaks and a faulty injector. You can look right into the throttle body of a TBI system and visually see if the injector is working....you can't with TPI.
Don't know how to respond to this. TPI is a bit more complicated system and has more parts to take apart, but not that bad once you do it a few times. With a good GM shop manual, either can be sucessfully diagnosed with minimal effort.
3. TBI accepts the stock air cleaner and can look factory to the unsuspecting eye.
True the air cleaner is stock appearing, but TPI looks cooler
4. TPI looks cooler, but your pretty much limited to a K&N air filter that bolts on the throttle body and get's pretty noisy. And if you do a 1989 or earlier with mass flow....it get's a little more complicated.
There are some who have used cold air; Mrvette, patslsvette and others. There is a current thread on this very topic. I have the k&n and I don't consider mine noisy. Whether you use the k&N or have a standard air cleaner TBI you are still pulling in underhood air so there is no real disadvantage to either IMHO. The TPI can use cold air with mods. Again, I would go Speed density regardless of the year TPI setup.
They both have their advantages
Agree
Having done TPI already, if I were to do another car....especially old muscle and wanted something really reliable and easy to mess with, I would go TBI.
I don't see TPI as any less relaible or harder to mess with than TBI. Performance parts-intakes, injectors, runners, throttle bodies...- are much more available for TPI than TBI. Custom PROMs are more readily available for TPI.
All I'm saying is that the extra torque and mileage you should get from TPI is worth the small extra cost IMHO.
How so? Harness is about the same price especially if you use an F-body TPI harness or make one from a '90-91 3.1 Corsica or Cavalier and add 2 injector leads. I would set it up speed density, especially on a stock bottom end. Now I will grant you that TBI dos not have VATS so you will need a custom PROM for TPI, but you would need one anyway if you get rid of EGR or canister purge.
2. TPI is a little harder to troubleshoot, especially if you have vacuum leaks and a faulty injector. You can look right into the throttle body of a TBI system and visually see if the injector is working....you can't with TPI.
Don't know how to respond to this. TPI is a bit more complicated system and has more parts to take apart, but not that bad once you do it a few times. With a good GM shop manual, either can be sucessfully diagnosed with minimal effort.
3. TBI accepts the stock air cleaner and can look factory to the unsuspecting eye.
True the air cleaner is stock appearing, but TPI looks cooler
4. TPI looks cooler, but your pretty much limited to a K&N air filter that bolts on the throttle body and get's pretty noisy. And if you do a 1989 or earlier with mass flow....it get's a little more complicated.
There are some who have used cold air; Mrvette, patslsvette and others. There is a current thread on this very topic. I have the k&n and I don't consider mine noisy. Whether you use the k&N or have a standard air cleaner TBI you are still pulling in underhood air so there is no real disadvantage to either IMHO. The TPI can use cold air with mods. Again, I would go Speed density regardless of the year TPI setup.
They both have their advantages
Agree
Having done TPI already, if I were to do another car....especially old muscle and wanted something really reliable and easy to mess with, I would go TBI.
I don't see TPI as any less relaible or harder to mess with than TBI. Performance parts-intakes, injectors, runners, throttle bodies...- are much more available for TPI than TBI. Custom PROMs are more readily available for TPI.
All I'm saying is that the extra torque and mileage you should get from TPI is worth the small extra cost IMHO.
