If you are looking to convert your car from a 305 TPI to a 350 TPI setup, then you should find the information below rather useful. These are all the needed changes to do the conversion.
First of all, the TPI intakes (manifold, plenum, fuel rails, throttle body, runners) were exactly the same between 305 and 350 engines of the same year. There were no differences in these parts whatsoever between one engine size and the other during any year (there were however differences between the intake manifold and fuel rails between the Camaros and Corvettes). For example, a 1987 intake was the same for both a 305 and 350. Please note that this does not mean all intakes are the same throughout the years, there are differences between a 1987 intake and a 1992 intake for example.
All your belt driven accessories, brackets, exhaust, etc... will transer over from the 305 to the 350 without any problems. Once you install the TPI intake on the larger engine, you will need to note the following items that need to be changed. These are the only things you will need to change or worry about to properly convert to a 350:
Injectors
The size of the injectors was a very important difference between 305 and 350 applications. ALL 305 TPI engines came from the factory with 19 lb injectors. ALL 350 TPI engines came from the factory with 22 lb injectors. The Corvettes did not have injectors any larger than the Camaro, as I have people often asking. If you want to use 19 lb injectors on a 350, or 22 lb injectors on a 305, you can, but you MUST have the injector size in the PROM changed. Otherwise, you will run into fueling problems.
Knock Sensor
The knock sensor physically looks the same between the 305 and 350 version, but they do are not the same. This is very important, and should not be overlooked. The knock sensor is responsible for detecting detonation. Detonation produces a specific frequency that travels through the engine block. This frequency is different depending on engine size. In addition, it is important to note that the 350 knock sensors were different between the 85-89 TPI setups and the 90-92 TPI setups. You must use the correct one for your application. The 305 knock sensors were also different between 85-89 and 90-92.
ESC Module
The 85-89 TPI setups used an external ESC module which was mounted by the firewall. This module was different between 305 and 350 engines. Changing this is as simple as disconnecting the 305 module, and plugging in a 350 module. The 90-92 TPI setups did not have an external ESC module. Instead, the ESC circuitry is contained inside the PROM. For this and several other reasons, it is important that you use the correct prom for the engine size you are using.
ECM
Although there were several different ECMs used depending on what year TPI setup you have, the same ECM was used for 305 and 350 engines for a given year. The difference between the engines was the prom. In other words, the 86-89 350 TPI engines used the 1227165 ECM, and so did the 86-89 305 TPI engines. The 90-92 350 TPI F-Body engines (Camaro and Firebird) used the 1227730 ECM, and so did the 90-92 305 TPI engines. The 1985 305 TPI engines used 1226870 ECM, which is the same as the 1985 350 TPI ECM (350 was only available on the Corvette in 1985).
The Corvette used the 1227727 ECM on the 90-91 350 TPI engines. Although the Corvette was never available with a 305, the 1227727 ECM can be used on a 305 if desired.
PROM
This is probably the most important change that needs to be made. Regardless of what ECM you are using, the 305 prom is setup very differently from a 350 prom. Which prom you need will depend on what ECM you use, transmission type, engine size, and a few other details. Contact us if you need help finding the correct PROM for your application.
If you have a 90-92 ECM, and you are having your PROM reprogrammed, you must start with a PROM that was originally for a 350. The 90-92 PROMs have the ESC circuitry onboard, and that cannot be changed.
The 85-89 PROMs can be changed from one engine size to another without worrying about ESC within the PROM, since the module is external on those years.

Originally Posted by T-rock Here is all the info you need.Troc 305 TPI to 350 TPI Conversion If you are looking to convert your car from a 305 TPI to a 350 TPI setup, then you should find the information below rather useful. These are all the needed changes to do the conversion. First of all, the TPI intakes (manifold, plenum, fuel rails, throttle body, runners) were exactly the same between 305 and 350 engines of the same year. There were no differences in these parts whatsoever between one engine size and the other during any year (there were however differences between the intake manifold and fuel rails between the Camaros and Corvettes). For example, a 1987 intake was the same for both a 305 and 350. Please note that this does not mean all intakes are the same throughout the years, there are differences between a 1987 intake and a 1992 intake for example. All your belt driven accessories, brackets, exhaust, etc... will transer over from the 305 to the 350 without any problems. Once you install the TPI intake on the larger engine, you will need to note the following items that need to be changed. These are the only things you will need to change or worry about to properly convert to a 350: Injectors The size of the injectors was a very important difference between 305 and 350 applications. ALL 305 TPI engines came from the factory with 19 lb injectors. ALL 350 TPI engines came from the factory with 22 lb injectors. The Corvettes did not have injectors any larger than the Camaro, as I have people often asking. If you want to use 19 lb injectors on a 350, or 22 lb injectors on a 305, you can, but you MUST have the injector size in the PROM changed. Otherwise, you will run into fueling problems. Knock Sensor The knock sensor physically looks the same between the 305 and 350 version, but they do are not the same. This is very important, and should not be overlooked. The knock sensor is responsible for detecting detonation. Detonation produces a specific frequency that travels through the engine block. This frequency is different depending on engine size. In addition, it is important to note that the 350 knock sensors were different between the 85-89 TPI setups and the 90-92 TPI setups. You must use the correct one for your application. The 305 knock sensors were also different between 85-89 and 90-92. ESC Module The 85-89 TPI setups used an external ESC module which was mounted by the firewall. This module was different between 305 and 350 engines. Changing this is as simple as disconnecting the 305 module, and plugging in a 350 module. The 90-92 TPI setups did not have an external ESC module. Instead, the ESC circuitry is contained inside the PROM. For this and several other reasons, it is important that you use the correct prom for the engine size you are using. ECM Although there were several different ECMs used depending on what year TPI setup you have, the same ECM was used for 305 and 350 engines for a given year. The difference between the engines was the prom. In other words, the 86-89 350 TPI engines used the 1227165 ECM, and so did the 86-89 305 TPI engines. The 90-92 350 TPI F-Body engines (Camaro and Firebird) used the 1227730 ECM, and so did the 90-92 305 TPI engines. The 1985 305 TPI engines used 1226870 ECM, which is the same as the 1985 350 TPI ECM (350 was only available on the Corvette in 1985). The Corvette used the 1227727 ECM on the 90-91 350 TPI engines. Although the Corvette was never available with a 305, the 1227727 ECM can be used on a 305 if desired. PROM This is probably the most important change that needs to be made. Regardless of what ECM you are using, the 305 prom is setup very differently from a 350 prom. Which prom you need will depend on what ECM you use, transmission type, engine size, and a few other details. Contact us if you need help finding the correct PROM for your application. If you have a 90-92 ECM, and you are having your PROM reprogrammed, you must start with a PROM that was originally for a 350. The 90-92 PROMs have the ESC circuitry onboard, and that cannot be changed. The 85-89 PROMs can be changed from one engine size to another without worrying about ESC within the PROM, since the module is external on those years.

Originally Posted by gregmy123 This was copied from tpiparts.com. Why don't you credit link as your source?

Originally Posted by Chevy86 IROC-Z We are here to help each other out, not attack or insult others.

Originally Posted by 85 ZXX I just finished making my order for a BBK-1534 Throttle body and a new IAC housing. I tried to remove the old housing and broke 5 of the torx head bolts. I got so fed up with the old throttle body, I just chucked it aside. It looked horrible anyway. LOL

Originally Posted by Chevy86 IROC-Z Grab that sucker out of the trash!!!!!! If your gonna throw it away, send it to me.... Ill pay for the shipping!!!!!!

Originally Posted by 85 ZXX Well, I am undecided on what to do with it right now. I have to remove the TPS, IAC and some linkage parts. I tried to remove the IAC housing and its stuck to the throttle body. I hope the BBK works good. I just checked the tracking and it should be here on the 21st. Sometimes it gets so frustrating trying to fix things in 100+ degree weather with high humidity and you have constant setbacks trying to get your ride back on the road. Today I installed an adj fuel pressure reg and two of the six torx screws stripped out. I had to get the Dremmel out and notch them for a flat screwdriver. Get this, nobody around here has these screws. The size is (M 3.5-.6X12). I had to reuse my old ones. This is a bastard size and I may have to tap for the larger M4 screws.

Originally Posted by C305 How badly would it effect a 350tpi engine running a 305tpi chip how much power would you lose

Originally Posted by 85 ZXX Thats hard to say, I have a L98 350 in my 85 Z and when it was installed it still had the TPI ECM 305 with 19lb FI. I've read all about changing knock sensor,ESC module, injectors,adj fuel reg,Prom, Cal pack ect. I did all of that and there wasn't much of a difference to justify the expense. I had a dead injector on #7 cyl that was leaking (19lb) that caused a miss so I upgraded to FIC Bosch III injectors (22lb) and went with a BBK 52mm Throttle body and BBK under drive pulleys. In close, my 350 hauled as* with the 305 ECM and 19lb injectors. Its a little faster now with a 350 Vette ECM with the improvements I made.....maybe 25hp increase. Upgrading to a 350 knock sensor and ESC was a waste of money...there was no noticeable difference.

Originally Posted by Chevy86 IROC-Z Up grading to a 350 knock sensor is a great investment. It will not make any performance better. All that it does is "hear" the different frequencies that a 350 does compaired to a 305 block when it's pinging. If it hears that frequency, it'll tell the ECm to back off on the advance spark know as "spark retard." Im sure that you would love for your engine to last right? You do know the dangers of detonation right? So off hand, its not a waste of money. A waste of money would be leaving in your 305 knock sensor, never notice any detonation, and destroy the block. you dont have to hear it to know that your engine in detonating. Most of the time you'll never hear engine knock.

Originally Posted by 85 ZXX Do you still have the 305 ecm in your Iroc?

Originally Posted by Chevy86 IROC-Z The solution? costs about $50 dollars. So if you have $50 dollars, let me know and I can send you to the right people.

Originally Posted by C305 Those knock sensors are for a 87 tpi 350 will it still work with my 91.