I’ve been searching for a while and I am still confused as I am reading somewhat conflicting information, and this isn’t my first 3rd gen, but it is my first swap.

I recently acquired a 1991 Firebird Formula with a blown 305 tbi motor. 5 speed manual. (T5????) I would like to swap with a 350 tpi. All that is under the hood of the 91 (engine wise) is the bottom of the block all uppers have been parted out.

I want to do this right, and I have some money, but not a lot.

What is my best bet for year range for the 350 to make the swap go the smoothest?

Mounting issues from the 305 to the 350?


I know I will need all the computers and wiring harnesses no matter what engine I go with, but what issues will I have with the 350 in terms of the wiring that’s on the car to begin with?

Exhaust issues? Headers?

Are there any other things that change between the 305 and the 350.

Thanks in advance for your help. I greatly appreciate it.

 

Welcome aboard thirdgen.org.

Engine-wise, you'd want one that is '87-up. Everything will mount/bolt up without issue.

TPI-wise, you'd want a '90-'92. You will need the engine (obviously), the full set of TPI hardware, the TPI harness, sensors, ECM, flexible fuel lines, fuel pump (electric, in the tank), throttle cables, hoses (probably best if bought new), and exhaust. The TBI exhaust will "fit", but it is horribly small and restrictive. Most people just get headers and aftermarket cat & cat-back for the TPI application. Otherwise, the hardware was identical. '90-'92 ECM tuning requires a 350 tune (the 305 tune won't cut it).

If you get the engine and TPI separately, it depends upon the year what issues you'd have. The 305 injectors were smaller than the 350 injectors. Exhaust was the same (although '91-'92 305 could have single cat exhaust, which was the same as TBI exhaust - terrible). The knock sensor may or may not be different.

T5's were only available with 305's, so any 350 you get will need to have a pilot bearing/bushing installed in the crank. If the 350 is '87-up, you won't have a problem putting your 305 flywheel/clutch on it.

Only f-bodies and Vettes got "good" 350's. Truck and Caprice 350's were LO5's with the dreaded swirlport heads. It will "work" with TPI, but the heads will limit upgrades, if you have any planned for the future.

 

Thanks for the info, it means a lot to have some help with this project.

What is all wrapped up in the term TPI hardware?

The flexible fuel lines would be ran from the tank to the motor or just connected to the existing lines??

Since this car has nothing in the engine compartment, I'm thinking a donor would be best? And if this is the case then either way i need a full donor weather i keep it a 305 or go to a 350. Is there any advantages keeping it a 305 besides the pilot bearing/bushing and the exhaust (changing it anyway)

I feel stupid, by f bodies what to you mean?

Just to make sure we are on the same page, besides the engine compartment area, all i need to change is the fuel pump and get a pilot bearing/bushing for the tranny.

 

f-body = Camaro & Firebird. The '82-'92 model years are the "third generation f-bodies".

TPI hardware - the induction system mounted on the engine (base, runners, plenum, throttle body, air filter & inlet ducting, and whatever is attached to them like injectors, fuel rails, EGR valve, etc.).

The flexible lines are the ones going from the chassis hard lines that end in the engine compartment, to the engine.

You will need to change the ECM (Engine Control Module - the computer) in the passenger compartment. The harness that runs from the ECM to the engine compartment will also need to be changed.

A donor car is a good idea. That way you can get whatever you need off of it. It would be best if it was a '91 or '92 model, and if it was a Firebird (rather than a Camaro) of one of those years, even better.

A pilot bearing/bushing was only used with manual transmissions. If a 305 had an automatic behind it, you would need to install a pilot bearing/bushing before installing the clutch & transmission.

The advantages of a 305 are: There are more donor cars with them out there; slightly better fuel economy; possibly lower insurance rates; slightly less likely to break the T5 transmission.

 

Thanks, this is really helpful.

Would I be able to use the pilot bearing/bushing from my current 305?

How well do T5s hold up with a stock L98 motor?

Also, how much should I expect to pay for a 5.7L donor car. I know this varies, but would 1000 for a good running 5.7L tpi be too much? (miles are not too big of a concern if they are freeway and adult driven. )

Thanks a bunch.

 

Just get a new pilot bearing, only around $15. A pilot bushing would be less than $5. Take your pick which you want to use, I prefer bearings, some prefer bushings.

A T5 will hold up fine as long as you don't do high-RPM clutch dumps or try to speed shift it. A '91 would be the stronger "World Class" T5, so that helps a little.

Hard to say what a donor car would cost. $1000 wouldn't be too bad.

 

I'll stick with the T5, this isn't going to be a race car.

What work can I do on my own to besides the fuel pump to get it ready for the motor to reduce garage costs as I don't have the garage space anymore (apartment)

Any Ideas where to look for a donor car, I have picked apart the Midwest on Craigs to no avail. I'm located in the Midwest.

 

You should be able to do everything but stab the engine in the parking lot (depending upon your apartment rules).

Check eBay, racingjunk.com, local ads, the classifieds on this Board, Board sponsor Hawks 3rd Gen.

 

Worry for the absence, i was waiting to pick up the car. The previous owner said it was a 5.0L tpi, even though i'm pretty sure according to the vin number says it was a 5.0L tbi. (verify?)

This brings up some questions form me.

If it is tpi? Can i use the wiring harness with a 5.7L tpi.

It is my understanding the the ecm will work if i get the Prom swapped.

Since I do not know what the car actually had in it, is my only way of checking what motor it had in it to look at the ecm?

What numbers would mean an ECM for tbi or tpi?

Thanks so much, i look forward to being able to move forward once i know what was under the hood.

 

Update:

The Vin for a tbi and the ECM number is from a tbi So it I'm pretty sure it is a tbi. Owner must be wrong. (Is there anyway it wasn't a tbi). The motor that was in there broke because a spark plug "broke" and the inside of the plug took out a cylinder.

This now leaves me with what was said earlier. New everything under the hood if i wanna go tpi. which means donor car.

I really do not wanna keep it tbi as i would like a 350.

Earlier it was said i needed a 87 and up engine with a 90-92 TPI system. I am looking to use a donor car so so this leads me to believe for simplicity get a 90-92 donor car. I am slightly confused because when the donor car was mentioned i was told 91 or 92 firebird would be the best. What is the difference between a donor car form 90 or 91? Please help me as i am finding a one or two cars from 1990?

Thanks for the continued help. It is making this project a lot less frustrating.

 

VIN "E" is 305 TBI. VIN "F" is 305 TPI. VIN "8" is 350 TPI.

305 TPI harness will work on 350 TPI.

In order to be technically legal, the engine/system you put in has to be of the same year or newer than the chassis. Firebird donor will match your Firebird, don't have to worry about differences between Firebird and Camaro.

 

Thanks for the continued help. Im gonna go off the vin and the ecm and say its a tbi. They previous owner must not know what he was talking about. (is there any way it could have been a tpi?)

I am still looking for a donor car. Hopefully one pops up because with the sites you gave me and craigs, the midwest is not being kind to me.

JOSH

 

Only if somebody put it on after the factory delivered the car.

 

So there is a change that it could have had a 305 tpi in it if someone had put one in, even if the ecm is for a tbi?

the ecm has this on it SERV. NO. 1228746. then next line 86 APTY K303410036.

 

Possibly, but not likely. Both TBI and '90-'92 TPI are speed density, but when somebody goes through the trouble of converting they typically get a TPI ECM.

 

Thanks for all your help!!!

I ended up going with a 305 tbi. it was going to be the easiest and cheapest. The 305 was from a 1990 Formula with an Auto.

Good:
Engine is in and all the necessary changes from auto to manual have been made.

Bad:
Engine won't run when it is started unless raw fuel is poured in manually. The shop that is putting the motor in said it is missing the "anti-theft box" from my 1991 Formula i had one from the 1990 that i found on the floor. I believe it is a 16 pin connector. the shop can not find a pigtail anywhere for it.

Any help would be greatly appreciated. PLease help.

Josh

 

https://www.thirdgen.org/vats_passkey_system

If pouring fuel in manually means it runs, it ain't the VATS system.

You've got a fuel delivery issue. Troubleshoot that. A fuel pump going bad after sitting for an extended period is pretty common.

But, make sure the pump is getting power. If it is, drop the tank, replace the pump and pick-up sock, and you should be good to go.

 

the only way they can get it to start is if they bypass the starter... when my dad calls me back i will know more about it.

 

I'm not sure how that fits with your previous description of the problem.

 

ok....i talked to my dad and something is wrong with the anti-theft system. anytime an attempt to start it using the key is made it will not start. the only way it will run is if the electronics are bypassed and it is started manually and having fuel put it manually.

My dad is working with the shop as i am currently out of the state.

the shop putting the motor in asked if we had the antitheft box. (apparently it was missing?) I found some electronic boxes on the floor of the 1990 donor car. the guy a the shop gave my dad a number and it matched one of the numbers on the boxes i found. my dad took it in and i believe it is a 16 pin connector on that box they could not find any such pigtail even after taking the whole dash apart.

Any advice would be appreciated.

Location of the box (drivers side under dash?)
differences between 1990 and 1991.

THe shop hours are getting rather expensive and this is quite confusing. Thanks for all your help.

 

any ideas?

 

any suggestions? This is really confusing me.

 

https://www.thirdgen.org/vats_passkey_system

 

What is standard equipment and what is optional equipment in terms of the VATS or antitheft sytems in these cars. Mine is a 1991 Pontiac Firebird Formula 5.0 L 5 Speed. with a motor from a 1990 Friebird.

My car doesn not have the 16 pin connector for the VATS.

What it does have is spade type female connector with 5 slots? (i believe as the car is not at my home) 3 going one way and 2 going the other way at a 90 degree angle. What could this be for. Its on the left side between the door and steering column.

the dash has been off completly and there have been no signs of any tampering or altering of the stock wiring.

Any suggestions would be wonderful. Thanks

Josh

 

what did you do about the ecm and the prom chip in it ?

 

i did nothing as then engine that went in was a 5.0L TBI just like the original motor. Also, the ECM from the donor car had all the same numbers as the ECM in the recipient car.