sublime7880

i wanted to start planning my summer project. i have a tired and weak 305 tbi. would converting it to a 350 tpi be resonable? or would i be better of rebuilding my 305 and maybe tuning it more towards performance? what about a 350 tbi?

david roush

iTrader: (1)

I am in no means "mr wrench head" but i would say you will be much happier with a 350. 305's motors are more suited for economy than performance ,not saying you can't build up a 305 but it would probably be just as costly and there's alot more you can do with a 350. I wrestled with this question myself awhile back, went with the 350 and definitly i made the right decision. The difference between the two are night and day. So if it is in your budget i'de go with the 350. But do plenty of reaserch before you decide on the topic ,what you want out of the engine and what you can afford.

pd23braves

hey I am looking to do the same thing. I have an 88 sport coupe with a 305 TBI 5-speed. I found a place by me that sells used complete 350's with TPI for $750. As soon as I have enough money I am doing it. It is definetly worth it to me, for I am going to make this 88 SC of fime into an IROC look alike. When I go to sell it I think the investment will pay off, for even though it is not a real IROC people will definetly like the 350 with a speed. I have looked into it and from what everyone has told me it isn't hard to do, when I get a little closer to it I can give you more details, or possibly you can do that for me if you beat me to the job. But I just think that if you are going to put in a new engine, do the complete changeover to TPI.

sublime7880

i have looked into a tpi change over and basically found out that it is expensive as hell and a pain in the a** several people on the board have told me that if i want a tpi i should just buy a car with a tpi already on it. i dont want to get rid of my car therfore i think im going to go with a 350 with a tbi.

speedracer

first off from a 305 to a 350 you have to move your motor mounts forward abit i don't have the number off the top of my head right now but it is about an inch. then it depends of weither you go from carb to tbi or tpi then you have to worry about getting all the appropiate things to get it to run right. The whole thing about price for swapping vs buying an 8. i look at it this way. it might be a bit more expensive and if you build your motor or get a rebuild motor at least you know what it been through plus for that little extra cash you get to add stuff to the engine while its not in the car vs taking the motor out modding it then reinstalling it.

hotrod

Tas

go for a 350 or 383 and keep TBI. Put a single plane intake on it or the Holley TBI intake with the bigger 2" bore TBI

David Petersen

I have swapped a 305 TBI to a 350 TPI, but I also had a wrecked donner car to pull everything from, I swapped the entire dash beacsue I found it eaiser than trying to figure out wiring. I would go with a 350 but as stated before woud stay with TBI or go carbed unless you have a donner car or resourses.

sublime7880

yeah im thinking the 350 tbi sounds pretty good. i dont have a donor car to work with. also this way i could work on my 350 and still have use of my car... i wont have to drive around in my wifes mazda........when i swap to a 350 what else will i have to swap?
i can think of a few of hand, is there anything im forgeting?
ECM
convert to dual fans
does holley make a TBI replacment for our cars? (ive seen them for trucks)


Thanks again for all your help!!!

David Petersen

The mechanical stuff pretty much swapped over, the tranny matched right up just dont forget the shaft bushing if you have a manual tranny, I aslo upgraded a few things to take the higer tourqe, sub frame connectors especally if you have T tops, new motor mounts etc, I also went through the brakes to make sure they were in good shape to stop the faster car, little did I know I would have to test them soon after the prodject was running, locked them up with only 6 inches to spare wheewww! I would spend a little itme with the rear end too, at least "boxing" off the panhand rod if not replacing it with the tubular one. I don't know about the intake manifold, and bigger injectors. Sounds like a good prodject.

david roush

iTrader: (1)

I can tell you this, when you switch over from the 305 to the 350 ,if you use the tbi system off of your 305 the car will still run good but it will fall flat on it's face around 3500 to 4000 rpm's. The injectors in the throttle body are smaller, if you look at the part numbers from the 305 to a 350 capri they are two different numbers, so you might want to swith to a different throttle body in the long run. As for being a pain i am sure it is but my neighbor did it and he said when he changed over to a 350 from a 305 it was a big difference but when he went from tbi to tpi the differance was like night and day. I am definitly putting mine on........someday.

Duzzit

i want to do the same swap but i can't get ANYONE to tell me what all is involved in it. i have a '88 camaro with a 305 tbi and want to replace it with a '90 model 350 tpi from an iroc that only has 70 something thousand miles on it. could someone...ANYONE who truly knows please let me know. i'm hoping to use a wiring harness from painless wiring...this has to be a start and i already know that i have to use the ecm from a doner car too.
thanx,Duzzit

sbrice18fan

I will be doing the 305 TBI to 350 TPI at the end of the month and can let you know what problems I run into after I'm finished. This project can be very expensive if you start buying aftermarket parts like myself. If you have a donor car and just swap it all, it would be much easier. I had the most trouble finding the block and harness. Scoggin-Dickey has new 350 hydrollic roller, one piece rear main seal blocks for a very reasonable price. I also bought a GM harness from Dal Lambert Chevy. If you surch the boards you'll find that most people did not like the painless harness. It seemed like the biggest complaint was that the harness was not long enough for all connections. Take a look at the Tech article on the tbi to tpi swap.

ir0cz

you DO NOT want to run a 350 and keep the 305 TBI. That's what I'm running right now. I bought a GM 350 that's rated at 220 HP, put it in place of my 305, but kept the 305 TBI. It runs great, but the TBI setup is holding me back (cause it's from a 305, not cause it's TBI). As far as HP mods, I have headers, no cat, flowmaster, open K&N element, Hypertech chip, ported throttle shaft, MSD wires, underdrive crank pulley, and a bunch of cooling mods. I ran my car on the Gtech the other day, and the best I could do was 230 HP (at the crank). Do you think all those mods are only worth 10 HP? NO! The motor is rated at 220 HP w/ a 350 TBI setup, and with me running a 305 TBI setup, it's killing my HP. So if you want 350 power, do it right the first time. If you do wanna stick w/ a TBI setup, which would get a lot cheaper, get a 350 TB and computer from a truck or 9C1 caprice.

Tas

a 350 TB and 305 are the same. only the injectors are different.

91banditt2

iTrader: (1)

dmair5_0

HeHe Bandit, good call! Move the motor mounts forward on a 350, thats the stupidist thing I have ever heard...... get your facts straight man! And with a change to a Holley 670cfm TB unit, you will get the same power from TBI as you will from TPI, TPI HOLD YOU BACK TOO!!!!

91banditt2

iTrader: (1)

that i do agree with!:rockon:
if you take the time to build your own motor or have some one build it for you you'll know what has been done to it.

piece of mind is priceless

and as allways:rockon:

ir0cz

When I say not to use a 305 TBI setup, i'm talkin mainly bout the computer.

jmd

iTrader: (4)

No, they are in the exact same spot

Sublime, your car's year makes a difference. Last time I looked at 91 wiring schematic, TBI and TPI wiring harnesses plugged right into the dash wiring the same ways, so a SD swap in a 90-92 would be simple.

Since your car is setup for EFI already, you will need to change the fuel pump, but the lines already in the car will work.

Seriously the cheapest and easiest way to do it is w/ a donor. If you can trust the yard to throw in all the harness and bits that you will need, you'll be ahead of the game.

ir0cz

Why if he has EFI already does he need a new fuel pump? I have '89 TBI and am about to switch to '88 TPI MAF, will i need a pump?

91banditt2

iTrader: (1)

if your switching from TBI to TPI you will need to get a different fuel pump.
TBI runs on 12-15lbs of pressure
TPI runs on 42-50ishlbs of pressure
so the pump you have in the tank will not be enough to supply the TPI with enough pressure.

Tas

then you get a Caprice 350 chip and knock sesor. the comptuer is the same. The chip is different. You want him to get Another TBI computer? :nono: just the chip

ausrs

i pulled the 305 this weekend from my 91 RS ...am installing a MAF 350 tpi ..an amazing amount of wiring goes into these cars ....kinda looks like an octopus has taken over my car

Joez88Camaro

BIG QUESTION:
So I don't have to curse at changing the fuel lines
WILL STOCK FUEL LINES WORK??
I know you gotta change the pump to get TPI but what about the actual steel main lines? I don't want to deal with pulling those bitches out and would like to know what people who've done the swap did. I would figure that you wouldn't have to.

David Petersen

I used the same fuel lines with no problems.

Snowdog 91 Formula

In my opinion, he should stick with TBI....
Get something like the motor I have.
Makes one HUGE difference!
:hail:

91banditt2

iTrader: (1)

i have heard that in 90 GM went with a 3/8 fuel line for both the TBI's and the TPI's.of course i haven't confermed this

PonyBabe

My I ask what Bti is?

Jza

quote:
--------------------------------------------------------------------------------
Originally posted by ir0cz


When I say not to use a 305 TBI setup, i'm talkin mainly bout the computer.
--------------------------------------------------------------------------------

Or could switch to the 7747...

pd23braves

do you mean TBI? throttle body injection... if bti I don't know what it is you are talking about.

Snowdog 91 Formula

First off...
If he is going from 305 TBI to 350 TBI there are a few things he needs to do:
Intake should be replaced. The 305 unit is way too restrictive for the air/fuel. I don't believe the 305 intake would fit anyway.
(At least replace the intake manifold! You can use the stock throttle body, but the Holley 502-6 is a high recommendation!)
Knock Sensor for the 350.
Stock chip will work fine. No need to play with the ECM unless you get into a radical camshaft.

Going from 305 TBI to 350 TPI...
This is a whole different story.
I believe the entire wiring harness has to be replaced.
You have to change the chip over to the TPI chip. (Not sure about the ECM)
Fuel pump has to be changed for the fuel system, plus the fuel lines have to be altered to fit to the TPI throttle body. You might want to rob some fuel lines off a donor vehicle. (Guess about the fuel lines, no flames.)
You may even need the entire cluster from a TPI car. I am not sure if the cluster is the same or not.

I don't know, but I think the easiest and more flexible thing to do is to go with TBI. You will have electronic fuel injection, plus all the flexibility.

With TPI you are kind of restricted to what you can really change. It's expensive too.

It's your money. That is the bottom line. TPI is very expensive to change over to unless you can obtain all the parts from a donor vehicle.

Look into what I have done along with others on the TBI board. I know I am extremely happy with what I have. Even so, it did cost quite a bit with what I did, but it would have cost me more to get less with TPI.

My .02

knoxbonnie

What kind of horsepower are you getting with your 91 Formlua? I have a 90 Formula I want to do the same thing with, with the exception of going with the Edelbrock TBI Intake. I probably wont start mine until I finish with the suspension though.....

Also, are any of you guys running the T5? Any problems with it handling the extra power?

Snowdog 91 Formula

I am guessing around 310 HP with all I have. It might be more or less. That's about all I wanted to do with mine. There are others that go even further than I do, but they are more serious. It's an excellent driver, and I love it.
I still have more to do. The rear-end gears I want to have done right the first time. I may even keep the 2.73's and just put posi in. (I am leaning toward 3.42's but I also want the speedo to be correct as well.) The car has power.
I always hear about the 1/4 mile, and I want to take it to the track, but I believe with my setup I'm not going to get spectactular numbers, possibly high 14's or low 15's.
I am realistic.
Even so, it's a lot better than "just a muffler". I've literally come close to double the horsepower that the car originally had. I'm happy, and that's what counts!

knoxbonnie

Thanks, I just wanted to make certain the TBI would take me to around 300 RWHP and handle it well. I am not going to get radicle with mine either, I just want it to be fun....