matt91rs

so i just bought my car (91 rs 305 tbi) i happen to have a tpi from an 87 iroc. i have the manifold, runners, plenum, throttle body, fuel rails (camaro not vette) and injectors as well as the harness, computer and maf sensor. my wuestions are

1) what do i need to complete the swap?

2) is it california legal?

and 3) is it worth it for the power gain?

giszo

As far as I know the TBI and TPI cars had different VSS sensors on the transmission. One more thing you have to figure out before the swap.

InjectorsPlus

iTrader: (1)

There will be no power gain. So if that is why you are doing it you're wasting your time.

Test after test after test demonstrates that there is no power gain between Carbs, TBI, MPI, or SMPI in terms of power.

I have a customer who switched from a carb to MPI it took him 14 dyno runs on the same dyno the same day, to match the power of his carb. 620+ RWHP.

What you get with FI, of any stripe, are easier starts, smoother acceleration, and more reliability.

EFI allows you to tune the bottom end as it does not depend on engine vacuum to control the fuel delivery, hence allowing to run a slightly more aggressive cam over a carb.

Bottom line is that if you are switching for power, its not going to happen.

anesthes

iTrader: (12)

There is a number of reasons a person might want to swap.

EFI and CARB, both supplying the same AFR and airflow will make the same power.

But in each system there couldbe limitations. Stock '746 ECM's (TBI) in an fbody are RPM limitted. Stock TBI throttle bodies are flow limitted. Stick a stock l03 throttle body on your 420 or whatever you built for your vette and tell me how much power it makes.


I've built all 3, in fact I've ran more types of EFI intakes than most people. You are 100% correct, they all cam make the same power. But stock TBI is very limitting. It's not apples to apples.

Now, if you want to compare apples to apples, compare a 4-injector holley TBI complete with holley ecm, to say a speed demon 850 carb..

We were talking 600hp motors right ?

-- Joe

InjectorsPlus

iTrader: (1)

Joe, no arguments on any of that I'm just saying if POWER is the primary factor, there may be other considerations.

Keeping the ECU and such and swapping TBs are you say is one of them.

I'm just sayin, the OP may have more options if power is the desired result.

Just trying to make his life easier/cheaper by using some of his existing infrastructure and trying to build around that.

Either way, up to him. Just throwing it out there for consideration.

Do you know Gary? "BIG G" on the forums, his car is the one I refer.

tonys91rs

iTrader: (17)

im actually curious about this as well. I have a 91 305 tbiand a 92 305 tpi speed density set up including harness and ecm. i wanted to do the switch more because i want a tpi. ive done some research and saw somewhere what all is needed to do the conversion. but i dont remember where i saw it.
ive planned this conversion since last winter, and will be home to start it. i also have an 88 vert that was a tpi and was carb converted by previous owner. i also have an 88 set up to switch that back.

91RS5speed

You wont pickup a lot of horsepower but you will get tons of torque. When I swapped mine it picked up about 10rwhp and 40rwtq.

G-reg

iTrader: (3)

A couple parts you didn't mention that you'll need are gaskets for the TPI setup, fuel feed and return lines, a longer throttle cable, and an intake or air filter for the end of the throttle body. One of the fuel lines (I can't remember which one) is no longer available, I ended up using braided stainless lines for both of them.

InjectorsPlus

iTrader: (1)

As a result of the intake swap, not the fuel delivery. Swap in a better TBI intake....problem solved.

Again, not pitching for either way, just trying to keep expectations straight.

John 89 Formula

The bulkhead connector on the 87 harness will not match up with the firewall conn on the car it will need to be repinned, it will fit the connector but all the wires are in the wrong places.
another option would be to have the existing tbi harness converted to tpi.

anesthes

iTrader: (12)

A Performer RPM with a 4150 flange TBI would spank any TPI intake hands down.

TBI in a stock fbody application has a few limitations, the intake being one, throttle body flow being another, and them the ECM being the ultimate limitation. (and not very functional either).


One of the biggest benefits to a "TPI" swap is swapping to a better, faster ECM with more control, extended RPM ranges, etc.. Another option is a modified ECM from dynamic EFI.

However, I would never in a million years recommend someone swap in an actual FACTORY TPI intake manifold..

-- Joe

InjectorsPlus

iTrader: (1)

RIGHT. Just depends on budget, desired results, and amount of work....

matt91rs

Wow lots of replies, i'll try to answer questions to me as best as i can. here's why i want to do this:
i already own the parts previously stated (i.e. ecu, harness [maf style], manifold etc.
I love the tpi look, I've read in several places that the factory tpi equipped cars made more power that the tbi
I want to see if I can do it
this cars my daily driver i want a little more power but reliability is worth more to me.
Switching to carb is not an option because i need to smog this car
getting ahold of parts in no problem to me

is there a tech article about this anywhere? i can't find one lol

anesthes

iTrader: (12)

If you search under my name I wrote a tech article a number of years ago about re-pinning your car to a '730 speed density TPI ecm. It is the fastest and most direct way to go multiport. I'd skip the MAF, really, you don't want that. Sell that harness you have along with the ECU.

Doing it with the replacement harness, and ECU is 20 times harder.. trust me..

-- Joe

jsleeper81

I'm new to a lot of this but this is somthing that I thought about.
reason being is power but seems like every one is saying there will be no power gain.
Correct me if I'm wrong though according to all the hp and tq. specs I have found says that the 305 tbi has 170 hp 255 tq. and for the 305 tpi it says 220-230 hp and 290-300 tq.
the numbers seemed signifantly different this is why I considered it so is the block and heads different is this why there will not be this kind of power gain.

Dector22

I have this same scenario. I'm not sure if the question got answered. I have a '91 RS, no engine (had been L03, 305, TBI), no transmission, no exhaust, no drive train. I do have a donor '87 (LB9, 305, TPI) with transmission, exhaust, drive train, Limited slip. In my initial research, it looks like I cannot use an older engine on my '91 here in California. My question is if it is the same block and similar engine and it is rebuilt as new can it be smog legal? Everywhere I look where someone asks about an engine swap, people will respond with encouraging LS swaps or LT1 swaps or something else. I want to keep this as low budget as possible and use what I have. Please someone point me in the right direction and/or give me hope that I can use what I have. Also, if I can use what I have, what is required regarding wiring harness and the computer?

gwarren007

iTrader: (1)

Block the deck and restamp

Dector22

Dector22

Can I use the same wiring harness from the 1991 Camaro RS (L03, TBI) for the 1987 Blue Z28 (LB9, TPI) engine?

anesthes

iTrader: (12)

You want to take the whole harness from a 91 TBI and install it in your 87 TPI ?

-- Joe

Dector22

I'm restoring the '91 former TBI. The '87 is just supplying the LB9 TPI engine (engine has junkyard writing on bottom "85 Camaro"), transmission (A4), drive train and LSD diff. They both have wiring harnesses. The '91 has a computer, the '87 does not have a computer. I'd love to be able to use the existing wiring harness and computer in the '91. I'm in California so also not sure of any smog issues.

anesthes

iTrader: (12)

OK. You can use the stock harness on the '91 and repin it to use a '730 ECM. (TPI).

As far as the smog legalities, I'm not sure. My understanding is that using the 87 engine in the '91 is illegal, but others may have better info. I have not had to deal with emissions requirements in over 15 years in this part of the country.

-- Joe

Dector22

Joe,
Thank you for the input. What if I were to use the block but purchase a TBI fuel injection system and take the TPI system off of the engine? Then I'd be re-creating the L03 that was originally in the '91. I realize when doing engine swaps, the L03 is not desirable but I am doing a project with my 11 year old and we've got years to work on it and I'd like to do it for as little as possible. If he wants to later put a beefier engine in.. fine. He doesn't need anything beefy now.

-- Dave

dmccain

iTrader: (2)

You can get plenty of power out of your TBI system already in place. No need in re-inventing the wheel. I swapped over to a 350 and upgraded my TBI system and it makes plenty of power. No longer out of breath at 4500 RPMs it pulls good to 5200-5500 now.

Dector22

So my '91 RS does not have an engine in it (L03 was original). The '87 Z28 has the LB9 with TPI. I'm wondering if I can use the block from the LB9 and find a TBI intake somewhere and make that engine work for my '91 RS.