i have a 1987 firebird 305carb 700r4... i want to drop in a L98, or at least upgrade the induction system to tpi for power and fuel economy purposes... ive read that it is easy to swap from carb to tpi and have owned a few tpi cars in the past... my concern is wiring this up properly becuase of the electronically controlled carb... i want everything to work, my air condition is in perfect working order as is the air pump... and i want this to be like a stock installation no rigs... i want the guages to work also... by the way i also want to swap in a 145mph speedo from a transam as my car has a 85mph one lol i would like to hear from someone who is knowledgeable about this swap and could give me a complete parts list and brief installation instructions...please pm or email me at rongsays@aol.com thanks so much- Ron G

 

Welcome to the boards Ron,

This swap is really not that difficult, an L98 is a much better choice than the LG4.

The easiest way to make this swap work is to get a TPI wiring harness that is similar to the year of your car. For example:

If your car is 87. and it is a camaro, it will not have a VSS sensor on the transmission. So if you get a harness that has the VSS connector for the transmission, you are kinda screwed, because the ECM relies on the signal for the VSS to run your speedo, transmission lock up, etc. You can swap in a new sensor in your transmission, but then you will have to replace and wire a new cluster.

 

thanks for your input... so if i get a 1987 L98 with everything complete i should be able to theoretically "bolt on and go" ?

 

I did that exact swap, less I kept my original Block...

It took me some time, but with the right car its not a bad swap...

You WILL need to replace your fuel pump, and I actually swapped my dash because the wiring is different for the FI and 4bbl cars behind the dash...

Pretty straight forward, you will learn alot...

Here is a journal of what I did:

The post is too long... go here : http://www.usol.com/~okfoz/modificat...conversion.htm
John

 

TPI is not a "power" upgrade. Low RPM torque, maybe, but not power.

The only way to wire this up properly is to remove all of the carb computer harness & ECM and replace it with the L98 stuff.

Can we assume you're planning on a complete exhaust replacement as well?

A properly tuned L98 under the stock LG4 induction should give you 25 MPG highway without any strain (assuming the exhaust is upgraded). How much is the TPI set-up going to cost you? (Or, how much can you get selling the TPI system if you already have it?) How much of an improvement in MPG will you need over what period of time to just break even?

Understand I am not a TPI hater. I would be making similar comments if you were going the other way. Just wanted to put a little real-life economics into the discussion.

 

I kind of disagree...
When I swapped from the LG4 to LB9, all things being equal I gained about 4mpg. 17mpg to 24 mpg ( I am running a 3.73 gear)

With the LG4, a SLP cam, .040 over 305, 3.73 gear I ran a 15.45 Quarter Mile. After the conversion With the addition of SLP Headers, & cat back I also went from a down to 14.8 in the quarter ( I also did some ECM tuning on the TPI ) In so many ways it was worth the effort. I learned so much about FI that I am not scared of it any more...

John

 

I don't complain about my carb mileage now, but looking back in the book (okay, maybe a little ****, but I keep a little spiral notebook in each vehicle and record the data for each fill-up), my stock LG4 mileage was always in the 20+ MPG commuting range. The one highway trip I took it averaged almost 27. That was with 3.08 (later the current 2.93) gears, running mid-15's sea level in the quarter.

After mods that took another second off the quarter mile times, mileage dropped to about what I'm getting now with the 350, which runs over a second quicker than the 305 ever did. I don't have any doubt that TPI would improve the fuel economy, but I also don't have any doubt that TPI would have a backwards effect on ET.

It's like the discussion that took place in the dominant media about people flying instead of driving over Memorial Day weekend because gas prices were so high - you can still buy a lot of gas for $1000. That's my point.

Again, not a TPI or EFI hater - I just advocate working with the system you've already got. It always works out best that way from an economics standpoint.

Of course, economics to us usually means, "Do I have enough cash/credit for that do-dad I've been wanting?"

 

Since we opened this wound up I figured I'd say my piece.

My car had TPI, I got 12 MPG and always drove it really hard. It ran a 14 second quarter mile.

I removed TPI for a RPM intake and 750 CFM edelbrock carb, Still drive it has hard before. Now I get 14 MPG and run a very low 13 with potential for high 12.

I miss the SES light deal. But I will not turn back.

 

THe thing I really like about TPI is I can tune it for best traction... Unfortuantely it takes alot of tuning to make it spot on. But If I am spinning the tires I can de-tune it until it no longer brakes loose... Unfortunately Pavement and concrete have different traction properties. Although there is more that goes on with FI, and trouble shooting is a bit more complecated, I prefer it over the old 4bbl... I dunno, its me. I guess different strokes for different folks. I do not think I will ever seek out another car with a 4bbl ever again. Drivability is not there for me personally.

John

 

Flippindabird

I did the LG-4 to L-98 swap in my 82 trans am. However I didn't run TPI I went with TBI. If you want help I can tell you everything you will need.

 

so im gonna reopen this thread... if i get a dash from a 1988 friebird that had tp[i then my 1988 tpi will bolt in and go???

 

You have to change:
All of the Emissions stuff.
-The Fuel tank pump... I was able to use my LG4 tank with the LB9 sender & pump.
-The fuel lines, filter,
-The Emissions lines
-The Battery location
-The dash helps a lot, It may be the same for your car and the L98 for the same year. The easiest way to check is look at the plugs on the passenger side where the ECM plugs into the Dash wire harness. If the wire colors are the same for both and in the same order and have the same number of plugs then you should be good to go.
-The wire engine harness obviously..

There are also the little things that you have to change, but that is thebig stuff that I can remember... I will never go back.

 

awesome thanks so much i just talked to "jimsperformance and he basically said the same thing if you can think of anything else that would help please im me, thanks

 

Jproz1167, I also have an 82 TA and about to go into a 350 TPI swap. Any pointers would be great. Thanks!!! I have an 87 TA donor - complete with a 305 TPI. Gonna lift the TPI onto my 350TBI on the engine stand.

 

Keep in mind that the injectors for a 305 & 350 are different... 19# for the 305 & 22# for the 350.

John