73duster

hey guys, i'm new to the world of chevy. I just purchased a 91 z28 with the 5.7 tpi and 700r4 setup. I'd like to know what's involved with swapping the tpi for a carburated 383 smallblock. especially when it comes to the wiring harness. Also how difficult is it and is it better to pull the motor and tranny as one unit? The wiring is much more complicated looking than what i'm used to. Thanks

five7kid

iTrader: (14)

Welcome aboard thirdgen.org.

All of the computer (ECM) harnessing and sensors can be removed as one piece. The computer harness is the big bundle that goes to the passenger side fender well. There is a plastic fender liner to remove, then you can unplug the harness at the pass-through to the passenger compartment. The wiring you need for gages, ignition, etc., are part of the harness that goes through the firewall on the driver's side.

The exception to this is the transmission torque converter clutch lock-up - it's part of the ECM harness, and you need that if you drive on the highway.

It would be better, IMO, to just upgrade the TPI to a Holley/Weiand Stealth Ram intake manifold. It'll handle a 383 fine. You'll retain the advantages of EFI, including torque converter clutch lock-up, with none of the disadvantages of carb. Since yours is a '91, it has speed density EFI, which is more sensitive to changes like displacement and flow than mass air flow, and will require computer tuning. But, that's no more complicated than converting to carb.

73duster

i thought about it, but i'm leaning towards a carbed 383. From what i've read in this forum, I don't see any tpi engines making decent power. What i mean is 400 hp and 450 ft lbs daily driven. It seems difficult and way too costly, not to mention carbed motors are simpler to operate and diagnose. I would love to run fuel injection, but it'll cost double to get it done. I've tried researching for more on the tpi setups and although i'd like to keep the benefits of tpi, it's just too costly and involved. I'm more familiar with dropping in a crate. I don't see any options like a crate that i could drop in and use the harness thats already in the car. Then i have to worry about tuning issues and ecu's.

blp226

Well I got good news for you. Your stock TPI will handle 400HP, you just need to get a cam ground for it, and then tune the ECM. I built my 383 specifically to go in my TPI vette. COMP ground one specifically for it. With my heads, rotating assymbly, and valvetrain, COMP assured me it would make over 400, their estimate was 420 to 430 at the crank. Of course it makes more in my camaro with a carb and intake, but it your goal is 400 then it will make that plus more torque with a TPI than with a carb! And get way better gas mileage. And you could always trick out the TPI. Edelbrock makes intake, runners, and throttlebodies, then your power output will get even better. Take your time and do it right. I did what your suggesting and I seriously regret it. You'll be happier in the long run. Trust me I would kill to have mine fuel injected!

SpeedMetalT/A

To convert your car from TPI to carb you'll have to do a few things

1. Get a fuel pressure regulator to turn the pressure down for the carb. Or get a mechanical fuel pump if you still have the block off plate in the block for a mechanical fuel pump and do something about the electric one.
2. You'll need an old style vacuum advance hei distributor and connectors for the coil b/c the current distributor gets its inputs for advance from the computer and if you just swapped to a carb you would have no advance in timing.
3. For the overdrive on the 700R4 you can buy a switch from jegs or summit to activate the overdrive instead of the computer.

If you do this and just lay the harness to the side everything else such as your gages and fans will work as they should and you will have that annoying SES light on though. Thats all I can think or for right now but I think thats everything.