Originally Posted by 1project2many (Post 8685219)

Another vote for EFI. The TBI systems are super reliable. They're so good that when a rust belt truck is little more than a pile of rust the owner often laments "It's a shame to junk it. It runs so good!"

I put Crossfire TBI into mine in '94 or '95 and it still runs well.

Originally Posted by Bridgeman57 (Post 8684684)

Putting the harness back together in another truck is what I’m worried about

Originally Posted by MiraclePieCo (Post 8685354)

Do you like dealing with Check Engine lights and a truck that won't run if even ONE sensor fails? Do you like being able to do roadside repairs, or prefer to take it to a shop with sophisticated diagnostic equipment for every little hiccup? Do you like having tons of extra wiring, sensors, and an EFI harness that adds complexity and associated failures? TBI was a pollution solution, had nothing to do with performance. Simplicity is a blessing. I've seen my last Check Engine light. Carbs run no matter what.

Originally Posted by Bridgeman57 (Post 8686142)

Thanks a lot. Going to stick with efi. But the tranny, 4L60 is 2wd. I need to convert it to 4x4. Is it worth doing or just find one that’s 4x4. I would like to just swap with a tb350/400 but idk how that would work with the computer from the 91. Anybody dealt with a newer motor and older tranny?

Originally Posted by joedoh (Post 8685443)

i think you might be a little over dramatic here, your current truck has been broken more times and inert for longer than anything with EFI/OBD I have owned in the last 25 years (which has been zero times, by the way, 3 CPI trucks, 1 SFI truck, 2 TBI trucks, and a daily LQ4 with 180k).

Originally Posted by MiraclePieCo (Post 8686450)

I believe you're thinking of someone else.
And dude, this is a discussion over induction systems - you sure as hell don't need to make it personal.

Originally Posted by joedoh (Post 8686273)

the4l60 in 1991 is not electronic (except the speedo) so there is a kickdown cable on the tbi and a lockup switch that i think runs through your brake wiring. no issues switching it to any other trans EXCEPT a 4l60e, you dont have the controller with your stuff.

needing overdrive is really about your rear gear. if you have a numerically low gear a th350 or th400 will do fine. also, look at your tire size, bigger tires lower gear ratio.

Originally Posted by 1project2many (Post 8685791)

Huh? Sophisticated diagnostic equipment? The ecm on a '91 350 is pretty basic stuff. You can read trouble codes with a paperclip! Most of the diagnostic tests for that ecm are available in "no scan tool available" format which uses a DVOM and simple observation testing to complete a diagnosis. The computers are programmed to run with five sensors (throttle position, coolant temperature, knock sensor, crank rotation, and vehicle speed) and the engine will usually run with any but the crank rotation sensor failed. It sounds like you don't want to learn about computerized systems, but the OBDI vehicles really aren't that bad.

Originally Posted by 1project2many (Post 8686375)

To build on what joedoh said, this was a common swap in the '80s and early '90s. The medium shaft THM 350 and the 700R4 (comon name for non-electronic version of 4L60E) are almost the same length. They use the same output shaft which means you won't have to change the driveshaft or yoke. The shifter for a 700 will fit a 350 (although the gears don't always match up). And generally speaking a stock 350 is more durable than a stock 700. Some differences to note: The 700R4 uses a computer controlled torque converter clutch which is not found on most THM 350/400 transmissions. Disconnecting the tcc can cause the ecm to set trouble codes. The solution is to use a manual transmission calibration or to use a custom chip. The cooler lines are in a slightly different location. The solution is to reshape the lines or replace them. The rear mount is located farther back than the 350 mount. The solution is to fabricate a custom mount or crossmember. The 700 throttle valve cable uses a different geometry at the throttle body attaching point than the thm350 detent cable. The solution is to determine a new pin location and move it on the throttle linkage. And finally the 700 uses a different vehicle speed sensor. To solve this problem you will need to use a two pulse per mile "reed type" VSS and connect it to the "optical VSS" pin (probably A10) at the ecm.

If you decide to use a "short shaft" THM 400 you will need a driveshaft yoke, connect a kickdown switch, and (again) deal with the tcc codes.

Both can work but it may be easier to use the 700.

Originally Posted by 1project2many (Post 8685791)

Huh? Sophisticated diagnostic equipment? The ecm on a '91 350 is pretty basic stuff. You can read trouble codes with a paperclip! Most of the diagnostic tests for that ecm are available in "no scan tool available" format which uses a DVOM and simple observation testing to complete a diagnosis. The computers are programmed to run with five sensors (throttle position, coolant temperature, knock sensor, crank rotation, and vehicle speed) and the engine will usually run with any but the crank rotation sensor failed. It sounds like you don't want to learn about computerized systems, but the OBDI vehicles really aren't that bad. Now if the choice was with a late model OBDII vehicle you might get more agreement.



But more airflow plus more fuel is really what makes more power. How how it's delivered is often less important than what's available. GM TBI systems are designed for V8 engines making less than 300 hp which is a very different world than an engine making 200+ hp/liter.

What EFI does that a carb can't do is provide for better fuel control over a wider range of conditions. And when you add computer controlled spark you improve the odds even more. Consider that computeized can add fuel or spark at one rpm range, reduce it at a higher range, then add it again as needed and you'll realize that's a hard combination to match with old-fashioned carb and distributor.

I think about it this way: Once upon a time getting into a 10 second drag car usually meant getting into a vehicle that was barely streetable. No cold weather compensation, no hot temp compensation, crazy cam needing crazy high idle and high stall converters. These days you can drive your ten second car to and from the track then cruise with it on the weekends after heading downtown to get groceries.