89 Jimmy TBI swap to Carb Engine

[K5pilot97]

My 89 Jimmy has from what I can tell the stock TBI 350 that was in it when I got whole truck out of the junk yard. It has served me well for 4 years but it’s getting extremely weak. I want to do the following and appreciate any suggestions on a drop in motor that would work in the application

1. I’m looking for a New/Crate fully dressed 350 crate motor with 4 bolt main that is carbureted.

2. I want to delete the factory ECM

3. Can I keep my factory electric fuel pump

4. I would like to have between 350-400hp.

5. I would like to do this on regular unleaded 87 octane pump gas

1989 GMC Jimmy V1500
700R4 built for towing
3.73 gears in factory 10 bolts
33x12.50 Tires
daily driver 45 mile commute on the interstate

*I apologize it this question has already been posted I’m still learning my way around the forum’s.

 

[cheavyk10]

Man going from TBI to a carb is like going backwards. The TBI system is reliable and well proven, and basically maintenance free. Sure you may get more power with a carb, but what about daily drivability, and running at any altitude and angle?
I understand the wanting of more power though, as TBI engines are rated at something like 190-230ish HP's factory.

 

[K5pilot97]

Man going from TBI to a carb is like going backwards. The TBI system is reliable and well proven, and basically maintenance free. Sure you may get more power with a carb, but what about daily drivability, and running at any altitude and angle?
I understand the wanting of more power though, as TBI engines are rated at something like 190-230ish HP's factory.

My main desire with a carb motor is simplicity. That being said I’m not completely married to the idea. If I did go with a fuel injection system I would leave the TBI behind for something like the sniper from Holley or another system I’m just learning about. I need power for towing my boat and better top end. I struggle to hit 65 right now and on the hills I’m losing ground to semi’s. Maybe there’s a way to get 350-400hp out of a TBI though I’m not sure.

 

[ZooMad75]

While I agree taking a TBI setup off is a backwards step. Getting a TBI system to properly run an engine with double the HP of a stock engine has proven to be very challenging. So it points back to a carb or aftermarket FI to do the job.

Here's my thoughts to the questions.

1. GM and many other engine companies sell fully dressed ready to run setups. Shop summit, jegs, surf the web there are many choices of small blocks out there.

2. Easy. Take it out. Pull the entire TBI harness with it. Keep it together and refrain from chopping wires. You have something someone else might pay good money for a complete TBI setup. Hell, you might get pissed at the carb and want to put it back on. You never know.

You will need a non-computer controlled distributator. HEI or any other aftermarket setup.

3. Yes you can use the pump. With the TBI wiring out you'll have to may have to reroute switched power to the relay to turn the pump on. The relay is not part of the TBI harness. You will need a fuel pressure regulator. 13-15 psi that the TBI pump puts out will push past the needle and seat of most carbs.

4. See engine choice you made in question 1.

5. Again depends on what engine you pick. Higher compression may require more octane. That is a key factor in what engine you are looking for.

The issue you are going to run into is the HP goal and octane limits you have set. Just looking at GM performance crate engines a ZZ6 turn key engine has 405 hp but uses 9.7:1 compression with aluminum heads. GM recommends premium fuel for this engine.

Even the sp350-385 gm crate has 9.6:1 compression and recommends premium fuel. The sp350-357 crate is 9.0:1 and they still require premium fuel.

The last two engines had 385hp and 357hp so right in the middle of your target range.

Just looking at summit found a blueprint fully dressed engine coming in with 365hp and 9.1:1 compression. Stands to reason it will probably require premium fuel though I didn't find any mention of fuel required.

What it means is getting to your hp goals you might need to make a change in fuel. Granted you could run any one of them on 87 but you stand a good chance of detonation if you got it under the right load conditions. On an efi setup if it felt the knock or pre-ignition it could just back the timing off until it quits. Yes you loose power but the engine don't kill itself. On a non computer controlled set up you can't do that. You can back the total timing down but you'll not be making the HP it was rated for and could still detonate.

 

[cheavyk10]

Or maybe even swap axle gear ratios to a 4.10 or 4.56. Then refresh the TBI motor and you should have no problem pulling grades.

 

[dyeager535]

Run a compression check on the cylinders. If they are all good, then personally I agree with the other statement regarding gears. I've got a vortec 350 in my truck at around 285HP (guesstimate) and even with a couple thousand pounds in tow, climbing hills it doesn't have power to spare.

With OD, 33's, and towing in the mix, 4.10s or even 4.56 would probably be my first choice at a mod. 3.73 to 4.10 is arguably not a massive jump.

The TBI motors are definitely not powerhouses.

 

[ZooMad75]

If not willing to regear, get a big block. Lower compression, still makes more hp/tq. 87 octane. It's a drop in replacement other than having to source the accessory drive.