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Discussion Starter #1
I've been looking for some extra horses on my daily(1993 2WD 2.8 5 speed) and I've been seeing some confusing posts on using a throttle body off a TBI 4.3. I've seen where people say it'll increase power which makes sense (more fuel, more air, more power right?). But I have also seen where people say it will not just bolt on, needs a lot of modification, etc.... My question is just how much does it take to make a 4.3 throttle body work on my 2.8?
Thanks all, sorry if I got a little wordy there.

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I can't answer the bolt on part, but I can say that if the engine is able to move the extra air it will make more power. If it isn't able to, then it won't do anything except maybe make the throttle response a little sluggish. Also the 4.3 fuel injectors can flow a lot more fuel which can cause the engine to overfuel and run too rich if the computer is unable to adjust to the bigger injector size.
 

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Discussion Starter #3
I can't answer the bolt on part, but I can say that if the engine is able to move the extra air it will make more power. If it isn't able to, then it won't do anything except maybe make the throttle response a little sluggish. Also the 4.3 fuel injectors can flow a lot more fuel which can cause the engine to overfuel and run too rich if the computer is unable to adjust to the bigger injector size.
So how can I be sure that the my engine can move the extra air

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A quick and dirty way is to hook up a vacuum gauge and go for a test drive. Go WOT and rev all the way out in a gear and see if the vacuum gauge climbs above 1.5" of vacuum. If it does, then the 4.3 throttle body will likely improve power, at least on the top end.
 

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Discussion Starter #5
A quick and dirty way is to hook up a vacuum gauge and go for a test drive. Go WOT and rev all the way out in a gear and see if the vacuum gauge climbs above 1.5" of vacuum. If it does, then the 4.3 throttle body will likely improve power, at least on the top end.
Sounds like a plan


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I'm going to throw my 2 cents in because I'm working with a 3.4 with a 4.3 throttle body.

1st: the 4.3 throttle body has bigger bores than the 2.8 throttle body. The stock intake for the 2.8 throttle body will not allow the 4.3 throttle to open completely unless you have the intake bored, or, you can try one of those TB spacers.

2nd: You are going to run A LOT leaner than you want. The ECM will not be able to correct enough unless you learn how to tune the ECM and get the equipment to reprogram chips.

3rd. Get a wideband o2 sensor if you are going to do all this.
 

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Hello,

I put a 4.3 TBI on my 2.8, and I put a 4.3 TBI on the 3.4 in Dad's '84 S-10 Blazer. I think both had 4.3 injectors, too, though Dad's may have Cadillac 4100 injectors.

A few notes to add to / concur with damanx.
1) The 4.3 TBI has 1 5/8" bores. A TBI spacer or even a very thick gasket is probably sufficient (the blades hit the intake, but not by much depending on gasket thickness). It is best to bore the intake to take advantage of the greater airflow.

2) The Holley TBI for the 2.8, rated at 390 CFM, is essentially a 4.3 TBI with slightly different injectors and few tweaks so it's a bolt-on. It will need the same spacer or boring as a 4.3 TBI. I had one on my 2.8 for a while, then wound up with a 4.3 TBI for cheap so I sold the Holley.

3) The throttle lever is "flipped" on the 4.3 TBI vs. the 2.8 TBI on every 4.3 TBI I've seen. Essentially, the cable mounting pins are on the wrong side of the lever. Grind the plat on the throttle shaft retaining the lever, remove the lever, flip it 180 degrees, and spot-weld it back on. Do NOT remove the throttle blade screws instead. Those are platted as well, but much more difficult to put back with strong confidence that the screws can't come out and fall into your engine later.

4) Newer 4.3 TBIs have the small, round TPS connector vs. the older flat connector. Electrically they are the same, so you'll just need to switch plugs if you end up with a newer 4.3 TBI. The newer ones are also non-adjustable (no slots where the mounting screws go) but that shouldn't cause you any real issues.
 

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Discussion Starter #8
I'm going to throw my 2 cents in because I'm working with a 3.4 with a 4.3 throttle body.

1st: the 4.3 throttle body has bigger bores than the 2.8 throttle body. The stock intake for the 2.8 throttle body will not allow the 4.3 throttle to open completely unless you have the intake bored, or, you can try one of those TB spacers.

2nd: You are going to run A LOT leaner than you want. The ECM will not be able to correct enough unless you learn how to tune the ECM and get the equipment to reprogram chips.

3rd. Get a wideband o2 sensor if you are going to do all this.


Hello,

I put a 4.3 TBI on my 2.8, and I put a 4.3 TBI on the 3.4 in Dad's '84 S-10 Blazer. I think both had 4.3 injectors, too, though Dad's may have Cadillac 4100 injectors.

A few notes to add to / concur with damanx.
1) The 4.3 TBI has 1 5/8" bores. A TBI spacer or even a very thick gasket is probably sufficient (the blades hit the intake, but not by much depending on gasket thickness). It is best to bore the intake to take advantage of the greater airflow.

2) The Holley TBI for the 2.8, rated at 390 CFM, is essentially a 4.3 TBI with slightly different injectors and few tweaks so it's a bolt-on. It will need the same spacer or boring as a 4.3 TBI. I had one on my 2.8 for a while, then wound up with a 4.3 TBI for cheap so I sold the Holley.

3) The throttle lever is "flipped" on the 4.3 TBI vs. the 2.8 TBI on every 4.3 TBI I've seen. Essentially, the cable mounting pins are on the wrong side of the lever. Grind the plat on the throttle shaft retaining the lever, remove the lever, flip it 180 degrees, and spot-weld it back on. Do NOT remove the throttle blade screws instead. Those are platted as well, but much more difficult to put back with strong confidence that the screws can't come out and fall into your engine later.

4) Newer 4.3 TBIs have the small, round TPS connector vs. the older flat connector. Electrically they are the same, so you'll just need to switch plugs if you end up with a newer 4.3 TBI. The newer ones are also non-adjustable (no slots where the mounting screws go) but that shouldn't cause you any real issues.
Thank you both. That's exactly what I was looking for. So just to clarify; 4.3 TBI I'll need a spacer first and foremost. Then fiddle with the throttle lever on the 4.3. ECM tune and wideband O2 sensor.

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it will be better if you start another thread about this. just link this one to your new one. I like your question though because there is a bit of mention about leaning out the 2.8l but nothing on how to fix it
 

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I remember when Holley offered a bigger tbi (4.3) but don't know what the injector size was. You could try the 4.3 tbi; with the smaller 2.8 injectors and see if it ran better. Changing to the 4.3 tbi on a 2.8 is a waste in my opinion without a cam upgrade and improved exhaust. The factory 3.4 cam and a cheap Dyno-max catback will wake up a 2.8 but don't expect miracles. The 4.3 tbi off an Astro-van fits easier.
 
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