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bigger tbi??

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Old 10-19-2003, 07:08 PM   #1
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bigger tbi??

hey ive heard of ppl putting tbis off of a 305 or 350 on a 4.3. is this possible? and if so what else is required when doing this. how much of a difference does it make in power(hp/tq) does it help/hurt gas mileage?? im really trying to get better mileage out of my truck, because i have the lift, tires and with my new rims my tires hang out from my rims about 2.5 inches and that killed my mileage bad. im down to about 17 on the highway:mad: lol, i would really like to make it better. im going through about 35 dollars of gas a week, and i cant afford it
Old 10-19-2003, 07:21 PM   #2
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There is no difference between the 4.3 TBI up to the 350.The only one that is bigger is the 454 TBI.The 305 and 350's use bigger injectors only.And if you decide to get a454 TBI you will have to enlarge the holes on the intake.Because they are are not big enough to just bolt the 454 TBI on.Also the 89 up TBI's have a different tps than older ones.
Old 03-29-2012, 01:07 AM   #3
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Re: bigger tbi??

How would one go about making the bores (on the intake manifold) bigger without a machine shop? I have a drill press, 2 inch bit and go to town? Sorry about the use of this thread but, I couldn't figure out how to explain the objective.
Old 03-29-2012, 11:08 AM   #4
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Re: bigger tbi??

on a side note. you do realize that having more air requires more fuel.

so when you upsized your tires, did you lower the gears. I gained 3mpg by goin from 3.08 to 3.73 and 31" tires.

17mpg on hwy is great. i only get aout 15 out of my 94.
Old 03-29-2012, 11:34 AM   #5
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Re: bigger tbi??

if you're looking for power gains from this,
think again.
the stock TBI's were adequate for the 350's,
they are more than adequate for 4.3's...

look elsewhere for power gains...
Old 03-29-2012, 12:05 PM   #6
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Re: bigger tbi??

^x2 a 454 tbi is too much for a 4.3 and you may end up loosing power due to the big bores reducing air velocity entering the plentum. 4.3, 5.0, and 5.7 flow somewhere in the area of 450~480 cfm. with the ultimate tbi mods you can get it better flow charicteristics. the 454 tbi flows in the ballpark of 670 cfm. I'm running a SBC in my other truck rated at 400 hp on a holley 650 and it hasn't ran out of air yet. matter of fact I noticed a performance increase when i switched from a 750 down to the 650. a good way to tell if you need a bigger tb is to monitor your manifold pressure. if you are seeing 100 kpa (0" Vac) WOT at peak RPM its the right size already, so Unless you plan on boosting this thing you are wasting your time.
Old 03-29-2012, 12:20 PM   #7
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Re: bigger tbi??

Will the injectors from a 350 TBI fit in the 4.3 TBI and if so are there any performances benefits?
Old 03-29-2012, 12:23 PM   #8
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Re: bigger tbi??

Quote: Originally Posted by zarmo24
Will the injectors from a 350 TBI fit in the 4.3 TBI and if so are there any performances benefits?
yes they will fit. no you will not see any performances benefits unless you did other mods to the engine that require LOTS of additional fuel. plus tuning for bigger injectors is always required. on a stock motor making the fuel pressure regulator adjustable and giving it 1 psi more pressure will show a slight increase in performance and a decrease in fuel economy with out tuning.
Old 03-29-2012, 01:43 PM   #9
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Re: bigger tbi??

Quote: Originally Posted by zarmo24
Will the injectors from a 350 TBI fit in the 4.3 TBI and if so are there any performances benefits?

I have actuatly swap an entire TBI unti from a 89 350 to a 89 4.3 to see if that was my problem.

i will say using 350 injectors on a stock 4.3 will make it run pig rich. I had a driveability on a 89 4.3 was thinking it was the TBI. My friend was rebuilding his 350 from his 89 truck so i used his TBI unit on my 89. Lets just say it cranked up, idled real rough and poured out black smoke. swapped back to teh 4.3 TBI and it idled like it should.
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