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post #1 of (permalink) Old 09-08-2000, 01:07 AM
jeeper131
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TBI vs. Holley

ok, I've been going back over some past postings and I'm rather confused on the 4.3 TBI vs the Holley replacement unit. Some people say that the 4.3 is a straight bolt on for the 2.8, if this is true for what years? Do all the sensors hook up fine ect? But others say that the 4.3 won't work and you have to order the holley unit. How much does one of these run? Finally, how much performance does tis really gain in the overall scheme and what are the tradeoffs. I put a weber carb on my last jeep and the affect was phenominal, can I expect the same out of this swap? I just wanted to try and gather all the information for the TBI swap into one place. Hopefully this isn't rehashing too much stuff for you guys. Thanks in advance

MudFlap
'87 YJ in the works
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post #2 of (permalink) Old 09-08-2000, 05:31 PM
**DONOTDELETE**
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Re: TBI vs. Holley

The 4.3 tbi unit and the 2.8l tbi unit have identical bolt patterns. The bores on the 4.3l are approx 1.750" DIA. The 2.8l are approx 1.375" DIA. The fuel in and return lines are in the same location and have identical fittings. The idle control valve has the same 4 pin connector. Depending on which generation (1 or 2) throttle position sensor your tbi has will probably be the only connector that will have to be replaced. My understanding is that the flat 3 pin connector is the generation 1 tps and the round 3 pin connector is the is the generation 2 sensor. See the post on "tps splice" for colors and wire placements. The injector connectors are the same. If your 2.8 had extras that the donor motor did not have , then you might not have one or more vacuum hook ups. I had that problem and had to add a "y" in one of the vacuum lines to get the vacuum. The throttle cable to tbi connection is also different. You could use the 2.8l bracket on the 4.3l tbi, but it looks like over time it would put a lot more strees on the unit. the 4.3 linkage has the throttlw cable wrapped around a kinda pully. I ground down the 2.8l cable to fit in the 4.3l channel and used the much shorter 4.3 throttle linkage bracket. if that makes sense. One thing that will make the whole thing worth it is to bore out the 2.8 intake manifold(1.375") to match the bores of the 4.3 tbi (1.750") I have heard that the holly includes a stepdown spacer to do the transition. but if that is used i think the tbi would not be able to flow to its potential. that seems like running your high flow heaaders into a single 1.5" exhaust!? I bored my intake manifold out myself. It was easy and fun and probably came out better than if I had a shop do it for $$$. Have pics soon. since I was in there, cleaned up and polished all the intake ports- didn't take much time in all -maybe 3 hours- well worth it. Emery cloth, cutting oil, air grinder, dremel, and a few metal working bits is all that took. As far as performance goes i don't know what the gains are going to be. oh yah, the holly unit runs about $315. A reman or used 4.3 tbi will cost about $50-80. my 2.8 was an 87 and the unit i bought was to my knowledge an 88 or 89. My truck should be done by the end of this weekend and broken in by the end of next week. I have done some other mods than this tbi so i am anxious to feel the improvements. hope this helps.

post #3 of (permalink) Old 09-08-2000, 07:31 PM
 
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Re: TBI vs. Holley

VERY detailed answer! Cool!

J.R. [img]/wwwthreads_images/icons/cool.gif[/img]

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