tbi to carb setup...tbi distributor/ecm still working???timing issues?

marty79

marty79

Well-Known Member
Joined
Dec 2, 2015
Location
Newton, NC
hey guys, this 89 chevy 2500 5.7TBI i bought has the intake and quadrajet carb on it and it ran pretty good considering some of the small things I found when taking it apart earlier this week (plug wires bad, vacuum leak,etc). I notice though that the factory distributor is still in use along with ignition module...
SO I've been doing some research and most people are saying you can't use tbi distributor with carb swap but a few I have found say that you can and the computer will still advance the timing enough to run it just fine ....any thoughts on this??
I wanna keep it simple and I suppose it's worked for as many years as it's been on the truck like this but was just looking for some info on if it's a "good enough" setup or will it be "that much better" switching to an HEI distributor with vacuum advance. Thanks for any help and clarification
 
So you're using a carb and the TBI ECU at the same time? I know the TBI ECU is pretty crude, but where is it getting a throttle position signal from, among other things? I'm assuming it's still using the factory MAP sensor? Does it just do some limp-mode super conservative ignition timing?
I've never heard of this patched-up hybrid carb method, so I'm more curious than anything. Worst of both worlds?
 
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Fabrik8 said:
So you're using a carb and the TBI ECU at the same time?
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Well I'm not lol, he/they did (whoever done the swap years ago, I can tell its been awhile). I get results showing it can and can't be done (like most anything) but just trying to learn about what they've done and is it going to perform the best. Thanks
 
It will work but it won't advance timing at all. You would basically be driving a locked timing turd. As cheap as an HEI distributor for an sbc is I don't see why you wouldn't...
 
braxton357 said:
It will work but it won't advance timing at all. You would basically be driving a locked timing turd. As cheap as an HEI distributor for an sbc is I don't see why you wouldn't...
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So that's what I wanted to know since I'm ordering a new one and need to know which one..thank you
 
braxton357 said:
It will work but it won't advance timing at all. You would basically be driving a locked timing turd. As cheap as an HEI distributor for an sbc is I don't see why you wouldn't...
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Hey btw, I'm looking to order one right now...HEI Full ready to go distributor and there are way too many options lol.
There's small cap...there's big cap...both have the coil and vacuum advance and ready to mount and go but is there a difference or is one just little better spark ...thanks
 
braxton357 said:
I'm not an HEI expert by any means but the small cap distributors only exist for fitment reasons. The only time I've seen one is behind a blower. Assuming that engine doesn't have some odd cam gear, the first one on this page should work... JEGS Chevy HEI Street Spark Distributors | JEGS
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Just ordered one like that with little better coil output. The gear issue I've read is only for vortex roller motors so this 89 is good to go from several places I've read on. Thank bud
(That ladder rack is sittin here for ya lol)
 
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