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tbi to carb

 
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bowtie44s
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Joined: 13 May 2012
Posts: 16

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PostPosted: Wed Sep 26, 2012 7:53 am    Post subject: tbi to carb Reply with quote

Hey guys, i'm sure this has been cussed and discussed a lot but i'm bringing it up again. Sorry to post a truck question but I have an 88 k3500 with a 454 that is currently tbi. Here is some of the motor specs:
300cc aluminum oval port heads
2.25 intake 1.88 exhaust
performer rpm intake

Hydraulic flat tappet
Duration at 050 inch Lift 218 int./228 exh.
Valve Lift 0.500 int./0.500 exh.
LSA 114

1 7/8" primary full length hookers

I have the 54mm throttle body and bigger in tank pump and upped the fuel pressure to 18psi. I had the chip made for it from tbichips.com
It runs good but it feels like the tbi is holding it back. It runs rich and sputters and takes a couple seconds to clean out. It feels like it is about a 500 cfm carb and just needs more air. If I switched to carb, how big would i need? Would a 750 be too big? What would I need to look for in a hei? I am just getting sick of messing with this tbi. I can't just throw in bigger jets with it. Do you guys think a carb would help performance?

I have been getting 11.9 mpg cruising around at 55. I just leave it in 5th gear all the time. I'm sure i'll lose a little with a carb but at this point i don't care. I either have to switch to a carb or get the cable and try my luck with that data logging. I wouldn't even know what to do with the sensor readings. Would i have to have another chip made to change the tune? The last one was $290 I think. That's almost the price of the carb.

Sorry for the length and thanks for any help.
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10sec.et
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Joined: 29 Mar 2006
Posts: 3473
Location: Houston,Texas
346658.74 points


1969 Oldsmobile Cutlass

PostPosted: Wed Sep 26, 2012 9:07 pm    Post subject: Reply with quote

yeah, youre pissing in the wind with that factory TBI setup. my opinion on the carb is go with an 850. the HEI, depends on wether or not you have an ignition box or are using the HEI module in the distributor.


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clay
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Joined: 24 Nov 2002
Posts: 3209
Location: South Carolina
318129.23 points


1972 Chevrolet Nova

PostPosted: Wed Sep 26, 2012 9:32 pm    Post subject: Reply with quote

Those era fuel injection setups have very little capablity to self correct - I have an 89 S-10 that I have done a few mods to. For what you have done, I'm with 10sec.et - ditch the tbi for a carb. I would suggest a slightly smaller carb though - 750 as I'm assuming you do some towing with it. If it's a daily driver I would look at the Edelbrock line of carbs. They can have problems with vapor lock due to the fuel bowl design but on a truck with plenty of room for airflow they are pretty good. I have used a 600 Edelbrock on a Vortec 350 and I was impressed at how good the drivability was out of the box. Clay
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87IrocTim
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Joined: 10 Jan 2006
Posts: 448

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PostPosted: Tue Jul 02, 2013 5:06 pm    Post subject: Reply with quote

ive done this before, cut the wire to the electric fuel pump, put in a cheap mechanical, and it built enough fuel pressure to draw it through the old pump. after a carb, fuel pump, pump pushrod, free intake manifold, vacuum advance distributor, and some beer later, we had it done for less then $200. Although, I don't think drawing gas out of a factory pump is going to flow so well, we had no issues on a factory 350 with a 650 edelbrock. And that my friends, is the cheapest most half-assed way to rid of fuel infection.
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bowtie44s
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Joined: 13 May 2012
Posts: 16

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PostPosted: Tue Jul 02, 2013 8:00 pm    Post subject: Reply with quote

Fuel infection, I like that. I just used a regulator and kept the electric pump. That makes it super easy to adjust float level.
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SMOKEmUP
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Joined: 30 May 2002
Posts: 3169

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1979 Chevrolet Camaro

PostPosted: Tue Jul 02, 2013 9:31 pm    Post subject: Reply with quote

bowtie44s wrote:
Fuel infection, I like that. I just used a regulator and kept the electric pump. That makes it super easy to adjust float level.

I was going to say the same thing.

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