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350 TBI performance mods

Whats the best way to soup up an old tbi 350?

350 TBI performance mods

Postby chevyripper [OP] » Jan 25 2012, 6:40am

Hi, I have a 1992 silverado with a throttle body 350. All I have done to it is an aftermarket edelbrock intake manifold and I have removed the catalytic converter and installed a flowmaster muffler. I was wondering if any of you guys have modified engines like this and if so what would you suggest doing? I was thinking about camming it and possibly installing new heads along with headers. Any suggestions on what I should buy or what cam and heads are best for this engine? Thanks!
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Re: 350 TBI performance mods

Postby starspangled6.0 » Jan 25 2012, 6:51pm

I had a 97 Sierra, with the 5.7L (not exactly the same as yours, but close). It REALLY woke up with a CAI and Flowmaster cat-back system. It was a lot faster, and I upped the fuel economy 2 MPG. That was all I ever did to it- it had close to 300,000 miles on it, so I traded it in for my current ride.
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Re: 350 TBI performance mods

Postby SRMN8R » Jan 25 2012, 10:35pm

You can call Crane Cams, or Edlebrock, or one of the other manufacturers and they will work up a package for you. I had a pretty good idea what I wanted to accomplish with my 55 Chevy truck (400ci Chevy motor) and I called Crane. They designed a package for me that produced an estimated 410 ft/lbs of torque and 300 hp. I'm pretty sure they have a package for the TBI motor, and I think I priced it a number of years ago... but there are too many projects to remember the ones that didn't get built.
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Re: 350 TBI performance mods

Postby marshallsdad07 » Mar 02 2012, 3:48pm

The computers in the tbi trucks don't like a lot of changes. I own a 95 tbi 454 big cam, intake, large oval port heads, most all bolt ons and had computer probs until I installed an adjustable map sensor. http://www.fuelsaver-mpg.com/simple-map ... 6ae4e6def6 the parts you can get cheap at radio shack. After that skys the limit. Hope I helped.
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Re: 350 TBI performance mods

Postby mfryanz » Feb 16 2013, 2:04am

I just bought a 1994 gmc suburban from a guy who put a gm performance crate motor in it with a bigger cam. I am getting around 8 miles to the gallon and my fuel trim is around 90 at idle. my map sensor is reading high around 2.1volts at idle. Do you think the adjustable map sensor would help with this? I am also having idle surging issues as well.
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Re: 350 TBI performance mods

Postby ely » Oct 02 2015, 9:20pm

I am facing the same dilemma, to junk the ECM and go Carburator or try and upgrade the TBI and ECM.

I found a great article from HotRod many years ago which still even today has much valuable information (see it here): http://www.hotrod.com/how-to/engine/hrd ... evy-build/

The Carburetor and HEI ignition can be improved upon and should get close to the 400HP mark.

The Crate Engine mentioned can be found here: http://gmpowertrainwarehouse.com/12530282.asp

Then finally the upgrade to the ECM and modification to be able to tune and flash a new Chip can be found here: http://www.moates.net/gm-19851995-c-64.html

For newer models: http://www.moates.net/gm-1996present-c-100.html

I'm still gathering parts and funds, checking just how deep I have to go into my old tired engine. The Compression test yielded 7 cylinders at about 150 psi and number 4 at about 145, so not real bad, but something to consider.

I have a bunch of 67-69 Chevy and GMC parts if anyone is interested...
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Re: 350 TBI performance mods

Postby Daly » Oct 02 2015, 9:44pm

Are you looking for a lot of power, or just to wake the truck up a bit?

If it's a lot of power the best power adder to an old 350 is to pull it and drop in an LS engine. Don't get me wrong 350's have potential, but dollar for dollar the LS will save you in the long run.

Now if you're just looking to breath some new life into a tired old truck, a LT1 hot cam, headers, ECM tune (few places still do it for TBI's), under or over drive pulleys and some cheap mods to the TBI are a good start (Look up Ultimate TBI mods for some good info).

If you get more then 350hp out of it I'll be surprised (from the stock bottom end that is), but if you do the factory TBI won't support it. Anything over that 350hp, I'd recommend switching to an Edelbrock replacement TBI or a modern TBI, like the FAST system. An affordable option to the $2-3k FAST systems is Fitech at $1k. Same can be done if you swap in an LS…

If my 305 ever gives out, that's likely the route I'll take. Swap in a 6.0, with a stand alone MSD box for spark and a FAST like EFI TBI set up…
1991 C2500 Silverado - Retired and back up workhorse Daly's 91 C2500 build
2016 F150 RCLB - XLT 5.0 4x4 Work truck/DD...
1969 D***e Coronet 500 - R/T clone, 440, 727…
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