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Discussion Starter · #1 ·
Hi everyone so I have some questions. I want to rebuild the TBI 350 in my truck. Reason being the engine has 306,000 miles on it and I started noticing that I am losing power and it doesn't seem to have the get up and go that it used to. After some diagnosis and compression testing I figured out that I have one cylinder thats low on compression (110 psi) while all the others are high (130 to 140 psi) and I have come to find that I think the bad cylinder has a bad intake valve. I have been told that if I'm going to replace 1 valve I better replace them all and if I'm doing that I might as well rebuild the whole motor. So first off let me tell you what I want. Its going to be a daily driver but I want it to go kinda fast but not super speed but also have some decent torque so I can do some towing still if needed but also have decent fuel mileage. I want to get the engine bored to a 355 and put a cam in it, nothing outrageous and people keep telling me about an rv cam and they are decent cams. I am also wondering that if I bore it if it will run with the automatic timing. I also know that these TBI 350's can't run with super big cams because of the automatic timing (sorry for the incorrect term if it is, thats just what it sounds like to me.) I have also heard that the swirl port heads on these engines are garbage so I was thinking about going to the scrap yard and trying to find a set of vortec heads and use those if they aren't damaged and have them machined when I get the block machined and bored. So now begins my questions after boring you with the descriptions of what I want. What should I do? How should I start? What more information can you give me? What parts should I buy? Also I haven't started anything the motor is still in the truck and it's still running decent minus the lack of power stated previously. Could you guys help me out I want this truck to keep going and she has been a good solid and reliable truck and I just want to put some pep back in her step. Thanks everyone any other questions you have just ask and I will try to answer them the best I can as quick as possible. Thanks again!!!
 

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True Hotrodder
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Do yourself a huge favor and purchase a crate engine. Then depending on your mechanical abilities and tool set - either swap it in or find someone to do it for you. The upside is that your truck will be down for a limited amount of time, the engine will have a warranty and probably run just as well as the original one did when it was new. Oh - and you will save yourself a lot of headaches and money.
 

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Discussion Starter · #3 ·
So my issue is I have limited funds and from what I little bit of math I have done its gonna be cheaper to rebuild it cause everywhere I look I new crate engine is minimum 2 grand and thats for a 190 hp engine which im fairly certain is less than my engine came with from factory
 

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Hard to do on 2 grand. A complete head rebuild will run 4 to 6 hundred, seats, valves, guides replace the tired springs. For the springs the TBI engine uses the mildest, lowest lift cam in GM history so any cam change will need better springs not crazy racing springs but good replacement springs.

Used L31 Vortec head’s are costly to rebuild and wrecking yard pieces are usually cracked so you must add this inspection to the rebuild cost as there is no point to rebuild anything with cracks, the same goes for your Swirl Port TBI head’s. An additional expense with factory Vortec us the unique bolt pattern drives a Vortec aftermarket 4 bbl intake which then needs an adapter to mount the TBI.

Yes the TBI is cam limited without a chip (another 300 bucks if it works more if it needs tweaking). About the most cam the TBI will accept on a fresh engine is in the range of 190-200 degrees measured from .050 intake and 200 to 205 degrees exhaust with an LSA of 110 degrees or more and lift at about .45 inch. Beyond these numbers you will have to rechip the computer. What you’re fighting is the ignition and fuel schedules are based on calculated relationships made by GM the system is not smart in the sense that it can NOT make sense of design changes that change the factory programmed relationships of RPM to throttle position to manifold vacuum (the factory calls the latter Manifold Absolute Pressure or MAP. So the factory program is expecting to see these as specific relationships when you up the cam timing these relationships change and the computer has no way to understand these different values, hence a reprogrammed chip.

Frankly the bottom cheap GM crate engine is basically what you can build on your TBI motor and in its delivered form it really puts out about 230-240 horsepower not the 190 they advertise. Problem is the head’s are old time SMOGgers with zip for compression but they breath decently. The down side is they don’t fit the TBI intake. What happens here is all the bolts appear in the same place on the 1987-95 engines compared to the 1955-86 engines but GM changed the angle that the bolts alongside the plenum make to the intake surface of the head’s. The traditional 6 bolt head have all the bolts at 90 degrees to the head’s machined intake surface but for the 87-95 TBI engines the bolts along the plenum meet the intake machined surface at 72 degrees. So you can’t put the TBI intake on older bolt pattern head’s, and certainly not on the 4 bolt Vortec head without a lot of machine work. Now it is possible to modify the TBI intake to the 55-86 plenum bolt angle by egging the bolt holes and using a 20 degree wedge washer to correct the angle the bottom of the bolt head makes to the surface angle of the intake’s bolt boss for these guys.


This thing just blew up a bunch more paragraphs I wrote and it’s late so I’m going to bag it for a while but I think you can see that a 2000 dollar budget isn’t likely to get you there. These vehicles after 1986 are a real PIA to do anything with and it gets a quantum worse after 1995 and OBD-II.

Bogie
 

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Discussion Starter · #5 ·
Its not so much the budget I was just using the 2000 as an example haha im willing to save and gather the money needed to do this project and do all the tuning for a bigger cam if I have to do it in case I do get a bigger cam but I more knowledge and list of parts especially if boring it is gonna be part of that tuning issue or if that doesn't matter and I just put a the basic internals with the bore to the 355 and also I though they made a intake that will bolt to the vortecs and then a tbi be used on it. But also thanks for that info so far the more I know the better
 

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So my issue is I have limited funds and from what I little bit of math I have done its gonna be cheaper to rebuild it cause everywhere I look I new crate engine is minimum 2 grand and thats for a 190 hp engine which im fairly certain is less than my engine came with from factory
I think you have no plan at this point. First you say you have limited funds - $2000 - then you say you can save up more - all you need for the project...believe me a bigger cam is not a one-piece-throw-at-it solution to increased power. A lot of guys here are a lot more knowledgeable about the later engines than I am but IF it was my truck I would go the crate engine route. Jegs has one for $1800 plus a core of $410. (JEGS 8758: Replacement Crate Engine for 1987-1995 GM Truck, SUV, Van with Chevy TBI 350 ci, 5.7L | JEGS) From what I can see that's a remove and replace project. Horsepower level is comparable to what your truck was new, the only truck with a 5.7 that had more HP was the Suburban which was rated at 210, everything else had a rating of 190.
 

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If you can do it considering emission testing, getting rid of the computer and the factory TBI for a carburetor or self learning aftermarket EFI solves a lot of problems if the transmission is a manual or the older hydro mechanical 700R4/4L60 and not the electronic 4L60E or the 4L80E found in some 350 engined heavy duty trucks. Not that this can’t be done with the electronic controlled transmissions but an additional throttle position sensor has to be added and tge original computer or a new transmission controller needs to be added.

All of this needs to be worked out on paper before pulling parts out and making purchases. An example of where there’s trouble waiting in in piston selection. One of these is using so called “rebuilder“ pistons, these are for the mass production rebuilder shops that will zero deck all blocks and want to restore original compression ratios. These pistons are .020 to .025 inch shorter than stock so in an undocked block they greatly lower the compression ratio and widen the squish/quench clearance. This is a lose/lose with less power and more detonation.

The reverse of this is certain performance pistons use a raised height by .020 to .025 inch these are for builds using aluminum head’s on block’s with the standard head deck height of 9.025 inches from the crank center line. These would be standard production blocks that are not decked. This is restore original squish/quench clearance of uncut deck blocks using aluminum head’s. Generally aluminum head’s require a thicker gasket to absorb thermal movement differential between the iron block and aluminum head so these tall pistons are used to restore compression and the squish/quench clearance on standard height block using aluminum head’s.

For eking out best power and efficiency on most any build the aftermarket provides a D dish piston to replace the inefficient round dish factory design piston. The D dish puts all the needed volume to correct the compression ratio and to increase the squish/quench function to that of a flat top piston while still trimming to an acceptable compression ratio. These put all the dish under the valve pocket.

I’m offering this as an example of where one can get into significant trouble on a rebuild when you start mixing and matching parts. This happens in a lot of cases with amateur builders which leads into expensive redos when the engine proves to be low on power and or just doesn’t run right.

Another thing you might find is in the TBI era many blocks have the provisions for a roller cam. These can vary from having the raw castings inside to any level of partially to completely machined. If these are there especially if finished you can convert to a factory roller cam which for a work-a-day TBI engine the L31, Vortec of 1996 to 2002 or so is an excellent choice and gets you around modern day flat tappet cam lobe and lifter wear issues. But you're gong to have to at least remove the intake to see if this stuff is present in the valley. What you would see are three cast bosses projecting upward from the main oil galley casting and raised and smooth machined too surface of the lifter pair blocks. The element you need but can’t see because it’s in the timing case is the provision for the cam thrust plate. But I have yet to encounter a block that if it has the valley provisions that it doesn’t also have the timing case provisions as well.

As far as the opening level of the suggested crate engine these use the two piece rear seal which requires the older flex plate or flywheel because the crank bolt pattern is different from the 86 and up blocks with the one piece rear seal.

So there are a lot of thing to consider when deviating from what the factory installed and a lot of changes in that mid 1980’s divide and again with the mid 1990’s divide.

Bogie
 

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These engines were meat and potatoes swap sources back in the late 1990’s through about 2010 or 2015. People with these 87-95 trucks seeking more power and the wide availability of these trucks and cars for swaps. So I got pretty familiar with them.

Bogie
 

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The reason why I like tbi so much is they are a cheap simple fuel injected engine.

Run the thing in stock form for 250 to 300k then when something goes grab a entire engine with all the acessories and parts the previous guy put on it for $300 then run it for another 50k.

The only reason I run tbi anymore is there are still tons of good engines that you can drop and plug in over a weekend.

If you want power start with a 5.3. Get the 200k engine under the hood for $2000 then drop another $2500 into pushing some boost/tuning(programs) it.

Streetable 500hp on pump gas and when it goes you grab another short block off of marketplace from a rusted out 1500 for $500 with all the acessories and parts the previous guy threw on it that engine.

After a few engines you will have boxes full of good "free" spare parts.

I have not bought oxygen sensors or tps sensors in years and I have a collection of starters and alternatiors starting. I gave away a pile of 30+ sbc starters when I moved 1.5 years ago because I just dont need them.


Just grab and drop another tbi if your on a budget.
 

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Discussion Starter · #12 ·
Hey sorry I have been busy with work you have given me a lot of information to go over and study the biggest thing I really wanted to do was just bore it out to a 355 and throw some vortec heads on it and maybe even throw a small cam in it or just stick with a stock one but my biggest concern was that even with just the bore and vortec heads was if the automatic timing adjustment would prevent it from running I guess I should have started with that from the beginning too. I'm also gonna see if I can adjust the valves as it is and replace the header gasket and see if that clears it up some. It doesn't burn oil or sound like it has a knock at all so I don't think its on its last leg....yet.
 

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Your stock 350 TBI was only rated for about 190 hp from the factory. The swirl port heads are fine for torque production, but they run out of breath at 4300 rpm, so if you're looking for more output, I would ditch the TBI heads. Even if you aren't looking for more power, you can get better overall torque and power with Vortecs.

The TBI will run poorly for longer than many engines will run well, so unless you have serious noises, issues, oil consumption, or metal in the oil, you should be fine to run it until you get the project going. Given the fact that 350s are a dime a dozen and you're on a tight budget, I would find a u-pull yard with a flat-rate policy and you can likely score a low-ish mileage 350 for $250-500. Do a compression test and do whatever modifications you want while it's on a stand and then swap in a weekend. The drawback is a little more up front, but then you can likely sell your TBI for the same money you used to buy the junkyard engine.

For a budget build, this is my go-to. In order to save money on my LS build, I bought a 6.0L LQ9 with 60k miles for $1000 and it included wiring, trans, computer, accessories, everything. It was in an escalade that did some unexpected off-roading, meaning someone pushed them off the road and they found themselves charging through the woods at 60mph. The insurance totaled it so it went to a junkyard. I didn't hesitate to put really good heads on it and stab in a hairy cam and it should make about 550 hp without even touching the bottom end. For your project, I might look for the lowest-mileage truck... something that got T-boned or a tree fell on it when it was young, buy the engine, check compression, and spray paint it so it's pretty.
 

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Stay out of the junkyards.
You can't get as many free parts that way.


I just bought a 5.7 tbi for $300

I have a spare waterpump, throttlebody, newer starter, newer hei, alternatior, power steering pump, and serpentine setup. So lets say half of the engine price is in those parts leaving me with a good longblock for $150.

At that price I am ok with 200hp and a lifespan of another 50k before I drop another $300 again.

Buy the tbi off craigslist or marketplace. I shoot video of mine running before I pull them or pull them the same day im handed cash letting them see it run.

Silverados had frame rot and cheap brake lines. Throw in the underbuilt 4l60e and you have a recipe for alot of good 200ish thousand 5.3 blocks to be available.

6.0's are hard to find and everyone wants $1000 for the ones you do find.

5.3's are a dime a dozen and can be had for $500 complete with harness and ecm.

It is not this engine to think about it is the next one to think about. The first swap is expensive. But the next longblock will be very cheap. Especially if you consider all those spares.
I have done the same thing with the LS engines that I did with tbi engines.

Coils are expensive at lets say $60-70. But a $500 5.3 comes with 8 of them all working when pulled. Throw in a starter and a few sensors on the throttlebody and you have a "free" longblock.



Plan on $2000 to swap a LS and another $1000 if you want to add a cam/exhaust. The little things add up fast.

But a simple cammed 5.3 will slap around a sbc dollar for dollar especially when you go over 400hp.
 

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This thread is getting entertaining.

I think you have someone that knows pretty much what someone told them or maybe they did some reading but I really doubt if it goes much beyond that information. But that's okay, that's why we ask questions. I'm enjoying these responses and getting the popcorn ready.
 
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