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Thread: tbi to carboratuer

  1. #1
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    tbi to carboratuer

    I have a 1993 GMC 2500k 5.7L. all stock. I want to make it better but i dont know if i can change the throttle body to a carb. so could someone tell me.

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    You can but why would you want to, its why auto makers stopped putting carbs on they were less efficient hard to tune, than injection, you get better mileage and better fuel burn with injection the mixture is always calibrated just right for whatever the conditions are for driving without having to take apart the carb to change jets. Is there something that is wrong with the TBI why you don't want it anymore?
    1994 white ext cab chevy silverado 5.7 rolling 230k miles
    stock with air filter lid flipped,
    open flowing exhaust to a 40 series flowmaster dumped.
    God Bless America, Support our Troops!

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    its not that there is any thing wrong with it i was wondering if tbi was better then a carb and if you could

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    Senior Member gmctrucks's Avatar
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    I was thinking of going with a carb as well on my 93 for the reason is I want to put Vortec heads on the engine im lost.......
    http://i961.photobucket.com/albums/ae98/falken86/dadnew-1.jpg

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    Vortec heads are great flowing but need extra work for egr work. The dart 165 heads are also good and are less money and dont need egr work done. Even if you went with vortec heads, better flowing intake, headers and a mild to moderate cam the TBI will keep up with 450 hp. Not to mention the computer hates any cam over 118 @ .50 duration so to do anything more than this you will need computer work done. Check out TBIchips.com, all the info for these 350 TBI engines are there.

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    Sorry i meant 218 duration cam. Stock there around 180 @.50

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    1. Intake and cam (with matching valve springs). I put these 2 together since you have to remove the intake to replace the cam. Stock TBI intake is just a bad design. The edelbrock performer 3704 TBI intake is a good EASY replacement. It will bolt right up and work. Another good option is the holley projection TBI manifold which flows more air but more difficult getting throttle linkage and such bolted up. Not too big of an issue. For more performance use any good carbureted intake which will require an adapter. Jegs and Summit sell it for $60 for spreadbore Holley17-41 and squarebore 17-45. Pretty much impossible to EGR properly functioning with the carb intakes and I can turn off the EGR if necessary in the chip although it may cost you some highway gas mileage. Next it requires fabricating a throttle cable bracket and a remote coil but the hp difference is worth the effort if you are going to change heads (more on that later).
    The cam in the TBI engine is just plain AWFUL. Specs on Stock TBI cam is .050" tappet lift (intake/exhaust) is 179/194; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is .350/.384. Valve springs are also VERY important due to the stock ones having a redline of 4500 rpm. With the proper cam and springs the redline can easily reach 6000rpm. Intake and cam is worth a good 40hp as long as you did the other mods too. I have listed a bunch of new cams at the bottom of the page. This should provide you with a sufficient assortment of cams for whatever power range you want for your motor. If you still don't know what cam to use, email me at sales@tbichips.com all of your engine and vehicle details and I will gladly recommend a cam for you.
    2. Rocker arms. I have had a lot of questions about rockers and I have had a lot of customers having issues with all the cheap rocker options. So I no longer recommend changing the rockers on TBI motors as the amount of power you gain on these mild engines isn't going to justify spending $300 on quality roller rockers.
    3. The exhaust. I recently moved the exhaust up on the priority list after seeing the dyno results on my Black Magic project truck. Change the WHOLE thing from the engine back ESPECIALLY THE Y PIPE. I used a flowmaster collector Summit Racing part number FLO-Y250300 to Y the 2 pipes into 1 with great results even on mild setups.. I recommend getting the headers and catback system any brand should do. I used these stainless headers 97 suv TRUCK HEADERS | eBay with Dynamax cat back. Get a 3" hi-flow catalytic converter. You can get them for about $60 on ebay. I have used the Summit Racing brand CATBACK on my budget vortec project and the kit could have been better. the tail pipes didn't fit well but for $160 its not horrible. If you use a long full length header, you need to use a 3 wire 02 which I have wiring info on the FAQ section. The exhaust configuration that I really like is what we used on the Blue Whale project which utilized standard shorty headers and then I had 2 2.5" pipes run as true duals for better low end torque and fed 2 mini flowmonster cats into a dynomax WLK-17553 muffler and then ran the tail pipes on out the back.
    Check out thiis exhaust combo I put together with reasonable parts from Summit Racing. Flowtech 11504YFLT - Flowtech Catalytic Converter Y-Pipes - Overview - SummitRacing.com and Flowtech 11504FLT - Flowtech Headers - Overview - SummitRacing.com (note these headers are mid length so Y pipe won't fit any other headers) with dynomax cat back Dynomax Performance 17324 - Dynomax Super Turbo Exhaust Systems - Overview - SummitRacing.com
    If you need cats and I highly recommend you use them, do a search on ebay for FLOWMONSTER CAT and I used these on the blue whale project and the black magic truck and they work great and they are CHEAP and that is the kind of combo I like.
    To see what affects decent exhaust can have on your engine project, check out the black magic project on the left and look at the dyno results of just an exhaust change.
    4. The Heads. The TBI heads are the worst flowing heads GM ever released. So the best bang for the buck is GM Vortec head but does require a special intake and lots of EGR work if you need EGR to remain emission legal. These heads are good for a minimum 50hp gain. Another good reasonably priced set of heads that will work nicely without special intakes on a TBI motor is a set of DART 165 iron heads. They flow well and the price isn't bad. The DART 180's also flow well and have a better exhaust flow than many small block heads and so I would keep the cams intake and exhaust duration tighter together. Now if you don't need EGR for emissions testing then check out these heads Click here for more information about Edelbrock 5089 - Edelbrock E-Street Cylinder Heads Next to the cam this is the most important choice. Compression ratios and pistons and all that stuff are not near as important as the head and cam choice. That decision will make or break your engine project and you wallet if your not careful.
    Also, tow beasts and 4x4 guys. This section has changed recently after the dyno results cam in for the plum crazy project. While the hp numbers up to 3000 rpms is pretty close to any other head the torque numbers were not. Plum crazy didn't make near the torque numbers the vortec headed projects did and even after a lot of work it didn't make a lot more torque than stock. . Well most 4x4s and tow beasts are more concerned about low end torque than having 500hp at 6500 rpms where they can't use that power. So you do want to keep the intake runner size on the heads at 180cc or less. The comp cams 12-249-4 cam along with the 1.6 rockers that I mentioned on item 2 will make really good power and torque on a 350 TBI motor up to 4000 rpms.
    5. The air cleaner. Ultimate TBI - ThirdGen.org The baffle on the TBI Truck is too small for a 2.8L V6 much less a 5.7L V8. Or you can run with a 3" tall 14" diameter open element filter with a flat base. Also toss the choke collar (has nothing to do with choke like a carburetor, its choke as in restriction) ,if you run the open element filter with flat base, that is between the TBI and the air cleaner assembly. Good for around 10hp
    Here are the summit racing air filters that I use and recommend.
    SUM-239421 14 in. diameter, chrome, flat base, 2in. element, air cleaner assembly for tight clearance hoods
    SUM-239431 14 in. diameter, chrome, flat base, 3in. element, air cleaner assembly
    SUM-239441 14 in. diameter, chrome, flat base, 4in. element, air cleaner assembly
    TBI spectre air cleaner. Spectre 47622 Spectre Xtra Flow Air Cleaner Assemblies RED or BLUE Spectre 47626 Spectre Xtra Flow Air Cleaner Assemblies with Hypertech powercharger Hypertech 4001 Hypertech TBI Power Charger and if your truck is a dual stud air cleaner here is the factory single stud which your throttle body has the provision for. Spectre 4215 Spectre Air Cleaner Studs which you may have to modify and make longer to use with this setup. I believe I had to on mine
    Now open elements are NOT really recommended for 4x4's (water holes can drown that open element filter assembly) or you may want to spend a little more money for colder air for more power gains. If either is the case then you need the Hypertech CFM Powercharger Air Intake - Hypertech Power Charger - 4.3/5.0/5.7 Full Size Truck and a Air Intake - Cold Air Intake Tube - Full Size GM Tbi Truck- New Product!!! with a K&N filter for the stock air cleaner assembly.

    6. Modify the throttle body. This one pretty cheap but does require removing the throttle body. UTIMATE MODS. NOTE: I recommend using to injector pod gaskets instead of trying to fabricate one thicker one. You may need longer bolts to put the pod back on. Good for 5hp but helps with the more mods that you make.
    If your going going to build a motor for over 270hp then you need more than the ultimate mods. Have one of these 2 companies bore your stock throttle body out for more air flow. www.rvmorsemachine.com or www.tbiparts.com . The stock 305 and 350 TBI unit has 2 (1 11/16") bores which flow 450 cfm of air. Compared to a 650 cfm carb that is bad. Holley does make an aftermarket TBI unit for the truck that will work with the cars with a little work and it has 52mm 2" bores and 65lb/hr injectors but Holley throttle bodies are plagued with bad injectors and base casting issues so I don't recommend using one. 454 TBI units are ok if you get a good one. www.tbiparts.com reconditions 454 TBI units as well as sell adapters and such you need to make it work well for you.
    One of my customers overhaul rebuild, Crossfire Kits items in TBI Throttle body injection 7.4L 454 5.7L 350 SBC BBC store on eBay! now carries a lot of TBI parts including a pigtail to use the 454 throttle bodies on the 4.3, 305, or 350 wiring harness.and www.rvmorsemachine.com can bore those 50mm 454 throttle bodies to 54mm for the most air currently available for TBI.

    7. Injectors. GM released 5 sizes of TBI injectors (actually more but those are the important ones) 40lb/hr for the 4.3L and 5L engines, 55lb/hr for 350 engines, 65lb/hr for cop car 350 engines and (80lb/hr and 90lb/hr) for 454 engines. Depending on how much horsepower you make you may need on of the other injectors. I have been recommending www.injectors4u.com for injectors lately.
    Instead of using adjustable fuel pressure regulators which has been all the rage in the past. I have tested several springs and had a custom spring 18 psi spring | eBay made that will yield 17-18psi at a much lower cost than buying a regulator and a fuel pressure gauge to set that regulator by. This way you can just slap the spring in and go and its a one time disassembly of the throttle body instead of 3 or 4 times to get the fuel pressure correct.
    Also, a new fuel pump ep381 155 | eBay is VERY important as the stocker is only good for about 250hp and won't maintain any higher fuel pressure. It can barely keep the fuel pressure maintained for the stock 9-12 psi.
    So what size injector or fuel pressure combo to use? Well here is a basic guideline.
    Stock 210hp 350 V8 up to 250hp the stock 55lb 350 truck injectors at the factory 9-12psi is fine.
    from 250hp to 260hp the fuel pressure should be bumped up to 13-14psi on stock 350 truck injectors which will change their flow rating to 60lb/hr
    From 270hp to 340hp you need to change the fuel pump as the stock pump can't maintain pressure over 270hp and you need to run 18psi on the 350 truck injectors for a flow rate of 72lb/hr
    From 340-360hp this is where you should be looking at the 454 injectors and run them at the 13-15psi for their 82lb/hr flow rate. If your closer to the 340hp, you can run them at the stock 9-12psi and still be fine for this power range.
    From 360-400hp you need to bump the fuel pressure up on the 454 injectors to the 15-18psi to increase their flow rate to 96lb/hr.
    For over 400hp you really should be looking at alternative injection system but for up to 450hp you would need to run 24psi of fuel pressure to increase the lb/hr rating on 454 injectors to 112lb/hr and that is as much pressure as I recommend applying to a set of TBI injectors. Check out http://www.auto-nomics.com/cgi-bin/s...part=12168-001 for this 4bbl TBI unit that uses 4 TPI style high impedance injectors and the TBI computer can run 4 high impedance injectors instead of the 2 low impedance TBI style injectors.
    8. The chip. Depending on how many of these modifications you do the more the need for a custom chip or chips. But a chip will give you the most bang for the buck of any mod you can do to the vehicle.
    I have put together a custom chip with the 18 psi spring and the 155lph fuel pump to make it easier for you guys to get everything you need at one time to get those fuel systems up to par. custom tbi chip kit | eBay
    9. Gears. One of the best ways to get the power to the ground is through gearing. A 3.73-4.10 gear makes a nice streetable rearend gear. Some of the trucks came with 2.73 and some with 3.08. These are terrible gears. I feel that the 3.42 gear is tolerable in a 2wd especially if its pretty stock. check out MOTOR - A Rear Axle Calculator and play with that calculator. I like my trucks to run around 2000-2400 rpms at 70mph in overdrive. Less than 2000 and you don't have any power in overdrive and it just shifts to 3rd at the least little thing. Over 2400 will make more power but gas mileage will suffer. In that range and the gas mileage will be fine. For speedo calibration for a tire and gear change go to www.tbichips.com/drac for 4L60E,4L80E or 5spd trucks and Speedometer Gear, Speedometer Gears, Ford, GM, Dodge 700R4 for 4L60 700R4 trucks.
    10. There is always the supercharger. Check out www.tbi-superchargers.com for some real fun.
    11. Torque converter for you automatic lovers. The stock V8 converter stalls at 1400 rpm which is very low. The 95+ S10 4.3L V6 torque converter stalls 2000-2200 rpm. That 600 rpms will help keep your engine in its powerband and thus make it faster. If you go with a cam with over 212 duration @ .050" then a higher stall would be advised for most street applications. The 2000 stall is a good upgrade that won't screw up your gas mileage, burn up your trans, break the budget, or be unbearable on the street.
    4x4 guys, I typically don't recommend the higher stall converter. If you go off roading that extra converter slippage can be a nuisance.
    12. Oil pumps, I have decided to add this on the list as TOO many people when building engines put high volume oil pumps in their motors and don't do this for a few reasons. 1. you would need to run a 7qt oil pan or you will suck the stock pan empty with any spirited use. 2. It takes 20hp to turn a high volume pump at higher rpms over a std volume pump. 3. Unless you prep the block properly you will end up sending too much oil to the hydraulic lifters and pump them up too much causing vacuum issues and poor performance. I use a std volume, high pressure pump Melling M-55A - Melling Oil Pumps - Overview - SummitRacing.com and its better than stock TBI oil pump and will save us both a LOT of headaches.
    13. For engines, talk with the 2 guys I have listed on the www.tbichips.com/tbimods.htm page and they should steer you in the right direction or I can work with them as well as you to help you achieve your goals.
    14. Never thought I would need to put this on here but just too many issues with these items to ignore. Avoid Bosch o2 sensors, for some reason they cause problems with TBI systems. I haven't figured out why they work differently yet but until then, I recommend avoiding them. Next is spark plugs, Avoid the fancy plugs like the Platinums and E3 plugs for some reason they don't work well with TBI either. I haven't found anything better than a good old AC Delco R44TS or R44LTS depending on which plug length you need for your heads. Most aluminum heads and the vortec heads require the longer LTS plug where the TBI heads and most old iron heads use the shorter TS plugs.
    15. I had a customer email me this link asking about it so I thought I had better post it on here. Biggest waste of $900 that I have seen for TBI. Crappy Holley throttle body stuck on a stock edlebrock intake with unmodified 42mm bores in that intake which isn't going to let near the airflow in that the 52mm Holley TBI has to offer even if the Holley throttle body wasn't so bad.
    Edelbrock 3704K2 JEGS 1987-95 GM Truck TBI Top End Kit



    I hope that this info is helpful.
    RECOMMENDED CAMS
    I have removed the Summit racing cams recently due to a lot of lifter issues with these cams.
    Crane cams
    Summit Part Number: CRN-113904
    Basic Operating RPM Range: 1,500-4,500
    Duration at 050 inch Lift: 206 int./218 exh.
    Advertised Duration: 256 int./268 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.432 int./0.459 exh. lift
    Lobe Separation (degrees): 112

    Summit Part Number: CRN-113932
    Basic Operating RPM Range: 1,600-5,200
    Duration at 050 inch Lift: 210 int./216 exh.
    Advertised Duration: 266 int./272 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.440 int./0.454 exh. lift
    Lobe Separation (degrees): 114
    Summit Part Number: CRN-113934
    Cam Style: Hydraulic flat tappet
    Basic Operating RPM Range: 1,600-5,200
    Duration at 050 inch Lift: 212 int./218 exh.
    Advertised Duration: 262 int./268 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.446 int./0.459 exh. lift
    Lobe Separation (degrees): 114

    Edelbrock cams

    SummitPart Number: EDL-3702
    Basic Operating RPM Range: Idle-5,500
    Duration at 050 inch Lift: 194 int./214 exh.
    Advertised Duration: 244 int./264 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.398 int./0.442 exh. lift
    Lobe Separation (degrees): 112

    Summit Part Number: EDL-2102
    Basic Operating RPM Range: Idle-5,500
    Duration at 050 inch Lift: 204 int./214 exh.
    Advertised Duration: 278 int./288 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.420 int./0.442 exh. lift
    Lobe Separation (degrees): 112

    Lunati cams

    Summit Part Number: LUN-60100LK
    Basic Operating RPM Range: 1,000-5,500
    Duration at 050 inch Lift: 207 int./213 exh.
    Advertised Duration: 250 int./256 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.437 int./0.454 exh. lift
    Lobe Separation (degrees): 112


    Summit Part Number: LUN-60101LK
    Basic Operating RPM Range: 1,000-5,500
    Duration at 050 inch Lift: 213 int./219 exh.
    Advertised Duration: 256 int./262 exh.
    Valve Lift with Factory Rocker Arm Ratio: 0.454 int./0.468 exh. lift
    Lobe Separation (degrees): 112
    Cheapy Sealed Power cams
    CS1014R
    1500-4000 RPM Range
    278 intake/288 exhaust Adv Dur
    Duration @.050 204 intake/214 exhaust
    Valve lift 420 intake/443 exhaust,
    Lobe C/L 112
    Strangely this cam has the exact same specs as a Summit 1102 HMM wonder who makes Summits Cams, Also looks exactly like the Edelbrock 2102 cam.

    CS1105R
    1800-4400 RPM Range
    283 intake/286 exhaust Adv Dur
    Duration @.050 209 intake/216 exhaust
    Valve Lift .435intake/.455 exhaust
    Lobe C/L 112
    I haven't tried this cam yet but I may give the 1105R a try on project Plum Simple
    Also Northern Autoparts Northern Auto Parts has the sealed power cams complete with timing chain and gears as well as the cam and lifters as a kit for under $100. Can't beat that for a budget build.

    COMP CAMS

    As you can see below as the duration gets higher so must the lobe separation angle.

    Choose one that provides the rpm range that you want your engine to run in. For you 93-95 TBI trucks, I can set the rev limiter to match the redline of those cams and the 4L60E automatics, I can set the shift points to match the powerband of those cams. All 87+ cars got roller cams but the trucks didn't get one until 1996 (Vortec). The trucks have all the provisions for the roller equipment but just didn't get the parts.
    Part list for converting to roller cam should you want to go that route.
    GMPP P/N 12371043 = timing chain/gears and roller cam retaining plate kit (1st and 2nd design plates!)
    GMPP P/N 12371042 = 2nd design (higher ball preload) roller lifters (16) with (8) lifter aligners and (1) spider hold-down and (3) spider attaching bolts/washers.
    GMPP P/N 10457356 = Distributor gear for use with roller camshaft.
    chevychase and Sodell like this.

  8. #8
    Senior Moderator chevychase's Avatar
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    Gitter done...cumminsfever

    Gitter done have fun. Running on empty...running blind...running behind.....

  9. #9
    Senior Member Sodell's Avatar
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    Cummins fever,

    I have the opportunity to buy a rebuilt vortec engine (95-99), how would I reuse my TBI parts? Is there a maniford I can buy for the TBI/touse with Vortec, and how hard would it be to use the EGR?

  10. #10
    Senior Member Sodell's Avatar
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    I am guessing I would have to run a pipe from the exhaust somehow.

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