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350 TBI Modifications

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by tommyboy, Apr 25, 2000.

  1. tommyboy

    tommyboy Newbie

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    I have an 89 with the stock 350 TBI. It has a hypertech chip, a 5" K&N filter, with stock exhaust manifolds with 2 1/2" pipe into three chamber Flowmasters. I plan on rebuilding the motor sometime this month. Might have it done to go to Silver Lake, MI. I have done some investigating into other mods, like boring over, cam, intake, etc. What will I be able to get away with the computer? Anyone using the Holly 650cfm throttle body unit? How well does it work. Also, does anyone make an itake manifold that will accept TBI and Vortec heads? thanks

    Tommyboy
     
  2. Truckfan2

    Truckfan2 1/2 ton status

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    Mann, I had those same thoughts. No, no one makes the TBI intake to fit the vortec heads (I checked on that this weekend). However, what I am planning on doing is the Holley 670 cfm TBI unit with vortec heads and an Edelbrock intake manifold. The heads I am going to have drilled to accept the old style intakes by a local machine shop if the rumor that chevy started drilling them at the factory is false. If you don't want to have the heads drilled, you could go with the "Fast Burn" heads from GM Performance parts but they run over twice as expencive as the vortecs (they are better than ported vortecs though) and are already drilled to take old and new intakes. Cam- some type of CompCams... whatever you feel is good. Computer-you could have Jet make you one if you send in the specs although they quoted me $400 for it!!! Expensive! If you end up going with a custom chip, build the bottom end whatever way you want... I'm thinking either 4-bolt main 355 or 383, a strong one anyhow. Get back to me on what you want to do, ok? Later~Pete

    NEVER been stuck... *yet*
     
  3. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

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    Now this is the stuff I like to see - technical & EFI in the same post!! Truckfan is right that nothing exists yet but I don't know if he checked with GM Performance parts or not. They were supposed to have a TBI to Vortec manifold available by now! If you're only doing a 350 rebuild with a mild over-bore, the computer should be fine. Most aftermarket intakes and cams etc are made to compliment the computer not fight with it.
    My plan for my 89 is to rebuild the engine using a Summit Racing 383 kit and re-use the stock TBI setup. It's hard getting straight answers from any of the professionals, especially when it's by email tag. (When I go to do my engine, I will be calling to talk to them in person first) The advice I have gotten is mixed. Some say Holley 670cfm unit and chip, some say high volume pump and regulator with TBI unit, and others say combinations of the above! Probably the best advice I got was from a GM Goodwrench Tech. He suggested trying completely stock with my 383 first and work from there. If I start modifying anything, I'll start with the a custom chip and then if necessary, a Holley 670cfm unit. From there, an adjustable fuel pressure regulator, and from there a high flow pump.
    Hopefully things will work in stock form! The reason I figure this is because according to the CFM formula (CID x RPM x Vol.Eff.)/3456, a 383 that stays under 5000rpm with Vol. Eff. of 80% (being generous on natural aspiration) should only require a CFM rating of 450 cfm!!
    According to most sources, the GM 350 in stock form runs lean so I figure the required upgrading will be on the fuel supply side more than the air flow side. I am intent on using TBI on my engine so I'll know in a few months time what it will take to make it work!
    Regarding a cam, I have been told that computers get squirelly if the cam is not a computer compatible cam. I am going with a Crane Compucam 114122 which gave a TPI 305 40 extra HP when tested by Summit Racing on an otherwise stock engine!

    Sorry to be longwinded but I hope some of this helps.

    Good Luck and please post anything you find out.

    Brian
    Still in search of the TBI KING!!


    P.S. Howell EFI makes custom chips for $125
     
  4. **b**

    **b** 1/2 ton status

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    Hey Tommyboy...
    how do you like the Flowmaster 3 chamber????
    I was planning on going that route...
    too loud???

    let me know...
     
  5. SnakeEyes

    SnakeEyes Registered Member

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    If your having Vortec heads drilled to accept an old manifold I believe it is a mistake. The roof of the manifold will be lower than the new roof of the Vortec heads. You will be giving up a significant amount of the flow advantage of Vortec heads. Why pay for the advantages of Vortec’s and then penalize yourself with an older setup? My advice would be to get the proper manifold.
     
  6. Truckfan2

    Truckfan2 1/2 ton status

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    I'm thinking of going with the "Fast Burn" heads that are drilled for both styles. They cost $580 a head but are twice as good as vortecs.

    NEVER been stuck... *yet*
     
  7. coopertwpk

    coopertwpk 1/2 ton status

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    Instead of using vortech heads look into the merlin aluminum heads already built the way you want them.
     
  8. SnakeEyes

    SnakeEyes Registered Member

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    TruckFan2, Have to ask you what you mean by "twice as good" The only good that counts for 4 wheelin is high flow numbers to the cylinder at low engine speeds. I can’t say one way or another, as I have not analyzed the flow numbers for the "Fast Burn Head" so I ask the question. In a high speed application engine I would tend to agree with you, although I would still want to see the data, but in a low speed application, I think you MAY be wasting your money. I’ve heard good things about the Merlins(can Da Grump do anything wrong?) also but the same comments apply. If they ain’t flowing at low RPM, relatively, why did you spend the extra money? Not saying the Fast Burns are bad, just don’t want to see you spend big bucks to become disappointed.
     
  9. Truckfan2

    Truckfan2 1/2 ton status

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    True... I know I've looked at the number comparison before and they flowed significantly better but I'll get the numbers and see what you think.

    NEVER been stuck... *yet*
     
  10. tommyboy

    tommyboy Newbie

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    The three chambers aren't really that bad. They have a nice sound to them. If the exhaust dumps under the truck at certain rpms the noise level isn't to bad. I would recommend them highly.
     
  11. Nrose07

    Nrose07 1/2 ton status

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    OK, let me clear up some confusion. 1.I know, I've just spent the last month doing this! 2.Don't mess with me I'm broke and got bloody knuckles! 3.Use a VORTEC intake for the heads, one of the design upgrades are raised ports. 4.Unless you live in Arz. get the Performer RPM intake. Why? Because the RPM makes better power in the whole RPM range. Also, since the vortec heads are designed for multiport F.I. the heads don't have provisions for EGR. They don't need to heat the intake under the carb for better atomization in cold weather. The regular Performer Vortec intake has nothing to compensate for this. The Performer RPM Vortec intake has a external coolant bypass that runs under the carb/intake just like the EGR would. This will help the engines efficency. 5.Use a Holley TBI to 4-barrel adapter, it works well. 6.Don't buy the Holley adapter if you have to pay more than $40. Why? Because it is a GM part! It was used on 454 TBI. Any dealer can get it for under $40. 7.The HOLLEY TBI, CRAP! Why use it if you don't need it? The stock is fine. Still not enough, get a TBI for a 454. The quality is better and the injectors are too. 8.Headers are great if you really want them. Want bad because you'll wonder why when your installing them. 9.Every dollar you spend on that pair of headers means you will sleep that much better. 10.JET, how much???? Forget it, contact Street & Performance Electronics 304 Smokey Lane, North Little Rock, AR 72117 Ph#(501)945-0354, I paid $160 and they are quality! 11. Cam, well what are you doing with it? The chip can be programmed for alot. I like Morrso. And their stickers look good on your tool box!
    Well I hope I covered everything, I have answers if you got Q's.

    Displacement, cubes, and did you say you drive a riceburner???
     
  12. Jamie

    Jamie Registered Member

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    Matt this questions for you. You say that the 7116 manifold has a place In the center of the Intake for a coolent passage. But how is that going to help when it takes quite a few minutes for the engine to come up to operating tempature. I'm asking cause I have a 79 with a 400 with vortec heads 2116 manifold and without the heat crossover when its colder than 30 degrees out I have to let the blazer warm up for at least 10 minutes in fast idle before I can leave. Recently I've been considering an aftermarket fuel injection system to aleaveiate this problem. I just want to get in and go. I've tried tighting the electric choke a little more but its touchy to tight and the choke does not open all the way and the gas mileage stinks. Any Ideas from anyone would be appriciated thanx.
     
  13. Nrose07

    Nrose07 1/2 ton status

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    The difference that it will make is better efficency once its warmed up. You will still have the initial startup cold-bloodedness. You will have more power once its warmed up, the fuel will atomize better hence better efficency. Hope that helps.

    Displacement, cubes, and did you say you drive a riceburner???
     
  14. jarheadk5

    jarheadk5 1/2 ton status

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    Quick question: Will most of these mods work on a TBI 305, and will most of the mod parts swap over to a replacement 350 (in the future)? Thanks.

    [​IMG] Semper Maintenance!
    [​IMG] So many ideas, so little money...
     
  15. KP3100

    KP3100 Registered Member

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    Does anyone know if someone makes an open air cleaner to fit a 350 efi out of a 1990 Blazer.

    I went through it the first, should been the last time.
     
  16. Nrose07

    Nrose07 1/2 ton status

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    Yes the mods will work on either 305 or 350, I'm not sure what the injector size is on a 305 but I know the computer is different. KP3100, if you want to make power use the stock intake out of a 90' tbi, why,, because cold air is dense, dense air has more O2 in it for it's size, and you don't get cold air from under the hood. A stock intake will pull air from in front of the radiator, nice and cold. Use a K&N filter and you will have good flow. If you still need more use a intake off a 454 tbi, they have 2 intake hoses. Matt

    Displacement, cubes, and did you say you drive a riceburner???
     
  17. K5 NUTT

    K5 NUTT 1/2 ton status

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    Questions...
    1) Without changing heads..do they make a TBI intake to bolt on an older GM crate without drillin holes and such?
    2) How hard is it to monkey the linkage from carb to TBI...do you just use an throttle cable from a 87 thru 91 K5?
    3) if number 1) is a nogo...refer to the GM 454 adapter?
    4) wanting to do the swap really soon...the electrical end doesn't phase me...got my own scanner and all...it the small details you run into like throttle cable etc. on a sunday afternoon that bite...lol. Are you runnin the small cap late model dist also or did you retain the big cap HEI?


    Thanx for the answers in advance!


    AZBLAZER

    1979 K5
    1976 K5 Chalet
    1972 K10 Suburban
     
  18. Nrose07

    Nrose07 1/2 ton status

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    #1. For intake manifolds you have 3 options for non-vortec heads. 1,stock 2,Edelbrock 3,Holley. If you want to upgrade to a larger 454TBI later the edelbrock will not work, you can't bore the mounting flange with out running into a coolant passage. The stock one is borable, and the holley is already enlarged for the Holley 670cfm tbi.
    #2. It should not be a problem if you use a stock tbi bracket.
    #3. I don't have a part number but the 454 didn't have a tbi intake, it was a stock castiron intake with a adapter.
    #4. Since I had the tbi from the factory I have the small hei with external coil. I would suggest getting a TBI wiring harness from painless wiring, you can get one from SummitRacing. I belive that you would not need to mess with the distributor with the harness.
    Hope it helps! Matt

    Displacement, cubes, and did you say you drive a riceburner???
     

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