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Found the knock in my engine, several options, opinions wanted please help!

Discussion in 'The Garage' started by dawson444, Dec 17, 2003.

  1. dawson444

    dawson444 1/2 ton status

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    Alright, I have a 350HO 350 from GM, it puts out 330 hp. It is in my 88K5 with stock throttle body and stock computer. I had a knock going on in it. I pulled one of the heads off, and pulled all 4 pistons out. On 2 of them I had broken a small piece off the side of the pistons, towards the top, which had scratched the piston some, and the cylinder some, but nothing too bad. All 4 of them were burnt fairly bad on the top too.

    Guy at GM dealer said that b/c I am running that engine with the stock computer, the cam is confusing it and thats messing it up and that's what caused the pistons to heat up so much and break the piece off. So he said I have to get a new chip burnt.

    Here is how everything adds up: (keep in mind this is a $2200 engine from the start)

    Option 1
    8 pistons, $300
    machine work $250
    rings and bearings $150
    new custom chip burnt $400

    total $1100


    Option 2
    stock 350
    $1600 with 3 yr parts and labor warranty, no computer mods.
    minus a little b/c I can sell what I have right now

    Option 3
    buy 383 kit from summit for $1100
    have machine work done $250
    new chip $400

    total $1750
    minus a little b/c I can sell the crank and maybe rods I have right now


    If you were in my shoes, which option would you take? I am leaning towards fixing what I have just because it is cheaper, and I don’t have much money right now. But I just wanted a couple of other opinions. Thanks!
     
  2. 87BrnRsd

    87BrnRsd 1/2 ton status

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    I would say just fix what you have. But, my engine was doing the same thing, and some of the bottoms of my pistons were broken off, and it was a bad bearing. Are you sure a bearing isnt bad? I hope you get that fixed and can come to Uwharrie again next year.
    -Harrison
     
  3. SUBFAN

    SUBFAN 1/2 ton status

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    Option 4: There are cheaper '383' kits out there. There are cheaper chips out there too. You will be happier with the 383 set up.

    I have not looked into the camshaft used in your combo, but I would research that some and see if a cam swap is in order too.
     
  4. Z3PR

    Z3PR Banned

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    Re: Found the knock in my engine, several options, opinions wanted please h

    [ QUOTE ]
    Option 3
    buy 383 kit from summit for $1100
    have machine work done $250
    new chip $400

    total $1750
    minus a little b/c I can sell the crank and maybe rods I have right now

    [/ QUOTE ] May be a few bucks more, but well worth it in my opinion.
     
  5. dawson444

    dawson444 1/2 ton status

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    I know there are cheaper chips out there, but the guy who will make this one, will put my truck on a chassie dyno and re make the chip until he is happy with it. Any ideas on a cheaper 383 kit? I don't want to start getting into crappy quality stuff though.
     
  6. Derf00

    Derf00 1/2 ton status

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    Dawson,

    I think #3 is you best option, of course I am partial to 383's; however, I don't think you have covered all the costs involved. A 383 will require a better induction system than your stock TB has to offer, and more than likely you will have to have a bigger fuel pump. I think you are lucky to find somebody that can chassi dyno a chip for you, and that is well worth the money.
     
  7. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    Alright, I have a 350HO 350 from GM, it puts out 330 hp. It is in my 88K5 with stock throttle body and stock computer.

    [/ QUOTE ]
    You have proven a point that I have made many times on here. A TBI system that was designed to feed a 200 HP engine, can NOT feed a 330 HP engine properly. Note the word "properly"! Yes, the engine will run. But it's been running WAY lean, especially under hard accelleration, because the stock fuel injectors simply can't provide the amount of fuel that the engine requires under those conditions. The O2 sensor is igonred at WOT, so the ECM doesn't even know that it's running the engine too lean. Running too lean creates extremely high combustion chamber temps, which can melt piston tops. /forums/images/graemlins/eek.gif : frown: If you had been doing a lot of towing, where you're typically in the throttle a lot more, it probably would have burned holes in the tops of the pistons. /forums/images/graemlins/shocked.gif

    Also, you don't just need a new chip. You also need larger injectors. The stock TBI 350 injectors just can't deliver fuel fast enough to make that kind of power. /forums/images/graemlins/frown.gif The ECM can compensate fairly well just cruising around, by simply increasing the pulse width to the injectors. But when you're hard into the throttle and the RPM's start to climb, the injectors get maxed out. They can only supply a certain amount of fuel, even when "on" 100% of the time. Once the needs of the engine exceed the amount of fuel that the injectors can supply, things start going to hell. /forums/images/graemlins/frown.gif
     
  8. Blaze

    Blaze 1/2 ton status

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    Doesn't that motor have a warranty on it?

    You just have bad luck, dude. Wasn't it about 2 years ago when I was out ther checking out your last motor with a spun bearing? /forums/images/graemlins/1zhelp.gif
     
  9. Blue85

    Blue85 Troll Premium Member

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    Would the 454 TBI throttle body and injectors work?
     
  10. HarryH3

    HarryH3 1 ton status Author

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    [ QUOTE ]
    Would the 454 TBI throttle body and injectors work?

    [/ QUOTE ]
    Possibly. But the right way to do it would be to work out the max fuel needs of the particular engine and then size the injectors to match. Once you change the flow rate of the injectors, the ECM has to be reprogrammed for the new rate.
     
  11. bigblock454

    bigblock454 Clack Clack Clack Premium Member

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    [ QUOTE ]
    Would the 454 TBI throttle body and injectors work?

    [/ QUOTE ]

    The stock 454SS were only 245 HP and then in '93 255 HP, the injectors will still be 105 HP off. The 454 TBI throttle body had 2" throttle bores and would flow about 600 CFM. The general formula used for CFM required:

    CFM required=((CID*Max RPM)/3456)*Volumetric Efficiency

    In your case that would be around 600 CFM, I would say with a properly tuned chip is would work, just by a hair. Your stock chip won't work over about 3/4 throttle when the ECM drops into open loop mode and the O2 sensor is ignored. The stock TBI engines had such a low RPM max torque the ECM is almost completly programmed wrong for your application.

    Turbocity.com sells ported TBIs that would flow more than enough, that is the direction I would go.
     
  12. dawson444

    dawson444 1/2 ton status

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    I would love to do a 383 right now, I really would, but I just simply don't have that kind of money. I think I am going to just rebuild what I have. The guy who will burn the chip said he can do it for $300 w/o the dyno, but he would just be guessing on what to program it for at WOT. He said it would be $400 to put it on the dyno and program it, he said he could dial in WOT perfectly then, and I would get dyno sheets and everything. The pistons getting too hot is exactly what happened.

    Blaze, yes I do have bad luck considering I had this engine out about 3 months ago because I broke a skirt off of a piston, now this. This engine is the replacement for the one that was knocking really bad a while back.
     
  13. dawson444

    dawson444 1/2 ton status

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    Oh, and about the warranty, since this was a performance engine, the warranty was 12mo, 12k mile, parts only. I broke the skirt off of the piston after about a year and a half, but only about 5k miles, but no warranty. If I did have the warranty, it would have been parts only ($100). I wish I had just gone with the stock 350, which would have been 3yr 30k mile parts AND LABOR. I now have about 6k miles on it, and this is going on with it /forums/images/graemlins/angryfire.gif.
     
  14. HarryH3

    HarryH3 1 ton status Author

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    Even if it failed within the warranty period, GM most likely would have said "so sorry" once they saw the melted piston tops. Their warranty doesn't cover owner-caused damage. /forums/images/graemlins/frown.gif
     
  15. Thunder

    Thunder 3/4 ton status

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    The 350 Ho was never designed to be ran with stock TBI. GM does not recomend it and will void warrenty.
    The main problem with the 350HO and TBI is that the cam has too much duration and the higher than stock compression ratio combined with that cam will not run on a stock chip. It really screws with the MAP sensor because it radically changes the manifold vacume at all speeds so the MAP sensor readings are not correct for engine loads. Usually resulting in a very lean condition at most all speeds. The MAP sensor is the main sensor that the ECM relys on to caculate fuel needs in open or closed loop.

    No matter what you do it aint going to be cheap. The cheapest route may be to go back to a stock 350.

    If you are going to run a performance engine either the 350HO or the 383. Some money will have to be put into the TBI system. And that will cost extra.. You cant take short cuts with fuel Injection (as you have learned) it has to be done right.
    To make that 350 run right get the chip reprogramed as you said. If you have the bucks do the Dyno chip burn. It is the best way to get things right. But your stock TBI still does not have enough flow(480cfm)to run it the way it should. You will never make the power you payed money and built the engine for. The TB should be modified.

    I would get one ofhttp://turbocity.com bored out Throttle bodys it will fit on your manifold with no mods and get the air flow up to where that 350 will run. Because of the higher compression ratio, I also think some 65 lb per hour flow matched injectors and an adjustable fuel pressure regulator are needed also. Turbocity has all of the stuff you will need to make it run right. Call them. Their tech guys can help you get things straightend out. They can help you out with a chip too.
    ALSO
    These guys make a TBI chip for the 350HOhttp://www.fastchip.com
    They do good chip work. It costs less than a dyno job.
    You should also get yourself a good scanner.
     
  16. BayouBlazer88

    BayouBlazer88 1/2 ton status

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    does the 350HO engine come with Vortec heads? If so, then I'm having pretty much the same problem with my freshly rebuilt 355 with Vortec heads and tbi and stock cam. I know Holley makes a 670cfm replacement TB, I have heard that their injectors are junk but I wonder if it would do the trick.
     
  17. dawson444

    dawson444 1/2 ton status

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    Thanks for the info, the 350HO does have vortec heads.
     
  18. Thunder

    Thunder 3/4 ton status

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    I see turbocity's site is still down so go here:
    cfm-tech.com
    They sell turbocity stuff and make the best TBI spacer on the market.
    Read that page then hit the "GM TBI tuning" button on the bottom of the page. Read all pages/links in their TBI tuning section.
    It will help you guys with your problems and hopefully give you a better understanding of TBI and what you need to do to make things right.
     
  19. BayouBlazer88

    BayouBlazer88 1/2 ton status

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    thanks for the link, Thunder. that really sheds some light on the tbi aftermarket part world. Looks like I'll be purchasing several things from them in the future.
     
  20. 91GMCSuburban

    91GMCSuburban 1/2 ton status

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    good stuff. What about a 454 t-body with 350 injectors and use an aftermarket chip like from jet?. I read somewhere that the injectors do well enough on their own and the 454 injectors provide to much fuel.
     

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