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How do you add Power to a TBI 350?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by 87superblaze, Jun 6, 2002.

  1. 87superblaze

    87superblaze 1/2 ton status

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    How should I go about adding horsepower to my 1987 Blazer with a TBI 350? It seems like there is no way to get any good power from it. It has 35" tires with 4.10 gears.

    It has hooker headers and 3" dual exhaust and turbo packs. The heads were shaved and the compression is up to 165 psi. Basically everything else is stock.

    I was thinking a mild cam would help and possibly upgrading the computer. What are your opinions?
    It seems that I had more power before I started to add things.

    The reason I am asking is I and torn between getting a big block and modify it mildly or keep the 350 TBI and modify it. I Want to save my good gas mileage because I tow car haulers and camping trailers!!
     
  2. jc71355

    jc71355 1/2 ton status

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    Holley Makes A super charger for it. I know www.jegs.com has it but it's pricey. You could get a bored Throttle body From www.turbocity.com I don't know about how much you could get out of a cam because you are restricted to what the computer can handle. I have a chip in my 91 but it was in there when i bought it so i can't tell you how much power it gives over stock. Some say that they aren't worth it while some say they are. Edelbrock sells a muilti port conversion that is supposed to give more pwer Hope this helps.

    James
     
  3. BrianDamage

    BrianDamage 1/2 ton status

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    Edelbrock's got a deal I was looking at...if you buy their TBI performer intake, performer heads, and one of their cams, send them a copy of the receipts, they will send you a chip for you computer for no charge...sounds pretty good to me--I think it's called the 'TBI Performer Package'
     
  4. 74k5inVA

    74k5inVA 1/2 ton status

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    have you thought about switching the gears to 4.56. from what i hear those gears with 35 inch tires will help keep your revs in the powerband of a 350, producing more hp and torque, possibly (don't know for a fact) but will save gas as it will take less getting on it to get on it.
     
  5. YtseJam

    YtseJam 1/2 ton status

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    The cheapest and best performance gain you will get will be from a camshaft swap. If you don't want to tear into the engine, replace the prom with a hyper tech chip, usually the only other adjustments may entail a 160° thermostat and playing with the timing. Also here is a tip. unplug that wire from the knock sensor. This will avoid the EST from going into bypass mode or retarding the hell out of the timing. Advance it until it pings and then back off. Make sure it starts easy and lock the distributor into place. adjust your idle and compensate so the TPS voltage is @ .550 V @ idle.
     
  6. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    <font color=orange>brain damage</font color=orange>... where did you hear/see this i am all of a sudden very interested.
     
  7. muddysub

    muddysub 1 ton suburban status Staff Member Moderator GMOTM Winner

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    <font color=orange>brain damage</font color=orange>... where did you hear/see this i am all of a sudden very interested.
     
  8. BrianDamage

    BrianDamage 1/2 ton status

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    on www.edelbrock.com

    actual page is: http://www.edelbrock.com/automotive/man_sbchev.html

    located a little over 1/2 way down


    Performer T.B.I. (Idle-5500 RPM)


    Designed for 1987-1995 305/350 c.i.d. (5.0/5.7L) Chevy Throttle Body Injection (T.B.I.) engines. Ideal for trucks, Blazers and Suburbans. #3704 is stock replacement/street legal part for 305 and 350 V8s with OEM T.B.I.; 1987-94. T.B.I. water jacket similar to stock. Accepts all OEM equipment and small-bore (1-11/16") throttle body injectors only. No chip changes or computer mods required unless entire 5.7L Power Package (manifold, cam, heads) is used. Computer chip (E.O. #D-215-13) is supplied free of charge with proof of purchase of manifold, cam and heads. The chip re-programs your computer for optimum power gains when the entire package is installed. This Total Power Package greatly improves performance.
     
  9. Thunder

    Thunder 3/4 ton status

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    First of all I think your exahust is a too big. That dual 3" pipe robs power from your low end. You would be better off with dual 2 1/2 " or a single mandrel bent 3" pipe espically if you tow. You want an exahust system that generates torque not top end HP. The TBI just doesn't flow enough to feed pipes that big.

    Check out this stuff fromfastchip.com It gave a improvement in power all through the RPM range and helped my midrange torque.

    These distributor modules also will help:<a target="_blank" href=http://www.performancedistributors.com/accessories.htm>performancedistributors.com Dyna Mod </a> the 8 pin dyna-mod works just about as good as a MSD box for building torque but is only half the price. They also work a lot better at high RPM than the stock module.
    I also have edelbrock headers into single 3" exahust and a flowmaster muff.
    I built my K5 to generate Torque not horsepower. I wanted it to be able to pull a load and get good fuel milage doing it. Towing my boat down the interstate at 60 -65 mph I usually get 16 mpg.
     
  10. 87superblaze

    87superblaze 1/2 ton status

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    Thanks for the good advise. I had a feeling the dual 3"er's might be too much. Lets say I put dual 2.5" pipes on and I end up switching to a Big Block, Will it be restricted by the 2.5" exhaust?

    What size tires are you running on your rig to get 16 mpg? Just Curious. I use to get that before I started to tinker with Everything.
     
  11. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Right now it sounds like your exhaust is what's killing your performance. I would recommend a single 3" exhaust. Even on a BBC 3" is plenty. When you go large and dual you are losing your bottom end torque but gaining at the top end. I shoot for low end torque over high end HP. My last engine in my 76 blazer made 365 HP @ 3500 RPM, but it made 508 ft. lbs. torque @ 2000 RPM.
     
  12. Thunder

    Thunder 3/4 ton status

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    I have 2 sets of tires. I get the best milage on the 10.50 x 31 ATs. Thats the size I usually tow with and run down the highway.
    For off road I run 12.50x 33 mt. when I run the 33s it usually knocks off 1-2 mpg . I run 3.73 gears.

    2.5" pipes wont hurt a big block a bit. They will really help build torque. But you should have a crossover pipe installed between both sides. That will do wonders for your low end.
     
  13. ftn96

    ftn96 1/2 ton status

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    The only problem with the chip and the 160 deg therm is that the TBI motors are designed to run between 190 and 210. And they haven't been all that co-operative with the 160 therms. Now! If they can get the chip to compensate for the temperature difference, then thay might have something. Till then....I'd stick with a mildy over stock cam!! /forums/images/icons/wink.gif
     
  14. 90K5

    90K5 1/2 ton status

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    I have 2 1/4 exhaust on mine after the muffler and it sounds mean, plus really helps for torque. <font color="black"> </font color>
     
  15. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That is a myth. Smaller exhaust tubing does not favor torque. Everything after the headers is restriction. 3" pipe is not necessary but it's certainly not robbing any power.

    Adding restriction to the exhaust NEVER gives you more torque.

    Anyone with DD 2000 can easily prove this. Add mufflers to any exhaust combination and you lose power throughout the power band, not just at high RPMs.

    We have gone over this MANY times at Chevytalk.com. The truth is that header primaries do affect the engine's powerband, but everything after that is just restriction and costs you power throughout the powerband.

    NOTHING makes power like open headers.
     
  16. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I've often wondered about that myself. We get bigger cams to flow out more exhaust. Some add bigger valves to clear our more exhaust. We add headers for better flow. THEN all of the suddenly we're supposed to put in smaller pipes or restrictive mufflers to make more power?!
     
  17. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    MORE POWER! Well lets see, try out the TBI cam from comp cams 12-249-4 it has .434/.444 lift 206 212 duration with a seperation 112 degrees. The heads unfortunately are probably a big limiting factor. Even with higher compression, the combustion chambers aren't anything too write home about. Nice for stock, but not for kicking butt. I would buy a set of Vortecs and the TBI intake from GM for them. It'll be pricey, but you're gonna notice a big difference.
     
  18. 84_Chevy_K10

    84_Chevy_K10 Banned

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    I know. It's all a bunch of BS. Exhaust restriction does not favor torque, it costs you power, PERIOD.
     
  19. Thunder

    Thunder 3/4 ton status

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    Smaller Exhust tubing does too favor torque.
    Smaller tubing increases the velocity of the exhaust gasses at LOW RPM. This allows the engine to build torque faster at low RPM. Because it scavenges the gasses out of the combustion chamber. Giving better off idle throttle response.
    Large diamater pipe slows down the velocity of the gasses and does not scavenge as well at LOW RPM. So it takes a little longer to start building torque.Once the RPMs get up Then of corse it will make more power than smaller pipe

    I doo agree that.The smaller diamater pipe will not build more torque than larger diamater pipe. But a smaller diamater will develope torque sooner in the rpm band which helps in a heavy truck driven in city traffic.
    This post was not about a highly modified free flowing engine. It was about a Stock TBI 350. And I still believe that dual 3" dual pipe is too large for good all around street driveability in a stock TBI engine even with a mild cam. Sure it will work. But smaller pipe will give a better blend of performance and economy.
     
  20. 84_Chevy_K10

    84_Chevy_K10 Banned

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    That's 100% BS.

    Maximum power AND torque will always be with open headers.

    I would like to see some proof of what you're saying if it's so true.

    3" duals are not necessary on a 350 that's mostly stock, but they will not cost you power. All the cylinder scavanging effect comes from the header primary tubes. After that, it's all restriction.

    I stand by my statements. This has got to be the biggest most BS bunch of crap myth that exists in the high performance world. I am not saying every 350 should have 3" duals. What I am saying is that you don't lose torque if you put 3" duals on your truck instead of 2 1/4". You might not gain anything, or what do you gain might be way up in the RPM range, but you're certainly not going to lose anything.
     

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