Vortec heads and TBI?

Discussion in '96+ Vortec Performance + Computer Swaps' started by Hipster, Jun 23, 2019.

  1. Hipster

    Hipster I'm Awesome

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    Hurry up! I need that chip yesterday. lol

    Deleted the egr?
     
  2. andy396

    andy396 I'm Awesome

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    I don’t think it’s a good idea to delete the EGR with the Vortec heads. It helps keep the combustion temperatures down and prevent knock.
     
  3. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    It helps prevent NOX but not Knocks, because the EGR is shut off at higher TPS% (generally above ~50) when knocks are more prone to occur. I have EGR delete and am running Hywy Lean Cruise with no big issues. I mostly get KC (knock counts) when at 90 MAP (WOT) at 4000-4800RPM. Now I'm in the process of pulling spark in those ranges where knock occurs.

    Note: the 45 count in green was when starting the engine - not a concern.

    upload_2019-6-24_14-40-23.png
     
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  4. andy396

    andy396 I'm Awesome

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    I hear ya. But would it be wrong to say that it helps at part throttle loads, cooling the combustion temperature allowing it to run more advance at a leaner mixture? If you don’t run egr you have to run a little more rich and less advance at light loads/part throttle. And in doing so it also would make the cats work harder? Or am I thinking about it all wrong? I’m sure you have more experience than I so feel free to put me in my place.
     
  5. Hipster

    Hipster I'm Awesome

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    Feel free to talk amongst yourselves. I'll sit here quietly trying to absorb this information .:)
     
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  6. L31MaxExpress

    L31MaxExpress I'm Awesome

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    It doesn't work like that at all. Need to datalong and preferably have a wideband to get things correct. Sure you can add fuel and timing to the chip and get into the ball park but you are leaving a lot on the table.

    Vortec heads are a actually a loss of torque anywhere under 4,000 rpm. The break even point is ~4,500 rpm. There is a reason GM went with a roller cam that is smaller than the TBI cam. The earlier IVC helps retain low-end torque and the vortecs flow added to the top-end even with the tiny cam.

    I had an 8.75:1 compression 350 TBI with the stock heads and cam that put down more torque than a 9.4:1 Vortec 350. Both had headers and were tuned to get the most torque out of them.
     
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  7. PlayingWithTBI

    PlayingWithTBI Desert Old Guy

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    That's one way to achieve the same goal, with EGR you're reducing the amount of combustibles, ie air/fuel ratio (and HP) thus cooling down the combustion chamber. The other way is to maintain proper AFR so it doesn't have to work as hard to maintain torque/horse power which, in turn, helps to keep the combustion chamber cooler. EGR and Hywy Lean Cruise (which cuts AFR and advances spark) were implemented and eliminated respectively because GM (and other manufacturers) couldn't meet the EPA NOx requirements in the late 80s and the 90s mainly due to catalytic technology, newer Cats are 3 stage which helps to reduce NOx.

    ^^^What he said, keep in mind the roller cam delivers more duration than a flat tappet which, gives you better breathing and performance, so you don't need as much lift to achieve the same results.

    Anytime you can increase flow in/out, the more efficient your engine/system is.
     
  8. Supercharged111

    Supercharged111 I'm Awesome

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    I really have to question 4000 RPM being the changeover point, because my tuned Vortec definitely runs a lot harder than my TBI did and it did so long before 4000 RPM. I will say off idle the TBI can't be beat, but long before 4000 Vortec will freight train the TBI. I'd argue, without data, that it's more in the mid 2000 range as the Vortecs, IMO, were held back more on a stock tune. My stock C1500 would bark tires long through 1st gear (3.42 truck) whereas my 1500 in sig in stock form would barely chirp a worn out right rear tire in stock form. Hit the on ramp and long before redline, buhbye TBI.
     
  9. 98 Nitro

    98 Nitro I'm Awesome

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    Ya I agree if he said the break even point was like 3000rpms I might agree but after that no way .
     
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  10. Gibson

    Gibson OBS Enthusiast

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    I don't have any "hard numbers" from a dyno, but in daily driving my '94 K3500 CCLB, vs the '97 K2500 Sub,, both with the 4L80/4.1, and both stock, the '94 TBI seemed a bit more responsive just off idle,, but the Vortec comes-on much stronger as the revs build a little.
    You can really hear the exhaust note change at ~3000 rpm,, the Vortec starts coming alive.
     

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