about how much hp would be gained?

I have a 355 chevy, and I am putting vortec heads on, but idk if I should go carb or tbi. how much hp is gained from tbi over carb? and how much of a pain is it to install tbi vs "bolt on and go" carb? i realize carbs aren't just bolt on and go, but it is fairly simple.

3 Answers

  • 1 decade ago
    Favorite Answer

    **EDIT** Carl.. I mean no disrespect but theres ALOT more to the edelbrock carb than just idle speed and idle air mixture screws. I'm a big fan of the weber design'ed carter AFB and edelbrock carbs for street use. I have been using and modding them for 15 years.

    You have float adjustment, set-up springs, metering rods, front and rear jets, along with pump shot and squirter size.

    Your the perfect example of what I ment by most people don't understand carbs well enough to dail them in perfect.

    The step up springs is the transfer between idle/cruise/power circits in carb. The setup spring needed should be picked by the vac level of your engine at idle. Springs sold in 3, 4, 5, 6, 7, 8 inch HG vac. Use the closest one to half of the amount of vac your engine pulls.

    Then metering rods is for light throttle and med throttle use. The rod tapers and goes into front jets to block off fuel flow. The tip is smaller and the upper part is larger. The step up springs moves these rods up and down based on vac

    Then you have a whole list of jet sizes to pick from. Best to tune with a wide band O2 to get perfect A/F ratio but you can track tune a carb by reading plugs and changing jets based on plug color

    ALOT more than bolting it on and turning a couple of screws to get it dailed in perfect for your engine.. Sure it will run out of the box, but it will run better and get better mileage once fully tuned.

    The last Edelbrock carb I ran was a 1405 600 cfm man. choke

    Stock .100" front jets, .095" rear jets, orange 5" HG springs, .070" x .047" rods, pump linkage rod in middle hole

    To dail it in perfect for my engine I ended up with .101" front jets, .104" rear jets, .068" x .042" rods, Pink 7" HG springs, pump linkage in top hole

    **EDIT OFF**

    Theres really no power diff between the two if both are fully dailed in right.

    Carb is much easier and cheaper to just bolt on and go. If tuned right using a wide band 02 sensor, etc you can get the same idle and fuel mileage from the old design TBI and a carb. Most people just don't understand carbs well enough or have the wide bad O2 or a 5 gas machine to get them dailed in that well though

    TBI is harder to install, need the wiring and computer, computer advance dizzy, but very simple to tune and its a 'self adjusting' system.

    Thats 1 major gain with any EFI over a carb on a performance engine used for street driving and racing.

    I run my engines on the edge, 212-218 psi cyl pressure on 93 octane, with a carb. Theres been times I had to pull over on side of road or interstate and adjust the timing or change jets to keep out of detonation

    .....MONKEY... Man, sorry to hear about your luck with the vortecs. You got to Email me and tell me the story on your bad vortec deal. I would like to hear more about that.

    I have been building vortec headed street performance engines for years and NEVER had that kind of trouble..

    The pressed in studs are a better press fit than the older heads. We have ran as much as .520" lift cams on stock vortec heads with pressed in studs

    Then only time I had a broken stud was when a customer ran stock rockers with a .510" lift cam and the rocker slot wasnt long enough for full travel, the rocker slot binded against studs and snapped a few of the exhaust rocker studs

    If stock rockers is a must, I grind the slots longer. Or use aftermarket long slot self alining rockers.

    For valve springs I use.. depending on cam lift and RPM

    Howards 1.240" to 1.265" 90 to 115 # seat presure

    98111 $25,

    98214 $28

    98212 $40

    All of these are drop in springs, but you do have to remove the flat inner damper spring for them to fit over the larger stock guides and seals

    To gain the retainer to seal clearance, I will grind .09375" (3/32") off the very bottom part of retainers. This gives enough clearance for .515 to .525" lift

  • 1 decade ago

    You aren't going to gain any noticeable power. Remember, when TBI was introduced, the heads and cams were changed, as was compression, so the TBI was just icing on the cake.

    Where fuel injection on the older motors shine is the driveability. You can get better mileage, the idle is better, and you can infinitely tune an electronic setup in timing and fueling, that you simply can't with a non-EFI setup.

    Also realize that Vortec heads will REQUIRE a tune to any EFI system, as they typically increase compression over other heads in use, and with the different chamber, require less timing than "old" chamber designs. With the same timing as old design heads, they WILL detonate.

    Also, if you haven't purchased them already, I'd avoid factory Vortec heads. The springs are weak/not rated for much lift/won't handle much lift, the castings are very thin and extremely prone to cracking, and the rocker arm studs are pressed in. For not a WHOLE lot more (certainly not if you consider the components already installed) you can get Vortec replacement heads from companies like RHS that eliminate all the problems stock vortecs have. Wish I had gone that route myself. Instead, spent money on having new springs installed, then later broke a rocker arm stud, so had screw in studs installed. And all this on a roller came with right around .450" lift.

    Source(s): TPI 355 with vortec heads in my '85 K5 Blazer
  • carl l
    Lv 4
    1 decade ago

    Edelbrock carbs are "just bolt on and go". Rich-lean adjustment and idle screw and that's it.

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