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benifits of porting heads

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by shupach, Jan 13, 2003.

  1. shupach

    shupach 1/2 ton status

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    i have cast iron heads w/ bigger valves and different springs etc, the only work not done to them is porting, is there a noticable difference or should i just keep the heads like they are and save up for a nicer set down the road?

    phill

    btw they're 64CC heads going on a 400sbc bored .030 over
     
  2. HarryH3

    HarryH3 1 ton status Author

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    Proper porting can create a set of heads that will make more power across the entire power band. But a really good porting job can take as much as 40 hours of shop time per head. /forums/images/graemlins/shocked.gif Most stock heads aren't worth the investment. A mild pocket porting, cleaning up the short-side radius and unshrouding the valves will give you a decent improvement in flow without spending tons of cash, but you'll still spend a decent chunk of change. Again, depending on the heads you have now, you may get better flow for the same or less money just by purchasing a new set of aftermarket heads or Vortec heads.

    I wouldn't bother with porting at all with a stock cam. A cam with higher lift and longer duration will take better advantage of the better flowing heads.
     
  3. Sandman

    Sandman 3/4 ton status Author

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    Like Harry said, it can take up lots of time to do this. But porting the heads can free up a lot of horsepower. It wont do much unless you balance it with a cam and maybe a set of headers though. In fact, My engine is currently limited in power now by the heads. I'm thinking of just pocket porting them myself to save the cash.
     
  4. shupach

    shupach 1/2 ton status

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    well heres what im putting into the engine, hyperuetectic pistons, comp cams 4x4 cam (.480/.498 lift), and TBI from a 91 burban

    phill
     
  5. Stroked72Blazer

    Stroked72Blazer 1/2 ton status

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    Whats the grind # for that cam? If its the one I think it is leave your heads alone except to gasket match. If you have a die grinder you might want to place the intake gasket on the heads and grind off any metal that would restrict flow on the inside of the gasket. Don't go any further than a 1/2" into the head. Repeat the proscess to the intake. Any more porting will raise the RPM range of the motor.
     
  6. Sidepipes

    Sidepipes 1/2 ton status

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    IF you can be careful, just smooth everything out, gasket match. Spend most of your time in the bowls, smoothing everythin out, reducing the valveguide size and making them a teardrop shape. On the exhasut side smooth everything out and mirror polish it. Increasing size in exhaust isn't as much of a problem but don't hog it too much.

    I did this to a set of smogger heads and gained around 2/10's in the quarter( but it was only a 14 sec car to begin with). You'll get minimal gains with an investment of time of around 40 hours total. It was an interesting project but next time I'm getting a good set of aluminum heads.

    JUST DO NOT INCREASE THE SIZE OF THE INTAKE PORT TOO MCUH!!!!! or you'll lose your low end torque.



    With this you are not significantly increasing the volume of the heads or the crossesctional area. This means that the velocity of your air charge will not be greatly reduced yet it will flow into the cyinder easier
     
  7. CHEVY 4WD

    CHEVY 4WD 1/2 ton status

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    about how much is it usually for a mild port job?
     
  8. Sidepipes

    Sidepipes 1/2 ton status

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    I had an air compressor and a grinder I used, I bought a small standard abrasives porting kit( I think it was called the intake manifold porting kit) for around $50 canadian, My time was free, other than that you ned head gaskets and intake gaskets.

    If you have to pay someone to do it , its not worth it, just get a set of Vortec heads and intake.

    Figure this person will probably charge around $10/hr for labour and expertise(probably higher) thats $400 already and you will not even match the Vortecs flow/ performance( unless you have some meaty heads.
     
  9. Stroked72Blazer

    Stroked72Blazer 1/2 ton status

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    I use a guy in AR that does a lot of dirt track heads. He works out of his Garage at home and has been offered a job working for NASCAR but dosnt want to deal with the stress. Needles to say he is damn good. I was talking to him about porting my Vortec heads and he said that he had done a set for one of the dirt track guys. When he finished they flowed better but they produced worse #s on the dyno than stock. The guy was adament about using ported Vortec heads so he repeated the proscess on 3 more sets of heads trying different porting styles. The #'s changed a little but never in the write direction. Just food for thought.
     
  10. bablazer73

    bablazer73 1/2 ton status

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    By porting out heads you can really make a difference in the motors power. But along with everything else, the flow must match your needs. By porting heads form stock, you will Increase cylinder heads flow, which is great, because you can increase the rpm the motor can make power at. the down side is, that low rpm torque will be decreased. larger heads flow slower at lower rpm's. slow fuel doesn't make power. Big port heads are great on a small block running 7,000 rpm, but suck at 2,000 rpm. Minor "pocket" porting, bowl blending, port matching, unshrouding valves, and basic polishing of runners will improve performace greatly. If you really need to go bigger, I would check out world products heads instead of spending the money on the labor intensive option of true porting heads. I have seen plenty of people over cut there heads and drop performance. The only true way to tell if all the porting work is really making a difference, is to test them on an air flow bench. At that point it's cheaper to buy new heads that have been computer designed to flow. But like I said, don't go nut's! make sure ALL your pieces are working in the SAME rpm range. Then maximum power will be achieved.
     
  11. HarryH3

    HarryH3 1 ton status Author

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    All of that stuff is why a good head porting wizard is worth his weight in gold. /forums/images/graemlins/wink.gif Anyone can grind out some of the metal and make the ports look nice. But someone that really knows what they're doing can make power anywhere you need it.

    Back when the TPI motors were first showing up in Corvettes, many folks were swearing that they would never be able to be hot rodded. The intake just restricted the high RPM flow too much to wind the engine past 5,500-6,000 RPM. John Lingenfelter started testing various porting designs and running them on a dyno and in the cars, to find out what worked and what didn't. When he was finished, he could make a TPI 383 put out 450 lb/ft of torque and 380 HP. The HP number looks low because you need to spin really high RPM's to make big horespower, but the TPI was still limiting the RPM. But 450 lb/ft from a totally streetable small block was unheard of at that time. Lingenfelter proved that you could port heads to make huge torque numbers at lower RPM. The bad news is that it took a LOT of work to massage the heads so that they would work their magic. A set of his ported L98 GM aluminum heads would set you back nearly $2,500, and this was around 1989, but you would have the baddest TPI ride in town. /forums/images/graemlins/thumb.gif

    That's the difference between someone that really knows how to properly port a particular head and someone that happens to own a die grinder. /forums/images/graemlins/wink.gif
     

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