HP gains from just a valve job?

Discussion in 'High Performance Modifications' started by need-for-speed, Oct 17, 2017.

  1. need-for-speed

    need-for-speed Veteran Member

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    Feb 7, 2003
    Conroe, TX
    Wow. Great discussion!

    I do have the heads back and they did a 3 angle valve job. The guy also said the intake seat (I think) was only about 85% open and supposedly he opened it up more.

    Can anyone explain that to me? Did he likely just remove cyl head material on the inlet / upstream side of the intake seat? i.e. Unshroud it ?

    Does anyone know if my Edelbrock performer heads 2003 vintage (170 cc inlet runner volume) came with a 3 angle cut / valve job?
     
  2. G72Zed

    G72Zed Veteran Member

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    Sep 8, 2015
    Canada
    I would think he is referring to the "valve throat percentage". As an example, if your heads have 2.02 int valves, multiply by .85 and your throat would be @ 1.717, just under the valve seat.

    Some take the valve OD and use x .98 or just take off 0.040 (or what they have) for actual effective area, almost the same results.

    As for the best throat % & valve size, that needs to be figured out what the engine/head combo like best, a flow bench and dyno is a must. I have used between 88.5 up to +92% (results did vary!) Top level heads are worth every penny, and the reason professional porting is expensive.

    Hope this explains a little, but, this is just my $0.02
     
  3. camaro71/holland

    camaro71/holland Veteran Member

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    Aug 27, 2003
    The Netherlands
    ^^^ What he said. Rule of thumb is opening the throat to 90% of the valve O.D.
     
  4. Blown Camaro

    Blown Camaro American by birth, drag racer by choice

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    Dec 13, 2009
    Deltona, FL
    Do not buy assembled heads without DISASSEMBLING them and checking everything, especially valve guide clearance AND the valve job. I absolutely guarantee you something will be off. I really got burned on this and it cost me $$$ to repair and could have cost me an engine. On the plus side, now I know how to setup heads! LOL. Assembled heads are built with budget parts. They try to keep the price point as low as possible so that they can compete.
     
  5. 1980RS

    1980RS Veteran Member

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    Jun 17, 2006
    MN
    You are spot on about new heads with cheapo parts. I now put every new valve on my Souix valve grinder and guess what? they are all off a bit when I touch them up. Almost all machine shops perform interference fit valve jobs IE: 45° 46° angles on a valve and seat and that is a killer for a performance head. A real performance head builder will never do this, they use quality parts and pay attention to detail, that's the reason it costs so much. Used heads are ok if the guy will let you take them apart to check them and they are what they are suppose to be.
     
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  6. Blown Camaro

    Blown Camaro American by birth, drag racer by choice

    1,199
    138
    Dec 13, 2009
    Deltona, FL
    A very big name manufacturer started my education with their "ready to bolt on" heads. 2 broken studs, 1 on each head! One pushrod snapped in half and one bent. This carnage happened at... 2500rpm! That's right, never even made it to the track. It lasted about 20 miles on the test drive to work and back. Thank God I didn't spin it up or I would need a motor! Valve spring installed heights were ALL OVER the place and because of that some of these .550 lift springs were stacking up way earlier than that. The spring pockets were not even cut deep enough into the heads and had to use a stepped retainer and offset locks to get the installed heights correct. NEVER AGAIN. Here's what I had to buy over again:

    Pushrods
    Valve springs
    Retainers
    Locks
    Shims
    Studs

    And of course, valve height micrometer & valve spring compressor. But hey, $1000 got me an education!!!
     
  7. APEowner

    APEowner Veteran Member

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    Dec 9, 2013
    Albuquerque, NM
    I have never seen reduced performance from using an interference angle on the valve and seat on either the flow bench or the dyno. I have, however seen improved high RPM performance when using an interference angle to compensate for valve deflection. A little more subjectively it seems like the initial leak down numbers and post dyno break in leak down numbers are more consistent when I use interference angles.
     
  8. 1980RS

    1980RS Veteran Member

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    Jun 17, 2006
    MN
    You will see it at the track, I know of 2 people that had this happen, one car went from 12.20's to 11.80 with the other guys valve job, nothing else done. Bad thing is when someone chatters the seats when cutters, if you do not lap the valves you will never find it. My 454 in 1998 I had that happen car went 11.19 had a minor lower end issue, fixed that and rechecked the heads and found the intakes not seating well, asked the machinist to recheck them he just said to put some miles on them and they would be ok, it's a "race car not a street car", car went 10.70's after that, now I always double check my valve work. After all I now do it myself. Oh and yes, you will see a difference on the flow bench.
     
  9. APEowner

    APEowner Veteran Member

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    Dec 9, 2013
    Albuquerque, NM
    Both of those instances sound more like poor workmanship rather than consequences from having an interference angle.
     
  10. 1980RS

    1980RS Veteran Member

    2,049
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    Jun 17, 2006
    MN
    In my case, Yes, poor workmanship. On the other the 2nd machinist who specializes in performance valve jobs swears by no interference fit in a performance application. I did talk with the guy who does my short block machining on this his answer was this, "if you are going to drive this as a daily driver the 1° interference works for that application, but if it's a performance engine that 1° will hurt HP until the heads have some time on them. He is a Super Gas NHRA champ who I have known since he was 16 years old, his work is top notch and I always respect his opinion. I guess I will leave it at that, we will agree to disagree, now let's get ready for racing season again.
     

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