GM Cam used in 330 HP 350 HO Eng.

Discussion in 'Engine Topic' started by robmaxfli, Dec 26, 2011.

  1. robmaxfli

    robmaxfli Member

    52
    0
    Nov 2, 2011
    Dallas, Tx.
    Part # 24502476 (212/222)

    I have been trying to figure out the missing piece of the puzzle as to why my 330HP clone is not as quick off the line as I thought it would be. I have verified my timing and that my Q-Jet secondaries are opening properly.

    Here is some advice that I received a local shop here re: this issue:

    "In order to get these GM cams to really pull you need to advance them to a 106 ICL. The 327/350 has an ICL of 110 degrees so I advance them 4 degrees. It makes all the difference in the world, either in a 327 or 350 they will pull like a freight train."

    I was curious if 1) you guys agreed with this?... and 2) how do you go about advancing the cam?

    thanks in advance ;)
     
  2. Damon

    Damon Veteran Member

    12,847
    2
    Nov 16, 2000
    Philly area
    You're not likely to feel much difference from 4* of cam advance. And if I recall correctly you aready have quite a bit more compression than a factory 350 HO so I'm not sure that raising the cylinder pressure any higher is a good course of action in this case (advancing the cam raises cranking compression).

    Why don't you start with a basic cranking compression test as it is now. I bet you're cranking 180 PSI or higher with that little cam and 10+:1 compresion already. Plus the compression test might reveal something (like if it's low across the board maybe you got the cam installed one tooth retarded at the chain).

    Wondering what secondary rods and hanger that QJet has in it as well. Where did you gat the carb and was it built for a street performance application?
     
  3. robmaxfli

    robmaxfli Member

    52
    0
    Nov 2, 2011
    Dallas, Tx.
    I'll see what I can do for the compression specs:

    Here are the specs on my Q-Jet:

    # 17059205

    Primary jets: 73
    Primary rods: 41K
    Secondary Rods: "AY"
    Secondary Rod Height: 41/64"
    Float Level: .420"
    Idle mixture screws: 4 turns
    Secondary windup: 3/4 turn
     
  4. Damon

    Damon Veteran Member

    12,847
    2
    Nov 16, 2000
    Philly area
    AY secondary rods are awful lean at tip-in (they don't make a set any leaner, actually). I found most QJets like a nice, fat tip-in. See if you can get hold of a set of DR or CP secondary rods the drop them in (they are installed from outside the carb by removing the hanger screw and lifting the assembly out). That's likely to make a pretty nice difference in torque right there.

    You can also try easing up on the air valve tension a bit- about half a turn from the zero tension point is usually more than sufficient.

    None of this is likely the biggest reason for your lack of power, it's just a little tuning that almost always helps on street driven QJet.
     
  5. robmaxfli

    robmaxfli Member

    52
    0
    Nov 2, 2011
    Dallas, Tx.
    Ok - I'll report back later on...thanks Damon
     
  6. robmaxfli

    robmaxfli Member

    52
    0
    Nov 2, 2011
    Dallas, Tx.
    I just finished a compression check on these cylinder numbers. Here are the results:

    1 - 120
    3 - 130
    5 - 130
    7 - 135

    I warmed up the car, pulled all the plugs, disconnected the ignition, and floored the throttle as I cranked away.
    BTW- only 1K miles on this rebuilt motor.

    What do you think of these numbers so far?
     
  7. Damon

    Damon Veteran Member

    12,847
    2
    Nov 16, 2000
    Philly area
    FAIL!!!!

    WAY WAY WAY too low for a 10:1 (or higher) motor with that small a cam in it. You should be up around 180, maybe 160 at the low end of the "sane" range. My gut says you got the cam installed 1 tooth retarded at the chain. But that's not the only thing it could be.

    Take a deep breath and look through the disappoinment I have just dealt to you (served up ice cold, I know) and realize this is ultimately a GOOD thing you have discovered. You now know it's not the carb, ignition timing, or anything to do with the tune. It's a HARDWARE issue. You have ABSOLUTELY discovered the reason your engine is a gutless wonder. My 8.0:1 blower motor with a similar cam (214/224* on a 112* LSA) puffs up about 135 on the gague. You're 2 full compression points higher than me and not making any more cylinder pressure. You see why the red flag on those numbers, right?
     
    Last edited: Dec 27, 2011
  8. cmonson

    cmonson Veteran Member Gold Member

    4,134
    0
    Apr 7, 2006
    Calgary, Alberta
    What is the compression on the other bank? I fully agree with Damon though.

    What is your compression ratio? Did you build the motor?
     
  9. gregh

    gregh Moderator Lifetime Gold Member

    My math says this engine is very low 9:1 compression(9.07:1) assuming a .039 4.100 bore head gasket & that those 4 relief pistons are actually -12cc's as some other websites claim.

    But even with that, 120-135 seems awfully low, I'd be checking the timing chain as Damon suggested.
     
  10. sweetsoul

    sweetsoul Veteran Member

    598
    0
    Jan 12, 2010
    Liberty sc
    maybe re lash your valves? they could all be too tight.
     

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