Someone please explaine in further detail.

Discussion in 'Race 400/430/455' started by 11SecondGS, Apr 29, 2002.

  1. 11SecondGS

    11SecondGS ROCK THIS

    Reading about lobe seperation angles in Carcraft.

    "Tighter lobe separation angles (less than 110 degrees) make more torque and horsepower, but, with more overlap, the engine experiences poor idle quality and high fuel consumption. Opening up the lobe separation angles (more than 110 degrees) broadens the power band while improving idle and part throttle characteristics. With these wider lobe separation angles, peak torque and power are generally reduced, but the engine becomes very smooth and drivable."

    I am in the process of building a 12:1 455, with the help of JW.
    We decided on the 308s, but would I benifit any with a lobe seperation angle of less than 108. Some guys on the board say they have lower than 108.

    Would I benifit from a lower angle seperation?
    Does 2 degrees even matter.

    Can someone tell me in detail why lower angles produce more power?


    Thanks, Just want to get things cleared up.

    Josh
     
  2. bobc455

    bobc455 Well-Known Member

    Let me see if I can take a stab at this.

    Overlap (the time both valves are open) is a direct effect of lobe seperation angle (and also of ramp speed, but ignore that for now).

    When exhaust is rushing out the exhaust valve, and the intake valve opens (during the overlap period), the inertia of the air flowing out the exhaust valve helps pull in air through the intake valve. Some of that intake air will go directly out the exhaust port (causing the reduced gas mileage), but the overall effect is that you get a stronger rush of air during the intake cycle.

    On a race motor, you want as much intake charge as possible in order to cram as much new air/fuel into the cylinder as possible, and since gas mileage is not an issue, who cares if some of the unburnt mixture goes straight out of the exhaust pipe.

    On a street motor, since you are sending unburnt gas out the exhaust pipe, emmisions gets worse and gas mileage goes down. Therefore you'd want less overlap (wider lobe seperation angle).

    With less overlap (wider LSA), your idle gets better because the cylinder has been more completley evacuated during the exhaust stroke and is emptier when it begins the intake stroke, causing it to pull more fresh charge into the cylinder.

    If you look at http://www.taperformance.com/camshaft.htm and compare the TA C118 with the TA C107, you'll see that the 118 has bigger lobes but has a lower RPM range.

    Hope that helps a bit, I'm sure more people will chime in with additional insight...

    -Bob Cunningham
    bobc@gnttype.org
     
  3. 11SecondGS

    11SecondGS ROCK THIS

    oohhh k

    Thanks for the reply


    so closer lobe seperation angles, cuases more overlap, thus moving more unburnt fuel/air mixture in faster, and more air in, and more air out = more HP.

    Obviously it affects torque to increase HP, but how? Does it move the torque curve up, or just rotate it by the rpm axis?

    I think maybe I am confusing my self.

    Is there anyway I could lose power by getting a 308s ground with a lower lobe seperation angle than 108, like 107 or 106. Would it be a benifit to do that.

    Josh
     
  4. cray1801

    cray1801 Too much is just right.

    Good information Bob! Here are some other general guidlines:

    Condition---------Wide LSA-----Narrow LSA
    overlap-----------decreased----increase
    low end power---lower---------higher
    hi end power-----higher--------lower
    Detonation-------less-----------more
    Intake events-----later----------earlier
    exh. events-------earlier--------later
    overlap-----------decrease------increase
    manif vac.--------higher--------lower
    Cyl. pressure-----lower---------higher

    The intake valve closing event is probably the most critical factor when considering how a cam effects detonation and cylinder pressure.
     
  5. gotbuick

    gotbuick What, me worry?

    Josh,
    Your motor sounds ready for the 308s. You get alot of overlap with it but it runs like a frieght train mid range up. :eek2:

    Are you running aluminum heads? If so it will be run cool and fast!!:TU:
     
  6. Buicks4Speed

    Buicks4Speed Advanced Member

    mY 2 BIT

    Closer lobe seperation help your midrange just like you've read but here is something to add. Closer lobe center also make up for ineffiency's such as poor intake port velocity and too big of cams. If you grind a 308 on 106 lobe centers you'll, in a sense, trying to help something that doesn't require any more help. The cam will try to pick up the midrange a little more but the cam profile might limit it but you will most likely shorten you power band limiting your much need rpm range. In the end you just lost usable power. The 308 is a tough cam to beat. You can get try to get a custom cam ground to your combination but you have to get your heads flowed, and all the details of your build up. You'll nver know if a custom cam would out run the 308 unless you compair it in you car, in your motor.
     
  7. 11SecondGS

    11SecondGS ROCK THIS

    cam tech

    So the only reason I would get a cam ground tighter is to make up for inefficaint head numbers, making the air rush in and out do to massive overlap, increasing torque?

    Why not get heads that flow, and really use the cam, and rpm range?

    Just discussion.

    Josh
     
  8. Earick Racing

    Earick Racing Member

    The 308s cam is a good overall-performing cam. You didnt mention which cylinder head you were going to use? Having a custom ground cam made for your exact application can make additional performance gains. The best way to know is to work with a profession engine building with dyno facilities. We were able to pick up our last engine with the 308s cam an additional 60HP by changing the cylinder heads valve job.
     
  9. Kerry s.

    Kerry s. Is Jesus YOUR Lord?

    Hi Guys,

    Brian........Is that from just a valve job, no additional port or bowl work involved other than some blending??:Do No:
     
  10. Earick Racing

    Earick Racing Member

    Kerry, You are correct. We changed the valve job and blend with no additional bowl or port work. Additional port and bowl work would attain additional HP gains.
     
  11. Kerry s.

    Kerry s. Is Jesus YOUR Lord?

    Hi Guys,

    Brian......What heads are you talking about here? Was the prior valve job not done properly (ie...by a Shivvie "specialist:grin:..)? So cfm wise what kind of gain did the new valve job give you? Would you mind maybe posting some numbers for all of us?:Do No:

    Thanks......:TU:
     
  12. Earick Racing

    Earick Racing Member

    Kerry, the cylinder heads were the aluminum street eliminator version. Buick specialist completed the cylinder heads previously. There was nothing physically wrong with them we just made adjustment so that they would make more HP. We didnt flow the cylinder heads. We employ the best people in the racing industry. With their combined professional talent to tap into we are able to bring technology to the Buick community that simply does not exist anywhere else. If I had the flow number I would post them. The ultimate numbers that count are the dyno numbers and gains in performance at the track.
     
  13. 11SecondGS

    11SecondGS ROCK THIS

    how much power

    just found out that my heads flow all most 280 on the intake, not sure the lift that was at......probably 500 or 600.

    With a 12:1 motor, and a 308, SP1, and a fat holley, what are horsepower numbers, torque, and ET's people have experianced with a similar setup.

    thanks
    Josh
     
  14. stage2man

    stage2man Well-Known Member

    The guy who does my heads uses the same technology as 18 deg. small block chevy heads. They have similar valve windows and are wedge motors.

    What would you charge to do one of these valve jobs to some street eliminator heads. I already have valves, springs, seats retainers ect...

    I am also running the 308s in a 13.3:1 venola piston motor.
     
  15. GSXMEN

    GSXMEN Got Jesus?

  16. Earick Racing

    Earick Racing Member

    David, it wouldnt be fair for me to guess what it would cost to do a competition style valve job on your heads without first looking at them. The prices go from $150 to $2500 and up depending on what HP level you want to achieve. I would be glad to assist you in any way.
     

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