Register now to get rid of these ads!

Technical Big block chevy needs excessive initial timing- will changing the cam timing help?

Discussion in 'The Hokey Ass Message Board' started by 327Eric, Jul 17, 2014.

  1. 327Eric
    Joined: May 9, 2008
    Posts: 1,537

    327Eric
    Member
    from Diablo Ca.

    I'm finally getting my 427 in my 59 to run pretty decent, but I am worried about the initial timing requirement. I have it running at 21 degrees initial, (with vacuum advance on manifold source)but it wants more. I can tailor the distributor where I need it, but am worried about detonation if I go more. The engine is a .030 over 427 Chevy, with 11.2; measured static compression, and this cam http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=4&sb=2
    the factory LS6 454 cam. If I advance or retard the cam, will this help so I can run less initial timing. I am currently running an HE!, but have a Mallory dual point(no vacuum advance) also. Setting mechanical advance , and total for either won't be a problem for either. Just looking for some advice, until I can save enough money to replace the pistons. Total power not an issue later. Just want to drive it. Any advice will be welcome.
     
  2. Mr48chev
    Joined: Dec 28, 2007
    Posts: 29,584

    Mr48chev
    ALLIANCE MEMBER

    Right now if I had access to a good distributor with vacuum advance and the wires to go with it I'd be thinking about popping the Mallory out and putting the other one in just as a test. The other thing I wold do is get the Mallory to someone who can set it up in a distributor machine properly. Years ago I worked for a gent in Waco Texas who was the go to guy in Central Texas to have a Mallory set up and I saw a lot of worn out ones come in the shop that racers had pawned off on kids with street cars.
     
  3. squirrel
    Joined: Sep 23, 2004
    Posts: 49,292

    squirrel
    Member

    If it cranks over ok with the initial timing it needs, then don't worry about it. With that cam you need a really high stall converter, and you won't be putting it under load at less than 3000 rpm anyways, so you don't need to worry about pinging under load at low rpm, right?
     
  4. Wanna be sure the harmonic balancer hasn't slipped throwing timing mark off and that you have the correct timing tab on the engine as well. All that said I had a blown SBC that ran at 32 degrees locked down and loved it.
     

  5. benchseat4speed
    Joined: Feb 11, 2008
    Posts: 383

    benchseat4speed
    Member
    from Golden, CO

    21's fine on the strip with good fuel. Seems like a lot for the street, but if it doesn't knock, what the heck. It's prolly pretty snappy with 11:1 and that cam, especially with 21 initial!

    Hopefully you have quiet pipes so you can hear if it's knockin. Don't put a dual point in it, I had one and man did it suck. Timing mark bouncing all over the place at rpm...replaced it with an old small cap delco with vacuum advance and a Mallory conversion kit. Solid timing mark and maybe worth some fuel mileage with the 'can.


    Posted using the Full Custom H.A.M.B. App!
     
  6. How much manifold vacuum does it pull at idle in neutral? If it's an auto trans how much vacuum do you have at idle in gear?

    Advancing the cam timing a couple degrees could make a little improvement in off-idle and low RPM power at the sacrifice of a little high RPM power.
     
    Last edited: Jul 18, 2014
  7. 327Eric
    Joined: May 9, 2008
    Posts: 1,537

    327Eric
    Member
    from Diablo Ca.

    It is a has a 4 speed, and about 19 inches of vacuum at idle right now The other issue, I see I forgot to post, is if I retard the timing any from where I am at, she runs really rich, like water the eyes rich. even with the secondary plates cracked open. I have tried several Carburetors, and the best so far is a 750 DP, which is on it now. I am going to throw together a 750 vacuum secondary unit and give it a try, as most of my driving is low speed. The balancer is a bonded unit and is accurate.
     
  8. I ran 14 degrees initial with my 402 on the street. Disconnect the vacuum advance and check your timing...that is how it is done. ^ I knew a few guys that would adjust their BBC timing by the way it cranked over......back the timing off until it would spin and not lug...
     
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 49,292

    squirrel
    Member

    I do it by setting total timing. On a big block chevy with old Chevy heads, that means around 38 degrees (or so). Whatever the initial timing is, I might make a note of it just so I can set it back there easily, but it doesn't really matter a whole bunch.

    usually when the exhaust makes the eyes water it's from misfiring, raw gas is coming out the exhaust. That can be caused by too rich of a mixture, or also by too lean of a mixture. If it's way too rich it will usually also produce some black smoke. If it's too lean, it will just spew raw fuel and run bad and cough. Having the timing too far one way or the other will also cause misfiring.
     
  10. 327Eric
    Joined: May 9, 2008
    Posts: 1,537

    327Eric
    Member
    from Diablo Ca.

    great advice and info guys, but back to the original question, of cam timing.(not ignition) If I retard the cam 4 degrees, for example, how will the engine respond, and would it pull down the initial timing requirements, or do I have to go the other direction. Is there a benefit, or is it not worth the hassle on an engine that will be replaced when funding is available.
     
    sidewayzz69 likes this.
  11. squirrel
    Joined: Sep 23, 2004
    Posts: 49,292

    squirrel
    Member

    Playing with cam timing, in order to change ignition timing requirements, is a kind of strange thing to do.

    As mentioned, advancing the cam a little might improve low end response. It also might make the pistons hit the valves.
     
  12. onedge
    Joined: May 25, 2006
    Posts: 1,000

    onedge
    Member

    Ditto... valve to piston clearance not worth playing with cam timing.
     
  13. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,747

    greybeard360
    Member

    This where a distributor machine comes in real handy. Your motor should crank fine at 10-12 degrees initial advance. Being a manual trans, you can get by with a little quicker advance. Put some lighter springs in the HEI and get it where total advance is all in about 3000 rpm and set it for total advance to be 36-38 (based on 10-12 initial) and leave the vacuum out of the picture. You can do it with a dial back timing light and trial and error method if you don't know anyone with a distributor machine. Use a hand held tach and dial back, check timing every 500 rpm to see where the timing is (without vacuum) starting from an initial of 10. Change the springs and do it again. It will take someone helping.... very hard to do all of this with only 2 hands :rolleyes:

    You may find this pretty close to what that motor will like, you may find it can take a little more or a little less, your driving habits will let you know in a hurry !
     
  14. squirrel
    Joined: Sep 23, 2004
    Posts: 49,292

    squirrel
    Member

    That's the process....but he says it wants more than 20 degrees initial timing.
     
  15. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Retarding the cam will delay intake closing, want more initial, not less. You set the timing where it wants to be, not where you think it should be. Not even gonna talk about carburation issues on the HAMB.
     
    Boryca likes this.
  16. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    FWIW, 21 initial is not out of line for a biggish cam. My guess is the IFRs are too big for the combo, and the engine wants the extra timing to crutch an overrich idle mixture.

    Please tell me the 21 degrees is with the vacuum advance plugged...You CANNOT CHECK INITIAL TIMING WITH THE ADVANCE CAN HOOKED UP.
     
    Boryca likes this.
  17. 327Eric
    Joined: May 9, 2008
    Posts: 1,537

    327Eric
    Member
    from Diablo Ca.

    Thanks guys for all the answers. got what I need info wise. believe me, I don't want to open the ignition and carburetion can of worms any further. She runs better every time I work on her, so I'll keep dialing in.
     
  18. Boryca
    Joined: Jul 18, 2011
    Posts: 695

    Boryca
    ALLIANCE MEMBER
    from Detroit

    I agree with FalconGeorge. Timing is timing, and mixture is mixture. Timing first, with a light and vacuum guage, then mixture to taste.

    That said, I've got a BBF running a magnetic pick-up distributor, and if memory serves it's up near the 20* mark....

    Mike
     

Share This Page

Register now to get rid of these ads!

Archive

Copyright © 1995-2021 The Jalopy Journal: Steal our stuff, we'll kick your teeth in. Terms of Service. Privacy Policy.

Atomic Industry
Forum software by XenForo™ ©2010-2014 XenForo Ltd.