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Technical SBC non-stock tune up - does this seem right?

Discussion in 'The Hokey Ass Message Board' started by David Gersic, Apr 22, 2019.

  1. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    Stock bottom end ‘74 SBC.
    Crane Fireball II cam.
    Edelbrock Performer manifold.
    Holley 1850-3 (4160 type / 600 CFM) carb.
    GM HEI distributor.

    Lift:
    Intake @cam: 3027 @Valve: 454
    Exhaust @cam: 3027 @Valve: 454
    Rocker Arm Ratio: 1.5

    Cam Timing @.001 Tappet Lift:
    Intake Opens: 35 BTDC Closes: 75 ABDC
    Exhaust Opens: 75 BBDC Closes: 35 ATDC
    Advertised Duration: 290

    Cam Timing @.050 Tappet Lift:
    Intake Opens: 3 BTDC Closes: 33 ABDC Max Lift: 105 ATDC Duration: 216
    Exhaust Opens: 43 BBDC Closes: (7) ATDC Max Lift: 115 BTDC Duration: 216

    I have no baseline for this engine. It was running but the valvetrain was messed up. Having replaced the lifters, pushrods, and rockers, and replaced the worn out mechanical advance in the distributor, I’m starting from scratch.

    With all vacuum hoses disconnected and the ports plugged, engine fully warmed up and temperature stable at 210F, it seems happiest at 25 degrees advanced, 1400 RPM, and 15” vacuum.

    With the transmission in gear, it drops to 750 RPM, and 7” vacuum.

    The idle bleed screws are both at 1 3/4 turns out.

    It seems like that’s too much advance on the static timing. Everything I can find to read on SBC non-stock timing says 16-18 degrees static, 20 degrees mechanical advance. The mechanical advance shouldn’t be kicking in until about 1800 RPM, and the advance does not change when I put the transmission in gear. The advance does move when the RPMs go up, so is working.

    The engine seems happy at these settings. I don’t have the experience to know if that seems right.




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  2. sdluck
    Joined: Sep 19, 2006
    Posts: 2,143

    sdluck
    Member

    If it runs good in the motors happy don't worry about it

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  3. sdluck
    Joined: Sep 19, 2006
    Posts: 2,143

    sdluck
    Member

    I suspect a motor has no compression that's why it likes all the timing

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  4. Is it a driver or a race car? 290* is sort of a lot of duration for a driver. 70* overlap will kill the vacuum. Probably needs a looser converter and a gear too.
    Did you have the heads off? What cc's in the chamber? Does it have flat-tops?
    Sounds like the typical over camming situation for the compression. :)
     
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  5. Gotta know the static CR for sure. Under 9 or 9.5:1 it may be on the doggy side especially with a stock converter and no gears. What is the LSA, do you have the full cam specs or a part number?
     
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  6. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    Driver. Heads have never been off that I know of. Stock heads, engine number decodes to a 74 Chevelle. Stock CR is 8.5:1, as far as I can tell.

    Converter is unknown. It may be getting replaced, but that’s another story.



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  7. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    [​IMG]

    There are some dodgy parts choices on this car. I’m working my way through, improving and fixing as I go.

    Seems to run ok. Pulls good from stopped to probably too fast for my own good.



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  8. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,438

    2OLD2FAST
    Member
    from illinois

    Initial timing is not critical , total timing ( initial + mech adv ) is. What is your total timing ? Carb idle screws do not need to be the same , adjust to highest vacuum + 1/4 turn or so more....

    From 50 miles south of you ......
     
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  9. King ford
    Joined: Mar 18, 2013
    Posts: 1,195

    King ford
    ALLIANCE MEMBER
    from 08302

    As has been stated, total advance is critical. Many racing engines use a locked distributor ( no advance curve) you will most likely have to modify your distributor to shorten the curve or lock it if you want to try that initial advance or lock it and bump total up to 34-36 ....then however it's an IF the starter will turn it . In racing applications we have separate start button and ign. Switch, you get the motor spinning and then flip on the spark....on the idle screws , if your engine " sneezes" or kind of pops through the carburetor when you yank it from idle to wide open and back, if you can't fix that with the accelerator pump shot sometimes you can richer the transition mode with the idle circuit.....
     
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  10. Hollywood-East
    Joined: Mar 13, 2008
    Posts: 1,005

    Hollywood-East
    Member

    Definitely a cam change, or IMO a 2200 converter... Way to much cam for a 74 SBC. Stock
     
  11. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    With initial at 25 degrees, HEI mechanical advance is supposed to be 20, so total would be 45 degrees.



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  12. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

  13. 427 sleeper
    Joined: Mar 8, 2017
    Posts: 476

    427 sleeper
    ALLIANCE MEMBER

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  14. Blues4U
    Joined: Oct 1, 2015
    Posts: 3,633

    Blues4U
    Member
    from So Cal

    I disagree, that'll be too fat. Find highest vacuum, then roll them in a little (shooting for about a 20 rpm drop), this is the lean roll, and will result in crisper throttle response and transition from idle to off idle speed.
     
  15. If it was me, I'd pull 10* out of the mechanical first and try that. Without the compression you have a lot of wiggle room. You didn't say, but does it have a vacuum adv? I would lock it out if it does. ;)
     
  16. I tried to search for the Crane Part #114802 and nothing came up. I did find out that S&S Cycle bought out Crane Cams. Here is the only thing I found useful for "FIREBALL"...

    Fireball
    Three unique cam designs for each application that deliver excellent horsepower gains & broad torque curve; perfect choice for muscle cars & street rods
    • Early intake valve opening & long exhaust duration create optimum overlap for powerful, hard-hitting exhaust note
    • Best with aftermarket converters & more rear gear
    There are no products listed under this category.

    I found this on another thread...
    I don't think the 216 number is @ .050. Somewhere I heard that Crane used a different reference # like @ .030? I don't remember.

    H-290 290/290 216/216 .454/.454 110 LSA 105 ICL
    Here's the specs i found for the fireball 290.
    It's a single pattern cam.
    It looks to be that the crane energizer cams is the new name for the fireball cams
     
    Last edited: Apr 23, 2019
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  17. LM14
    Joined: Dec 18, 2009
    Posts: 1,620

    LM14
    Member
    from Iowa

    Used to run a Crane Fireball in one of my engines. The only way to get it to act civil is using an adjustable vacuum advance, looser converter and it really needs about 2 points more compression and a good gear in the rear end. Don't work worth a crap with a stock converter and didn't work much better with a looser converter. Liked more gear.

    I would swap to a milder cam. Fireball wasn't that great and something like a 268H Comp Cams cam would be much happier in a lower compression street engine.

    SPark
     
  18. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,438

    2OLD2FAST
    Member
    from illinois

    Thats fine if your usual drive is over 10 miles , under ten most engines will be a little finicky being cold AND lean IME.....
     
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  19. Tickety Boo
    Joined: Feb 2, 2015
    Posts: 941

    Tickety Boo
    Member
    from Wisconsin

    With a friends help test the timing curve, set your timing at 34-36 degrees during a short spurt of 4000 r.p.m then check where it falls at idle and also 3000 r.p.m. and 2000 r.p.m. build a chart like you have.;)
    If not sticking there should be about 22 degree movement on a stock distributor..
    When using an aggressive cam I try to get advance to all in A.S.A.P. but get burn't sometimes with using both of the lightest springs. They work cold but when hot lose strength and can't return the weights.
     
  20. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    Any less advance, the engine starts trying to stall. That’s why I’m at 25. Yes, there is a vacuum advance, disconnected and plugged while adjusting initial advance + idle.



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  21. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    A cam swap is more disassembly than I want to get in to right now. 37 Chevy, with fenders, so a lot of front end has to come off to get to the front cover. That’s an off season project.

    I’d like to tune this to reasonable running for the summer.



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  22. vtx1800
    Joined: Oct 4, 2009
    Posts: 824

    vtx1800
    ALLIANCE MEMBER

     
  23. jaw22w
    Joined: Mar 2, 2013
    Posts: 773

    jaw22w
    Member
    from Indiana

    Verify #1 TDC against your timing pointer. Should not take 25* advance to run. Use a piston stop. Rotate crank one way. Mark balancer. Rotate crank other direction. Mark balancer. TDC is halfway in between.
     
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  24. On a '37 Chevy, you have to pull the front end off to get to the balancer. Don't ask me how I now. :rolleyes:
     
  25. Blues4U
    Joined: Oct 1, 2015
    Posts: 3,633

    Blues4U
    Member
    from So Cal

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  26. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 1,438

    2OLD2FAST
    Member
    from illinois

    Arbitrary timing if you must , just be careful you don't get in to detonation , doesn't take long to eat a piston ......
     
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  27. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    TDC vs tab verified with the oil pan off.



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  28. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    Not a lot of room up front there. I can get a wrench on the balancer nut, barely, but can only turn it 1/10 of a turn or so. Changing the belts means removing the water pump.



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  29. David Gersic
    Joined: Feb 15, 2015
    Posts: 1,880

    David Gersic
    Member
    from DeKalb, IL

    Agreed, there’s no way to spec what’s right with a non stock assembly. But guidelines are usually a good place to start.

    I think SPark is on to something here. The area I’m not happy with is idle and off idle. Once moving, no problem. Probably a stock torque converter (unknown, assuming). Trans is a 700R4, so 1st gear is pretty low (3.06). Rear end is a 2.73.

    It idled better with the screwed up valvetrain. Lash was loose, beyond what the lifters could take up. That would have reduced the lift, and some of the overlap. Basically a milder cam setup.




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  30. Now, if that was a 3.73... ;)
     

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