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Advancing a Thumpr for bottom end torque

Discussion in 'COMP Cams Support Forum' started by mlake01, May 20, 2018.

  1. mlake01

    mlake01 New Member

    Joined:
    May 5, 2016
    Hi - my question is about advancing a Thumpr cam for a bit more low-end torque. I've searched the forum a bit, but haven't been able to find any clear direction on the subject other than to put the cam in straight up and that it has about 4deg of advance ground into it.

    Background info - I am running a 429 Ford in a 3,200 lb pro street truck with a 2,500 rpm stall, 3:27 gears, and pretty short rear tires - it turns about 3,000 rpm at 65mph. The engine is built as follows: DOVE heads, 3 angle valve job, 9.4:1 compression, 2" shorty headers to a full 3" dual system, CL34-600-9 Thumpr cam (hydraulic roller) that was degreed in perfectly straight up, Magnum roller tip rockers, CCA-7122 timing set, port-matched Edelbrock Victor intake, Edelbrock 1411 750cfm carb, ignition timing set to 24deg initial, 12deg mechanical all-in at 2500rpm, ported vacuum advance.

    I'm pretty happy with the way it runs, but to be perfectly honest, I feel like I probably over-cammed the engine and/or the intake is for way too high of an rpm range. I lost a significant amount of idle-to-2500rpm punch compared to the way it was previously (Performer cam and manifold). I can accept this - it's my fault for getting hooked on that awesome Thumpr idle sound - I love that part!

    I am already planning to go back to a shorter dual-plane manifold (Weiand Stealth), but I am curious about advancing the cam from the straight-up position. I have done this with other more mild grinds and flat-tappet cams, but am wondering about your thoughts on this application. Would it help my cause a bit to advance this cam a few degrees? If so, how much would you recommend?

    This is a primarily street-driven vehicle that might see the strip once a year, and rarely turns beyond 4,500 to 5,000 rpm. I'm looking to get that giggle factor back that I had previously when I could easily do giant smoky burnouts and drift corners in the 2000 to 3500 rpm range.

    Thank you in advance!!
    -Mike
     
  2. mlake01

    mlake01 New Member

    Joined:
    May 5, 2016
    Thanks for the reply and information - I appreciate it! I will leave the cam in straight-up and work on curving my distributor a little more in the direction you suggest. It idles with about 8" of vacuum, which I thought was fairly good for a cam with this much duration. I'm also putting a Weiand Stealth intake back on (1,000-5,800 rpm range vs. the 3,500-8,500 range of my Victor).

    I believe your camshaft recommendation, but I'm curious for the future - how would I know which is best when making the decision to purchase? My Thumpr (CL34-600-9) is advertised as having an operating range of 1,900-5,600 rpm, and the Extreme Energy you mention (CCA-34-432-9) has a range of 2,200-5,800 rpm. I had selected the Thumpr because it had one of the lowest rpm ranges of the semi-aggressive roller grinds that Comp offers. Should I be looking at duration, lobe separation, or something else?

    Thanks again,
    -Mike
     
  3. mlake01

    mlake01 New Member

    Joined:
    May 5, 2016
    Thank you for the advice! I’ll do some more tuning and let you know how it goes.

    Thanks,
    -Mike
     
  4. mlake01

    mlake01 New Member

    Joined:
    May 5, 2016
    Still tinkering with it, but it's running better all the time. I bumped the idle a little bit to around 900, and have been tuning the carb some. Changed the step-up springs to better match the lower vacuum signal, richened it up a bit in cruise mode, and leaned it a touch at idle. I run a wide-band sensor and AFR meter so it's easy to see where things are at different transition points.

    All the plugs are side gapped at .035", clocked to face the intake valves, and the ceramics look really good. I'm running a Pertronix Flamethrower 3 ignition system. There are no signs or sounds of detonation, and this engine still really likes a lot of initial advance. Backing it off to 16 deg or so initial kills the idle vacuum and makes it a bit more doggy right off idle. Bumping it back up into the 22 deg range or so pretty much fixes that.

    I was going to put a Weiand Stealth dual plane manifold on next, but your comment about TBI got me thinking about something I've wanted to do for a long time anyway... This weekend I will install an FiTech 600hp self-tuning EFI setup on the Victor! It's only money, right? I'd like to run this for awhile and assess the impact on drivability just from TBI, and then possibly try the dual plane manifold with it as well.

    I'm curious about the single plane vs. dual plane characteristics with TBI as opposed to a carb. It seems like they would be the same, assuming AFR is constant? My assumption is runner volume between the throttle plates and the intake valves affect low rpm cylinder filling efficiency, so the smaller dual plane manifold should show improvements at low rpm regardless of how the fuel is being added to the intake charge?

    Thanks,
    Mike
     

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