Flat tappet and (factory) roller cam interchange possibilites- the ANSWERS

Discussion in 'High Performance Modifications' started by Damon, Jan 7, 2004.

  1. Damon

    Damon Veteran Member

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    OK, I teased you a little. Haven't done it yet. I am ripping apart 2 motors tonight- an early (86-down) with typical flat tappet cam and a late model 87-up with a factory roller cam and doing a complete compare-and-contrast. I'm doing it with an eye towards "what swaps and what doesn't." The kinda stuff that we low buck hotrodders really want to know.

    I've found the information to be scattered about here and there, and a lot of "internet wisdom" to be just plain wrong or conflicting.

    The REAL answers to follow later tonight after I break out my stright edge, machinist's rule and calipers...
     
  2. Todd80Z28

    Todd80Z28 Moderator Staff Member Lifetime Gold Member

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    What are you looking for? Several of the early rollers (e.g. late 80s TPI cams) vary so little in spec from the factory flat tappets of the day (e.g. the L69 cam) that they'll likely look near identical. It wasn't until LT1 in '92 that GM actually started wising up to putting the roller on the tip of that lifter to good use. [​IMG]

    I can't speak to the metallurgy, though. They probably ought to be different, but knowing GM, they might not be.

    Todd
     
  3. 1978LT

    1978LT Veteran Member

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    Even the '92 and up LT1 didn't have all that impressive lift, around .450-.460 I think. The LS1 got some badass lift. Only thing that sucks about the factory EFI stuff is that most if not all of them didn't have the fuel pump lobe. The HOT cam and a few other factory offerings do have them. I understand that if you grind the ears off the factory thrustplate you can use it and a late model timing set for use in an early model block, just use a thrust button. Then you need the melonized distributor gear. After that, just figure out what to do for lifters. I think most factory cams are billet, not sure if all of them are, but some.

    [This message has been edited by 1978LT (edited January 07, 2004).]
     
  4. Damon

    Damon Veteran Member

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    Many people want to shove a factory roller cam (including the popular "Hot" cam and other higher performance factory offerings) into an early block for obvious reasons or a flat tappet cam into a later model block for low cost and simplicity.

    Anyways, here's the poop for what it's worth:

    1. Cam bearings are exactly the same and you can physically shove either cam into either block type.

    2. Front end of the block where the snout of the cam sticks out is machined basically the same (no offset difference at all) but the roller cam block has two bolt holes drilled way out on either side of the cam to bolt on the factory roller cam "retaining plate" that fits between the block and the top timing gear.

    3. The factory roller cam is notched or "necked down" on the front 5/32" of it's length so that it slides THROUGH the factory retaining plate and has a "shoulder" for the retainign plate to push against to retain it from walking out the front of the block. The snout of the roler cam is also ever so slightly longer overall than a flat tappet in that area becuase it's gotta slide THROUGH the rather thick (1/8") retaining plate and still have just a smidge of length left to fit snugly into it's receiver on the back of the timing gear.

    4. The roller cam top timing gear also has a different amount of "offset" to it to compensate for the longer cam snout and the thickness of the retining plate, but keep the chain itself in the same location as a flat tappet cam.

    5. The BOLT PATTERN and DOWEL LOCATION on the snout of the roller cam/top timing gear is smaller in diameter than that of a flat tappet cam. THIS IS THE MAIN REASON WHY YOU MUST USE A ROLLER CAM TYPE TIMING CHAIN WITH A FACTORY ROLLER CAM. You can't physically bolt the gear to the front of the cam if you've got the wrong type of timing chain.

    6. The lifter bores on a LATE model roller block will accept both flat tappet and factory roller lifters- the oil feed holes to the lifters are in exactly the same location. Flat tappet lifters in a roller block will look a little funny sitting way down in their bores, but they'll work perfectly.

    7. The lifter bores on an EARLY block won't take the taller factory roller lifters for several reasons. First, they are not tall enough. The factory "dog bone" retainers will be way too far down on the body of the lifter and they'll get chewed up for sure. Second, there's no way to mount the factory "spider" in the lifter valley to hold them down.

    8. The original 1987 L-98 cam DOES have a fuel pump eccentric ground into the cam so you could use a mechanical block-mounted fuel pump on it if you got hold of an appropriate SBC fuel pump pushrod. Later model cams or performance factory replacement cams? No idea of they have an eccentric to drive a fuel pump or not.

    Interchange possibilities....

    Flat tappet cam in a roller cam block? Easy. Shove the cam in, leave off the factory retaining plate, use a standard flat tappet cam timing chain, drop the flat tappet lifters in the bores, get the right length pushrods and away you go.

    Roller lifter in an early block? More difficult. Shove in the cam, install the factory retaining plate (with the "ears" machined off- just use it as a spacer), install factory roller cam timing chain, install cam button (to keep cam from walking forward now that the retaining plate no longer "retains" the cam), and use aftermarket roller lifters, retainers/anit-rotators, and appropriate length pushrods.


    [This message has been edited by Damon (edited January 07, 2004).]
     
  5. Dirt Reynolds

    Dirt Reynolds Veteran Member Lifetime Gold Member

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    Surprisingly, the 1988-89 L98 350 and 305 TPI with manual 5-speed transmission got the longest duration cams of any small block roller cam engine right up to the LS6. At 207/213 @.050", those 2 years - and only for the two listed engines - had this cam. In 1990, GM 'tamed' it down some. The LT4 is 203/210; the LT1 201/208. Even the LS1 had a smaller grind in terms of duration. Lift is another matter; the 'big' TPI cam had .415"/.435" lift with stock rockers. The LT1/4 engines had more lift, and the LS1/6 had the most lift thanks in large part to the use of a roller-fulcrum 1.7 rocker arm.

    ------------------
    1977 Z/28 'Silver Bullet'
    12.15 @ 110.52 1.68 60'
    413" small-block, Vortec heads, TH400, 4:10's
    1989 GTA L98
    Daily driver
     
  6. AJ_72

    AJ_72 Veteran Member

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    Here's a list of 3rd gen F-body cams. (The 1987 LM1 305 cam has a typo. It's not 291* on the intake valve, it's 201*)

    [​IMG]

    Here's one of nearly all LT1 and LT4 cams. I say "nearly" because there is one I know of that isn't listed on this chart.

    It was a 1997 cam that was 203*/208*, .450"/.460", 116* lobe seperation.

    [​IMG]

    ------------------
    350CID, Vortec 062 heads, Magnum 280, Performer Intake, Holley 650 DP, 3.42 rear w/ Auburn posi, 2600 Stall/TC
    "So what if you have more horsepower per liter. I have more horsepower per car!!"
     
  7. patgizz

    patgizz Moderator Lifetime Gold Member

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    i have a new factory roller cam from i think a vortec truck, it is .431/.451, duration 196/206 w/ a 109* centerline

    its definitely billet. i'm putting it in a '95 pickup block. it had a flat tappet cam stock but is drilled for the thrust plate and lifter spider.

    probably the cheapest alternative is to start with a late model roller block.
     
  8. 1978LT

    1978LT Veteran Member

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    You might be surprised. That cam in the 350 MPFI crate engine is rated at 350 hp and 400 torque.
     
  9. 1978LT

    1978LT Veteran Member

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    Hmmm, interesting! So that guy selling instructions on Ebay on how to use the late model lifters in an early model block is basically full of sh*t! We beat this around a few months ago here http://www.nastyz28.com/ubb/Forum5/HTML/007611.html
     
  10. danbrennan

    danbrennan Veteran Member Lifetime Gold Member

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    Interesting, only a 111 deg LSA on my Impala SS. That might explain some of the higher RPM power, I had wondered about that.

    Patgizz, did you have to drill your block for the thrust plate and lifter retainer, or did it come that way from the factory?
     

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