Comp Cams Dyno Sheets

Discussion in 'High Performance Modifications' started by Greg Mc, May 19, 2005.

  1. Greg Mc

    Greg Mc Veteran Member

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    Mar 18, 1999
    Hernando, MS
    Looking at Comps web site dyno sheet section it makes you wonder why all the mags praised the XE268. Unless I am missing something it looks like the XE262 or the XE274 are a much better choice. The 274 would be the cam of choice for a mild SBC with the 262 being second and 268 third. When I was freshening my 350, vortec motor I decided to go with the XE262 over the XE268...not a bad choice but apparently I picked #2 instead of the #1 choice for my combo. I don't know how Vortec heads compare to the Dart S/R head Comp used on their dyno sheets. Just thinking out loud guys.

    http://www.compcams.com/Technical/DynoSheets/
     
  2. Damon

    Damon Veteran Member

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    Nov 16, 2000
    Philly area
    Link is down right now, but I get your point.

    Sometimes a smaller cam will work a little better in a motor than one that's a little bigger. I don't think there's anything wrong with the XE268, but something in that combo probably liked a little less or a little more duration that it gave. It happens. I've put together some combos that just flat WORK, despite the fact they don't look like an optimum match on paper. Usually, I stumble across them because trial and error is my only teacher.

    What I'm saying is that the XE268 may not have been that BAD, it's just that something about the smaller cam just WORKED with that combo and produced better numbers. But change one thing in the combo (especially something as important as the heads) and the results are likely to change again.

    The Vortec heads are quite a bit better than the S/R Torquers in my experience. Better flow on the intake by quite a bit, and a much better combustion chamber.


    [This message has been edited by Damon (edited May 19, 2005).]
     
  3. Greg Mc

    Greg Mc Veteran Member

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    Mar 18, 1999
    Hernando, MS
    I know what you mean about some combos working better than others. I was just surprised at the results posted. The engine on the dyno sheet.

    355 CID
    9.25 compression
    Holley 750 VS carb
    Performer intake
    S/R heads

    XE262 was 348HP @ 5300 415TQ @ 3700
    XE268 was 342HP @ 5000 413TQ @ 3800
    XE274 was 369HP @ 5900 410TQ @ 3900

    What surprised me is the XE274 did that well with 9.25 compression, performer intake, same heads and carb. Plus it has a wide torque curve; is above 400 ftlbs from 3300-4500 rpm and is over 350 ftlbs 300 rpm sooner than the XE262 and 400 rpms sooner than the XE268. That sounds like a good cam for our heavy cars. If I get bored this summer, I may have to do a cam swap.
     
  4. Damon

    Damon Veteran Member

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    Nov 16, 2000
    Philly area
    You'll notice that the HP peak of the XE268 is at a lower RPM point than either of the other 2 cams. Peak HP with that cam should be between the other 2 cams in terms of raw number as well as the RPM point. Torque, however, makes a nice orderly progression to hither RPMs the bigger the cam.

    That's a classic indication of some weird interaction of those particular parts together. For some reason the XE268 on THAT ENGINE took a little "dip" in the upper RPMs that the other 2 cams did not for whatever reason. If it didn't take that dip up top the peak HP would have occurred around 5600 and I'll bet horsepower would have come in right around 360.

    A slightly different XE 268 (ground on a wider 114* LSA) in my roots-blown 383 peaks out a few hundred shy of 6000 and there are no abnormal "dips" in the the torque curve anywhere in the RPM range. Big, flat torque curve, slowly fading away as the RPMs climb.


    [This message has been edited by Damon (edited May 19, 2005).]
     
  5. 1978LT

    1978LT Veteran Member

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    Feb 24, 2002
    Poquoson, VA USA
    I noticed that also. Strange.

    Oh, and Vortecs are 25-30 HP better than S/R Torquers usually.
     
  6. pdq67

    pdq67 BANNED

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    Jul 26, 2001
    Columbia, MO, USA
    I think it was CHP mag that did a test QUITE some time back using a decent street 350 motor and compared the XE268 to the good old 268HE and the 268HE beat the XE cam..

    AND the Cam-Father himself, Mr. Ed Isky always said that a single pattern cam that was right for the motor would out power a dual pattern cam!!

    pdq67
     
  7. 1978LT

    1978LT Veteran Member

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    Feb 24, 2002
    Poquoson, VA USA
    I remember that test! It was about 1-1/2 years ago. They were also using S/R Torquers, but they home ported them and did a before and after. They got a nice improvement! I believe the 268 HE cam with the ported heads was nearing 380 FWHP.
     

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