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Reversion possibility question on SBC with XM270HR cam


Reversion possibility question on SBC with XM270HR cam

Old 07-19-2014, 01:27 AM
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Thank you for all the feedback.
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Old 07-19-2014, 11:33 PM
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I had a 355 vortec truck motor in my Stinger (blew up the 383 in spectacular fashion). I ran a GM "Hot" cam with Z06 springs on the stock vortec heads. Reliable and powerful. If you have the vortec engine, go roller and this route. Proven 380-400 HP and rock solid.
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Old 07-20-2014, 09:46 AM
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Originally Posted by befu View Post
Hello, I basically have a stock L31 (5.7 vortec truck motor) with aftermarket valve springs to handle a higher lift cam. Motor has a dual plane intake with a quadrajet carburetor and HEI ignition. Alpha drives.

I am wondering if a Comp Cams XM270HR cam would cause resonance reversion with the stock mercruiser manifolds and 4" mercruiser risers, standard through hull exhaust?

The next cam up, the 276, says it needs better exhaust. Wondering if this one is ok with the stock exhaust?


Intake Duration at 050 inch Lift:218
Exhaust Duration at 050 inch Lift:224
Duration at 050 inch Lift:218 int./224 exh.
Advertised Intake Duration:270
Advertised Exhaust Duration:276
Advertised Duration:270 int./276 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.495 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.503 in.
Love seperation is 112
Intake centerline is 110
I have no experience with the XM270, I did run the XM276HR in a 355 ci years back. I ran it with 1.6 rockers on the intake. With stock location mixing the water/exhaust I had tiny puddles of water in the center runners of my manifolds after idling at 750 for one minute. I ended welding longer extensions onto the risers to combat the reversion. Cam ran great for what it was. Even with the AFR heads it ran out of steam around 5700rpms.

SB, Thanks for the bump and kind words! I must be getting old, I've had nightmares of leaving the VR1 stock lately! Or, at least until the 496 tires out....
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