What cam for single cab 2WDshortbed with new L31R

Discussion in '96+ Vortec Performance + Computer Swaps' started by homeslice, Oct 12, 2018 at 8:29 AM.

  1. homeslice

    homeslice Newbie

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    Hey Guys,

    I've been watching these forums for a while and finally able to play with my 96 SC stepside. This is now my hotrod truck, and its in great shape: has relatively new 4L60e Goodwrench rebuilt tranny; with stock 3:73, I just put a new L31R crate longblock in with stock intake. I believe the TC is stock stall, which I have read to be about 1800rpm. I don't plan on changing the TC. I did upgrade the MPFI injection unit to the new Delphi spider. Other add ons: Summit billet Vortec distributor, Thorley long tube tri y's, 2.25" exhaust with high flow cats, xpipe, and 2 magnaflows. I've removed the lip from the stock TB blade. I've currently repinned for the 0411 pcm, and am waiting for my flash/tune from Blackbear.

    So now I'm looking at taking advantage of the 0411 and its tuning capabilities, and would like to change the cam. While I'm in there, I might as well upgrade ignition to 24x which allows for coil per cyl ignition.

    This will be a hotrod cruiser that will need to still have high reliability, I don't plan on towing. Being this engine is new, I'd rather not take the heads off to accommodate a cam. I plan on upgrading the intake from stock, but I don't know when, as that will be a costly upgrade; so stock intake for now.

    OK, given all of the above - I like the '395 and the LT4 Hotcam. Something tells me the sweetspot is somewhere inbetween. I also believe I'm limited due to minimum of 112 LSA to allow 0411 tuning. What say the experts that have already been doing this for 15yrs ???

    Thanks in advance for any advice,
    Mike
     
  2. L31MaxExpress

    L31MaxExpress I'm Awesome

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    GM SPO 357 HP 350 Vortec camshaft. Absolutely screamed in my Express van.

    GM 12677151

    215/223 @ .050
    .474/.474" lift
    108* LSA
    109* ICL

    With the setup you are considering, I would pickup a 3 way adjustable single roller timing set and advance the cam 4* to a 105* ICL. That would bring the torque curve down about 300-400 rpm and be a great match for the factory intake manifold and the converter you are running.

    It is OVERLAP that messes with the PCM but the 0411 can run ALOT more cam than most people realize.

    I have tuned a 232/240 @ .050 on a 110 LSA roller cam in a 383 with one that ran very well. Idle speed was 850 rpm.
     
    Last edited: Oct 12, 2018 at 11:56 AM
  3. homeslice

    homeslice Newbie

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    Immediately after I posted the question, I found the SPO 357 cam; and then the above post from L31Max. It sure looks like this cam was designed to optimize performance on an L31 setup with vortec heads and stock induction. I'm guessing the best route to this setup is to upgrade to roller rockers, upgraded springs with higher seat pressure, upgraded retainers and locks for additional clearance.
    on the SPO357 cam - can you run 1.6 rockers without having to modify the heads ? And is it worth it ?
     
  4. L31MaxExpress

    L31MaxExpress I'm Awesome

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    The GM crate engine runs factory 1.5 rockers with the stock vortec springs. You could use a set of Comp 787 retainers and a set of LS6 springs as a bit of an upgrade if you felt it. 1.6:1 rockers may require drilling the pushrod holes out to 1/2". With a decent 1/2" drill bit the cast iron drills out like butter, talking maybe 10 seconds per hole when I did it. Problem is it is a messy process and the drill shavings will wreak havoc on your engines internals if they are not all removed. You would want the heads off the engine to do that. At that point I would have a hard time not pulling the heads and installing 0.016" compressed rubber embossed steel shim head gaskets if it were my engine. Compared to the OEM gasket that gives better quench and a slightly higher compression ratio. ~9.6:1 vs 9.4:1. That being said IMO there is really no need to bump up to the 1.6:1 ratio with the stock heads and stock intake manifold with that cam. If anything use 1.5:1 narrow body full roller rockers for friction reduction and call it a day. GM dropped their version of the 1.6s and replaced them in the Ramjet 350 with the 1.5s recently and revised both the part number and power output of the Ramjet 350. However the Ramjet has the much smaller 395' cam in it. The thinner head gaskets and 1.6:1 rockers MIGHT give you another 5-10 hp compared to the 1.5 roller rockers and factory head gaskets but you are fighting a losing battle with the hecho en mexico heads poor head flow at higher lifts and the factory intake manifold with all the spider crap in the way of incoming airflow. Finally I really do not see a need to upgrade the springs with this cam and a factory 1.5:1 ratio roller rocker. The aluminum roller rocker almost has less weight over the valve and in motion than the factory stamped steel rocker. Keep the fuel kill at 5,600 rpm and set your shift points as close to 5,500 rpm (probably about 5,250 rpm in the PCM programming) as you can get and it will run a long time.
     
    Last edited: Oct 12, 2018 at 12:44 PM
  5. homeslice

    homeslice Newbie

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    Thanks for your quick edit, you read my mind on 1.6 rocker ratio probably not being worth the trouble. I've read the HechoEM head port flows top out at just over .450" lift, and I'm sure GM spent considerable $$ for R&D on this new grind; so this is probably the most aggressive I can go without needing to upgrade intake and TC.

    I'm not sure why I've seen folks doggin you on other posts. Your feedback seems thoughtful and legit to me. Thank you.
     
  6. L31MaxExpress

    L31MaxExpress I'm Awesome

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    Port flow drops off pretty bad from .450 to .500 on the Hecho en Mexico 062s. Goes from like 215 cfm to 208 cfm.

    It is the most aggressive cam I would run with the factory intake.

    That being said I did help a coworker setup the 5.7 Vortec in his 1998 4x4 Yukon last year. He already had a nicely built 4L60E with a 2,000 rpm aftermarket stall converter in it. Ended up using a Lunati Bare Bones version of the Hotcam (218/228 @ .050, .503/.503" lift, 112 LSA, 108 ICL) and 1.5:1 roller rockers. Used Comp 787 retainers and LS6 springs. He had shorty headers and a decent exhaust already on the truck. He used a Volant CAI on it. A week after he put the fresh engine in it, the 8.5" 10-bolt exploded. After ALOT of discussion he finally trusted my use of a gearing calculator and knowledge of these trucks to put a 5.13 gear in the rear end for his 35" tall tires. After gears it ran like a monster. I was able to get it to run very well with the Black Box although it was begging for a better intake manifold, an 0411 swap and more RPM.
     
  7. homeslice

    homeslice Newbie

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    This cam looks to be exactly what I'm looking for. That said, I can't find much on it, doesn't seem to be too many people posting about the SP350/357 setup. It appears that GM performance came out with this cam 1-2 years ago, and looks to address the bezillions of L31 and L31R longblocks that have been purchased.

    Is anyone other than L31Max running this cam ?
     
  8. L31MaxExpress

    L31MaxExpress I'm Awesome

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    I have been keeping an eye out for an update from another member on here that put one in his suburban.

    I know if he finds someone that can get it even halfway decently dialed in, it will run very well.

    Just waiting for his response and reaction to how it runs.

    https://www.gmt400.com/threads/doug-thorley-headers-installed.43017/
     

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