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Thread: 98 vortec l31 updating to mild 383

  1. #1
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    98 vortec l31 updating to mild 383

    In the process of building a mild 383 pump gas engine for my 98 z71. was wondering if some of the experts in here could give me a few basics I need to change with my HPT in order to meet my basic fuel requirements? I can supply all cam specs etc. Any help would be appreciated bigtime...Jim

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    Are you looking to tune the black box pcm or do a 0411 pcm swap.

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    98 vortec pcm is fully supported by HPT...97 and earlier are the problem childs if Im not mistaken.

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    It is supported but still has a few issues I swapped my 97 and didn't look back you can tune the black box for sure. but the 0411 swap is fairly simple for the results it gives. And tuning capabilities go throught the roof compared to the black box. But by all means pick your poison both will do the job just the 0411 pcm is faster with by far more parameters to adjust.

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    Im just trying to keep it simple for the time being....seems like there enough table to get what I need... was hoping to find the basic info I needed to get started. Mild cam, but Im sure it will need coaxing a tad,,,any help would be appreciated.

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    your current pcm should be just fine depending on what you consider a mild cam is. we need way more info to answer your question with any certainty. whats your ultimate goal with the project?

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    383 kit 5.75 rods, 9.3-1 cr.....cam is a Sig Erson hydraulic roller 480/480 208Intake 214 ex duration @.050....114 lobe centers.276/282 advertised duration, 1.5 rockers. Stock heads, stock exhaust...stock induction (has the mpfi conversion kit...stock vortec spider style)...I'm just wanting a tourqey truck engine that tows well with decent milage.....exhaust may be changed....but I've read somewhere the vortec induction will only support around 330hp...not sure of that accuracy...I'll hold on the exhaust until I'm more informed...thanks

    More cam info:
    http://www.usaperform.com/cams-lifte...4-centers.html
    Last edited by PassionRE; 01-19-2017 at 06:30 PM.

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    well thats more than i expected for mild honestly. the cam will make it very tame for the displacement. i would say one could probably get away with 330hp without running out of fuel. I would venture to say before i swapped my intake my truck was probably pushing 285hp i was at 76% duty cycle. this was with the original poppet injectors. to be honest with you since your building what seems like a nice engine. i would spend a little more money and find a decent efi intake. try to find a nice used marine vortec intake on the cheap. and remember since your using the black box its hard coded to cut injector pulse at 5800rpm.

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    yea that cam would be considered mild in that engine setup. Should idle pretty tame as well. a 112 or lower lobe separation would have idles more aggressive.
    2000 silverado rcsb lq4/4l80e. Custom s480 turbo setup. 93oct meth injected. SD Tuned by me.

    2007 tbss ls2/4l80e. Nitrous!!! MAF Only Tuned by me.

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    Quote Originally Posted by Oleblu View Post
    well thats more than i expected for mild honestly. the cam will make it very tame for the displacement. i would say one could probably get away with 330hp without running out of fuel. I would venture to say before i swapped my intake my truck was probably pushing 285hp i was at 76% duty cycle. this was with the original poppet injectors. to be honest with you since your building what seems like a nice engine. i would spend a little more money and find a decent efi intake. try to find a nice used marine vortec intake on the cheap. and remember since your using the black box its hard coded to cut injector pulse at 5800rpm.

    Stock junk 062 mexico heads and factory LT4 cam Vortec 5.7 in my Express van was running 82-84% duty cycle when I had the MFI spider at the stock 62 psi fuel pressure. It had the LT4 cam, 1.6:1 full roller rockers, ported stock intake manifold base, 454 throttle body on a modified upper plenum,Thorley Tri-Y headers, high flow 3" cats into a dual 3" in, single 4" out walker dynomax muffler. Was making around 340 HP at the crank.

    The MFI spider at 70 psi flows right at 24 lb/hr and is good for about 400 HP. I have tested both the factory poppets and MFI spider up to 90-100 psi during cleaning and I can assure you the do open and the fuel stream is a good 15 ft long!
    Last edited by Fast4.7; 01-22-2017 at 01:03 PM.

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    Well that's encouraging news on fuel delivery capability....makes me wonder if I should run 1.6 rockers on that mild cam I have....any thoughts on that?

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    I think it would respond very well to the rockers if your heads can support the added lift. Also need to make sure your piston to valve clearance is good.

    I have a friend that runs a very similar flat tappet cam in a 406 small block in a Vortec 5.7 based P30 box van. His engine is around 9.5:1 and has Edelbrock Etec 170s on it. The intake manifold, MFI spider, exhaust manifolds and exhaust is all GM spec. The P30 hauls around dirt bikes and tools as well as a 21' travel trailer behind it. Makes plenty of torque even above 5,000 ft elevation. Stock spider runs around 98% duty cycle at 5,000 rpm.

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    Most the time to run 1.6 rockers on the vortec heads you must enlarge the pushrod hole to 1/2 inch. So the pushrods don't rub the heads.

  14. #14
    For the price to re-do vortec heads for larger valves and rr you can buy assault aluminum heads bare for about 400$. There 1:1 cops of dart dart heads. I have a set . I own a machine shop . I went over mine with a fine tooth comb on a surface plate . They are manufactured unbelievable well .
    Allot of third gen guys use them . Great substitute. Allot better option then working old vortecs. Flow better come with 2.02 1.65 valves . ready for 3/8 studs .100 thicker. Aluminum. Setup for both convention intakes and vortec.
    If interested search assault 200cc dart copys you will get 100 different threads.

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    Interesting this is the first I have heard of these.

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    Funny you should bring up head choices...thanks for the info btw.
    I suspect I'll find cracks in my stock 062's when I get to tearing down this engine so looking for heads will probably be my next task. I ran across some decent reviews of some of the PROMAXX offerings. The only thing I'm concerned with is the fact I'm committed to the stock l31 induction components. I'm not certain how 185+cc runners and 2.02 intakes are going to affect intake velocity with that stock intake.....more decisions......although I did manage to decide on comp cams 1.52 magnum rollers....they are on the way.
    Last edited by PassionRE; 01-24-2017 at 08:04 PM.

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    Good choice on the rockers. As much as I like to take advantage of the ratio increase of 1.6 rockers....they would have put you over the top bumping your .480" lift up to .512". Your 1.52 rockers put you up to .486" lift at the valve. L31 valve guides usually cannot handle much more than .480" without trimming and going to a different style seal. The stock springs should not be run with much more than .480" either. You will probably be just fine but it will be worth it to spin it over a few times checking for contact at the valve seals.

    As far as quality I have run the Magnum 1.52 and 1.6 rockers on lots of motors with no problems. Cool combination!

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    Yeah, I'm running 115 lb. Springs with 55 Rockwell moly retainers rated at .600 lift....I've got that part covered. I'll inspect for seal clearance once I've settled on what heads I'll run.

  19. #19
    I cant speak for the promaxx heads . I know there different than the heads I use. I can only attest to the assault 200cc dart copys.
    The assault heads have standard sbc intake bolt pattern and vortec. The valve covers use standard style valve covers . Everything from the L31 will bolt right up besides your valve covers and you can use pre-vortec valve covers.
    You can also step up to the assault efi single plane, holley accel intake that has efi bungs cast and machined into them. You could run true MPFI using the 0411 . You can also up your compression a bit without the worry of detonation.
    Point being , if your going to spend money spend it smart. I have comp stainless valves ls9 beehives forged comp retainers forged keepers magnum roller rockers .80 hardened pushrods for my comp 280xfi cam. I built my heads for under 1000 I want to say .They could be built cheaper too.
    Here is my thread if should give you some ideas.
    http://www.theturboforums.com/thread...nd-his-L31-GMC

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    I have a hard time buying something the chinese stole from a US companies engineering. That being said the Etec 170s work very well and are good spring wise up to 0.575. The 170cc ports with 1.94/1.55 valves flow as well if not better than some of those 185-200cc cheap heads. The Etecs also work with the stock valve covers and have a dedicated vortec intake port and bolt pattern. To me they are a better choice especially with the stock intake manifold. Mine came with guide plates to run non self aligning roller rockers if you want. They are ready to bolt on out of the box and are a quality casting with beautiful machine work. They have bronze guides and a 3 angle valve job out of the box. You get what you pay for with them.

    FWIW both sets of 062s I have had were cracked. I have had 3 sets of canadian 906s and they were solid. The Hecho en Mexico 06s flow horribly too compared to the Canadian 906s or earlier 062s.