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Thread: Ordered parts and last thoughts before build up

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  1. #1
    Fuel Injected!
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    Ordered parts and last thoughts before build up

    Here is what I'll be running.

    Stock L31 GMPP Long Block
    Edelbrock 7116 Performer RPM Intake Manifold
    ACDelco EP341 Fuel Pump
    Holley 670CFM throttle body w/stock 61# injectors with 28PSI Spring (Effectively 89.9# of fuel per injector)
    Shorty Ebay Stainless Steel Headers w/ 2.25" dual exhaust all the way back no cats no crossovers
    AEM 30-4110 WBO2 Unit for Closed Loop tuning
    BJYK Modified base tune from Dave W.

    Anybody see any glaring issues with this setup? I'm aware I should have significantly more fuel than I need for a stock L31. With that being said I would rather have more than I need than not enough. Not trying to self destruct it on the first drive :) If it is consistently running too rich I might buy an aftermarket AFPR and go to around 20-22PSI

  2. #2
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    What cam are you running and whats your intended RPM range?
    That's a fair bit of fuel pressure, I'm assuming Dave has set your base tune around that fuel pressure.
    The PCM will potentially compensate for excess fuel pressure if it needs to when in closed loop but it might be a bit rich while warming up in open loop.

  3. #3
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    Quote Originally Posted by Kitch View Post
    What cam are you running and whats your intended RPM range?
    That's a fair bit of fuel pressure, I'm assuming Dave has set your base tune around that fuel pressure.
    The PCM will potentially compensate for excess fuel pressure if it needs to when in closed loop but it might be a bit rich while warming up in open loop.
    It is a bone stock L31 so the .414" Intake cam and I forget the exhaust lift, its in the .428" range I believe. RPM range at 70 MPH will be somewhere around 1900-2000 until I change gears out at a later point. I would really like to switch to 4.56 gears when I install a lift and larger tires (35" or 38"). At that point with the gear swap I would only be moving my cruising RPMs up to 2300 which isn't a huge change.

    The PCM is a 16197427 and I initially told Dave I would be running BBC injectors at lower pressure but changed my mind. I adjusted the injector flow rate in the bin from the mark he set to the new mark.

    Again, I know it will be rich, but for install and initial tuning I want to be on that side of the fence rather than lean. Don't want to melt hard parts and destroy it on the first start up. Eventually I will likely bring that pressure down if I choose not to install a cam.

  4. #4
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    I have a similar combo, L31 long block, ported Vortec heads, Chevrolet Performance Vortec to TBI intake manifold, Headman long tube headers and a small CompCams 252XFI HR-13 cam, 650CFM throttle body with stock injectors.
    I initially had this combo running fine on 15.5 PSI fuel pressure.
    I had the RPM limit initially set at 4500 but raising the RPM limit to 5200 had the injector DC% hitting 100% at W.O.T., I was monitoring it with a Wideband O2 sensor but ideally you want your injectors to be at 80% of their maximum capacity at W.O.T..
    I've now increased the fuel pressure to 18 PSI and the injector DC% at W.O.T. does look better. For my current combo I think 19-20 PSI will be what I need, most of the time I'm driving around in the 1700-2500 range.

    That's not to say you can't dial in your combo with 28 PSI but I would have thought it's way more than you need at the moment.

  5. #5
    Fuel Injected! steveo's Avatar
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    having way too much injector flow means it'll idle rich rough because your injector pulse can't be short enough.

    Don't want to melt hard parts and destroy it on the first start up
    there's this misconception that running pig rich is better than risking being a bit lean.

    it's incredibly hard to blow up a four stroke liquid cooled engine from being lean for a few minutes or hours, unless you're putting a bunch of load on it.

    especially 'on first startup', it's probably not happening, and if you hear any popping and stuttering, just shut 'er down?

    running pig rich, on the other hand, trying to be 'safe'... might as well throw sand down your intake, carbon is just as abrasive.

    i would start by fueling an engine by my best guess and see how it goes.

  6. #6
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    Steveo has a good point about the injectors at idle with too much fuel pressure, if you're too rich you might wash your bores down with fuel.

    I accidentally started my new L31 engine with it's last best stock TBI engine tune and it idled okay, it wouldn't of had enough acceleration enrichment to make it move but it ran. I still had 15.5 PSI of fuel pressure though.

    My stock TBI engine with headers was running out at 4000 RPM with the stock fuel pressure.

    The requirements for the Vortec/TBI combo with the stock cam aren't huge but it can use more timing than the stock TBI timing tables have.

  7. #7
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    Quote Originally Posted by steveo View Post
    having way too much injector flow means it'll idle rich rough because your injector pulse can't be short enough.



    there's this misconception that running pig rich is better than risking being a bit lean.

    it's incredibly hard to blow up a four stroke liquid cooled engine from being lean for a few minutes or hours, unless you're putting a bunch of load on it.

    especially 'on first startup', it's probably not happening, and if you hear any popping and stuttering, just shut 'er down?

    running pig rich, on the other hand, trying to be 'safe'... might as well throw sand down your intake, carbon is just as abrasive.

    i would start by fueling an engine by my best guess and see how it goes.
    I would tend to agree with you, and you've convinced me to order the 18PSI spring as well. I'll start at that point and change to the 28 PSI spring only if needed.

    You'll have to excuse my hyperbole but hopefully you can understand my concern with being underfueled. Then engine I currently have in the truck lived a very short life before cracking the head due to what I believe to be lean condition so I am trying to be overly cautious.

  8. #8
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    Quote Originally Posted by bgott View Post
    I would tend to agree with you, and you've convinced me to order the 18PSI spring as well. I'll start at that point and change to the 28 PSI spring only if needed.

    You'll have to excuse my hyperbole but hopefully you can understand my concern with being underfueled. Then engine I currently have in the truck lived a very short life before cracking the head due to what I believe to be lean condition so I am trying to be overly cautious.
    You would lose a piston or valve seat long before you cracked a head from running lean.

    I run the Express van about 16.5:1 at highway crusing speed. My old Q-Jet fed 350 in my G20 van was running 17:1 at steady highway speeds. I swapped a big block TBI unit in the Q-jets place and then had to figure out why my fuel mileage went down and the wideband told me why. I had to do alot of tuning and enable lean cruise to get back the same MPG I got with the carb.
    Last edited by Fast355; 07-09-2018 at 06:14 PM.

  9. #9
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    Quote Originally Posted by bgott View Post
    I would tend to agree with you, and you've convinced me to order the 18PSI spring as well. I'll start at that point and change to the 28 PSI spring only if needed
    I can't find my notes, do one of you guys have the 18 psi and 30 psi spring part number handy?

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