383 stroker timing/performance and temperature

Discussion in 'Troubleshooting & Diagnosis' started by erhan ergin, Apr 25, 2020.

  1. jeff swisher

    jeff swisher Veteran Member

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    A lot of camshaft overlap will cause low vacuum signal.
    Usually long duration cams have a lot of overlap and those cams sometimes hurt low speed power.

    Large runner cylinder heads kill the vacuum signal even more than the large cam.
    If you have lazy cylinder heads that will hurt the bottom end even more.

    I did a 253@ .050 flat tappet on a 106LSA with AFR 210 heads it pulled 5" vacuum .. ran a 5500 stall ran 42 total timing.

    I had 2 other 350's that had 41 total timing for best power..one used milled 186 heads with chamber work and porting the other was 601 heads and 244@ .050 cam again lots of chamber work and porting.

    If the flame speed in the chamber is slow then it will like a lot of timing.
    My vortec 906 heads made best power with 35 total.
    Another set of 601 heads made best power with 38 total and was down 3 HP at 35 total and 3 hp lost at 40 total.

    That one had a smallish cam 218 @ .050, 225 psi cranking pressure.

    All the above were ran on 91 octane
     
  2. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    do you have a vacuum advance on your distributor?
    where does it get vacuum from?
     
  3. erhan ergin

    erhan ergin Member

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    I am not 100% sure I did a hand calculation using my tire/wheel size and tach reading combined with speedo reading. I calculated it to be around 4.10. I see over 3500 rpm at 60 mph crusing. This is also puzzling as I think such a gear ratio should give very good pull.
    When I got the car, vacuum advance of the distributor was laying on the intake. The hose was not connected. I connected it to a port on the front of the carb. When I do the timing I unplug this. Put a screw in the hose and plug the port on the carb.
    Based on Jeff's comment I may be OK with 28 degree idle timing and > 40 degrees total timing. How can I tell if I am hurting the engine with so much advance? Is there some sign I should be looking for?
    I will post some pics so people have a better idea what I am talking about. Also I may be missing something obvious that you can see via the pics.

    Thanks
     
  4. erhan ergin

    erhan ergin Member

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    Here are some pics showing vacuum/timing etc.
     

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  5. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    jack the whole rear end up and see how many turns the driveshaft goes in one revolution of a wheel (in neutral), if they spin opposite you have to multiply by 2 i believe
     
  6. Lowend

    Lowend Administrator. .a car, a man, a maraca. Staff Member Lifetime Gold Member

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    Are you just leaving the vacuum line open, or plugging it up?

    If you are leaving the line open, as bourbon_scotch previously stated the engine is going much leaner which is what's causing the RPM's to raise. This tends to indicate that the carb is too rich at idle.

    Can you check if there is a part number or manufacturer's name stamped on the front of the cylinder heads? Are they aluminum or iron? I want to start unwinding what this engine is.

    It occurs to me, have you checked to make sure your ignition wires are in the right order on the distributor? You wouldn't be the first guy to have mixed them up
    [​IMG]
    http://www.hcdmag.com/chevy-v8-firing-order/

    I bet that cam idled at 1100+ RPM
     
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  7. erhan ergin

    erhan ergin Member

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    I left the vacuum line open.
    The plugs are connected properly.
    It is aluminum heads.
    I opened the valve cover to see if there is any stamping but could not find one. The A/F is at 1 1/2 out from seated position. I am wondering if the power valve is blown like Bc_homegrown suggested or maybe it is sized bad.
    I am going to investigate the vacuum leak possibility, I will spray some carb cleaner and see what happens around the intake. I am also going to check that the PCV valve is working.
    I am a bit doubtful as the car idles, starts and runs fine. It seems it is setup for high rpm power. One more detail, I was able to turn the distributor a bit more and got the idle advance over 32 degrees, vacuum went up to about 7.5 Hg.


    Can someone comment on this question:

    "Based on Jeff's comment I may be OK with 28 degree idle timing and > 40 degrees total timing. How can I tell if I am hurting the engine with so much advance? Is there some sign I should be looking for?"

    Thanks
     
  8. jeff swisher

    jeff swisher Veteran Member

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    I check total timing by driving the car in high gear and putting it under a load.
    Slow speed 25-30 mph in high gear apply throttle slowly and have your foot on the brakes to simulate pulling a heavy trailer up a hill.
    Do not allow the trans to kick down into another lower gear.
    Listen for pinging.

    If your exhaust is so loud you can't hear anything over it then you will be best served with some added mufflers.
    Or a drag strip.

    Maybe a friend with good hearing can drive beside you with him listening at the front of the car where the engine is at.
    Retard timing until pinging goes away and pull another 2 more degrees out.
    Sometimes power breaking it in the driveway will make it ping. Do not let the tires spin.
    Maybe apply emergency brake and foot brake.

    I ported some Edelbrock 185cc heads for a buddies 355" and ran a 230@ .050 cam on a 106LSA
    at the track I kept adding timing I started with 35 total and at the end of the night the engine liked 42 for best MPH.

    read here.
    http://nastyz28.com/threads/update-edelbrock-e-street-5089-heads-track-et.328031/
     
    Last edited: Apr 27, 2020
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  9. erhan ergin

    erhan ergin Member

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    Thanks will try. As a precaution I will back off timing as I am not sure I am able to hear pinging over the exhaust noise.
     
  10. jeff swisher

    jeff swisher Veteran Member

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    Yea that is a dangerous situation.. friend had a dial back timing light and did not really understand how to use it. Even though I told him many times and showed him.
    He set the dial at 35 degrees and then advanced the distributor until the 35 degree mark on the balancer lined up with 0 on the timing tab.

    He said it came out of the hole really hard and wanted to race me as he had just put the TUNE on the truck.

    OK we race and I was behind him about 2 car lengths he is running 4" Borla mufflers and 4" pipe dumped behind the cab of the truck.
    I asked him if he shifted early because it was pinging he said no I shifted at 7000 because I was ahead of you and it's not pinging ..I said I could hear it from way behind you.

    He insisted it was not pinging and wanted to race again so we did and he ruined the engine.
    Pistons held up but bearings took a beating.
    It was knocking after the second race.
    He stuck bearings in it from under the vehicle and I said too much debris in engine it needs to come all the way apart.
    After 3 times changing bearings and failing he took it apart.
    Did not last more than 5 miles after a bearing change and it was knocking again.

    I like quiet exhaust for a first build and tune of a combo that is unfamiliar.
    Or read plugs and look at track MPH or just stick it on a dyno and look at HP gained or lost.

    Some people have dyno days and you can get 3 pulls or so ..Change timing and see what happens.

    Sure hate to see an engine killed from the wrong tune.

    For the timing impaired that total timing my buddy dialed into the engine was 70 degrees total.

    Yea makes you wonder why it even ran.
    And he still beat me.
     
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