383 stroker timing/performance and temperature

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

  1. erhan ergin

    erhan ergin Member

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    Hi Folks

    I am having trouble with engine performance on a 383 stroker. Unfortunately I have no idea on the engine spec sheet. It is a couple of year old build with a few thousand miles on it. It has a 650cfm Brawler carb. No idea on the jetting but I assume it is all stock. It was idling fine but had bad low end power. I read several threads and got some feedback people suggesting to advance the timing. Also I had very low vacuum (~ 6Hg). I advanced the timing as much as I can, the distributor pretty much will not go any further counter clockwise. I checked the timing and it shows 28 degrees at idle (idling around 800rpm). The car starts fine and idles fine. In fact it was idling a bit high at first even with the idle screw all the way out so I pulled the A/F screws out to about 2 1/2 turn and idle came down from ~900 to 800. All these are with car warm and in gear. I think this is still a bit high. I took of the vacuum line and plugged it. Then reve'd the engine to ~ 3000rpm and I see 42-43 degrees. The engine seems to take this high an advance and runs fine. Performance is better then where I started. It is running quite rich however. That is probably a good thing with so much advance. Here are some questions:

    1- The engine seems to run hot. If I let it idle it settles around 200 degrees but if I drive around a bit, it creeps up to ~ 230 and it cannot seem to cool down. I have recently installed dual electric fans which kick in around 190 degrees. Is it running hot due to the high advance?
    2- Why is the car idling high with the idle screw all the way out? I did not check the vacuum but I believe it improved quite a bit with so much advance. Some of you may have seen my other thread where I had trouble with HVAC vacuum lines. After finding the thorn line under the dash and this advance update, the hvac controls are working fine.
    3- I had a flex fan earlier with a factory shroud. The original Air guys suggested I get rid off the flex fan as it would not work well with the A/C thus I added the dual fans. When I did this I put the fans on the radiator and left the shroud as is. I am not sure if the pull fans are affected by the shroud behind them negatively. I doubt it but I have not seen any examples of people leaving the shroud and putting electric fans (I have seen electric fans that have their own shroud, I am talking about leaving the factory shroud as is). It is possible that air gets trapped between the fans and the shroud and working against me. Any ideas?
    BTW again idling in the garage the car is not overheating.

    Thanks for any suggestions in advance.
     
  2. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    Last edited: Apr 25, 2020
  3. erhan ergin

    erhan ergin Member

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    Thanks for the link. I think I first need to verify the mark on the crank. The TDC is marked with a white marker but I cannot say that is really TDC. I will look into that tomorrow.
     
  4. bourbon_scotch

    bourbon_scotch Veteran Member Lifetime Gold Member

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    smart move i was thinking the same
     
  5. tom3

    tom3 Veteran Member

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    Old school way to set timing on a small block Chevy. Unhook vacuum advance and block off the vacuum line. Rev the engine to about 3000 rpm and hold it steady. Rotate the distributor to the advanced point where the engine runs fastest and smoothest, then back it off just a bit to where you hear the motor slow down some. Leave the vacuum advance unhooked. Should be the best point for power, but may need more retard if it's hard to start when hot.

    But you really need to dig into it much deeper, adjustable vacuum advance, centrifugal weights and springs dialed in, maximum advance set, initial advance to cam manufacturer's spec, maybe a ported vacuum supply to settle down that idle. Get the carb jetted and adjusted to suit the engine. Lot of work there but can sure unlock some horsepower and driveability.
     
  6. erhan ergin

    erhan ergin Member

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    I read what you described elsewhere and thus I mentioned, I unhooked the vacuum advanced and plugged it. However, I had already advanced it all the way I can before this. I just reved and checked what the timing is at ~3000 rpm. I got ~42-43 as it was jumping a little. I have no problem starting. I was just worried that this much advance was causing hot temps but looking at the link Bourboun_scotch gace it is the opposite. Essentially retarding apparently causes an engine to run hot.
    Any comment on the high idle speed? I have the idle screw all the way out. It is still idling at 800rpm (in grear) In park it does to just under 1K rpm.
    Also any idea about leaving shroud with the electric fans? I will take it off and see if it makes a difference tomorrow but maybe someone already tried this.
    Thanks for all the responses.
     
  7. Lowend

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

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    I may be missing something, but my baselines for street engines
    Idle, 4-8 deg BTDC at idle, ~32 degrees total timing all in ~ 2400 RPM

    6hg of vacuum at idle is really low unless you are running an absolutely massive cam.

    My guess, you have a vacuum leak.
     
  8. 81Z28LS

    81Z28LS New Member

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    I agree with Lowend about the vacuum. I would torque the intake manifold using correct sequence and torque. Check for vacuum leaks all over the carb, intake and any vacuum accessories.

    I would also think about valve adjustment. I've seen engines run very poorly due to excessively tight valve adjustment.
     
  9. erhan ergin

    erhan ergin Member

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    6Hg vacuum was earlier. I had been chasing after that while trying to fix the HVAC control issue. I have not checked vacuum since but I am sure it is not 6Hg anymore. When it was that low, the vacuum controlled doors were not responding at all. I have an older thread on that. I do not believe there is a vacuum leak but will check what the current reading is. BTW one more detail, before advancing the timing, the car was running rich, I pulled out #1 plug and it was fouled with fuel. I checked the carb float level and adjusted it. It was very high, could see from the windows on the side of the carb. I did not bother changing all the plugs. There is no miss and the car starts right up. I am sure the plugs were all fouled. I am wondering if that would manifest it self like this. Here are the steps I am planning
    1- Check that the TDC mark is correct on the crank
    2- Check vacuum reading
    3- Pull back timing to ~ 18 degrees at idle. All info I found on forums so far suggests this should be a good starting point. I think 28 degrees is too aggressive. 4-8 degrees at idle will not work on this cam I am sure, I do not know the cam specs but I think it is quite aggressive from the way the engine sounds and the lumpy idle.
    4- Also I think the stock fan shroud is actually hurting the electric fans performance as the shroud is behind the fans. The air gets trapped between the shroud and the back of the fans which I think is a problem.

    I will post my findings.

    Thanks for all the suggestions.
     
  10. xten

    xten Veteran Member

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    I think there are multiple problems here. First, verify TDC. If your balancer has spun, the readings will not be correct and you could still be retarded.(not you, the engine). This problem drove me nuts.
    I'd bet there's a vacuum leak somewhere.
    Assuming your fans are pullers (not pushers) with a stock shroud,it could be creating turbulence inside the shroud.
    Verify your fans are both running the same direction. If they are pushers they could be running the wrong way. Also the pitch of the blades could be wrong for your application. Are the fans each on a separate relay?
    Did you try a stock clutch fan with the shroud before you swapped to electric?
     

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