Help with idle EGTs. Can't get 'em down...

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Scouder, May 9, 2010.

  1. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    Here's the deal. 511 KB hemi. Brad fuel heads. Mert 14 hh. 990 pump. K valve.

    Question 1: When I leaked the barrel valve, I capped everything except the hat outlet. I left the hat outlet wide open because I didn't want to blow through my fuel flow meter. Is this OK, or should the hat line be hooked up? It would be difficult to flow just the hats, as the line splits to the hats and ports after the flow meter.

    Question 2: What kind of idle timing is typical? I started at 25 which seemed to be way too far back, so I am currently at 30. Keep in mind, my density altitude here, as I type, is 8000 feet and usually worse. Since there is no pressure here, and not much boost at idle, is it possible that it might take even more timing at idle?

    Question 3: It seems that I am getting some drop in EGT as I lean the barrel valve. My last measurement was at 65%, measured as described above, and got my EGTs down to high 500 range. That seems to indicate that I am burning fuel in the pipe. So, should I try it at 60% to see if they continue to drop, or should I give it more idle timing?

    Maybe I'm wrong, but it seems to me that the only way to adjust idle EGT is with timing and the barrel valve. True?

    By the way. Don't worry about the idle timing being advanced. I will use the 8973 to bring it back during the burnout and during the run.

    Any help would be appreciated.

    -Brian
     
    #1
  2. Mike Canter

    Mike Canter Top Dragster

    Joined:
    Mar 10, 2004
    Messages:
    3,987
    Likes Received:
    53
    Can't tell you what the timing should be with the fuel heads but somebody will chime in and tell you.

    As far as the leak down on the BV it sounds like you have it hooked up correctly. Idle return capped and outlet hose totally off the only question I have is that you keep turning it so the percent is less which is leaner and hotter on EGTs. The more the leak down gauge goes towards zero or the greater the percent is the richer it is. If the EGTs are high at idle then you need more fuel. You need to be i the 78 to 83% leakdown range.

    Here is something to check. Make sure on your timing that you are on the Before Top Dead Center and not timed at 25-30 degrees After Top Dead Center. Double check because of the rotation of the motor it is reverse in logic and one can get on the wrong side of TDC. It will run but will be shooting small flames out the zoomies.

    Being on the wrong side of TDC might make the EGTs drop the leaner you adjust the BV.
     
    #2
  3. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    Thanks Mike,

    I set TDC with a piston stop and degree wheel with the heads off, so I'm pretty sure it's close. Pulling the engine through clockwise, the 30 degree mark hits the pointer before the TDC mark, so that seems right as well. No flames in the pipes.

    I guess the thing that has me scratching my head is that by moving the barrel valve from 87 all the way down to 65 I should have seen HUGE changes in idle EGT, and they just weren't there. 87 sure made my eyes water though!

    That's why I am thinking the timing isn't enough for this altitude. The symptoms point to retarded timing and fuel burning in the pipe. I just don't have enough experience with these engines to make that call with confidence.

    -Brian
     
    #3
  4. Fuel Cars

    Fuel Cars AA/AM

    Joined:
    Aug 20, 2003
    Messages:
    282
    Likes Received:
    2
    Mike, I'm just learning this myself, but, I thought the leak down should go through the hat nozzles?

    Won't a .040 nozzle flow differently than .080 nozzle at the same 100 lbs leak down pressure thus affecting the barrel-valve percentage?

    I thought the leak down percentage was for setting a specific amount of flow at idle through a specific size opening, the hat nozzles, am I wrong?

    Just asking because I want to learn, thanks.
     
    #4
  5. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    Update: I am getting info through the back-channels that the fuel heads take alot more lead than the Fat heads. I set my idle timing at 30 thinking it was a bunch, and it turns out it's probably still way back from where it should be. I'm also going to make sure the ports aren't cracking, which would make the barrel valve not respond to changes. That would certainly explain the symptoms.

    I'll do some more testing tonite.

    -Brian
     
    #5
  6. wfh

    wfh New Member

    Joined:
    Apr 22, 2010
    Messages:
    19
    Likes Received:
    0
    you need to have the hat hooked up to and then get percentage.
     
    #6
  7. Flyboy68

    Flyboy68 Member

    Joined:
    Mar 26, 2006
    Messages:
    564
    Likes Received:
    0
    Hey Brian, we run the same setup as you, 526kb, 14hh 27% over, brad fuel heads, promag 44. Before the winter when we fired it up we had 30 degrees timing, and i'm looking at our data right now. cyl 4 was around 250, cyl 7 was 650-700. The rest were from 350-500. I believe our leakdown was 75 leak in the motor, however after startup we adjusted the barrel valve until we seen desired egt temps. Idle was about 1800, no boost.
     
    #7
  8. Flyboy68

    Flyboy68 Member

    Joined:
    Mar 26, 2006
    Messages:
    564
    Likes Received:
    0
    We also leaked the barrel valve w/ the hat nozzles hooked up. Even though you're leaking the bv itself, I would think the lack of back pressure on the backside would make a difference? Guess you could hook it up both ways and see.

    Josh
     
    #8
  9. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    With the barrel valve leaned out a little I see balanced temps, but high, around 700. If I richen it up I start to see what you show above, the EGTs spread out real bad. I'll drown some out, so they go cold, 100-250 spitting raw fuel, and others are still lit and dry and show 700.

    I have been told I should be able to balance them pretty close and be in the 350-400 range, so sump'n ain't right yet.

    Right now my plan for after work is to move the timing forward more, and re-blow the bv to 75% and start over. I'll also check to make sure my ports aren't opening at idle.

    -Brian
     
    #9
  10. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    Edit. I think I'll set it to 80% instead of 75 for my next start.

    Question: Is it common for the pipes to spit fuel at idle? If so, maybe that's an indicator I need to watch for.

    -Brian
     
    #10
  11. Flyboy68

    Flyboy68 Member

    Joined:
    Mar 26, 2006
    Messages:
    564
    Likes Received:
    0
    You might see if they even out if you bring the motor up until the port nozzles open up.
     
    #11
  12. Fuel Cars

    Fuel Cars AA/AM

    Joined:
    Aug 20, 2003
    Messages:
    282
    Likes Received:
    2
    One other thing I would look at is the butterfly gap before re-doing the leak down.
     
    #12
  13. Mike Canter

    Mike Canter Top Dragster

    Joined:
    Mar 10, 2004
    Messages:
    3,987
    Likes Received:
    53
    As far as having the output of the BV hooked to the hat nozzles. Maybe I am just different because if you have it hooked up to the port nozzles then will have a difference from one car to another because of difference size hat nozzles. I was taught to do it with the output hose off the BV and the idle return blocked off. Really it doesn't make a difference because the percentage leakdown in a BV is your reference so you can always return to that adjustment if you have changed anything. You should be asjusting the BV linkage to give you the correct crisp off idle response with the EGTs becing in the correct range. Once you have adjusted the idle response (mixture) then you should do a leakdown and see where it is at and then record that so you can always return to that point.

    Because of all that you should not take a leakdown percentage that somebody gives as gospel but as an approximate area and adjust yours from that point. Like I said if you are leaking it down through the hat nozzles then it is going to be different from car to car. Or if you change the size of any of your hat nozzles then you are going to change the leakdown percentage.
     
    #13
  14. Flyboy68

    Flyboy68 Member

    Joined:
    Mar 26, 2006
    Messages:
    564
    Likes Received:
    0
    That's true. BV leakage is just a reference. Everyone should be clear however on what the numbers refer to so you're not far off on start up.
     
    #14
  15. Fuel Cars

    Fuel Cars AA/AM

    Joined:
    Aug 20, 2003
    Messages:
    282
    Likes Received:
    2
    OK, I just tested it on my system, Bird w/Enderle square bv, and there was a 2% difference between having the outlet wide open versus going thru the hat nozzles.

    The wide open outlet showed more flow when compared to the nozzles which is what I expected although I thought it would have been more of a difference than 2%.

    Probably not enough to worry about but need to be consistent on method used.
     
    #15
  16. Flyboy68

    Flyboy68 Member

    Joined:
    Mar 26, 2006
    Messages:
    564
    Likes Received:
    0
    Good to know Paul.
     
    #16
  17. bruce mullins

    bruce mullins Top Dragster

    Joined:
    Aug 2, 2003
    Messages:
    981
    Likes Received:
    3
    I ran brad fuel heads for years and ran real fast so I have some knowledge of them. . .First off, you will be safe at 32 degrees. ( i ran as much as 36 with a 44 amp mag in bad air) second. . .are your return poppets pointed in the right direction and are the poppets in the correct place one is an idle check (around 6lbs) and one is a pump saver (around 175 or higher). . I have always set the bv with everything hooked up just cap the two returns (idle check and pump saver) set bv at 78 to 80 percent. your air gap on the blades should be about 10 to 14 depending on the hat and that thing should idle around 1600 to 1800 rpm. (are you using a K-style or square barrel valve) should be the K-style.
     
    #17
  18. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    Bruce,

    Thanks for your post. I'll check everything out, fire it with the new settings and report back in a little while. I appreciate the timing advice. We always have bad air, 8500-10,200 feet, so your info gives me some good parameters to work with.

    -Brian
     
    #18
  19. alcohol altered

    alcohol altered New Member

    Joined:
    Apr 22, 2007
    Messages:
    144
    Likes Received:
    0
    I had a very similar problem on my blown BBC and it turned out my Enderle pump was bad. I put a new one on and egts at idle came down. My old pump was tested only a few weeks before the problem popped it's head up and it tested within spec.
     
    #19
  20. Scouder

    Scouder New Member

    Joined:
    Jan 2, 2009
    Messages:
    378
    Likes Received:
    0
    OK, got some improvement finally.

    Butterflies: .010
    Timing: 36
    Idle: 1800
    Fuel Pressure: 9.5
    Idle poppet: 10
    Ports: 14
    Density altitude at test time: 8150 feet.

    I set the BV to 80% with the backside open. On startup, EGTs climbed hard, head temps went with them. Got pissed, started cranking flats into it until I got spray out #1, then brought it back just enough to dry it up. By this time she had been running for a minute and a half or so, so I killed it.

    When head temp dropped to 145 I fired it again. She was fighting the starter just a little, but fired off. I checked the timing real quick and then started a data log. By the time I started the log the head temps were up to 160. Heres the start and finish numbers on a 30 second log:

    Start Finish
    Head temp 160 183
    Egt 1 422 360
    Egt 2 432 468
    Egt 3 442 423
    Egt 4 400 272
    Egt 5 560 653
    Egt 6 466 578
    Egt 7 552 651
    Egt 8 518 640

    After I killed it I re-blew the BV to see what it was set at. It showed 93%. Again, this is with the hat lines off.

    So, here are my observations:

    1. EGTs fell on the front cylinders, and went up on the rear during the warmup.
    2. The engine liked the timing, going from 30 to 36 and would probably like more, but is starting to work against the starter.
    3. The head temp rise, 22 degrees in 30 seconds seems too fast.
    4. The BV seems too rich. I wonder if the EGTs would drop if I brought it back to 85%.

    What do you guys think. Is this a runnable combination, or do I need to keep tweaking on it and get the EGTs more balanced and slow the head temp rise?

    -Brian
     
    #20

Share This Page