Torched head and block

Discussion in 'PSI Superchargers Tech Questions' started by Jeffwiebe, Jul 14, 2015.

  1. Jeffwiebe

    Jeffwiebe New Member

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    572 BBC 1471 Blower 20psi boost. We were trying to get down a greasy track on the weekend. The one pass we did I had 15* timing out from 36* total on the hit and had it all back in in 5 seconds. It torched #2 at the outside of the intake valve, head and block. We are running Cometic .065 head gaskets. I have one engine builder telling me we cant have that much timing out that long and it hydraulic the cylinder pushing the gasket out. Another engine builder said that's not possible it was detonation from too much timing and boost at the top end with not enough fuel. Not sure what route to take on fixing the problem. Any advise is appreciated.
     
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  2. Bjs344

    Bjs344 Member

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    maybe they're both right. Exhaust valve may have been glowing by the time the timing came bac in, which could cause detonation.

    Also, where is phasing set and are you sure you can pull 15 without crossfire.

    When you didn't get down the track on the previous passes, were you riding the high side limiter at any point?
     
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  3. Blownalky

    Blownalky Top Sportsman

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    Don't care what Cometic tells you, copper is bulletproof if set up correctly. Turbo, nitrous or blown is the same as boost is boost and cylinder pressure is cylinder pressure. Don't see any top fuel folks with Cometic gaskets and I doubt any AFD, AAFC or Pro Mod or fast Top Dragster or Top Sportsman use them. Once a gasket fails or the heads lift, you will torch the block and head.
     
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  4. Jeffwiebe

    Jeffwiebe New Member

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    The exhaust valve looks like new, it didn't get hot. We are running a MSD Pro Mag 20 without crank trigger and MSD Grid, no idea where rotor phase is with 15* out. We tried 5* and all in by 2.5 seconds, 10* all in by 3 seconds. Both times blew the tires off. It never got on the high side limiter except a bit on the burnout, its set at 7800. Spark plugs look like new, no sign of detonation.
     
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  5. Jeffwiebe

    Jeffwiebe New Member

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    Do we need to O ring the block to run copper? Its an aluminum block.
     
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  6. Blownalky

    Blownalky Top Sportsman

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    Normally O-Ring the heads and put a receiver groove in the sleeves. You can also put O-Rings in both the heads and sleeves.
     
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  7. SoDak

    SoDak Active Member

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    Is this a new engine?
     
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  8. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    retard

    If the car was running so rich with the timing retarded that it hydraulic'ed the cylinder and pushed the head gasket out, it wouldn't go anywhere. It would look like an irrigation system going down the track. There have been so many times something has gone wrong in ignition and dropped a cylinder or something, dead plug, dead wire, etc., where there is no fire and you don't hear about that being a cause of pushing a head gasket, so how would it push a head gasket with it partially burning that fuel? I run a Top Dragster that is so backed down to run 6.00 that it doesn't have close to full timing back in it until after the 1/8 mile.

    Occam's razor says the simplest explanation is usually the correct one. More than likely 36 is over center on timing for your fuel and compression combination. What does the upper rod bearing look like? If it was detonating enough to push a head gasket, it probably beat it up, an it should be closed up at the top compared to a normal bearing.

    If it isn't tune up, it could be a torquing or sealing issue. Also could be a problem with the fuel system causing a lean spot. Maybe the reason why it won't go down the track is the fuel system is leaner than you think it is if the pump is going away. Also could be cavitating down track.
     
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  9. Jeffwiebe

    Jeffwiebe New Member

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    Thanks. I'll tell the engine builder.
     
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  10. Jeffwiebe

    Jeffwiebe New Member

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    Yes, all new engine, fuel system etc.
     
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  11. Jeffwiebe

    Jeffwiebe New Member

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    Thank you so much. Kinda the same thing I was thinking. The fuel system and engine are brand new. We tuned it on the chassis dyno and thought it would run with no issues. I think I have a game plan for the next race now.
     
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  12. Will Hanna

    Will Hanna We put the 'inside' in Top Alcohol
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    timing and fuel

    Just remember it's a hell of a lot easier to work your way from the rich side down than the lean side up...
     
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  13. 32 bantam

    32 bantam Member

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    Piston to head "quench" is very important in BBC. Alum. rod engine. Should be approx. .062. Too much and you will have head or piston torching issues. Too little and the piston hits the head!!!!!
     
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  14. SoDak

    SoDak Active Member

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    In my BBC experience,
    -36 degrees is too much for a supermag and way too much for a MSD, which do you have?
    -you don't need receiving grooves with copper head gaskets, with cometic I have no idea (I have no experience with them)

    How much has this engine been run, dyno and track?

    How much static compression?

    Port nozzles also or only hat nozzles?
     
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  15. bandit496

    bandit496 Member

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    When we were running 540 BBC with 14-71, number 2 cylinder was always a bit%$ keeping enough fuel in it to keep it from torching pistons, head or block. Especially when not being on top of throttle control (transitioning from hat to port). We ran as much as 40 degrees of timing at times and as low as 28. Always made sure block and heads were square, used Clark copper gaskets with o-rings. Finally ended up putting two nozzles with smaller openings to increase amount of fuel with increased pressure. That seemed to work for us. Of course, we tractor pull, so our runs last longer than 6 seconds (12-15 seconds at WOT-lol). For what it is worth. JW
     
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  16. Jeffwiebe

    Jeffwiebe New Member

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    We run an MSD Pro Mag 20. It made 8 dyno pulls, Two of them to 200mph. Two 100' passes and one 1/4 mile pass at the track. Compression is 11-1. It has hat and port nozzles.
    .56 in the two front hat
    .52 in the rest of the hat
    .50 cyl 1 and 2 port
    .46 in the rest of the ports.
    This was our dyno starting point. We tuned by reading plugs and went with .49 in #4 port and .50 in #6 port.
    All other cylinders look mint, like new. Just #2 is toast. I tried talking the owner into getting EGT''s, he might do it now.
     
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    Last edited: Jul 16, 2015
  17. Jeffwiebe

    Jeffwiebe New Member

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    We are running old Pontiac Big Chief heads. I don't think we will ever see 40* timing in this one. I think i'll drop it to 32*, lower boost and raise #2 nozzle a size. If it goes down track I can tune it from there. We have a data logger but can't get it to load the information to the laptop. I'll try and have that working next time out. I'll also try and get egt's on it.
     
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  18. overkill69

    overkill69 Member

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    chevy

    We always ran more boost but way less timing in Chevys.32 max with a conventional head and 30 max with 14/18 degree chiefs. They were always mean down low but soft above 8500rpm.
    Had plenty of headgasket issues with oem parts. The big studs and solid castings with o rings cured all that.
    I was warned that the GM prostock water castings are too light for boost if thats what you have.
     
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  19. SoDak

    SoDak Active Member

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    Apparently the timing wasn't optimized on the dyno?

    If not and it were mine, I would put it at 28 and this winter I would dyno tune the ignition timing. I bet I'm pretty close...
     
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  20. Jeffwiebe

    Jeffwiebe New Member

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    Yes these are Pro Stock water castings. Very good to know, thanks.
     
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