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Thread: Detonation ?

  1. #1
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    Detonation ?

    Hay guys, has anyone ever had a detonation issue with the 320's when running higher compression ? I just beat the tops out of two pistons at Bonneville running 13:1 pistons and with 33 degree of timing. Like to hear your ideas.

    Dale

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    Do any other spark plugs and pistons show signs of detonation?
    What octane fuel are you running? What type of manifold and carbs?

    Paul

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    the plug readings don't show any definate signs of detenation............what does show is that the front four plugs look richer than the back four...........wich seam to mean that the carbs are not balanced but .but A/F ratio showed 13.4 on the LM1.................but number two piston had a hole right at the spark plug and a crack running over the top of the piston.........I run a rather large plentum with 1 7/8 inch runners.........and two 650 Holleys............and sence I first ask this post question, the motor is apart and number five looks as if it was getting hot.......I run pryometer in number eight and never got over 850 degree ?

    I am beginng to think that reversion is a bigger deal in these motors than I thought...........never have any problems on dyno pulls or in the first 1 1/2 miles, but in the second mile all goes to hell................thinking about lower compresson ratio and adding water injection on top end ? strange things are happening on prolonged throttle and never lifting to let engine breath................has anyone ever tried to grind a can with "scattered" valve timing?

    I run ERC 110K with a 115.5 (research method) octane rating
    Last edited by saltracer; 10-17-2010 at 05:06 AM.

  4. #4
    A/F ratio showed 13.4 on the LM1

    Where is the sample taken from?

  5. #5
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    Quote Originally Posted by saltracer View Post
    the plug readings don't show any definate signs of detenation............what does show is that the front four plugs look richer than the back four...........wich seam to mean that the carbs are not balanced but .but A/F ratio showed 13.4 on the LM1.................but number two piston had a hole right at the spark plug and a crack running over the top of the piston.........I run a rather large plentum with 1 7/8 inch runners.........and two 650 Holleys............and sence I first ask this post question, the motor is apart and number five looks as if it was getting hot.......I run pryometer in number eight and never got over 850 degree ?

    I am beginng to think that reversion is a bigger deal in these motors than I thought...........never have any problems on dyno pulls or in the first 1 1/2 miles, but in the second mile all goes to hell................thinking about lower compresson ratio and adding water injection on top end ? strange things are happening on prolonged throttle and never lifting to let engine breath................has anyone ever tried to grind a can with "scattered" valve timing?

    I run ERC 110K with a 115.5 (research method) octane rating
    Is the piston dome on the side away from the spark plug forming a pocket around the plug area or just a symmetrical pop-up?
    Would the rules allow you to inject alcohol rather than just water?
    Have not worked with “scattered” valve timing. Some cams simply change timing between intake lobes for the cylinders that share an intake port. Other cams include a different duration for each lobe. Many hours of dyno R&D time. Since these timing variations only involve a few degrees you could try timing changes by varying the valve clearance. (Temporary dyno experiment)

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    Dale, I think I know what your problem is, almost exactly the same thing happened to my 248 once apon a time. About 30 years ago, I put a supercharger on my 248. I ran it around town for a while and it seemed fine. So I thought that it was time for a real run up to my cabin, about 100 miles away. Boy!, did that thing run!! But by the time I rolled in the drive, something was not quite right. By the time I managed to get back home, things were diffinatly not right. I pulled the head, partly melted pistons, holes in pistons and tops of pistons broken off the skirts up in the cumbustion chambers. The stock type piston certainly were not up to the job, but there was more going on. That was the end of the supercharging expierment, I just did'ent have the money or knowhow to make it work.

    Over the years of expiermenting on my engines I have determined that at high levels of power, not sure exactly where, the str8 develops thermal distribution problems. The spark plug is way over on one side, actually over the deck, a really bad location, this makes the plug side of the piston much hotter than the far side. If there is a big dome in the way, it gets worse. There could be 2-300 degrees difference between sides. The piston can't take it. The only solution that I can come up with is to install oil squirters like the chevy LS engines have, aimed at the underside of the piston right at the hottest spot, and give it a good bath. And keep the oil cool. The next problem is that the front of the engine is always cooler than the back. The out put of the water pump must go into the engine at the center frost plug hole, then depending upon which block you are using, plug the coolant holes or drill new holes in the deck in order to warm the front and cool the rear. And, yes, there is a reversion problem with these engines. If the intake is too big or there is too much cam it's almost a sure bet. The way you can tell is if you are getting fuel stand-off above the carb/carbs or to a lessor degree, carbon tracking in the intake. Not a lot of fix other than less intake or cam. Have fun! alleycat

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    Alleycat brings up some good points. Piston domes should occupy the chamber space away from the spark plug. This pushes the fuel mixture around the plug for faster burn and keeps the piston aluminum away from the hot spot. Additional problems include the fact that the intake ports are nestled between two exhaust ports, with the already mentioned cooling problems and during prolonged runs (Salt Racing) the intake charge is getting heated enough to cause detonation. If you can inject alcohol into the intake ports it will help cool the intake air.
    When you made reference to “Scattered valve timing” cams, I’m assuming you are talking about when one cylinder is robbing from the other during the time both intake valves are open in a common port (Cross-port interference). Some help can be found with cam timing. Installing a wedged dam at the back center of the intake port if you can remove some of the radius at the first turn will also help. A lot of work for small returns. Data logging all 8 exhaust gas temps really helps with fuel distribution and fuel mixture info and exactly when things go bad during a run.
    We never leave home without it.
    Paul

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    alleycat............I think it might be a little of everything you said and more, but I was thinking of running a "blower motor" class thinking forcing the air in might cure all, but guess not.

    your right the spark plug in in the wrong place, was thinking about closing the combustion chamber up on the far side and running flater pistons?

    and oil squirters.........I did install them this year, worked good on the bench, but at Bonneville the oil pressure dropped to low and had to un-hook them.............but now I know that it was the fault of too small of a "round" oil pick-up screen, ......(by the way I also installed a new HV Ford 351W oil pump this year and worked like a charm) so next time not only will I have squirters, but I can use them.

    the cooling issue you talked about, I have taken care of that......I run a copper head gasket and did not open any of the water holes exceot the two in the back, I run the water into the front of the head so that it floods the entire head befor it goes into the block (at the back) and come out the front of the block. I have a 3/8 inch balance tube that ties the front and the back of the head to keep out any "hot spots or steam"and run a small 1/4 inch line mid way in the motor to keep the block even(works well I read temp in two places).......I only cool the top of the block due to having filled the bottom of the block in order tho keep the sleeves from moving around

    but reversion is a big problem....and I think gets bigger at high RPMs.................was thinking today about at the end of the small intake splitter at the back of the runner , if adding about one onch of wire screen "gather" any reversion.......... give me your thought guys.


    pmuller9 ........by injecting alcohol "at Bonneville" puts me in a "fuel class" that might be my easiest move, because that record is abut the same as the class I am running.........plus 80% alcohol+20%nitro+a shot of NO2 sounds interesting , but hell on the bottom end,

    but also part of this is the valve timing..........before I spend the money grinding a "scattered " cam...........I am going to try and see what happens if I retard the timing , widen the rich cylinder valve lash and change the rocker ratio on the cylinder back to 1.5 to 1 and leave the lean one at 1.6 to 1...........and go to a .044 head gasket instead of the .032...........

    and I know your right , but I only gather one EGT when racing but all eight on the dyno


    but anyway guys it has been good for my brain to have you guys helping me figure this out........."it's a funny posion we picked for ourself"

    again thanks..........Dale
    Last edited by saltracer; 10-18-2010 at 05:52 PM.

  9. #9
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    Dale
    Looks like you’ve done a ton of problem solving already. I prefer to see a racer totally destroy the record in the class they’re in before moving on but that’s just me.
    You mentioned closing the combustion chamber up on the far side and running flatter pistons. When the valves are this deep in the chamber, any closing of the chamber creates too much valve shrouding. It is actually better to open the chamber up if you are over stock bore (You mentioned something about sleeves) use a stepped piston that’s high on one side and drops down to deck level where the plug is. Now there is minimum shrouding and some turbulence during compression.
    There is a possibility of eliminating both reversion and cross-port interference but it is way outside of the box thinking and may not be legal. Would the class rules allow you to use an aftermarket crank with a different configuration?
    Paul

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    Quote Originally Posted by pmuller9 View Post
    Dale
    Looks like you’ve done a ton of problem solving already. I prefer to see a racer totally destroy the record in the class they’re in before moving on but that’s just me.
    You mentioned closing the combustion chamber up on the far side and running flatter pistons. When the valves are this deep in the chamber, any closing of the chamber creates too much valve shrouding. It is actually better to open the chamber up if you are over stock bore (You mentioned something about sleeves) use a stepped piston that’s high on one side and drops down to deck level where the plug is. Now there is minimum shrouding and some turbulence during compression.
    There is a possibility of eliminating both reversion and cross-port interference but it is way outside of the box thinking and may not be legal. Would the class rules allow you to use an aftermarket crank with a different configuration?
    Paul

    Paul..........I thought about a crank with a different configuration, but have never looked into pricing. Also what about turning the engine around and running eight intakes and four exhaust ?

    Dale

    ps I hold the record in my class now , but the idea of more speed is just personal........but also know that it might be hard pushing a Model A Coupe much faster
    Last edited by saltracer; 10-19-2010 at 09:29 AM.

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