Detonation control

[wobblywalrus]

The iridium plugs should work good when the motor is sorted and flame control is OK.  They are my plugs of choice.

Take the head off the engine and move the pistons to 5 degrees ATDC.  Push down on the crowns.  It is hard to make them move.  Try again at 10 degrees ATDC, and at 15 and 20 degrees.  Progressively it is easier to push them down.  This illustrates a big problem with poor flame control from detonation or pre-ignition.  The burn is too near to TDC.  The pressure spike in the combustion chamber occurs at a period in the cycle when the leverage ratios between the crank and the rod are not optimum.  Best power occurs when the pressure spike occurs more past TDC when piston and rod's leverage on the crank is favorable.  It takes a controlled burn to get this.

Stainless and the others on this topic give good advice.  My meagre contribution is this.  A poorly controlled huge pressure spike from lots of gas and compression may not make as much power as a smaller and more controlled spike at the optimum point to give max power.  Dyno testing works best to figure this out.

I think you are on the right track and doing the things you should,  This is an interesting problem. 

[racer x]

I hope to solve this problem with careful testing and tuning. Pushing engines to the limit is always interesting.I am looking into getting a dyno of my own. I can use it at work and make money plus save money . The neighbors will like it too.

[maj]

That damaged head looks familiar
 spark plug selection helped our prob,
 initially we indexed the plugs we had, so the gnd side of the tip was between the inlet valves and cooler, (damaged cyls  always had the tip near the exhaust valve, we also used an extra washer to pull the plug out of the head more.
but in the end went with a cooler range plug without the extended gnd strap..

[racer x]

I have gotten my head around what you are saying about a smaller explotion later when the crank leverage is optimal . Thanks for that.
   I think a combination of a cooler plug with a different ground electrode shape and gap. Then polish the combusion chamber and recess the plug. With 13 to 1 pistons. Add 118 octane fuel up from 111 .And 25 deg BTDC timing instead of 32 I tried last time. Will be my basic set up. Now I just have to test the fuel and nitrous ratio and volume put it all together with a new exhaust system and try again.

[wobblywalrus]

The suggestion about an iridium plug working good is based on a lot of experience with NA motors.  I was not thinking and forgot that this is a nitrous burning setup.  Ignore that advice I had about the iridium plug working good.

[racer x]

I can't ignore anything from this forum.I will save that info for my all motor thinking. I like the idea of them but I have trouble reading them and when as you said .I would not use them untill things are perfect otherwise.

[racer x]

Well I did some testing.No matter how I test it I am lean on the right cylinder.That explanes the hole in the piston. I will work with the rest to get rid of the ping or crackle I was getting in lower gears. No nitrous till I figure out both of these issues.I am going to work on data logging and testin for a while.

[racer x]

 I sent my system back to the manufacturer. They tested it for me and found the same thing I found. There was a machining defect in one injector.They have had some problems with drawing such a small amount of fuel.

They made me a new set up that they tested. I will test it myself today and see how it goes. Since they are having problems with 10 hp I decided to go with 15 hp. I should have enough clutch for that.

But apparently my problem was not preignition or detonation. At least that was not blowing a hole in the right cylinder. I was dry shotting the engine at least on the right side

I have am still going to do all I can to prevent preignition. First I am going to use cr10e plugs with the tip removed and regapped. I will take the gap from .028 to .019. I also cleaned up the damage to the head and polished it to remove any ruff edges. As for timing.I am a bit gun shy. I have had success with the stock timing setting of 35 deg BTDC, But I will start out with 28 just to be safe. All that with 118 octane fuel should be better than the last run.

[racer x]

OK I ran the nitrous flow test. I need to do it again to measure the volume out.I hoped it would blow nitrous up and the fuel would collect in the jar, But it is so well atomized it blew the fuel everywhere . BUT it looks even and there IS fuel flow .When I did this before there was no fuel flow at all or a little after it started spraying. This is looking much better.

http://youtu.be/Gr4_azWJ688

[joea]

believe me, the fuel is not well atomized coming out of a typical nitrous
injector......ask NOS....about their own testing......(eyeballs dont see
atomization very well).....

why not buy a spark plug such as is available from Champion thru say ERC that
is made for what you are doing such as was suggested a long time ago, rather than carve
on a plug hoping to do better..?..

and yes it was detonation that put a hole in your piston......

Joe

[racer x]

Didn't the detonation come from a lean condition? Yes I will look into proper plugs.I am afraid I might fatigue the tip when I bend it.

This is not a a regular nitrous injector. This system uses nitrous to pull the fuel in (no pump). The nitrous and fuel mix inside the injector.

[joea]

you bet...detonation from inadequate fuel supply..

wow no fuel pump...learned something again today..thanks for that...out
of my league on that one...we used to use a large graduated burette as the
fuel supply...run system...and record fuel in burette at start and at end...

Joe

[racer x]

     Today I was looking at the videos of the nitrous test I did . I wanted to re do it and catch the fuel. When I looked at the video the right side looked like it was flowing more gasses or at least making a bigger cloud. I retested it and it did look different from side to side. I then swapped some parts from one side to the other and not only does it look more even, it looks like it is making a much bigger cloud.  When I was swapping the parts fuel was dribbling out of the feed lines. I think it might have primed the system.

    I am afraid of bad gas so I remove all the old fuel from the system as soon as I get home. IF the first video is any indication of what I have been doing. Then it might explain why one side is running OK and the other side is damaging a piston .The next time I push the button will be interesting .

test 1
http://youtu.be/62QMp_4KIHY

test 2
http://youtu.be/VpT34a-iBQA

[Stainless1]

By the looks of your test, since you have no fuel pump and must use N20 to pull fuel you need to weigh the fuel in the supply tube before and after the test.  Run for at least 20 seconds, weigh the fuel and the n20 before and after the test, that will give you the ratio you are running. 
Just my random thought... you are getting N20 before you get gas since the N20 is used to draw the fuel.  To me that says you are already starting in a lean comdition then it comes back to a ratio, that instant of lean will fry pistons, valves and heads. 
scares me and I'm fearless.... no wait, I'm Stainless.... 

[racer x]

The nitrous system has what are called nitrous powered fuel injectors. The nitrous powers the injectors that draw the fuel. There is enough draw to lift fuel as much as a couple feet. Though my set up is gravity fed. From the data logger the system starts rich then goes to the proper mixture.
    I cant tell how much fuel is coming out. But it did leave an even amount of gas in the jar after I removed the injectors from the manifolds and aimed them at the jar. I did measure the volume though. I sprayed one pound of nitrous and it drew in 40cc of fuel.I think it is 13.5to1