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Old 09-29-2012, 05:57 PM   #41
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It's at the top, under "Spark".

FWIW, upload the whole MSQ file. There are other potential gotchas, such as spark table switching which could be at play.

Verifying the base timing rather thoroughly with a timing light is also absolutely necessary, in order to ensure that the timing in the table is actually what you're getting.
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Old 10-04-2012, 04:33 PM   #42
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Tough luck Vasken.

I am curious about 99s with piggy backs being "most" prone to venting. Links?
Here's mine. Looks quite similar....

https://www.miataturbo.net/meet-gree...15/#post873698

'99 with link piggyback. Conservative spark. No signs of severe det on the pistons I could find. All rods bent. And after the piston collided with the valves, I had bent valves too. The previous owner is a very good friend and a somewhat careful guy. He's never over-revved and neither did I. But we did run 14psi on stock rods.
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Old 10-04-2012, 05:25 PM   #43
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Good info.
I guess 14psi on stock rods was the significant factor.
Nice to know as I have been inching up boost with a similar set up.
It could be time to stop before
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Old 10-05-2012, 10:47 AM   #44
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Good info.
I guess 14psi on stock rods was the significant factor.
Nice to know as I have been inching up boost with a similar set up.
It could be time to stop before
14psi on one turbo = 10psi on another turbo with regard to cylinder pressure so be careful with generalizations about psi. Intake manifold pressure is directly related to exhaust flow restrictions and is not a direct measure of cylinder inlet volume, but rather the flow limitations of the system.

Bending rods can also be indicative of overly high cylinder pressures being caused by timing being too advanced. If the charge in the combustion chamber reaches too great a pressure as the piston is still rising toward top dead center the rods may bend under the load. There are situations where the fuel octane and other related parameters are adequate to prevent detonation at a particular cylinder pressure and spark timing but the cylinder pressure may still overcome the strength of the rods. Tuning to prevent detonation is important but should not be the only consideration.

Good luck.
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Old 10-05-2012, 10:46 PM   #45
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Old 10-05-2012, 11:46 PM   #46
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Any one mind posting the ignition map as a pic for us non ms users?
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Old 10-07-2012, 04:21 PM   #47
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Bending rods can also be indicative of overly high cylinder pressures being caused by timing being too advanced. If the charge in the combustion chamber reaches too great a pressure as the piston is still rising toward top dead center the rods may bend under the load. There are situations where the fuel octane and other related parameters are adequate to prevent detonation at a particular cylinder pressure and spark timing but the cylinder pressure may still overcome the strength of the rods. Tuning to prevent detonation is important but should not be the only consideration.
Good information sixshooter. Thank you +1 for taking the time.
I run 98 ron and now that the weather is cooler it is difficult to induce ping even with advanced timing. I will proceed with caution.

Quote:
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14psi on one turbo = 10psi on another turbo with regard to cylinder pressure so be careful with generalizations about psi. Intake manifold pressure is directly related to exhaust flow restrictions and is not a direct measure of cylinder inlet volume, but rather the flow limitations of the system.
I understand exhaust back pressure being a significant limiting factor regarding regarding potential power... but I don't fully understand the "14psi on one turbo = 10psi on another" comparison. Is this a hot side or cold side effect, or both?

I guess the hot side on a smaller turbo would create more exhaust back pressure and therefore limit power if the turbo/wastegate is the bottleneck in the exhaust.

As for cold side, I imagined that a given air pressure and temperature downstream of the throttle for a given engine/exhaust would result in the same power irregardless of what was producing the air flow.

But are there some additional effects due to things like more turbulent air or shock waves going on that limit power when producing boost with a smaller turbo?

Any further insight would be appreciated.
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Old 10-07-2012, 04:35 PM   #48
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The turbine-side is a big part of it, especially during the ramp-in where the wastegate is still fully closed.

A smaller / more restrictive turbine will cause back-pressure to be greater, specifically in the area just outside the exhaust valve in the head. The practical effect of this is that cylinder scavenging in the exhaust phase is less complete- more exhaust gas remains inside the cylinder at the end of the exhaust cycle. Thus, the amount of fresh air / fuel which is drawn into the cylinder during the intake cycle (by mass) is less for a given manifold pressure. Or, it takes more manifold pressure to force the same amount of air/fuel into the cylinder during the intake cycle.
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Old 10-07-2012, 04:44 PM   #49
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Joe, I'm intimidated by your knowledge as displayed in your reply to this and countless other posts scattered throughout the forum.
In short, you are far too clever to be posting here
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Old 10-07-2012, 05:23 PM   #50
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Attached Thumbnails
Terrorist attack in cylinder 1-reginald.gif   Terrorist attack in cylinder 1-reginald2.gif  
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Old 10-07-2012, 05:26 PM   #51
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In short, you are far too clever to be posting here

And apparently has WAY too much time on his hands.
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Old 10-07-2012, 05:37 PM   #52
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And apparently has WAY too much time on his hands.
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Old 10-07-2012, 05:40 PM   #53
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Can you sell me some?
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Old 10-07-2012, 05:46 PM   #54
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I guess I shoulda seen that coming.
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Old 10-07-2012, 06:04 PM   #55
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Old 10-07-2012, 06:33 PM   #56
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Brilliant!
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Old 10-07-2012, 07:16 PM   #57
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Great title. And wow, that is the BEST destroyed engine I've seen. Sorry for your loss, but wow, lol.
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Old 10-07-2012, 07:23 PM   #58
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My motor just let go on Friday. Sounded like someone left the silverware drawer in the garbage disposal. I was hoping to see similar levels of destruction, but everything stayed inside as far as I can tell. So now I have a broke motor and no epic block holeage.
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Old 10-07-2012, 09:13 PM   #59
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Did that msq file work?

FRT, thanks but again, a friend of mine came up with that on the night of.

czubaka, sorry to hear about your unimpressive engine failure. Just do a burn out and im sure something will poke its head out. lol so whats next for you?
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Old 10-07-2012, 10:43 PM   #60
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Haha! I wish, car won't start. Pulled the plugs today, #3 is smashed. Looking down in the hole showed a piston broke in half.

Plans depend on what's borked. Base plan is just to get a salvage motor and drop it in. If anything is still serviceable in the motor, I may put in stouter pistons/rods. With all the coolant in the oil pan, the block is probably toast. Now seeing the plug electrode smashed, that doesn't bode well for the head.

This would all be much easier to pay for if I had a job right now. :(
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