Probably a Quick question: Pre-ignition at Redline or nothing? - Miata Turbo Forum - Boost cars, acquire cats.

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Old 02-14-2013, 04:49 PM   #1
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Default Probably a Quick question: Pre-ignition at Redline or nothing?

Got an FMII kit with Megasquirt DIYPNP built by Brain. Drifted for the first time last Saturday. I noticed this happening at the event and did not pay too much attention to it and now I am probably overthinking it. When I am hitting spark cut at redline, my engine starts dropping revs and reving back up to redline very quickly. I am wondering if this is normal or if it something bad like pre-ignition and/or rod knock. Here is a vid.


It can clearly be seen around 2:05. And by then I am starting to overheat which I did NOT notice at the time. I definitely WILL next time. Thanks for the help!
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Old 02-14-2013, 04:57 PM   #2
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Sounds normal. I mean you're at WOT at probably full boost at 7k rpm. 200-300 rpm oscillation is easily gained in under a second.
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Old 02-15-2013, 12:22 PM   #3
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Ok cool. I just wanted to get a second opinion. I am still slightly confused on what is causing the rev drop though. Because you can see during certain moments the revs are just pegged at 7k without any sputter at all. Seems to me that unless something is ******* up it should be like that all the time. But anyway. I am not TOO worried about it if you think it sounds normal.

One more kinda random but still DIY question:

What is a safe horsepower/boost limit for my car on these bad boys? :

Saturated Injector SL9-0440

I run these currently.
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Old 02-15-2013, 02:55 PM   #4
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Its normal for the rpms to oscillate 200-300rpm on revlimiter cut, that being said hitting the revlimiter at wot in full boost for a minute straight isnt too healthy for your motor.
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Old 02-15-2013, 03:06 PM   #5
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id have to look at your rev limiter settings, but that looks like a glitch.
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Old 02-15-2013, 03:12 PM   #6
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I'm sure the physics glitch will be patched in Revs MS4 release.
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Old 02-15-2013, 03:13 PM   #7
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lol @ your warped-*** head.
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Old 02-15-2013, 03:14 PM   #8
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Quote:
Originally Posted by PJnB View Post
It can clearly be seen around 2:05. And by then I am starting to overheat which I did NOT notice at the time. I definitely WILL next time. Thanks for the help!
"Starting to overheat"? More like starting to melt-down the headgasket.
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Old 02-15-2013, 03:22 PM   #9
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I'm assuming your gauge is stock and not recalibrated? Yeah at that angle you're probably flowing 250 degree coolant.
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Old 02-15-2013, 03:45 PM   #10
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Oh ****. Well. Now I AM worried again. Brain, what info do you need from my tune to see if the rev limiter has a glitch? And what are the chances my car needs a new heart? That vid was the last run of the day. I immediately pulled off the track and blasted my heater and let the motor cool down to operating temperature. Took it about 3 minutes or something. Then continued to let it run for a while. Then left the event and went and ate dinner for about an hour with the car off, letting the motor cool completely (at least for the most part). Then drove the thing home.....200 miles. Didn't notice anything too alarming. Checked for leaks basically every time I stopped. No smoke blowing out the tail. So. What else should I check?
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Old 02-15-2013, 03:48 PM   #11
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And yes my gauge is stock.
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Old 02-15-2013, 04:12 PM   #12
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Check compression and leak down.
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Old 02-15-2013, 04:32 PM   #13
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Keep driving it if you start seeing coolant in your oil or bubbles in your overflow tank then you probably cooked the head gasket/warped the head.
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Old 02-15-2013, 04:52 PM   #14
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Triple would you say that if I drove it around and didn't show signs of a blown head gasket after a while then chances are I am fine? I was reading around a little and read that usually the warped head and blown head gasket is sort of a combo......? If it comes down to it I can do a compression check but I am just trying to see if there is a more simple way. Thanks for the help guys.
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Old 02-15-2013, 05:33 PM   #15
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if you're worried, just check for coolant in your oil (milky coffee color). check the underside of your oil cap and dip stick and if it's not what oil looks like normally, then you've got a leak.

If all your coolant blows into your reservoir and you start seeing crazy white smoke out your exhaust, you've got a leak

this is all short of doing a compression test obviously
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Old 02-15-2013, 05:37 PM   #16
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Is your rev limiter set for spark cut, fuel cut or both?

If I was going to run mine in a similar manner to that, I'd lower the redline by a couple hundred to get it closer to peak torque and to protect it from having the oil pump gears explode or some of the other fun that could possibly occur.
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Old 02-15-2013, 05:43 PM   #17
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Check for coolant in ur oil, look for continuous bubbles in the overflow tank (before shutting the car down after a long drive), keep an eye on the exhaust for white/black smoke, you can do a compression test for the hell of it but if you melted something the above symptoms are the common. If they arent there then keep driving.
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Old 02-15-2013, 05:50 PM   #18
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Cool thanks guys. I will keep a eye out for these signs. And lowering my rev limit a couple hundred does sound like a good idea. I also do want to see if there is a glitch. Guess I need to wait for Brain for that?
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Old 02-15-2013, 06:48 PM   #19
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post msq.
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Old 02-15-2013, 06:51 PM   #20
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Why guess, why wait for the signs to show themselves? Not every blown headgasket has a thumb sized passage, some only leak under certain conditions and can be that way for a while before being a big problem.

Comp, leak down and block/coolant test. All or a comb of these tests will tell you now or atleast give you an idea how bad it is if it Is.

Block test, pressurised coolant system shows leaks from fluid comming out and or pressure falling.
Coolant test, tests coolant for the presents of combustion gasses.
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