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Discussion Starter #1 (Edited)
Well, I went out to one of the car meets in town this evening and met up with some friends. Me and a 11 sec. cobra ended up racing down the interstate. We started off at 40 and I speed shifted at 6500~6600 to 3rd. To my dismay I missed third, and revved to 7500ish then I still tried to catch him and I speed shifted to 4th and......... I missed again, and over revved again! So at this point I'm dissapointed in myself and we line up again now going 40~50mph. We take off and I pull him but as I'm pulling ahead I hear a strange sound coming from one of our cars, so I let off and the noise went away. I took the next exit and stopped at a gas station, popped the hood and oped the TB up a couple of times. At about 1700 and up I hear what sounds like valves lightly tapping the piston, or maybe detonation. I've never heard either these sounds before, because I'm still new to the world of racing. My friend says it sounds like detonation, I'm still not convinced thats what it is b/c hes not mechanically inclined. Can any of you guys shed some light on what these two things are supposed to sound like so I can start narrowing things down a bit. thanks

Mods are in the profile.

BTW- The timing still looks on (looking at the gears) so I don't think it jumped a tooth or anything, but I'll hit it with the timing light just to make sure.
 

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gt35/40?
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i have misshifted too except i went to 9,000 rpms, the motor is still fine.... no big problems, just dont speedshift itll cause more problems. I learned from my mistake.... my snap ring came off the throwout bearing on the misshift and i had to drop the tranny and replace it. Now everything is fine. I think with such a low misshift you should be fine
 

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Discussion Starter #3
This isn't my first time misshifting. The last time I did it it went a bit higher, like 7,800 but it didn't do anything. I'm just worried b/c I come from the SR family in the 240sx community. If we over rev the SR20DE(T) it'll fling out a rocker arm. And I'm talking about going 500~700rpm over redline! It's the only downside to the motor.

BTW- This noise definatley sounds like its coming from under the valve cover!
 

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T66_rice said:
BTW- This noise definatley sounds like its coming from under the valve cover!

well its definatly not coming from anything above the valve cover :lol:

What part of LA do you live in, I can maybe come give it a listen and tell you whats up. Ive had my share of deonation, bent valves, and spun rod bearings.
 

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No need for a timing light, just check the marks on the cam gears vs. the mark on the crank pulley. 7500 isint that high, i used to rev my single Supra that high with stock cams and valvetrain all the time. Double check the timing and compression, i bet you are fine.
 

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Crap that sucks. I hope you didn't do anything seroius. Follow up with us what happens.

I am wondering myself how high i can rev. I have 272 cams and some sort of upgraded valve springs.
 
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Yeah its good that nothing broke. If anything broke I could imagine the cobra owner laughing at you :( . (thats in a bad way):D
 

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Discussion Starter #12
I had a friend come over and take a look, he said it may be the flywheel bolts. I added a new flywheel and reused the bolts w/o using lock-tite. I will check it, but it still sounds as if its somewhere in the head. I changed the oil the next day @2600 semi-hard miles and oil looked great no shavings.

If thats not it ill pull off the valve covers,then I'm sure I'll be back on the forums for more help.
 

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sadil said:
I am guessing that u have a stock limitter than how can u rev 7800.
Because he mechanically over-revved his car.

Just do a compression test and see if you are leaking anywhere. If you have any bent valves you will see it in your numbers. Most likely you'll be ok since this is a non-interference engine.
 

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Discussion Starter #14
I find it wierd that it still performs well. That, and the noise sounds like it disappears above 2500rpm under hi throttle.
 

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I seriously doubt it's timing/detonation. The only way timing would have changed would be if it jumped timing and the chances of the timing belt jumping a tooth is slim to none. If the shim came out of a bucket it would be more than just a little "tapping" sound. I would say the chances of a spun bearing/valvetrain damage are higher than any of the other things you listed. Another thing to think about is if you can hear this over your car and a mustang while both people are getting on it then you definetly have more than just a "little light tapping" , damage has been done somewhere, I would find it before it ruins anything else. If you have ever heard a car with a spun bearing it's similar to the sound you are describing.
 

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Discussion Starter #16 (Edited)
Would'nt that mean there would be metal shavings in the oil? I checked and it was very clean! and wouldn't the knock get louder as the rpms went up especially when under boost? If it did spin a bearing that still leaves me without a good reason why this happened at 70,000 miles.
 

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There wouldnt necessarily be shavings in the oil, if the bearing is spinning on the crank it wont positivly leave shavings. A h22 motor (prelude vtec) that spun a bearing was loud at low rpm's but as they rose it was hard to hear any knock over the sound of the motor. Took the motor apart and sure enough, spun bearing. I actually remember taking the valve covers off the car at the time to check valve clearance because the sound seemed like it was coming from the head...but it wasnt. You have a perfectly good reason for a spun bearing, you over revved a motor that was not setup for that load. I'm not trying to discourage you, I'm just telling you what I have in personal experience. My motor now revs out to 8500 and has no funny noises whatsoever, BUT, I have fuel/timing control/valvetrain that allows that. Another thing to remember is that factory tachs are not super accurate, there is no way to tell what rpm you TRULY went up to. Again, I'm not trying to discourage you and hope everything comes out the best it can for you but just be ready for it to be more than just a simple fix...If it is a simple fix then I'm appy for you as no one wants to go through the headache of major repairs.
 

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Rod knock is possible like Chnco said, but you could have floated a valve, or bent a valve which is very common with over revved engines.

I have mechanically revved mine to well over 8000 several times, but I have Titanium springs and retainers, which may or may not have helped.
 
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