Guest ZmeFly Posted May 3, 2004 Share Posted May 3, 2004 . Quote Link to comment Share on other sites More sharing options...
Hybrid240z Posted May 3, 2004 Share Posted May 3, 2004 Compression measurements are supposed to be taken with the throttle plate open. Having it closed should still yield similar results but will take more cranking time to get there. Edit: Oh, about the over-revving i'm not too sure. Maybe someone else can chime in on that one. Marcos Quote Link to comment Share on other sites More sharing options...
wheelman Posted May 3, 2004 Share Posted May 3, 2004 Having the throttle plate open allows the engine to pull more air in for each stroke of the pistion. With more air in the cylinder the compression reading on the guage will top out in fewer strokes. Wheelman Quote Link to comment Share on other sites More sharing options...
SleeperZ Posted May 3, 2004 Share Posted May 3, 2004 I've hit 6500 before, and the ECU slammed on the fuel cut. Don't think you have much to worry about unless you went much further past 6500. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 3, 2004 Share Posted May 3, 2004 I think the first thing most likely to get damaged if you overrev are valves. At really high RPM with stock valve springs the valves will 'float', things are going so fast that the valves dont have a chance to close, and will get hit by the pistons. Rods can also break or rings can fail, but especially on the stock L6's, I'd expect to bend a valve first. L6's can put up with minor overrevving... I used to abuse the hell out of my N/A 2.9L, revving it to 7k quite a bit, for over 3 years, and when I had the engine apart to fix a stuck and bent valve (due to a bad batch of really old fuel, not from overrevving) the thing looked great, like a newly rebuilt motor should. Before removing it compression was very good and even on all cylinders. I think you should be just fine... if you went over 7000 I might worry but if you got off it quick and there are no apparent ill effects, you should be okay. If you DID go much over 7000 though there is a chance you may see some problem further down the road. Quote Link to comment Share on other sites More sharing options...
akeizm Posted May 4, 2004 Share Posted May 4, 2004 I'm not sure if you would have damaged it from over-reving. I missed third and my tacho's needle went past 8000rpm and I didn't damage a thing. Maybe I got lucky for once heh. (btw I'm running a nearly stock l26) Quote Link to comment Share on other sites More sharing options...
Guest 73TPIZ Posted May 4, 2004 Share Posted May 4, 2004 A buddy of mine missed third gear on my '81 ZX years ago and afterwards the lifters were tapping like crazy. I was able to get it home and the next day pulled the valve cover and the adjusting lock nut thingy (tech term) on 2 of the rockers had loosened and the pin thingy had backed out all the way loose. I ran it back down to the spec with a feeler gauge, tightened the nut and she was as good as new. A year later I missed third and it did the same thing again. Pulled the cover off and readjusted and good as new. Scared the crap out of me the first time as i thought the motor was screwed. Second time no biggie. hope this helps Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted May 4, 2004 Share Posted May 4, 2004 A buddy of mine missed third gear on my '81 ZX years ago and afterwards the lifters were tapping like crazy. I was able to get it home and the next day pulled the valve cover and the adjusting lock nut thingy (tech term) on 2 of the rockers had loosened and the pin thingy had backed out all the way loose. I ran it back down to the spec with a feeler gauge' date=' tightened the nut and she was as good as new. A year later I missed third and it did the same thing again. Pulled the cover off and readjusted and good as new. Scared the crap out of me the first time as i thought the motor was screwed. Second time no biggie. hope this helps[/quote'] That happened to me when I first rebuilt my N/A engine... hadn't even broken it in yet and the throttle got stuck on me and I panicked and it overrevved before I cut the ignition. It was tapping like mad and I was sure I'd broken something... but same deal just popped the valve cover adn found that one of the locknuts had come loose. I didn't mention this because I figured if that had happened he'd have known something was up But now that I think about it it is a good idea to pop the valve cover and check the tightness on those lock nuts just in case. Quote Link to comment Share on other sites More sharing options...
Bluto Posted May 4, 2004 Share Posted May 4, 2004 Too funny, I read this thread after I got off work. Abit after I had to run a friend to his moms house to look for a few specialty tools to do some work to his car.. Sounds simple enough right? Well on the way I wanted to get his butt dyno calibrated to the na engine so I could get an unbiased opinion after I swapped to the l28et(next weekend or so). After a nice launce and abit of shifting thru the gears my throttle decided to get stuck wide open... YaY! After I realized what was goin on I shut it down but it was well into the red on the tach.. Whoops guess the throttle cable set up needs a little more tweeking! anywho.. once before when I had over reved the motor it had started running really rough like Zmefly had mentioned but it worked itself out like his did.. funny stuff for sure Sam Quote Link to comment Share on other sites More sharing options...
MrWOT Posted May 4, 2004 Share Posted May 4, 2004 As was previously mentioned one of the dangers of overrev is valve float and piston contact with the valve. The other is your con rods. As engine speeds increase the inertial loads on the rods increase exponentially on a non-linear scale. In english this means that the strain on the rods increasing 1000 rpm from 5000 rpm to 6000 rpm is MUCH lower then the strain of going from 6000 to 7000 RPM. Eventually the rod itself will stretch, as will the bolts, it will either shear, whack a valve, or in the worst case (as if shearing wasnt bad enough) it will gain so much clearance it will finally destroy the crank, valves, and most likely will go out the side of your block making a fist sized hole...... Moral of the story, don't overrev Quote Link to comment Share on other sites More sharing options...
Guest z-pilot Posted May 19, 2004 Share Posted May 19, 2004 I know this is an older thread, but rather than start a new one... Great. My throttle stuck open on the way home today. It was probably in the red, probably around 8K for about 2 seconds before I could get it turned off (my ignition key binds a bit). It seems OK though. This a a 3L stroker with the heavy '73 rods/bolts. At the track, I have seen rod bolts shear due to overreving, usually immediatly after the overrev. Is there any way to get a feel for risk of that happening without a rebuild? If the engine seems fine for a period of time, say 50 miles, can I start feeling comfortable about it again? Thanks Quote Link to comment Share on other sites More sharing options...
Guest norm[T12SDSUD] Posted May 19, 2004 Share Posted May 19, 2004 For those that may not know, the originator of this thread James Burgess aka ZMEFLY is no longer with us. He passed away suddenly last week. There is a thread on Zcar in the tech section. Later,Norm Quote Link to comment Share on other sites More sharing options...
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