Unghh.....3rd to 2nd downshift....over rev?
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Posts: 2,068
From: Kernersville, NC
Unghh.....3rd to 2nd downshift....over rev?
Well, tonight I did something I haven't done since high school when I was first learning to drive a manual. I went from full 3rd(6000ish....so around 90-100mph) to 2nd.
I didn't get the clutch all the way out, but out far enough for it to grab very hard. The car barked the tires, fishtailed the rear, and when I looked down I saw 80mph, but didn't pay attention to the tach. By the time I saw 80mph I had the clutch in and was
, I can't believe I did that......
So.....I guess the big concern could be bent pushrods or valves as possible damage?
The car sounds fine. Does not miss. Does not idle funny. In the past, as kind of a safe way to look at performance on the road, I'll time a 2nd gear pull from 30 to 50mph. It's still as fast as before my stupid move(2.1sec from 30-50, stock it was 2.4).
So I'm hoping I have dodged a big expensive mistake. Opinions given my valvetrain?
Comp Cams Magnum Pushrods 7.2"
Comp Cams Pro Mags 1.6
PAC 1518 springs
Valves stock
I'm hoping the springs were good enough to control the valves during that and the Magnum pushrods were strong enough to take my stupid mistake.
Anyone ever pulled such an maneuver on an LT1\T56? Any fallout from it?
Hehe, I must say in looking around on the net I ran across a thread on LS1GTO where a couple of guys bashed the LT1 pretty bad in an overrev thread and Machinistone set them straight. Hehe nice.
Bad Mechanical Overrev - LS1GTO.com Forums
I just really wished I had glanced at the tach instead of the speedometer. Acoording to my rough estimate 88mph shakes out to be 8000rpm in 2nd....so if it did go that high it would have pegged the tach easy.
I didn't get the clutch all the way out, but out far enough for it to grab very hard. The car barked the tires, fishtailed the rear, and when I looked down I saw 80mph, but didn't pay attention to the tach. By the time I saw 80mph I had the clutch in and was
, I can't believe I did that...... So.....I guess the big concern could be bent pushrods or valves as possible damage?
The car sounds fine. Does not miss. Does not idle funny. In the past, as kind of a safe way to look at performance on the road, I'll time a 2nd gear pull from 30 to 50mph. It's still as fast as before my stupid move(2.1sec from 30-50, stock it was 2.4).
So I'm hoping I have dodged a big expensive mistake. Opinions given my valvetrain?
Comp Cams Magnum Pushrods 7.2"
Comp Cams Pro Mags 1.6
PAC 1518 springs
Valves stock
I'm hoping the springs were good enough to control the valves during that and the Magnum pushrods were strong enough to take my stupid mistake.
Anyone ever pulled such an maneuver on an LT1\T56? Any fallout from it?
Hehe, I must say in looking around on the net I ran across a thread on LS1GTO where a couple of guys bashed the LT1 pretty bad in an overrev thread and Machinistone set them straight. Hehe nice.
Bad Mechanical Overrev - LS1GTO.com Forums
I just really wished I had glanced at the tach instead of the speedometer. Acoording to my rough estimate 88mph shakes out to be 8000rpm in 2nd....so if it did go that high it would have pegged the tach easy.
Last edited by ACE1252; May 6, 2013 at 10:44 PM.
Registered User
Joined: May 2012
Posts: 660
From: idaho
ive done it lol. Didnt have any problems afterwards I did the shift at 5700-5800 and was quick to get to the clutch. Made me feel like a total tool. Was glad no one was around to witness it. I did have a chance to check all pushrods and nothing was bent. I guess id ask if you dumped the clutch and hit the gas or got back on clutch nearly instant. You may have been quick enough to not get wicked revs from the compression slowing the motor. I think thats what saved me being quick to dump the clutch back in.
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Thread Starter
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Joined: Mar 1999
Posts: 2,068
From: Kernersville, NC
Re: Unghh.....3rd to 2nd downshift....over rev?
Was doing some data logging today to compare data since my major screwup. The SES light flagged insufficient activity on Bank 1 Sensor 1(AFS75 sensor) as I was driving. Never had this before last night. The O2's are over 5 years old, so this may be real, but I didn't start logging until after it set.
I can say that it appears to lock down in open loop mode with this happens. Hehe, LTFT's were 0%, injector pulse widths were nice and equal.
I reset it and have done some logging.....I'll compare to my previous logs to see if there are any major changes.
In the mean time, I've already ordered 2 new upstream sensors as these are over 5 years old(mostly WOT track runs too).
In all my "testing" spots the power seems the same. Blows the tires off at around 5000 in first from 5mph roll.
I think stuff like this makes us more paranoid than anything.....riding along....wait did you hear that? I know I heard something!
I can say that it appears to lock down in open loop mode with this happens. Hehe, LTFT's were 0%, injector pulse widths were nice and equal.
I reset it and have done some logging.....I'll compare to my previous logs to see if there are any major changes.
In the mean time, I've already ordered 2 new upstream sensors as these are over 5 years old(mostly WOT track runs too).
In all my "testing" spots the power seems the same. Blows the tires off at around 5000 in first from 5mph roll.
I think stuff like this makes us more paranoid than anything.....riding along....wait did you hear that? I know I heard something!
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Posts: 71,121
From: Hell was full so they sent me to NJ
Re: Unghh.....3rd to 2nd downshift....over rev?
Stock rev limiter cuts fuel.... and no, as stated above, it can not prevent the engine from over-revving due to downshifting into the wrong gear.
I have been known to miss a gear or two (hence the change to the TH400) and I have a documented data log showing the engine hitting just under 8,000rpm on one incident. No harm. But that's with a stout valve train for the solid roller cam. I would assume Eric's valve train is similar in quality.
I have been known to miss a gear or two (hence the change to the TH400) and I have a documented data log showing the engine hitting just under 8,000rpm on one incident. No harm. But that's with a stout valve train for the solid roller cam. I would assume Eric's valve train is similar in quality.
Thread Starter
Registered User
Joined: Mar 1999
Posts: 2,068
From: Kernersville, NC
Re: Unghh.....3rd to 2nd downshift....over rev?
Stock rev limiter cuts fuel.... and no, as stated above, it can not prevent the engine from over-revving due to downshifting into the wrong gear.
I have been known to miss a gear or two (hence the change to the TH400) and I have a documented data log showing the engine hitting just under 8,000rpm on one incident. No harm. But that's with a stout valve train for the solid roller cam. I would assume Eric's valve train is similar in quality.
I have been known to miss a gear or two (hence the change to the TH400) and I have a documented data log showing the engine hitting just under 8,000rpm on one incident. No harm. But that's with a stout valve train for the solid roller cam. I would assume Eric's valve train is similar in quality.
My data logs look normal. No abnormal fuel trims. Just not sure what caused the O2 code. At least it's on the driver's side. I'll at least go through leakdown/compression testing on that side.
I'll take it back to the track in a week or two and see if the times or mph has fallen off as well.
That leads me to another question. How do you determine the max rpm of a spring? I guess the mass that the spring has to control factors into it(valve weight, retainer weight, etc). Is there a quick way to know how many rpm a valve spring can handle?
Thread Starter
Registered User
Joined: Mar 1999
Posts: 2,068
From: Kernersville, NC
Re: Unghh.....3rd to 2nd downshift....over rev?
I did a quick compression test on the drivers side with a cracked o-ring on the compression tester...starting to dry rot....
1 - 203
3 - 197
5 - 200
7 - 205
I didn't crank 3 quite as much as the rest, but that looks a little better than I remember back when it was stock(190-195).
I think I'm going to call it a dodged bullet for now and verify it with times at the track in a week or two.
Hehe, I really love this hobby, but it's much less nerve racking to fix my ZR1 in Forza 4 when I screw up than on this thing when I screw up.
I have read that over revving a valve spring can weaken it, but I hope to have new LE2 or AI heads(with new valve springs, valves, etc) on it in the next 6-months or so.
1 - 203
3 - 197
5 - 200
7 - 205
I didn't crank 3 quite as much as the rest, but that looks a little better than I remember back when it was stock(190-195).
I think I'm going to call it a dodged bullet for now and verify it with times at the track in a week or two.
Hehe, I really love this hobby, but it's much less nerve racking to fix my ZR1 in Forza 4 when I screw up than on this thing when I screw up.
I have read that over revving a valve spring can weaken it, but I hope to have new LE2 or AI heads(with new valve springs, valves, etc) on it in the next 6-months or so.
Last edited by ACE1252; May 5, 2013 at 09:06 PM.
Thread Starter
Registered User
Joined: Mar 1999
Posts: 2,068
From: Kernersville, NC
Re: Unghh.....3rd to 2nd downshift....over rev?
I have not got all the way through this, but so far it has proven to be a very interesting thread on valve springs, rpm, float, etc. It should be mentioned that the engines spoken of below are of the "Sportsman" level(I think....).
valvesprings • Speed Talk
This seems really informative(bottom of thread above)....Quotes from Darin Morgan
valvesprings • Speed Talk
This seems really informative(bottom of thread above)....Quotes from Darin Morgan
Valve train design and tuning is a science all its own and has a little touch of mysticism as well. The Kinematic motion of a valve train is extremely complex. Simply stating that a spring needs "more" or "less" pressure is overly simplistic. It overlooks the finer tuning aspects of the system and especially the spring. The spring can encounter many different problems; float being just one of them. The spring can encounter Resonance, Coil surge, Float or simple Fatigue due to excessive heat or use. Float is the term most often used to describe the spring not controlling the valve train and in most cases people are correct in using this term because Float is the predominant valve train problem in most racing engines operating at moderately high engine speeds in the 7500 to 8000rpm range. This is due to either the builder not using the correct spring to control the valve train or the springs being used have fatigued with time and or heat. This is where the valves can bounces off the seat as much as .020 bleeding off the rising cylinder pressure back up the intake tract effectively shutting the engine off or keeping it from accelerating any further. Having two or three valve bounces of about .005 at the valve is a normal but albeit unhealthy occurrence in high rpm racing engines. We would like to have zero bounce, but that just doesn't happen. Coil surge is a scenario that takes place when the spring is set up to far away from coil bind giving the middle coils room to bounce back and forth from top to bottom as the spring is closing. This usually takes place with a highly energized spring (fast ramp rate) at high engine speeds. Having a spring with not enough rate can exacerbate the problem and having a spring with both to little rate and not enough seat/nose pressure in conjunction with being set up to far from coil bind is down right deadly. I have seen springs turn blue, shatter and literally melt due to this scenario. This will cause valve bounce similar to floating the system and letting the valve hit the seat. Resonance is a killer but I find it a rare occurrence with the Super Series engines or other engines that operate at or below 7500rpm. In the big Block Chevy engine there are two distinct points within the rpm range that present a problem. 7600to 7800 and 9800-10000. 7600-7800 is usually just before the cam goes into loft (not float) and the 9800+ range is where the loft goes Bozo for a lack of a better term. The 7600-7800rpm point has been shown to excite certain types of springs that are considered to be "better" because of there increased rate and pressures. I put a set of PSI 048 style springs on a truck puller engine with the Raptor heads. I mistakenly thought that the "better " spring would lend some protection to the valve train because this guy revved the engine to 9600rpm+ and at time free revved the engine to 9500rpm+. Well he called me the after a week and said that he had broken six valve springs and the rest where Jell-O. They had lost 100lbs of seat pressure. I instantly knew to ask him one question. Do you hold the engine at or around 7600-7800rpm for any length of time? He reported that that is exactly where the engine dropped back down to when the sled came in. BINGO, resonance! I sent him A set of Comp 048 springs and told him to change them when they dropped below 285lbs. He has over 100runs on the engine and going strong. He replaces the valve springs about every 25 runs. This is the point I was trying to make. Just because a spring has more pressure or rate does not mean that it is a good match for the valve train system you are using them on. On a Drag racing engine that goes to 7600-8000 or 8500rpm on the shift, you won't generally encounter this problem because the spring goes in and out of resonance so fast its of no consequence. If you just go to the point of resonance or just past it and back down through it, you're generally ok. It's when you "hang" there for any length of time that the damage becomes evident.
_________________
Darin Morgan
There is no pat answer for the proper procedure to set up valve springs. There are guide lines you should follow such as not taking the coils to bind and trying to set it up close to the manufactures recommendations. I always tell people that .050 away from coil bind is as tight as I would ever run a spring. I have never seen ( at least with the engines I have worked with) a spring that benefited from running it tighter than .050. Some springs like to be farther away from coil bind than others. On a Pro Stock engine they are about .120 away from coil bind. It depends on, the spring design, the camshafts lobe design, valve train weight and the amount of loft your are trying to control. The valve train weight and loft usually come into play with engine that operate at extreme engine speeds at or around 9000-10000rpm but Nextel Cup engines use these techniques as well.
To answer some of your questions, yes we do worry about both the open and closed pressures but the seat pressure much less than the open. In a perfect world the spring would have little pressure at close and about 1200 over the nose but this is not a perfect world so we have to set them up at about 425 on the seat to get that over the nose pressure and the proper rate to control the valve action. I wish I could get 200 on the seat and 1200 over the nose but they cant make a spring with that rate. An engine design is an exercise in compromise and that goes double for the valve train! The only way to learn what makes a particular engines valve train work is to get on a Spin Tron and the dyno and work it out over time. otherwise, you go off the camshaft and spring manufactures recommendations.
General rules of thumb,
(1) Don't get any closer than .050 to coil bind.
(2) As far as Seat pressure goes, A little too much will not hurt you but too little will DESTROY you!
(3) Follow the manufacture recommendations first before you venture out on your own. I say this because if you pick the wrong spring for a camshaft you will induce resonance into the valve train and hurt parts. Even if the spring has more pressure than what the manufacture wanted you to run! I cant count how many times people purchased some wiz bang HIGH pressure spring only to discover that its rate and coil design induced resonance some where in the power band and beat everything to death! Spring design still rates as a black art in my book.
_________________
Darin Morgan
_________________
Darin Morgan
There is no pat answer for the proper procedure to set up valve springs. There are guide lines you should follow such as not taking the coils to bind and trying to set it up close to the manufactures recommendations. I always tell people that .050 away from coil bind is as tight as I would ever run a spring. I have never seen ( at least with the engines I have worked with) a spring that benefited from running it tighter than .050. Some springs like to be farther away from coil bind than others. On a Pro Stock engine they are about .120 away from coil bind. It depends on, the spring design, the camshafts lobe design, valve train weight and the amount of loft your are trying to control. The valve train weight and loft usually come into play with engine that operate at extreme engine speeds at or around 9000-10000rpm but Nextel Cup engines use these techniques as well.
To answer some of your questions, yes we do worry about both the open and closed pressures but the seat pressure much less than the open. In a perfect world the spring would have little pressure at close and about 1200 over the nose but this is not a perfect world so we have to set them up at about 425 on the seat to get that over the nose pressure and the proper rate to control the valve action. I wish I could get 200 on the seat and 1200 over the nose but they cant make a spring with that rate. An engine design is an exercise in compromise and that goes double for the valve train! The only way to learn what makes a particular engines valve train work is to get on a Spin Tron and the dyno and work it out over time. otherwise, you go off the camshaft and spring manufactures recommendations.
General rules of thumb,
(1) Don't get any closer than .050 to coil bind.
(2) As far as Seat pressure goes, A little too much will not hurt you but too little will DESTROY you!
(3) Follow the manufacture recommendations first before you venture out on your own. I say this because if you pick the wrong spring for a camshaft you will induce resonance into the valve train and hurt parts. Even if the spring has more pressure than what the manufacture wanted you to run! I cant count how many times people purchased some wiz bang HIGH pressure spring only to discover that its rate and coil design induced resonance some where in the power band and beat everything to death! Spring design still rates as a black art in my book.
_________________
Darin Morgan
Last edited by ACE1252; May 7, 2013 at 12:12 AM.
Thread Starter
Registered User
Joined: Mar 1999
Posts: 2,068
From: Kernersville, NC
Re: Unghh.....3rd to 2nd downshift....over rev?
Just to put a period on this issue.
I took it back to the track a couple of weeks a ago and it ran a little faster than before I screwed up on the shifting. The 330' to 660' times are right on top of each other compared to where I ran my 8.558 the week before the screw up. It's also not far off my best altogether.
8.558(86.94mph)-5.707 = 2.851(before screw up)
8.552(87.11mph)-5.698 = 2.854(after screw up....fair weather)
8.333(89.07mph)-5.533 = 2.8(best ever 3.13.13 - really good weather)
I think it's okay. Looks like I'm in the clear.
I took it back to the track a couple of weeks a ago and it ran a little faster than before I screwed up on the shifting. The 330' to 660' times are right on top of each other compared to where I ran my 8.558 the week before the screw up. It's also not far off my best altogether.
8.558(86.94mph)-5.707 = 2.851(before screw up)
8.552(87.11mph)-5.698 = 2.854(after screw up....fair weather)
8.333(89.07mph)-5.533 = 2.8(best ever 3.13.13 - really good weather)
I think it's okay. Looks like I'm in the clear.
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