Z-Gad Posted September 26, 2002 Share Posted September 26, 2002 Hopefully someone can answer a couple'a questions for me. I have heard the phrase of hydraulic lifters "bleeding down" above 7k rpms, but what would the symptoms of that be and how would that effect the way the engine runs? I am trying to identify the symptoms my turbo engine gives me once in a while... Thanks, Mike Quote Link to comment Share on other sites More sharing options...
Mike C Posted September 26, 2002 Share Posted September 26, 2002 bleed down is when the valvetrain pushes harder against the lifter than the oil pressure does inside. Usually the motor will just fall on its face since the lift and duration on the cam are significantly reduced. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted September 26, 2002 Share Posted September 26, 2002 well, sort of... Mike is right, but the explanation is unclear. The lifter is pressurized by oil pressure. As the cam rolls around and starts to push on the follower and valve, an internal check ball/valve in the lifter "engages" and locks the lifter in its current position. when that ball/valve fails to seal, the lifter slowly "bleeds down" meaning the valve sees less and less of the amount of lift it is supposed to. Symptoms would include a drop off in power, or just plain refusual to go above a certain rpm. The motor still runs, it just has less power, in some cases, much less. First, are you talking about taking your turbo over 7k? If that is what you are doing, lifter bleed down is not really a problem, but airflow capabilities of the head/intake/exhaust. On my P-90A 3.1L, with good lifters, I have taken it to 7300+ with no lifter problem. I wasn't making much power up there due to other issues,(cam was too small for that rpm powerband). To better identify your issues, you need to provide more info on what is happening. -Bob Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 26, 2002 Author Share Posted September 26, 2002 Thank you for the clarification on bleed down. My latest issue is as follows.... When I run the car hard above around ~6500 rpm, the engine will begin to run rough almost as though all of the cylinders aren't firing, or the valves aren't opening completely. I will allow the engine to idle far a while and after 5-10 minutes, it will be back to normal. It only seems to happen when the engine is spun up to high rpm very quickly (easy to do w/ the turbo). I began to think that the valve springs may be too stiff and the lifters aren't able to pump up properly. When the car is idling, the oil pressure is 15 - 20 lbs. If I get into it too quickly, maybe the oil pressure needs more time to build to properly to pressurize the lifters than the motor is giving it due to the stiffer valve springs... Anyway, when I put together the engine, I replaced the stock valve spings with significantly stiffer valve springs. I do not remember the stiffness, but I remember checking them on a spring compressor and seeing that they were about twice as strong. (They came off an old 240z GT2 race motor). Could these be my problem? Thanks for your input, mike Quote Link to comment Share on other sites More sharing options...
David K Posted September 26, 2002 Share Posted September 26, 2002 Originally posted by Z-Gad:[QB] If I get into it too quickly, maybe the oil pressure needs more time to build to properly to pressurize the lifters than the motor is giving it due to the stiffer valve springs... oooh ooooh oohhhh i know. After reading this post again, it has to be the valve springs. I dont think the oil pump has supplys enough pressure to work with those springs at that rpm! i dont know if they make a better pump than the one i have, i have a oil pump out of a bluebird. might wanna try that. Better yet, change the springs to stock turbo ones and see what happens. Quote Link to comment Share on other sites More sharing options...
Lockjaw Posted September 26, 2002 Share Posted September 26, 2002 If you have a turbo engine, you should be using the turbo automatic trans oil pump. What kind of cam are you running that you need a spring that tight? Lifters that bleed down make a lot of racket, and they will do it at idle and going down the road. There is also the power loss issue, and I am certain you are losing power due to frictional losses alone. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted September 27, 2002 Share Posted September 27, 2002 Mike, Good lord, GT-2 spring pressures on a hydrualic turbo head?! I would bet good money that is a large problem, not to mention what John said about it robbing you of power. Take a look at my webpage,(link in my signature). Look at the P-90 page and read what Nissan Motorsports said about the hydraulic lifters... I am running about 30-35% more pressure than stock and that is what I consider to be the upper limit that the lifters can take. You have shown they will survive with much more up through about 6500. Save your lifters, swap them out for stock springs,(if you have close to a stock cam), or very mild springs at best. You'll be amazed at several things, first, no more problems above 6500, and two, more power for the reasons John cited. -Bob Quote Link to comment Share on other sites More sharing options...
David K Posted September 27, 2002 Share Posted September 27, 2002 Originally posted by Z-Gad:Anyway, when I put together the engine, I replaced the stock valve spings with significantly stiffer valve springs. I do not remember the stiffness, but I remember checking them on a spring compressor and seeing that they were about twice as strong. (They came off an old 240z GT2 race motor). Could these be my problem? Thanks for your input, mike Maybe since the springs are so stiff, the valves are not staying open long enough at high rpms as in a normal engine they will float a bit under the same rpms therefor the valves are almost as good as shut??? Quote Link to comment Share on other sites More sharing options...
johnc Posted September 27, 2002 Share Posted September 27, 2002 GT2 race motors occaisionally see 9,000 rpm and thus have a need for valve springs that stiff. L6 engines that are kept under 7,500 rpm work fine with stock valve springs and can even be made to work very well with valve springs 25% less stiff then stock. I don't know for sure if the stiff valve springs are the cause of your problem, but I do know the stiffer valve springs are not helping your engine at all. In fact, they are robbing you of torque because of the effort needed to compress them. A turbo motor does not need stiff valve springs or radical cams (which might require the stiff valve springs.) Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 28, 2002 Author Share Posted September 28, 2002 Thanks everyone. My thought was that the springs were too stiff, but it is nice to get some other feedback. I will go back to the stock springs. I have a couple of sets. I am using the turbo automatic oil pump w/ the performance springs so I have plenty of pressure. If I am losing power due to this, I can't see it being too much. If it is then My buddy and I burried the speedometer in the turbo last night on a nice long empty stretch of highway in the middle of nowhere...just wanted to see if the car could do it Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted September 28, 2002 Share Posted September 28, 2002 My buddy and I burried the speedometer in the turbo last night on a nice long empty stretch of highway in the middle of nowhere...just wanted to see if the car could do it Is this after the valve springs swapout? I hope you were on 417 or somewhere in the backroads of Boggy Creek. I know it is pointless to try and preach to the masses, but to you and others I know personally, PLEASE, PLEASE, PLEASE BE CAREFUL! You and Jeff know the black supercharged Jetta and we might even have stopped to talk with him and his buddy in the pits. Well, he was racing a Mustang on SR50 (OF ALL PLACES. HOW STOOOPID!) and they crashed. The Jetta was hit so hard, it split in 2! He survived but his buddy died instantly. Now, not only has he lost the car, but he has to live the rest of his life haunted with his friend's death and he will surely be jailed for involuntary manslaughter. This young man just ruined his life and chances are he will not get another license. ...AND FOR WHAT? Sorry, folks. They had a memorial at the track for him last night and it hit me emotionally. Will you be ready to go out Wed night? I am planning on going out again but not driving. I want to give the old lady some seat time. Low boost (18psi ), street timing and DRs. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 29, 2002 Author Share Posted September 29, 2002 Wow Scottie, I think I know the car and think I know the people you are talking about... I know it is not the safest nor brightest thing to do, but it was on SR 528 leaving Cocoa and returning to Orlando ~ 2am Friday morning. There were no other cars on the road, and we weren't racing anyone. I don't plan on ever doing it again, but I felt I just had to try it once. Anyway, I haven't swapped the valve springs yet though. I don't want to run again @ the track until I do so. I have to see if I can get my hands on a valve spring compressor, where I don't have to remove the head and I have to figure out a way to hold the valves up while I swap the springs. I am too tired of taking the head off this block. I have done it WAAAYYYY too many times now. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted September 30, 2002 Author Share Posted September 30, 2002 Proficiency is one thing, but desire currently rules... Yep, 2mm gasket is on and I don't wanna do it again so soon if I can help it. Quote Link to comment Share on other sites More sharing options...
Jeff Posted September 30, 2002 Share Posted September 30, 2002 Scottie, I think I know the car as well, makes me glad I didn't go to the track Friday night, just too depressing. Mike, Be careful out there The only way I know to hold the valves in place is with compressed air. I don't have a valve spring compressor but I'm sure you can rent one if all other sources fail. Since you don't want to pull the head I'm assuming you already put the 2mm gasket on. You certainly should be getting proficient at it by now Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted October 4, 2002 Author Share Posted October 4, 2002 Just a quick update... I replaced the stiffer valve springs with the stock hydraulic valve springs yesterday. It wasn't as bad as I thought it would be. A buddy of mine made a u-shaped ended tool to compress the valve springs and I used the ole "stuff vacuum line into the cylinder and bring the piston up trick" to hold the valves up and in place while I compressed the springs. The results: The engine seemed to run smoother after hard acceleration and also seemed to have more pull through the higher RPM's (I am assuming the valves are able to open fully now). The idle also seemed to be more smooth. All of this is of course subjective since anytime you make a change which should improve performance, it always FEELS like it improved performance. The butt dyno isn't nearly as accurate as hard numbers, so if I get the go ahead from the better half this evening, I'll be at the track Thanks again for the advise and will update you all on my progress. Quote Link to comment Share on other sites More sharing options...
David K Posted October 4, 2002 Share Posted October 4, 2002 wooohoooo another z running perfect and on the road. Quote Link to comment Share on other sites More sharing options...
Scottie-GNZ Posted October 4, 2002 Share Posted October 4, 2002 Mike, I will see if I can make it over. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted October 5, 2002 Author Share Posted October 5, 2002 Well, depressing night at the drag strip. All I could muster were 2 passes almost identical. 13.4_ @ 107._ Swapping to the stock lifters didn't solve my problem of the car stalling after the burnout. My stock 77 fuel filter was clogged with crud (I saw some in the bottom of the fuel jug), so I am replacing it with a Fram performance one, but I don't feel that it is the root of my problem. I am beginning to think that it may be a fuel starvation problem and that the Bosch 95psi pump (unsure of the gph on it) may not be up to the task of running above 15 lbs of boost. I can increase the fuel mixture at boost with no real results as it appears by the plugs to be running lean (kinda white-ish residue which could also come from the race gas I have been running). Ok, it's getting late and I am beginning to ramble... Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted October 8, 2002 Author Share Posted October 8, 2002 Another update... I replaced the stock fuel filter w/ a remote filter and also ran a temporary fuel pressure gauge into the car. I checked my fuel pressure and it was ~38psi, so I adjusted it back to where it should have been @ 43psi. I took the car for a drive and low and behold, fuel pressure rose under boost until ~7-8 lbs of boost or 50-52 psi on the fuel pressure gauge and then it plummeted down to 38, while still under boost !! Now, I have narrowed the problem down to a fuel pressure problem. I am picking up a Walbro 255 high pressure pump this week to replace the old 95 psi Bosch pump I have on the car (which came off of an old 280zxt parts car) and see if it corrects the problem. If not, then the Aeromotive FPR must be the culprit, but the fuel pump upgrade is a necessary thing anyway, so that'll be first. Quote Link to comment Share on other sites More sharing options...
David K Posted October 8, 2002 Share Posted October 8, 2002 if you are losing fuel pressure under boost like that, it has to be your fuel pump. it cant keep up with the demand. Quote Link to comment Share on other sites More sharing options...
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