2bridges

Geeze guys....... stop all this talk of bad new lifters after I just dumped a load of cash into new cam and lifters after **** went bad.

So far <1K miles on new cam/lifters (INA new)
I don't even want to know how much **** is gonna go flyin across the garage if these go south

Please let me stay ignorant, I will pretend I never read this thred (or the other ten) talking about inferior new lifters....... BLA BLA BLA I AM NOT LISTENING!!!!!!

RolexNJ

Sounds good to me. Anyway, I am done contributing here. But I am sure others will keep riding the wave. Peace.

ninefiveone

Not to be combative but are you trying to say that people have only begun running over 16psi very recently? Because there have been 951's running higher boost almost since they first came out in '86. The number has gone up in the 90's and even more so since 2000 but regardless, I'm only seeing issues with the new INA lifters. That's an issue with the lifters, not an issue with running 16psi.

Laust Pedersen

Last comments on this issue (I hope).

BB started the thread asking for recommendations and opinions on going for LR’s springs and titanium retainers, so here is mine.

BB,
One spring broken certainly raises the question, will another one break soon?
Look for reasons why that spring broke and if there is no particular reason why, then it may be a good idea to go for a new set of springs. It may also be a good idea to measure the seating force and compare it to specs (I don’t know what they are), but apparently between 90 and 120 pounds according to Pauerman’s post # 31.
If you don’t plan on frequent racing or spin the engine above 6500 rpm, then I see no reason for Ti retainers (ref Porschefile’s post # 14)


RDK,
Valve float and boost: Certainly the main mechanism behind valve float (mechanical separation between valve-follower-cam) is the inertia of the valve and particularly the cam follower mass. That occurs just after the cam tip has passed the follower or at about 100º ATDC of the intake stroke. At that point the valve is fully open and the only thing that in addition to inertia pushes against the spring is the inrush of air on the open valve head. LR’s discussion directly converts intake pressure to a force and uses that for a semi quantification of the boost vs. valve float. The static analysis for this purpose is outright wrong. What needs to be used in the discussion is the dynamic pressure, namely what force does the inrush of air exert on the fully open valve. For those who have time that should not be too difficult to calculate, if you know the air velocity and density of the air column just in front of the valve at that crank angle. In my judgment, that amounts to a very small force. You need to blow a lot of air on a valve head to exert even a few pounds of force.
When valves float, they normally slam down on the closing side of the cam profile and only in very extreme cases do they slam down on the valve seat. In any case that is a noisy process that I certainly can hear on another engine of mine and am quite sure I would be able to hear it on this one too, but simple have not heard it. Just in case you would ask: No, I am not going to verify that statement on my 951 engine.

New vs. old lifters: It certainly appears that the new INA lifters are softer than the older ones, but by how much? 10%? If so then Porsche had an awfully thin margin for failure in the original lifters. I did take a look at LR’s “disaster lifter” picture and there is definitely more going on than a 10% reduction of the surface hardness can explain.
You said: “3 failed lifters after 13,000 miles running higher boost levels and one of them a brand new INA replacement.”
Was there more than one INA lifter installed? If so, then it would certainly appear that the hardness difference is not that important. If not, then did the INA lifter look much worse than the other two old lifters?


As you may see from the above, I seriously think there is something else going on with your (and apparently also Rolex’s old 3.0L) valve train. I would verify the oil pressure to the lifters possibly by simply drilling a hole to the supply oil channel in the cam tower and measure the pressure there at high rpm.

Laust

RKD in OKC

On last posting and then I am done.

My engine had 170K on it when the previous owner rebuilt it, and only one lifter needed replaced in his opinion. The three lifters that were bad were not to the point of destruction, they were soft (not holding pressure). You could push in the button looking thing with your finger. The INA lifter looked just like the two original high mileage lifters. All the failed lifters had some scratching where they followed the cam, I was told that was an indication of floating. The other "good" lifters were hard (you could not push the button in at all), and had no scratching. The material hardness difference is something LR noted when first trying to find why the INA lifters were failing. AND there are a LOT of our cars out there experiencing this problem.

Again the hydraulic lifters DO NOT crater immediately. It is the nature of the hydraulic lifters to cushion the forces. What happens when they start floating is they do not fully pump up, ie. loose pressure in the lifter and provide less and less lift to the valve. The reason lifter damage was suspected was not valve train noise, it was the flattening of the power from 5000 rpm to red line as seen on the dyno. Also, increasing the boost above 16 psi did not give the expected incresse in power above 5000 rpm. Power did increase, but not nearly as much as expected. If I remember right the car started with 320 rwhp at 16 psi and only made it to 340 at 20 psi. This was with a K27/8.

After repairing the lifters and swapping to a Super61 turbo I dyno tuned the car at 16, 18, and 20 psi. The power increase was 350 at 16psi, 375 at 18, and 400 at 20.

I suspect there are a lot of owners out there with bad hydraulic lifters that do not know it. When you get a good spool and the boost hits hard below 5000 rpm you don't feel anything missing in the top end. I thought my car pulled hard bounced the tach off red line. It wasn't until I started tuning on the dyno and didn't get the results you would expect from increasing the boost that the lifters were suspect. Honestly, until Rolex's car this would probably have been written off to the old "every car is different" addage when adding power mods.

If you do not think boost effects valve operation and valve spring requirements look at the older 911 vs 911 Turbo. Are the valve springs the same, NO. They have the same cam, and valves, the only difference in the valve train is the valve springs. And if you put 911 valve springs in a 911 turbo, you get valve float from 5000 rpm up. Imagine that. Again the difference is boost.

I wish those running higher boost with the stock valve train the best of luck, really I do. Some of the original hydraulic lifters do seem to hold up better than others.

I'm done.

Porschefile

Sorry but, you are completely wrong. They do not have the same cams. As others have previously explained, a different cam alone can cause issues with lifters due to different ramp up angles among other things. You are using some really vague and broad examples to form an opinion on something, and there are far too many other variables that could account for lifter failure, lower hp/boost increases on the dyno, etc etc. You can't refute science with he said, she said arguments. Laust has completely valid points and an excellent explanation of what will cause lifter failure. End of discussion.

Chris White

Good points - but we need to add the other type of valve ‘float’. If the valve springs are on the weak side (seat pressure) the valves can ‘bounce’ off the valve seat at high rpm. The fast closing valve will actually rebound off the seat and not seal when it is suppose to. This is the main cause of valve train induced loss of power.

Tom M'Guinn

Would be great to get a health check from you on those lifters after a few more miles. I'm guessing you'll be just fine.

Laust Pedersen

Very last comment on this issue (I really hope)

That’s true, but it is worth adding a few qualifiers.

The higher the seating velocity of the valve is, the higher the risk of bouncing.
Cams are ground so the valves get a soft landing when closing (near zero valve velocity). Unfortunately all valve-trains with solid lifters need some clearance, so the seating velocity increases as the valve lash increases.

One of the good ideas behind hydraulic lifters is an automatic zeroing of the valve-lash, but they also bleed (oil and reduce height) as they are loaded, meaning that the seating occurs on a portion of the cam that does not provide near zero velocity.

In other words good hydraulic lifters (or followers) with little bleed-off will be much gentler on the valve-train.

Laust

PS It may be a little easier to follow what I am saying with a cam-lift vs. crank/cam angle graph nearby.

ptuomov

I'm with you on the intake float. If the cam has a lift curve that is at all appropriate for the engine, the higher density inside the cylinder offsets the higher pressure in the intake manifold. There shouldn't be any need for stiffer intake springs.

However, what about exhaust springs? The exhaust manifold absolute pressure in these old cars could be as bad as 2:1. At 16 psi boost it means the absolute exhaust pressure is 2*(14.7+16) = 61.4 psia or 46.7 psig. When the exhaust valve is about to close and end the overlap, there's often a high-pressure wave being reflected back to the exhaust valve, adding to that 61.4 psia pressure on the valve head. Simultaneously, the piston is descending and sucking charge into the cylinder. How about need for more spring on the exhaust side at the end of the overlap period?

Chris White

Suddenly back from the dead 6 years later!

Dutch944

Wauw you can say that again Chris!

I always love it when people bring back topics from way back with a lot of technical info which would otherwise be lost..

ptuomov

And I'm about to do it again!

After some experiments, I am now more firmly of the opinion is that rpms, component weights, and camshaft negative accelerations determine the required open load. Boost does not enter the equation. However, the boost does enter the equation for the required seated load on the exhaust side.

333pg333

Good to catch up again. See you in 2026!