Solid Lifters

[opticaltrigger 52]

Hi mmt,

The abillity of the valve to track the cam at speed is handeled by the spring as we know.

The function of the "hydraulic" liffter is to regulate the clearence between the two.

The hydraulic liffter works on the principle that a fluid such as oil is incompressable.By alowing oil to be held under a small piston in the liffter the clearence can thus be achived by controling the amount of oil under the piston.

Here it all starts to come down to compromises and windows of operation really.The problem is in the control of the oil to and from the liffter.In the desighn stage,the engineers calculate the dimentions of the supply and drain galleries for the liffter.They get to thiss by knowing how much peak pressure will be applied to the liffter piston by the valve spring,once they have that they can call up the oil guys and ask how much pressure it will take to move a given amount fo oil through a known size oriffice and in what amount of time.

As you can see by thiss,the amount of variables soon becomes mind blowing as you must know also how long peak pressure will be applied for and also the rise and decay times of that pressure.

The upshot of all this is that you cant have it perfect all through the RPM range because the liffter can only be callibrated to be giving the correct clearence at a very specific temprature,viscosity,speed,position,etc,etc.

So what the engineers do is they look at the most common tempratures,pressures,speeds,etc,etc that the power plant is desighned to opperate in and callibrate the liffter to work best there.If you had all the relavent data it would be possible to plot a graph and see where peak efficiency was and also the rise and decay of efficiency for that liffter.On the other hand a solid shimmed liffter only has to worry about temprature changes causing expansion and contraction and within limits does'nt care about how fast it has to accelerate or what the pressure is or for how long the pressure lasts

 

All the best

O.T.

[mmt 15]

Thanks for your answer. Very interesting and educating reading.

 

I guess that I can expect that the 6 bar xu10 spring that I`ve fittet in the oil pump pressure valve will help the hyd. lifters and might prospone the valve float.

[opticaltrigger 52]

It will help across the board from top to bottom.

The offset once again will be that your clearences will be slightly tighter in the lower end of the RPM range but will exercise slightly more accurate control at the top end.Provided of course that the temprature and grade of oil remain constant.

 

With some experimentation it should be possible to modifiy the liffters performance window slightly by changing the oil grade,as this will shift the accuracy of the liffter more to the top or the bottom of the RPM range but it would need to be done in conjunction with the temprature of the oil also.It's those terrible compromises again I'm affraid.

But as I said and its just a personal veiw.I think at around the 8000 mark,my feeling is that your at the back end of a hydraulic liffters abbility to opperate with much degree of accuracy really.But I think it's ok for short bursts.

 

All the best

O.T.

[petert 588]

Here's some more to add to the '92 Bathurst trivia:

 

http://www.racecarsales.com.au/classifieds...9f12a/index.htm

 

I'm not sure what ever happened to his more famous '05' car, but after it blew a clutch he jumped into the '45' car to finish the race.

[Sandy 191]

Mint!

[petert 588]

I was wrong, Brock started the race in car '45'. Read more here:

 

http://www.aussiefrogs.com/forum/showthread.php?t=10594

 

My memory is slipping!