Thanks for your patience on me getting back to you all on this. The facts reported here are not meant to be critical of anyone or any organization in our community - they are - just facts.
I have not gotten my data back from my camshaft consultant in California (he went on vacation) but I do feel I have enough information to conclude what factors were involved with the failure of the new lightweight lifters in Nick's engine.
Before I move on to the lifters themselves, I think it would be beneficial if I took a moment to describe some of the mechanical and dynamic factors which effect valve train components in general and our 5 cylinder lifters in particular. You can all imagine that valve spring rates have an effect on the required material and design strength of the various components which activate the valves. In addition I am sure you are aware that cam lobe shape and more specifically what is referred to as "lobe acceleration rates" also impact the same components.
What you may not be aware of is the differences between factory and aftermarket cams in the way that they interact geometrically with the cam followers - be they bucket type, finger follower, lever arm and etc. It is an unfortunate circumstance that most aftermarket cams end up having smaller base circles than the factory cams they replace. This factor is consistent throughout the industry whether you are dealing American V8's or Asian or German engines. This is due to space envelope constrictions and in a lot of cases a lack of a appropriate core blanks from which cam makers work.
The case of the Audi I 5 is a good example of space restrictions around the cams limiting how large the base circle can be if adequate lift figures are to be obtained. The lobes can only be so tall before unacceptable amounts of machining and clearancing of the head become necessary to let the cams rotate. So, the base circle diameter must be reduced to achieve the desired net lift at the bucket / valve.
The downside to base circle reduction with Audi bucket style lifters is that the lifter then rides higher out of its bore, which mean it is less supported and more tippy in the bore which increases side thrust on the bucket and required opening force (to some probably unknowable degree). When you combine this factor with higher spring rates and more aggressive lobes, is it easy to see how the top of the lifter bucket
becomes more highly stressed. The factory Audi I 5 cams have a base circle diameter of 1.497 inches. The Cat cams in Nick"s motor have base circles of 1.455 on the intake and 1.460 on the exhaust.
The other factor, which is dynamic, is simply boost pressure. Turbo engines, particularly small displacement engines running on relatively high boost pressures, run in constant pressurization of the cylinders when under hi boost. In other words there is never any actual vacuum in the cylinders. Even at full exhaust blow down there is still residual pressure so intake valve opening forces are mildly affected. The exhaust valves are another thing all together. Turbo engine exhaust valves have to open against considerably more pressure than in N.A. motors.
Depending on dynamic conditions, (boost pressure, rpm, valve timing) the forces that exhaust lifter buckets see during valve activation increase dramatically. This is why all of Nick's failing lifters were on the exhaust cam.
Now on to the lifters themselves;
I dissected a factory lifter, an INA lightweight lifter and an INA OEM standard weight lifter and the lifters were all weighed on a gram scale.
Here are the particulars.
The factory lifter weighs 71 grams, the INA OEM replacement lifter weighs 64 grams, and the INA lightweight lifter weighs 50 grams.
Material thicknesses were;
Factory lifter- deck face .097 and side wall .060
INA OEM lifter - deck face .094 and side wall .060
INA Lightweight lifter - deck face .078 and side wall .039
There are additional differences in the internal bridging and buttressing which you will be able to see clearly in the pictures I have sent to Hank for posting with this article.
The factory lifter is typical Audi super robust meant to last 300K miles type stuff.
The INA OEM replacement "standard weight lifter" appears to be well constructed with adequate material thickness and stiff structure.
The INA LW lifter is, upon deconstruction, clearly inadequate - in material thickness and internal bracing - for use with aftermarket cams and springs in a high performance turbo engine.
These lifters may work adequately and have an acceptable service life with stock Audi cams (including 7A) with boost levels up to about 23 pounds - but I would not recommend them even for that type of use. They are absolutely unsuited for any type of real high performance use.
I am sorry that I was unaware of the inadequacy of these parts, but I had in fact, relied on statements and the belief that their use was wide
spread in our familiar engines in high performance specification / application. I have only installed 3 sets total in my customer engines and one set was supplied by the customer. Fortunately, 2 of the three are not yet in service and will have the LW lifters replaced with standard weight lifters. ALL of the other Audi I5's engines that have come from FRP have either retained the factory lifters or have been solid lifter conversions.
If you have factory lifters that do not exhibit leak down and clacking, ticking etc. and do not have a discernible wear pattern on the contact surface I would suggest keeping them and just going with up rated valve springs and lightweight retainers. If you are installing new cams I suspect that using cam break in lube during install and zinc treatment in your oil for the first oil change after install will allow the cams to mate just fine to your used factory lifters.
If your factory lifters are in bad shape I am relatively certain you will have good luck with the INA OEM replacements. I have just purchased a
set for a customer engine currently under construction and I will be stocking them from here on.
Lightweight on left, Stock center, stock replacments right
OT
