<VV> PG 140 motor rebuild, more

[BobHelt at aol.com]

In a message dated 11/6/05 6:33:29 PM US Mountain Standard Time, 
dsjkling at sbcglobal.net writes:

> I used to have the 891 cam in my 4spd Greenbrier.  When I went thru the
> engine, I switched to the Clark's 260 grind.  The only other thing I changed
> at the time was to electronic ignition.  My observations are all "seat of
> the pants" driving experience.  Yes, it does seem to have more low end and
> mid-range torque comparing it to the 891. 

Hi Dan,
I'll try to give you my opinions. You know of course that youth is always 
eager and optimistic. Old timers get skeptical and cynical from their many 
disapointing experiences along the way to gettin old. I guess that I fall into the 
later category.

First let's note that the factory did a lot of designing and testing to 
arrive at the cams they used. You can use all the computer programs you want for 
designing the cams and incorporating them into the engines (i.e., flow 
analysis). But you finally have to make that cam and install it into a running engine 
and test what you have. The factory did a lot of that. Sure they had to balance 
performance with reliability, but aren't those both items you want?

Then there are the aftermarket cams. They are all either copies of the 
factory cams or their own special design. Copies might be copies of Corvair cams or 
copies of other cams (i.e.copies of the lobes). If copies of Corvair cams, 
then they are the same as factory. Copies of other cams might or might not be 
applicable to the Corvair. Who knows?

Let's focus on the special designs. These are almost always paper designs. No 
aftermarket designers, or cam makers test their designs on a running Corvair 
engine to obtain torque and hp data. They are not only not set up to do so, 
but the cost is prohibitive for such a low production item as a Corvair cam. 
Consider that an aftermarket cam would really have to be tested in each of the 
factory hp offerings for them to know how it performed. Imagine a cam maker 
running their Corvair cam on a dyno for the 95, 110, 140, and 180 engines? Do you 
really think that they do that and collect data too? No way. All aftermarket 
designs are "paper designs".

So then paper designs have to be analyzed in terms of their specs. But what 
are any cam's specs? Clark's says 21-61 and 61-21 for their 260 cam. Neat! But 
at what lift points? Is this seat-to-seat? or at 0.050 in. as is normal? Who 
makes this cam? Can we go to the maker and ask? Now I'm sure that Clark's is 
completely honest, so I'm not being critical of them. But with data like this, 
how does one compare one cam against another? How do we know that it has better 
low speed performance? Better than what, and how much better?

So in my opinion, buying an aftermarket cam is somewhat of a gamble. You are 
depending on a few words of performance, but without any data. Like the slots 
here in LV, you take your chances. You might hit it big and get great 
improvement. But you might not too. The problem is that you will never really know 
until you install that cam and run your tests. And human nature being what it is, 
you won't run any "before" tests to use for your "after" tests for 
comparison. How good is seat of the pants testing? It relieves you of the tough 
analysis. You don't have to face any possibility of performance failure.

Your buds aren't of any help either. Just think of the many different 
versions typically given of a multiple eye-witness accident. Personal opinions sure 
can vary.

There are also some factors one might have missed in using aftermarket cams. 
First is the fact that all the factory Corvair cams had a ground-in advance. 
Most aftermarket cams are ground straight-up. Do you advance or not? How much?
Also aftermarket cams usually have a higher lift than stock. That opens the 
door for better valve springs than stock. Are you planning to use those? How 
about reliability? The cam's ability to prevent multiple valve bounces at high 
rpm may drastically affect valve life. How do you know what the aftermarket's 
cam is doing about this? There's more too, but I'm running out of gas....

So experiment for sure. Take your chances of an aftermarket cam. Just be 
aware of the fact that you are leaving the safety of factory stock and verturing 
out into the unknown.

Regards,
Bob Helt