Don Terrill’s Speed-Talk

Depending on what the application of this engine and what your goals are, you have a couple options. If this is going to be a "max effort" kinda deal where you are trying to make as much HP as possible, I would highly suggest looking at the PAC-1427H conical spring. If this is more of a st...

What Rocker Ratio?

I would entertain the PAC-1222X installed 1.750"

201lbs seat and 470 open.

A big question not answered is what rocker arms are we using? A factory or roller setup?

Frequency - This one is very hard to dictate and requires a lot of mathing to really determine desired frequency. With the proper information, you can figure out your hertz range and you would want to choose a spring that the natural frequency is not in the power band of that hz range. Not many peo...

List your order of importance of valve spring properties: Spring rate Installed height Distance to bind Pressure @ max lift Seat pressure Diameter Type (straight, conical, beehive etc) Frequency Number of coils Anything else 1 - Type of spring - this will be dictated by tappet type, max lift and ma...

Contact Ken @ Motorsports Unlimited. 216-433-7223 - been doing BBC marine stuff for years.

0.730" lift is pretty healthy for any single to keep up with, usually just not enough rate and seat load. Now if you had time to test lobes and a spintron, I am sure you would be able to come up with a killer single spring package. This usually takes some time and quite a bit of money, somethin...

PRI new products will be exciting for PAC racing

As heat energy was mentioned as a downside, the upside is the heat lost in the intake travel too.

Ive had mine milled down to get better geometry with a factory rocker. Not sure if this helps you but yes, they can be milled.

The nice thing about conicals is the design itself can do more with less, meaning you can control valve acceleration loads with less pressures than conventional double springs. So not only do you lose mass in spring and retainer, the varying coils diameter have its own frequency through the spring ...

The nice thing about conicals is the design itself can do more with less, meaning you can control valve acceleration loads with less pressures than conventional double springs. So not only do you lose mass in spring and retainer, the varying coils diameter have its own frequency through the spring ...

That's why in 2019 I ran stock rockers on my Vortec 406 over the roller rockers I had at the time. More weight on the valve tip means earlier valve float and IMO that's what roller rockers can do to an engine. I have never seen and better track performance with roller rockers on my street engines t...

Someone correct me if I am wrong, but I would think that if in any point in your motors operating range you have spring surge taking place then at that point in time the whole / total mass of the spring can be taken into account since it's not touching the head any longer. That would be a serious p...