Pure stock and cam lobe design?????

[Bernhard]

Originally Posted by bigfoot584

I don't think I'd worry about springs, with 4.75 lift I worry
about a block large enough to handle the lift LOL.


You really meant .475 lift, I hope.

Yes .475

How do the IHRA measure spring pressure, is it at the factory installed height ?

Originally Posted by Bernhard

Yes .475

How do the IHRA measure spring pressure, is it at the factory installed height ?

Yes it is.

Call Bullet and ask for John. He is a Stock guru and ground us a Pure Stock cam that we were very happy with and helped the car a bunch while still remaining legal.

Scott

[Dwight Southerland]

Originally Posted by Bernhard

How do the IHRA measure spring pressure, is it at the factory installed height ?

If they do it like NHRA did when they were still checking, they willl measure the installed height of the valve spring on your engine when the spring is removed and that is the height they will use to check the pressure of the valve spring. The specs will give a seat pressure and a pressure at a designated height and the inspector will use the difference to check the spring rate.
Example: Common SBC spring was spec'd at 84 lbs on the seat @ 1.700" and 206 lbs open pressure @1.250". That's .450" difference between the seat and the open spec. The tech measures the installed height on your engine of the spring he removes and finds that measurement to be 1.765". He uses a micrometer type instrument on a valve spring pressure checker to find out the pressure of your spring at 1.765". If it is 84 lbs or less, you're okay. Then he compresses the spring an additional .450" and your spring should be less than 206 lbs.


They are concerned that you are not exceeeding the pressure specifications, not the factory specified installed height.