So, it’s not the “correct” spring for the aluminum heads with 1.800” installed height.
-Are the springs shimmed up to get to 1.660?
-Are the springs installed at a height enough taller than 1.660 to have a lower enough spring load to affect performance?
-Did they just swap the springs for something that’s a better fit on those heads?
This is actually a fairly common occurrence.
Several engine platforms use fairly short spring installed heights....... and their aftermarket counterparts often have taller heights.
Someone orders the springs in the catalog to go with their cam....... but the catalog parts are assuming you’re using stock heads with stock installed heights.
It’s best not to order springs until you know what installed height you’re working with.
I just went through this on some aftermarket SBF heads.
Customer had a healthy solid roller cam, and ordered the “matching” springs.
The problem was...... the springs were designed for a 1.700 installed height(for stock heads), but the new heads set up at 1.900.
No one checked....... so the 1.700 springs were in at 1.900, with the result being 130lbs on the seat instead of the 220lbs the cam wanted.
Needless to say....... the motor didn’t rpm very well.
Might be worth you verifying what you have.
Installed height, spring load at that height, load at open height, etc.
Using the numbers you provided, those springs would be-
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