Thursday, December 31, 2009

Hydroboost measurements

-----------------------------94 Astro ------------99 Astro ----------------Dodge

Input rod -------------------.595 -----------------.595-------------------- .545

Power piston ---------------1.56 -----------------1.56-------------------- 1.56

Lever ratio------------------- .62------------------ .62 -----------------------.73

Stock pedal ratio ---------dunno ----------------5.2:1------------------- 4.2:1

All of these had the bigger power piston. The Dodge unit had the smaller input rod for more gain and the 73% lever for more relative motion of the valve spool.

Here is a pic of the Dodge pieces on the left compared to the 94 Astro. You can see the difference in the lever pivots. I can't tell any difference between the valve spools.

The GMC steering pump is supposed to be set at 1,400 psi. If I did the calculations right this would be 2,675 lbs of force to the master cylinder with a power piston 1.56" diameter and 1.911 square inches in area. This would be with an input rod force of 326 lbs with a rod dimeter of .545" and an area of .233 square inches. The force at the pedal with the GMC's stock 4:1 pedal ratio would be 82 lbs. All of this would make 2180 psi brake line pressure with a 1.25 diameter master cylinder. Way more than the vacuum booster.

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