truckman5000

What is the difference in a 8in vs 11in booster? Stock is 8in, but i was trying to get a new one and some are 8in wide instead of 11inches. I was confused at nappa as the guy said the 11in was for drums all around. And the 8in is front disks, i knew it seemed wrong but bought it anyways.

Both were listed for a cutlass 1970

joe_padavano

Stock booster for every 1967-up Cutlass is 11" diameter. 1964-66 cars came with 9" boosters - which is why 442s in those years didn't need notched valve covers.

The only thing that governs how much assist a brake booster produces is the diaphragm area. Air pressure is the same for both, so do the math.

A single diaphragm 8" booster has about 50 sq in of diaphragm area. An 11" booster has 95 sq in, or just about double the area - and thus double the assist force. A dual diaphragm 8" booster obviously has 100 sq in and thus double the assist of the single 8" also.

truckman5000

Thanks, Joe. Learned something today