yes, it is with mine, and I have the smaller booster

 

I got the small booster to, is you pedal a little hard or soft?

 

I also have small booster and it does ok. Works great until stop and go traffic then it gets hard like your saying. I think its normal. Some say you can hear it whining if the booster is bad but there's no way I could over the motor.
Does anyone have the dual diaphram booster on a 68 or 69? I am thinking of getting one and wanted to know if it bolts right up.

 

Is that 12 -13 in gear?? or in park???

 

It in gear at like 750 rpm

 

Hello, my 396/408 BBC Runs the same vacuum and my brakes suck after a few pumps! Do not spend any money on boosters, they will not make a differance been there done that. WE need more vacuum period!
What cam are you running I have the Comp Cam 270H?
Good luck
Gary.

 

Hello, my 396/408 BBC Runs the same vacuum and my brakes suck after a few pumps! Do not spend any money on boosters, they will not make a differance been there done that. WE need more vacuum period!
What cam are you running I have the Comp Cam 270H?
Good luck
Gary.

I got the comp XE268, which is pretty mild but sounds pretty good in gear but i thought vacuum wasnt going to be an issue.

 

I have 9-10" and my factory setup seems to work real good...better than my 01 Tahoe actually. Maybe the manual trans helps generate more vacuum??

 

12-13, you should be good. If not, consider raising idle to 800 rpm, I bet you'll get a little more out of it.

Or you can bump your initial timing, and reduce the amount of mechanical advance to keep your total the same - you should see a slight increase in vacuum at idle by doing so.

Might want to drive it first before you mess with it.

 

9 to 10" here and love the brakes with a factory booster. Everyone is different, but I think 10" is enough if everything else is right.

 

FWIW, I have a dual diapragm 7" booster and 5 inches Vac in gear at idle. Is this low? Yep. Do I have good brakes? Yep