5.5in vacuum at 10,000 ft, I need more for the booster? (1 Viewer)

[ripple]

I replaced the brake booster and high speed braking is amazing. Low speed is terrible, especially when starting cold. This 80 is reading 5.5in of vac and there has been no loss of power or anything weird going on with the motor. My 74 40 with a booster is at 4in of vac and works like a charm.

Is there a bolt on vacuum pump that I can install? Or is the new booster the real problem now.

(FYI the fsm reading of 16in is reduced 1in for every 1000 ft above sea level, 5.5 ain't bad I guess)

thanks in advance for the advice

 

[OLD DAWG]

Summit Racing has electric vacuum pumps for use on big cammed cars.

 

[NLXTACY]

Sounds like it’s within spec. Perhaps a vacuum accumulator.

 

[inkpot]

I did not monitor my vacuum gauge on the trip, but last summer I ran Pikes Peak, 14,000+ ft. Virtually no traffic, so I pushed hard both up and down. Made the up, gate to top, in 45 minutes. No record, but I was either in boost or brakes all the way up. I ran low range for the entire round trip, mostly 3rd and 4th, and second gear for the sharper turns. Brakes worked good all the way down. It didn't seem like I lost a whole lot of vacuum and boost even around the top of the mountain, but obviously I had to loose some.
Definitely one of those OMG Events that I will never forget.
I would check your bleed/bypass valve on the charger to insure it is closing all the way when it should?!

 

[Landseer]

I routinely drive my 80 up to 9 or 10k feet (and occasionally up to 12k), I've never noticed any problems with the brakes.

 

[ripple]

thanks,
I made a slight adjustment to timing to dial it in at 3, idle dropped to ~650 and it seems to have improved the booster, but no increase in vacuum at idle. Maybe the motor can recover vacuum quicker at lower rpm? We'll see in the morning when it's colder. Still not there but a little bit better. Now I am suspect of a vacuum leak.
I like the accumulator and may try it once this works like it should.

 

[NLXTACY]

Commonly overlooking vacuum leak source is the larger vacuum hose going to the booster.

 

[inkpot]

thanks,
I made a slight adjustment to timing to dial it in at 3, idle dropped to ~650 and it seems to have improved the booster, but no increase in vacuum at idle. Maybe the motor can recover vacuum quicker at lower rpm? We'll see in the morning when it's colder. Still not there but a little bit better. Now I am suspect of a vacuum leak.
I like the accumulator and may try it once this works like it should.

3 years ago I drove all the popular passes in Ouray with no noticable/unexpected lack of performance. There was some, but not a problem. Also make sure that your throttle cable is not adjusted too tight on the throttle body. Even though it sounds like your 650 idle is good, it could be a bit open, reducing vacuum.