Big Cam No Vacuum

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Dan B.

Dan B.

78 and still going.
Joined
Jan 14, 2017
Messages
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Location
Cold Spring, MN
72 Duster with big cam, no/little vacuum... When I first hit the brakes they react like they should. If I hit the pedal again there is little Boost assist. To stop I have to stand on the brakes. (fronts are disc, back are drums). Since the brakes act like they should on the first stop I am going to assume that everything is as it should be except for the vacuum. I ordered a Dorman 904-214 vacuum motor and plan on hooking it up with my current vacuum line. First, has anyone reading this done this? In what order did you plum the vacuum line from the vacuum motor into the current vacuum line. Before or after? Where did you locate the new pump, frame? (I would just as well not mount it on the inside fender well. Not any room because of other add ons. No room on firewall because of NOS hook-ups and other components). And where did you hook up the power? I've got a Flex-a-Lite control box with a hot wire. I have a fuse block (painless wiring harness) on the inside fire wall and also the ignition switch on the column. (mine is unique in that the ignition switch only energizes the starter for starting. I have to flip a switch under the dash for the car to actually start when the ignition switch is turned. To shut the car down, I flip the switch to the off position and then turn off the ignition switch). It's obvious that there is a hot wire on the switch under the dash (?) but i'm afraid that if I pull power from that switch it may be too much load on the switch. There is probably a hot wire in the ignition switch wiring since the radio plays with just the ignition switch turned on. And there is the Fuse block which I am leaning to. I could also fuse the wire there. A friend suggested that I also add a switch to shut the vacuum pump off so I could manually shut it down if for any reason I needed to. (I believe the pump has an internal on and off switch regulated by vacuum pressure?). I was just going to add another canister (home made from PVC) but I have that problem of having enough room except for the inside. fender well).
chrome booster.jpg
L side top engine.JPG
R side engine.JPG
Duster A arms.jpg
Duster collector.jpg


Duster frame.jpg
 
Sounds pretty normal. Where is initial timing set? If you don't have enough, pulling in more may help, but probably not much.
 
Cute little power brake chamber. It doesn't hold much. A pump may help. A reservoir may help a bit too. Just for fun, what are your can specs and engine combo?
 
RustyRatRod said:
Sounds pretty normal. Where is initial timing set? If you don't have enough, pulling in more may help, but probably not much.
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The timing is set at 36 degrees total. According to the Dyno this seemed to work best with the NOS. The cam is a roller cam. .288 intake. .292 exhaust duration, and .501/.513 lift. 1.6:1 rockers. 439.5 # Torque and 343 HP at 4100 RPM. and 398.6 # at 5400 RPM and 409 HP. These numbers are without the NOS.
 
Hey Rusty, where's the best place to get vacuum for power brakes? Carb or intake?
 
toolmanmike said:
Cute little power brake chamber. It doesn't hold much. A pump may help. A reservoir may help a bit too. Just for fun, what are your can specs and engine combo?
Click to expand...
Here is the engine specs.... 390 hp. Magnum Crate engine. Thermo-block is bored .020 over. Magnum R/T Big Valve cylinder heads. Mopar cast Al. valve covers. High strength SS Valves, 2.02" Int., 1.62" Ex. Heavy duty valve springs. Hydraulic Roller Camshaft- 230'/234' Duration @ .050"/0.513" lift. pistons 9:1 C.R. Double Roller timing chain and sprockets. Single plane manifold w/650 Double pumper. 150 hp. shot of NOS. Line lock. 3000 rpm stall. Hughes racing transmission w/B-M floor shift. All MSD ignition. MSD 6AL Control box w/MSD pro-billet distributor. Blaster 2 coil. 8 3/4" rear with 2.73 gears. (had 4.11 but changed them for better cruising). Dyno: 439.5 ft-lbs at 4100 rpm. 409 hp at 5400 rpm. Fun to drive.
 
toolmanmike said:
Hey Rusty, where's the best place to get vacuum for power brakes? Carb or intake?
Click to expand...

Off the large port (manifold vacuum port) on the carb if you can.
Second choice would be direct to the intake as close to the carb as possible.

The reason I like right off the carb base is because it spreads that change in vacuum when the brakes are cycled over 8 cylinders instead of say cylinders 7&8 (or just the back 4 cylinders)
When you release the brakes the closest cylinders will go lean for a second or two, and I would rather spread that lean condition over 8 cylinders instead of two or four.

I realize you didn't ask me directly so, sorry if I butted in. :D
 
TrailBeast said:
Off the large port (manifold vacuum port) on the carb if you can.
Second choice would be direct to the intake as close to the carb as possible.

The reason I like right off the carb base is because it spreads that change in vacuum when the brakes are cycled over 8 cylinders instead of say cylinders 7&8 (or just the back 4 cylinders)
When you release the brakes the closest cylinders will go lean for a second or two, and I would rather spread that lean condition over 8 cylinders instead of two or four.

I realize you didn't ask me directly so, sorry if I butted in. :D
Click to expand...
Off the carb. port.
 
TrailBeast said:
Off the large port (manifold vacuum port) on the carb if you can.
Second choice would be direct to the intake as close to the carb as possible.

The reason I like right off the carb base is because it spreads that change in vacuum when the brakes are cycled over 8 cylinders instead of say cylinders 7&8 (or just the back 4 cylinders)
When you release the brakes the closest cylinders will go lean for a second or two, and I would rather spread that lean condition over 8 cylinders instead of two or four.

I realize you didn't ask me directly so, sorry if I butted in. :D
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Toolmanmike... No, don't apologize. I always like as much input as I can get. It give me more possibilities to think about.
 
A few of our members have went that add on vacuum pump route. From what I've seen, majority of them eventually turned around and went the manual brake route.
The right small bore master cylinder will work about the same in pedal effort and stopping the car.
Good luck though.
 
RedFish said:
A few of our members have went that add on vacuum pump route. From what I've seen, majority of them eventually turned around and went the manual brake route.
The right small bore master cylinder will work about the same in pedal effort and stopping the car.
Good luck though.
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Thanks RedFish... I thought about that but then again I would have to change all my chrome lines and re-do my line lock plumbing. So, taking the easy way out I thought of just adding the pump.
 
Have you put a gauge on it? How much vacuum do you have at idle in gear? That camshaft you have isn't what I'd call "big." You may be able to get by with some very basic tuning and not even need an aux vacuum pump.
 
mopowers said:
Have you put a gauge on it? How much vacuum do you have at idle in gear? That camshaft you have isn't what I'd call "big." You may be able to get by with some very basic tuning and not even need an aux vacuum pump.
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I had a friend that runs Pro Stock do the tuning for me so i'm pretty sure he set it up to run the best over all. (he owns a shop that specializes in racing engines) Although he probably did not tune it to get the max vacuum. I checked the vacuum and it was about 15" at idol 600 RPM in gear) however it was not in gear.
 
Dan B. said:
The timing is set at 36 degrees total. According to the Dyno this seemed to work best with the NOS. The cam is a roller cam. .288 intake. .292 exhaust duration, and .501/.513 lift. 1.6:1 rockers. 439.5 # Torque and 343 HP at 4100 RPM. and 398.6 # at 5400 RPM and 409 HP. These numbers are without the NOS.
Click to expand...

Dan B. said:
Here is the engine specs.... 390 hp. Magnum Crate engine. Thermo-block is bored .020 over. Magnum R/T Big Valve cylinder heads. Mopar cast Al. valve covers. High strength SS Valves, 2.02" Int., 1.62" Ex. Heavy duty valve springs. Hydraulic Roller Camshaft- 230'/234' Duration @ .050"/0.513" lift. pistons 9:1 C.R. Double Roller timing chain and sprockets. Single plane manifold w/650 Double pumper. 150 hp. shot of NOS. Line lock. 3000 rpm stall. Hughes racing transmission w/B-M floor shift. All MSD ignition. MSD 6AL Control box w/MSD pro-billet distributor. Blaster 2 coil. 8 3/4" rear with 2.73 gears. (had 4.11 but changed them for better cruising). Dyno: 439.5 ft-lbs at 4100 rpm. 409 hp at 5400 rpm. Fun to drive.
Click to expand...

Given all this. There is ABSOLUTELY no reason you should have power braking problems. That cam isn't big by any means. I run 230/236 @50 cam and run power brakes no problemo.

Dan B. said:
I had a friend that runs Pro Stock do the tuning for me so i'm pretty sure he set it up to run the best over all. (he owns a shop that specializes in racing engines) Although he probably did not tune it to get the max vacuum. I checked the vacuum and it was about 15" at idol 600 RPM in gear) however it was not in gear.
Click to expand...

Your post is a little confusing here. Was it in gear or not in gear? 15" of vacuum at 600 rpm doesn't sound quite right. But that cam should have in the area of 12-15" at idle around 900 rpm I would think. Double check what your vacuum is at idle in gear. Your in gear idle should be 750-850 rpm minimum I would think. Personally I prefer to idle mine at 850-900. I occassionally have even played with it at 1000. Check your initial timing. That cam you should be 18-22 as a starting point. Tune for best vacuum. Then re-time your distributor to get your total back at 36.

Which brake booster are you running? The chrome or the black one? I run a 73-76 k member with power brakes and I get 3 FULL hard brakes out of my booster before it's out of juice.
 
Lustle said:
Given all this. There is ABSOLUTELY no reason you should have power braking problems. That cam isn't big by any means. I run 230/236 @50 cam and run power brakes no problemo.



Your post is a little confusing here. Was it in gear or not in gear? 15" of vacuum at 600 rpm doesn't sound quite right. But that cam should have in the area of 12-15" at idle around 900 rpm I would think. Double check what your vacuum is at idle in gear. Your in gear idle should be 750-850 rpm minimum I would think. Personally I prefer to idle mine at 850-900. I occassionally have even played with it at 1000. Check your initial timing. That cam you should be 18-22 as a starting point. Tune for best vacuum. Then re-time your distributor to get your total back at 36.

Which brake booster are you running? The chrome or the black one? I run a 73-76 k member with power brakes and I get 3 FULL hard brakes out of my booster before it's out of juice.
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It was not in gear. The numbers I quoted are from memory from last summer when I really wasn't really fooling with the vacuum. (I was busy getting rid of a noisy el. fuel pump). I have the car put up for the winter right now so I can't go out and start it. Here in Minnesota it was 30 below last week so we tend to put them away for the winter.... When you say you set your RPM at 850-900 is that in gear? Also. since I really wasn't paying attention when I took the vacuum test last summer I did not check for any leaks. I guess it could be that I have a leak somewhere?... Thanks for all your input.
 
Dan B. said:
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It was not in gear. The numbers I quoted are from memory from last summer when I really wasn't really fooling with the vacuum. (I was busy getting rid of a noisy el. fuel pump). I have the car put up for the winter right now so I can't go out and start it. Here in Minnesota it was 30 below last week so we tend to put them away for the winter.... When you say you set your RPM at 850-900 is that in gear? Also. since I really wasn't paying attention when I took the vacuum test last summer I did not check for any leaks. I guess it could be that I have a leak somewhere?... Thanks for all your input.
Click to expand...
Also, I am running the chrome one from Sumitt.
 
Dan B. said:
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It was not in gear. The numbers I quoted are from memory from last summer when I really wasn't really fooling with the vacuum. (I was busy getting rid of a noisy el. fuel pump). I have the car put up for the winter right now so I can't go out and start it. Here in Minnesota it was 30 below last week so we tend to put them away for the winter.... When you say you set your RPM at 850-900 is that in gear? Also. since I really wasn't paying attention when I took the vacuum test last summer I did not check for any leaks. I guess it could be that I have a leak somewhere?... Thanks for all your input.
Click to expand...

Dan B. said:
Also, I am running the chrome one from Sumitt.
Click to expand...

My RPM in gear is 850-900. I find with my setup it runs best there. Hit's hard. Engine likes a little more idle with my cam.

You might have a leak. But for right now no point in worrying about it if you can't look at it. What I would do when you get the weather. Is get it running and warmed up. Check initial timing. Check vacuum. And go from there.
 
Lustle said:
My RPM in gear is 850-900. I find with my setup it runs best there. Hit's hard. Engine likes a little more idle with my cam.

You might have a leak. But for right now no point in worrying about it if you can't look at it. What I would do when you get the weather. Is get it running and warmed up. Check initial timing. Check vacuum. And go from there.
Click to expand...
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Thanks for your input Lustle. All the advise and ideas from everyone are appreciated.
 
I agree with Lustle. Your cam ain't that big.

I realize you would have to redo a bunch of lines and all that, but you'd be far ahead of the game making it manual brakes. It's cleaner, and when done correctly it will stop much better. I have done it many many times. Starting with my first car. I always ditch the power brakes.
 
The total timing monster strikes again.

Bushing color in distributor?

If you need a bushing that provides more initial timing than what MSD has, I sell them in a 10* and 14* sizes. $10 each + shipping
 
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yellow rose said:
I agree with Lustle. Your cam ain't that big.

I realize you would have to redo a bunch of lines and all that, but you'd be far ahead of the game making it manual brakes. It's cleaner, and when done correctly it will stop much better. I have done it many many times. Starting with my first car. I always ditch the power brakes.
Click to expand...
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Since I already have the pump I may as well give it a try. If it doesn't work I'll go to manual. Thanks!
 
FYI
I ran the 292/508 with a 4-speed tho, and plenty of boost, after initial charge. But the m/t does not allow the rpm to drop as fast as a loose TC. Plus with the rear wheels driving the engine into compression braking and simultaneously maxing the vacuum, I guess I should just not have said anything.Sorry
You need a clutch,lol
 
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