Is this cam too wild for power brakes?

-
Valkman

Valkman

Well-Known Member
Joined
Sep 13, 2012
Messages
954
Reaction score
291
Location
NC
I just bought a Challenger with a 340 4spd. It has x heads 10:1 with a pretty wild Lunati 10200705 Voodo cam:
Advertised Duration (Int/Exh): 284/292
  • Duration @ .050 (Int/Exh): 242/252
  • Gross Valve Lift (Int/Exh): .533/.552
  • LSA/ICL: 110/106
I'm having trouble with power break boosting or lack there of and I want to know if this could be caused by cam or is this in the booster?
 
Valkman said:
I just bought a Challenger with a 340 4spd. It has x heads 10:1 with a pretty wild Lunati 10200705 Voodo cam:
Advertised Duration (Int/Exh): 284/292
  • Duration @ .050 (Int/Exh): 242/252
  • Gross Valve Lift (Int/Exh): .533/.552
  • LSA/ICL: 110/106
I'm having trouble with power break boosting or lack there of and I want to know if this could be caused by cam or is this in the booster?
Click to expand...
-----------I`d say it probly is. u might double check the valve on the booster tho.
 
My 70 Cuda had a MP .296 .572 and my power brakes worked fine
 
Funny my Challenger has a big lunati solid cam and does not make a lot of vacuum.
Brakes have a great 1st stomp but seem to lack a very good vacuum.
My to do list includes putting my vacuum pump on the booster to make sure it's not bleeding down.
 
Vacuum reservoirs are a good option if you are on the border of available vacuum. If not decide between manual, hydroboost, or vacuum pump.
 
I ran the solid mp 528/286 in my Cuda and even with a new booster, in traffic the pedal would get hard after a few stops. I considered adding an extra reservoir, but I lived with it til I sold it. I would think with a stick it would recover quicker. Like above, check your vacum
 
The big diameter booster in my 70 Cuda must have been the difference, I could pump the pedal and never run out of vacuum.
 
Put it in neutral, and slowly rev it up til you hit about 13 or 14 inches of vacuum. That is about the minimum vacuum required to operate a booster. If it happens at 1200 rpm then That is the minimum rpm to operate the booster.
However if you have a manual trans, compression braking will artificially keep the vacuum up,to a lower rpm.
You have to have the engine idle bugged out, That is; the T-port has to be synced and the idle-timing properly arrived at. If your timing is too retarded the vacuum will be low. If your compression is weak, the vacuum will be weak.If you run too low a rear gear, the vacuum will stay low for a fair few miles per hour.
That cam wants a minimum 3.55 gears and probably a compression ratio up near 10/1
But here is the thing, as soon as the car is moving, the vacuum will rise, and you are good to go.
When coming to a stop, you will be downshifting as you go so the vacuum will remain high enough to just before you clutch it and stop.

I ran the 292/292/108 cam, and my 73 Swinger booster was fine with it. Except at first start. But a couple of blips on the throttle and away I went.
That cam did not like the small dual diaphragm booster.I almost solved that with a 15/16 M/C, but in the end I swapped that booster out.
 
BB73Challenger said:
Funny my Challenger has a big lunati solid cam and does not make a lot of vacuum.
Brakes have a great 1st stomp but seem to lack a very good vacuum.
My to do list includes putting my vacuum pump on the booster to make sure it's not bleeding down.
Click to expand...
If it's not the booster, I'm thinking a milder cam might be a better solution. The engine is pretty much stock with the exception of a set of headers, and with 3.23 gears it's a dog off the line. Beside I'm not racing this car.
 
Valkman said:
If it's not the booster, I'm thinking a milder cam might be a better solution. The engine is pretty much stock with the exception of a set of headers, and with 3.23 gears it's a dog off the line. Beside I'm not racing this car.
Click to expand...
That is a lot of cam for 3:23 gears. If the engine is pretty much stock, even with the x heads, it needs to breathe. Try with timing to get your vacum and acceleration better, but for what you want, it probably is too much cam
 
That's a pretty nasty cam. I can see why it doesn't produce much vacuum.
 
Unless you want to keep it numbers matching, convert it to manual brakes. It will stop better. Power brakes are over rated.
 
I know this is about an e-body, but the only difference, to the driver, between power and non power disc brakes, in an a-body, is that the guy with power brakes can say "look, I have power brakes."
 
I agree with the manual vs power difference, I had an E body with manual brakes and steering and loved it, this car has completely restored to stock (with the exception of the engine ) and I don't want to do any heavy modifying to it. This is more of show/investment car, my 65 Barracuda my fun lets see what I can do with it car. By the way that one has manual brake and steering and I wouldn't have any other way:thumbsup:
 
Last edited:
With 5 in-Hg of vacuum at idle and it max's out on 9 in-Hg, so I'm thinking the cam is culprit.
 
Valkman said:
With 5 in-Hg of vacuum at idle and it max's out on 9 in-Hg, so I'm thinking the cam is culprit.
Click to expand...

Yeah, I think you're right. Mine is around 13-14 (absolute minimum for power brakes), and my brakes don't feel exactly right. I'm swapping over to manual.
 
Gear up! 3.91s should should turn up the wick!!:thumbsup: Keep the cam to smoke some rice & late muscle cars! Smaller cam = boring!:p
 
I guess I'm boring:rolleyes: I'll end up changing the cam sometime or another, this is a cruiser not a racer. That's what my other car is for
 
Another option is Rhoads leak-down lifters. They make the cam act smaller at lower rpm, also increasing vacuum, mileage, and torque. Kind of an poor-man's "variable valve timing" like some high-end Honda's. I have bought a Mopar SB set for $25 on ebay, but takes time to find such deals (not selling mine).
 
Understood! These large cams can be a bit much for cruisers. Especially if it is driven almost on a daily basis or even often!
 
See where the initial timing is. If it;s too far retarded, there's your sign. Advance as much as it will take initially and limit the total to 34-36*.

That should help if it doesn't have a lot of initial advance. It should have on the order of somewhere between 18-20* initial. If not, that's where your problem could be.
 
You must log in or register to reply here.
-

Back
Top