Huge Roller Cam NO vaccum
05-21-2009, 06:27 PM
#1
Pro
Thread Starter
Huge Roller Cam NO vaccum
I get my motor from the machine shop this week or the next I'm trying to paint the engine compartment button up some wiring buy some goodies I'm really exited but the local corvette shop that i have been dealing with has kinda burst-ed my bubble the are telling me the due to the CAM size and exhaust intake overlap i will have a problem with my vacuum the said a healthy car stock 350 will have about 18+ inches of vacuum and they wouldn't be surprised if my cam makes no where near this!! so I'm askin what i gotta do to make vacuum happen. what are the tricks what do u guys running radical motors and supper chargers do?? oh by the way my motor will be a 4 bolt All forged 496 big block 10:3/4 to 1 Air flow Research heads And i don't know the duration off the cam off the top of my head but the lift numbers are around .711 lift Roller cam. Its in a 1975 I have had A 350 smog motor in there be for with about a 165 hp The machine shop said ill be looking at about 700hp and about 600+ ft/lbs and the car has all the necessary things done to handle this kind of power. Except the vacuum problem!
05-21-2009, 06:50 PM
#3
Race Director
I hope you are not planning on running vacuum brakes. If so this might be a problem. The headlights and such don't take much vacuum. I idle around 8 to 9 inches and they work just fine. The brakes are a different story but I hope you canned the useless vacuum brakes with a motor like that.
05-21-2009, 06:53 PM
#4
Le Mans Master
I'd say don't worry about it until you see exactly what you have. I run 12-13" of vacuum and other than the headlights being a little slow I really don't notice anything. I suspect that 2 or 3 stops would affect the brakes, but I've not ever felt any "bad" symptoms.
If you do have a problem, there are a couple of ways around it- one is a vacuum can that stores vacuum, another way is an electric vacuum pump, and the 3rd way would be a hydroboost. that won't do anything for the headlights, but it will insure the brakes are 100% as long as the engine is running.
If you do have a problem, there are a couple of ways around it- one is a vacuum can that stores vacuum, another way is an electric vacuum pump, and the 3rd way would be a hydroboost. that won't do anything for the headlights, but it will insure the brakes are 100% as long as the engine is running.
05-21-2009, 11:21 PM
#5
Ahhh.. big inch, and Big Power! Ya gotta love it!
Now's the time to open up some under hood space. Go to manual brakes, Install good quality brake pads like Hawk. Install an adjustable proportioning valve from Willwood. The consistent and predictability of manual brakes, compared to the uninspiring nature of the low vacuum, will inspire confidence in its stopping ability.
With all that power, you'll be wanting to focus on keeping it pointed in the right direction.
The lights? Face that when you get to that moment, you may find that you have enough to open and close. Or you could go Electric actuators for the headlights.
These are things that I have had to do with mine. They work very well!IMO
Now's the time to open up some under hood space. Go to manual brakes, Install good quality brake pads like Hawk. Install an adjustable proportioning valve from Willwood. The consistent and predictability of manual brakes, compared to the uninspiring nature of the low vacuum, will inspire confidence in its stopping ability.
With all that power, you'll be wanting to focus on keeping it pointed in the right direction.
The lights? Face that when you get to that moment, you may find that you have enough to open and close. Or you could go Electric actuators for the headlights.
These are things that I have had to do with mine. They work very well!IMO
05-21-2009, 11:27 PM
#7
Race Director
With 10 3/4 to 1 if your camed right you will probably be ok. To make that kind of power your cam is well matched to the motor. You don't need 18" of vacuum.
05-21-2009, 11:38 PM
#8
Burning Brakes
my car makes ~6inches of vacuum, the headlights and wiper door work fast, with no issues...but I have a vacuum reserve tank...in '75 did they have a tank, or use a part of the frame as a reserve?
05-22-2009, 02:13 AM
#9
Burning Brakes
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I suppose the 75 has the large vacuum tank on the front...if so you should have no problems.
I have a 69 , with its small vacuum tank,and lights works, even isf slowly.
my engine has just 7" hg. no problem with brakes when the car is at speed. in the traffic the brakes use is sometimes disappointing because after a couple of brakings , then no vacuum anymore , so you need to apply more force.Ah , I have manual transmission and vacuum of course is very low when braking and applying the clutch.
it's disappointing the sensation that brakes are working-not working in the traffic, but due to low speed, you stop the car anyway.
for Timat . we have about the same cam but very different vacuum...I think we should find the reason...
I have a 69 , with its small vacuum tank,and lights works, even isf slowly.
my engine has just 7" hg. no problem with brakes when the car is at speed. in the traffic the brakes use is sometimes disappointing because after a couple of brakings , then no vacuum anymore , so you need to apply more force.Ah , I have manual transmission and vacuum of course is very low when braking and applying the clutch.
it's disappointing the sensation that brakes are working-not working in the traffic, but due to low speed, you stop the car anyway.
for Timat . we have about the same cam but very different vacuum...I think we should find the reason...
Last edited by elle88; 05-22-2009 at 02:24 AM.
05-22-2009, 09:38 AM
#10
Team Owner
Find out your cam car .050 number for us please.
.700 lift is actually kind of wimpy for nearly 500 ci
.700 lift is actually kind of wimpy for nearly 500 ci