New Cam - Vacuum???
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Instructor
Joined: May 2004
Posts: 164
Likes: 2
From: Bristol PA
New Cam - Vacuum???
I am looking at putting a 383 in my car. The cam I am looking at is 502 lift and 240/250 duration. Will I have enough vacuum??? If not where will I run into vacuum problems??
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Not with a 383. Even with very wide (over 114 degree) LSA, I doubt you'll see 10 in/hg. If you have manual brakes, then you can expect some peculiar behavior out of your systems that require vacuum like the headlights and the HVAC system until you get a sufficient level of vacuum in the tank. If you have power brakes, then you have created a problem that will not let you rest.
But all is not lost. You can do as I have done on my '67 Fairlane...get an SSBC electric vacuum pump. Turns on at 18" and off at 24" and works great. Or you could go with Hydroboost for the brakes if you have power steering, but that doesn't address the vacuum items like the HVAC and lights.
A reserve vacuum tank is very doubtful if this car sees regular street use.
But all is not lost. You can do as I have done on my '67 Fairlane...get an SSBC electric vacuum pump. Turns on at 18" and off at 24" and works great. Or you could go with Hydroboost for the brakes if you have power steering, but that doesn't address the vacuum items like the HVAC and lights.
A reserve vacuum tank is very doubtful if this car sees regular street use.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I have a solid cam with 248 @ .050 and .525 lift. I get around 8 to 9 inches at idle. My headlights work with no problem. Ido not have power brakes (Hydroboost on mine) so that was not a problem. A 383 can stand a little more duration than a 350 due to larger cubic inches. I don't think you will have a problem unless you are running power brakes.
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
I'm also putting in fairly large cam in my 78 / 454 for a weekend driver. I bought a vacuum reservor..but according to the last post that may not help either???? I'm using all Edlebrock recommended components (heads, manifold, carb, etc.) I'm thinking I'm going to be borderline for vacuum, but still need the power brakes to work.... Comments on the this cam please.
Edelbrock 7162
050 DUR LIFT ADV DUR LOBE
INT/EXH INT/EXH INT/EXH SEP.
All 240/246 .560/.573 300/306 112
Edelbrock 7162
050 DUR LIFT ADV DUR LOBE
INT/EXH INT/EXH INT/EXH SEP.
All 240/246 .560/.573 300/306 112
Melting Slicks
Joined: Dec 2000
Posts: 2,041
Likes: 0
From: Wichita, KS
Nobody has listed their static or dynamic compression ratio. This matters as much as the cam selection as to weather you will have proper vacuum or not. My 406 has a cam that measures 256/270 at .050 and I have 10 inches of vacuum at idle in gear. The compression ratio on my engine is 11.8 to 1.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
The compression ratio has no bearing on the engine vacuum or I should say little to do. The larger an engine in cubic inches the more duration it can handle. What gives 9 inches on a 350 might give 13 inches on a 400. I would not worry so much about headlight operation as I would worry about having good brakes. Crawling in traffic with no power brakes can be a problem. If the headlights don't go up give it a little throttle to build vacuum and the headlights will work. You only need it momentarly for the headlights. Once up and once down. For a 383 a cam in the 230 to 240 @.050 should be a very good performer. I know mine has to much duration and will someday switch to a roller cm or just go 383 with a roller cam
Last edited by Gordonm; Dec 30, 2004 at 01:29 PM.
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Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Originally Posted by Gordonm
The compression ratio has no bearing on the engine vacuum or I should say little to do. The larger an engine in cubic inches the more duration it can handle. What gives 9 inches on a 350 might give 13 inches on a 400. ...
Displacement alone can tame a big cam because it can suck more air, making charge dilution less apparant.
I agree on the other points, including how to make a poor sucker's headlights, wiper door and hvac work.
Also, two cams with identical valve events, one being hydraulic, the other solid, the solid will generate more vacuum due to the lash.
Safety Car
Joined: Aug 2000
Posts: 3,711
Likes: 43
From: San Antonio TX
Originally Posted by DeanW
I did a search on Hydroboost. A little pricy ($800-$900) for the budget I am on. Will a 230 to 240 @.050 cam give me enough vacuum to operate my power brakes?
As to the cam...maybe. But for $260, you can get the electric vacuum pump and the cam then becomes a non-issue as far as your brake booster function: http://store.summitracing.com/defaul...pump&x=14&y=11
Again, my Fairlane pulls 11" hg and the brakes were dangerous at best. The electric vacuum pump works great. I don't have to worry about multiple brake applications. I run a Hydroboost on the 'Vette and can attest to its performance. So either solution works. Just different approaches to the same problem.
Race Director
Joined: Dec 1999
Posts: 19,610
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From: Forked River NJ
Yup you are right on the compression. Brain fart on that one. I installed my Hydroboost for 500 when they had a discount on them. What a difference in the brakes. Of course I went from manual to power but they have a better feel than power (vacuum) brakes. The system is quite small and works very well.
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
That is a tough one to answer. The 230 will be a better choice for torque and for the vacuum but the 240 will really wake up the motor in the upper rpms if you have the heads for it. If you stick with the 230 to 235 with a 383 you should be OK. With a 9.5 to 1 motor I would stay closer to the 230. In the 240 range it will be real soggy in the lower rpms. I know you are looking for a yes or no answer but it is almost impossible to answer. Every car and motor will be a little different.
Drifting
Joined: Sep 2003
Posts: 1,325
Likes: 6
From: FRANKLIN GA
As for my 383, my cam adjusted for the 1.6 roller rockers is 240/242@.050 with a 520/522 lift and my vacuum is fine for the brakes and the lights. I don't even run a canister, hosed straight off the intake. Brakes are fine even in downtown ATL traffic. I am running 11.9:1 compression ratio though don't know if that has anything to do with it.
