I've got the new .484 cam in my 340 now,and it is so much different than the old one. I used to have a .513 cam in it,but no vacum and driveability was bad,but over about 2500rpm and she would scream. I'm actually putting 1.6 rockers on as my next step,as i like the driveability of the new MP .484. The centerline and the duration are about right on for a large vehicle.Vacum is right around 14,and my power brakes work now. Idle is good,with a bit of a lopey sound. It is a healthy cam for a small or big block.Anyone with a big block should save all this info.There is an article there about porting stock heads. No pics yet,but a simple bowl blend really wakes them up.
I use a solid-roller, .675 lift, 260/264 duration at .050, 112 lobe separation and my power brakes on my 67 Fury work marvelously. My manifold vacuum guage shows 12 lbs.
I think the trick here is the 112 lobe separation.
However, I also ran a .630 lift, 250/256, with a 108 degree separation with just a vacuum booster tank with great success. Make sure your power brake booster is in perfect condition and no leaks. Don't just assume lack of vacuum is because of the cam as many do with much milder cams than I've had great experiences with.
Personally- I cannot stand the sound of an electric vacuum pump. The one's I've seen used are very noisy.
Joined: Sat Aug 19 2006, 05:03PM
Location: Ontario, Canada
Posts: 2919
If you want to stick with a hydraulic flat-tappet cam...
My brother has Comp (High Energy) 268H in the 440 in his 66 NYer. It is a mostly stock rebuild except for "six-pack" forged pistons. Great power and never a problem stopping, except he must run 94 octane gas or detonation is a problem.
I have the Comp Extreme Energy XE268H in my 451 stroker. I forget what the idle vacuum is, but this cam is prob a bit more radical than you want. My power brakes are kinda weak when idling, but I've converted to front disc brakes and still running a drum booster.
Have you looked at the Comp "Magnum Muscle" 268AH-10? These are supposed to be Comp's interpretation of the Mopar HP cams with an updated lobe profile. It is also a dual-profile cam. This is supposed to help exhaust scavenging in engines with a restrictive exhaust system.
Unfortunately, LSA of all the cams I mentioned is 110*. I wish Comp made some catalog cams with wider LSA to cater to people that want lots of low-end torque and decent idle quality (and vacuum).
I read an article last year that said the current Vettes have lots of torque and still good idle and emissions because they use a cam with high-lift but exceptionally wide LSA to keep valve overlap down. (Of course the fact it is a roller cam would help too.)
Joined: Sat Sep 23 2006, 04:30AM
Location: Sharpsburg, GA
Posts: 924
I have some other limiting factors-
I have an original '68 440 with only 49,000 miles on it. No measureable wear on the cylinders,pistons or crank so I will be using original pistons (On a budget). With no valve reliefs, that limits lift to about .500, right? I want to stay with an original 750 cfm AVS carb, low rise dual plane intake and factory HP exhaust manifolds.
I will get a valve job with a 30 deg back cut and try to blend the bowls with the templates. I will consider any brand cam that is a good match for this engine, keep my brakes working and provide lots of low end torque for the street. I'm not into the drag racing, but might try it someday.
I spent 5 years in the Tampa area. Sure miss that weather! What happened to those house prices? OUCH!