What should I expect to get for vacuum on a new 292 +.030 a little better than stock cam stock heads and a John Mummert intake reds headers and T85 overdrive. I am only getting 11 inches at idle, having brake booster/ hard brake pedal problems.

tom in iowa

54 Merc wagon

54 sunvalley

What are the specs on the "a little better than stock cam?"



Lawrenceville, GA

advertised duration in-288   ex-288

tom in iowa

54 Merc wagon

54 sunvalley

Late valve timeing ?


  AussieBill            YYYY    Forever Y Block     YYYY

 Down Under, Australia

I think you're in the ballpark at 11.  You might get a little more with some tuning but probably not what you need for the power brakes.



Lawrenceville, GA

Further to Charlie's note, your cam isn't really a "little better" than stock. Using Mummert's chart as a guide, you're about 3 steps above stock. For instance his next cam down is 224 deg @0.50 lift. And that's 2 steps up from stock. Also you didn't mention the LSA which might be a factor.. . 


Paul

Thanks for all your reply's, Not sure what LSA is

tom in iowa

54 Merc wagon

54 sunvalley

While you listed 288°/228° for the 0.050” cam specs, I suspect that should be showing something like 238°?  But as Charlie and Paul both bring up, that camshaft is several steps above stock which will be driving the manifold vacuum down.  You didn’t list the lobe centerline (LSA) but if its 108° or 110°, the manifold vacuum will also be considerably lower.  How the camshaft is degreed in will also be a player as if the camshaft is installed straight up or retarded, manifold vacuum is lower than if the camshaft was installed 4°advanced.  If the camshaft was not degreed in when it was installed, then all that’s known is that the cam was installed with 12 pins between the ‘dots’.  As brought up by Bill, advancing the initial ignition timing may also help bring the manifold vacuum up some.

Lorena, Texas (South of Waco)

Thanks Ted    the lobe centerline is 110.  the cam is a Camcraft part#312-2828-10AZ     this was my first y-block and was rebuilt by local shop.  they come highly recommended.  I am not sure were cam was degreed in at. but I will inquire tomorrow.  sure runs runs good

tom in iowa

54 Merc wagon

54 sunvalley

They probably have it degreed correctly, then.  Even if it's not, it's probably just too big a cam to work properly with power brakes.  You'll need to either live with it, convert to non assisted brakes, or have a more appropriate cam swapped in.  Oh, you could look into a vacuum pump as well.



Lawrenceville, GA