Question about duration @ .050". I have a 496 going under for a rebuild. I am considering swapping the 781s for RR Ovals. Current cam has FT 234/241 @ .050", 110 LSA and runs the power brakes pretty well. I am considering changing to a HR 244/255 @ .050" 112 LSA.

How well will this run my power brakes at low speed?

Cheers! :beers:
E

I reckon it will be just a little less vaccum than you have now, maybe 2-3"Hg less. Just a guess.

Eric, all depends on what you consider low speed. For comparison, we ran the Comp 245/252, 110LSA in a 454 motor. Specs are 306/314, 245/252, 110LSA/106ICL. It pulled about 9" vac at 1000 rpm idle. Vac came up fast though and was 10.5" by 1100 RPM and 11.5-12" by 1200. This cam has 90* overlap at seat, 28.5* overlap at .050. Your 244/255 cam on 112LSA has 25.5* overlap at .050 and I am going to guess it will come in around 85* at seat [based on seat timing of 304/315 (.050+60*), typical of most hyd roller cams]. But you have slightly more exhaust timing and even though it is on a 112LSA, it will probably get ground/installed at 110LSA to put the exhaust closing point about the same place as my 245/252. So, bottum line, I would say expect similiar vacuum as my 245/252.

FYI, I gave this more thought and have done more research on this and come to the conclusion - regarding vacuum at idle, at some point there is going to be a sacrifice. I am going with it regardless. Have a vac canister ready to install just for that little added reserve vac.

Gents,

I blew my post. The new cam with the 245/255 @ .050 with a 112 LS is a solid roller not hydraulic. I'm sure that changes things. Sorry about the brain lock, but I would like to hear your comments on a solid roller change.

Thanks,
E

You'll need to compare the full duration specs and overlap. If they are similar then you should have numbers pretty close to the FT ones.

Full specs
Existing:
Hydraulic flat tappet
276/284 advertised
233/241 @ .050
.554"/.572" lift
110 LSA
106 intake centline 4 degrees advanced

New:
Solid roller
298/300 advertised (this is approx)
245/255 @ .050
.650"/.650" lift
112 LSA
108 intake center line 4 degrees advanced

E

The roller has 15* more overlap so I would bet you'll lose some vacuum, how much is the issue.

Jimmy,

Not real sure. I have to run my power brakes, so that was why I was asking.

Thanks,
E

That cam only has 75* of overlap, so you'll more then likely be fine with 496 cubes.

Even if the 244/255 on 112LSA was a hyd, it would still draw enough vac for power brakes. Being as it's a solid roller, it will pull more than enough.

Even if the 244/255 on 112LSA was a hyd, it would still draw enough vac for power brakes. Being as it's a solid roller, it will pull more than enough.
Great!

I appreciate the feedback guys. :)

E

I know everybody get's tired of seeing it's spec's, but here's Harold's little solid flat-tappet lifter cam he made for my about 9.8 to 1 CR'd 496.

278/249/161, 110/106, .618" gross lift and need's .018" lash hot.

pdq67

Paul,

I like those specs but I don't think they will work with my brakes. Future plans include a brake upgrade with hydroboost or a electric vacuum pump. If I do that, then I can change the cam to anything I want. I plan on installing a timing cover that has a removable front plate so I don't have to pull the engine to change the cam. :)

I kept the cam specs in my notebook.... :beers:

E.