270 magnum flat tappet idle speed and vacuum thoughts?

[abi]

Hi, just wondering if this cam will be able to idle down to say 700 or 750 and pull more than 16 or 17 inches? The motor is a +60 over 350 flattop zero decked with 63cc ported heads. measured compression is 10.3 to one. q jet on a dual plane and iron manifolds. was thinking of running it with 1.6 rockers for .500 lift@ valve.
Sorry about the basic question
Initial timing and vac advance and carb will be optimized to suit.
If too much cam, any off the shelf grinds to suit 5500rpm peak power and shifting a 4 speed at 6000?
Cheers for any of your thoughts.

[F-BIRD'88]

It will idle fine at 750 rpm. Vac will be a bit lower but no problem.

24-26 deg base at idle.

[BobbyB]

Fbird, how do you know 24 to 26 degrees base timing?

Do you have a rule of thumb based on cam duration or something?

What is this cams duration at .050?

[Tom Walker]

224 on both I believe.

[abi]

270/270 @0.006. 224/224@0.05 110 lobe separation. 60deg overlap. IO 29 BTDC, IC 61 ABDC.

[abi]

Thanks Fbird, how much lower will the vac be do you think?
I Liked the lobes on this cam and thought it would work well for my self imposed rev limit. The motor has cast pistons with translots behind the oil rings and only has the GM factory balance job but the motor is fresh including what looks like a recent close and hone of the rods. I'm thinking 5500 max power and 6000 rev limit, maybe 6200 at a pinch.
Will the rams horns be a problem?

[travis]

That cam has 50* overlap@.006”. Will produce 14-15” idle vac at 750 rpm idle. Something like this I usually use 14* or so initial timing, manifold vac advance with a 10-14* vac can, and whatever total timing it likes...usually in the 34-38* range (mechanical). I think it is a good cam choice for what you’re looking to accomplish

[68maliblue]

I ran that cam 20 years ago in a 350 and had 2" ram's horns on it when I first installed the engine in my 56 Chevy. The engine was much happier when I installed headers and 2-1/2" exhaust. It would nose over and feel flat at approximately 4500 rpm with the ram's horns. It might go higher with 2-1/2" ram's horns but with headers it pulled to 6k no problem and felt like it could go higher. In my opinion you are leaving a lot on the table with ram's horns. As far as engine vaccum it was about 13-14" at 750 idle in drive. It could idle lower but I did not like it any lower than 750 rpm in my car.

[abi]

Thanks Travis and 68. Sorry yes 50 deg overlap, i'll try to fix previous post.

[econo racer]

If his cam had 55 degrees overlap would it idle rougher and make more top end HP?

[travis]

If his cam had 55 degrees overlap would it idle rougher and make more top end HP?

With ram horns, I would expect a rougher idle and little to no extra top end power.

The 270 magnum is big enough to really benefit from a set of headers.

[econo racer]

What do you have for heads?

[abi]

The heads are 462 double humps with 202 and 1.6 valves, bowl blend, slimmed down guide bosses and opened up around the turn.

[BobbyB]

Do you have to have an off the shelf cam? Why not have a custom if you have the time? I am guessing your head flows can be estimated pretty close if you don't have actual flow numbers.

[mag2555]

If your taking about a duel plane such as the Edelbrock performer 5500 rpm is at the top of its range and the HP being made will be nosed over very hard by 6000 rpm!