I want to avoid the Comp XE268 ramps and go for Magnum type series with same specs of 110 LSA and 224 duration at 050. The only cam that comes close is the Magnum 270 but it's a single pattern so exhaust is same as intake. I'm using AFR195 heads so I'm thinking the issue for using dual pattern to help the exhaust may not be necessary, right? Not sure. All comments appreciated.

 

Check Crane Cams offerings...

 

Yes that is the reason for the dual pattern. GM factory heads do not flow as well on the exhaust side so the cams designed for them typicaly have longer exhaust durations relative to the intake duration.

AFR's have a better exhaust port so single pattern works fine.

The old Cam Dynamics Energizer cams (now sold by Crane) have single patterns as well. I used to run one in my Camaro years ago.

-Mark.

 

It's not just a head flow issue it's also the total amount of exhaust back pressure.

So AFR 195cc heads with headers and freeflowing exhaust would require less exhaust duration to accomplish it's mission.

IMO - go with a dual with only 6 or so difference on the dual pattern Some of them have really big differences like 12-14 degrees.

 

Do you actually lose or gain any low end by going with single, or vice versa?

 

I use "custom lobes billet steel cams" Life is a learning experience. I spent all kinds of time on desktop dyno figuring out the perfect cam lobes for my project. But what i didn't understand untill I called nearly every cam manufacture is:

Custom cam doesn't mean that your pick a lobe lift and duration. Tooling costs lots of money! So each cam manufacturer only has a small sellection of lobe profiles. You have to choose from their list.

So many of their "Magnum " cams are from yester year. Like 25+ years ago. Technology has changed. They found out that additional exhaust duration and lift increased hp without the detrimental effects caused by additional intake duration

 

Unfortunately I cant find any that have just 6 degrees of extra exhaust duration with 224 intake. They all seem to have 10 plus. I may end up with the XE268 after all even though I'm spooked by all the bad press.

 

I used the Crane power max 272 for years. It's a very good cam for 10 to 1 or less compression. If you have over 10 step up to the 278. Look at their web site

 

Actually I just found Crane has a new series called "Zcam" which has the specs I'm looking for. Z-274-2 looks like a winner. THANKS

 

This is the 278 specs that i ran when i had 355 ci and 10.7 compression. I used the Crane Hi-intensity lifters and the good crane billet timing set. Chroemoly 80 wall .100+ length pushrods. Better springs so i wasn't limited with valve float to over 7000 rpm.

Your Z-cam is simular, but even a newer design.

Part Number: 113801 Grind Number: H-278-2 (REPLACES HMV-278-2)
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1957 1987 CHEVROLET 8 GOOD IDLE, DAILY PERFORMANCE USAGE, MILD BRACKET RACING, 3000-3400 CRUISE RPM, 9.5 TO 10.75 COMPRESSION RATIO ADVISED. BASIC RPM 2500-5500
Engine Size Configuration
262-400 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 3114 @Valve 467 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 3294 @Valve 494
Rocker Arm Ratio 1.5

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 26 BTDC 72 ABDC 278 °
Exhaust 80 BBDC 30 ATDC 290 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99848
Loads Closed 114 LBS @ 1.700 or 1 45/64
Open 324 LBS @ 1.230
Recommended RPM range with matching components
Minimum RPM 2200
Maximum RPM 6200
Valve Float 6800

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 2 BTDC 40 ABDC 109 222 °
Exhaust 56 BBDC (2) BTDC 119 234 °

 

I used the 270H on my 355ci with Sportman II heads, It made 285RWHP, nice cam