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  #1  
Old 03-06-2006, 03:25 PM
Dart14 Dart14 is offline
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Default Cam size effect on engine vacuum

Does anyone have any figures on cam size and effects on engine vacuum ? Bottom line is engine has to pull 14" of vacuum @ 1000 rpms - how much valve lift and duration or combination can you do and still keep 14" of vacuum?
Engine is a 10.5 compression 340
Previous 318 with a .454 lift and 268 duration only pulled about 14.4".Had 360 unmilled heads so compression was lowwwww.
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Old 03-06-2006, 05:35 PM
340duster1 340duster1 is offline
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This would be a tough one to answer so I would rec'd you talk to a cam supplier - hughes engines would be a good choice as they likely have experience with this, especially if you are going to buy an new cam anyways.
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Old 03-18-2006, 09:54 PM
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MONKEYSPANKER MONKEYSPANKER is offline
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We Run A Comp Hyd .484 Lift 239 Int Dur 246 Ex Dur 106 Cl In Our Limited Mod. With Variable Duration Lifters In Our 360 It Pulls Over 15 Inches At 1200. Pulls Very Hard From 2700 Up To Around
6700.
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Old 03-19-2006, 12:04 AM
TK TK is offline
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I have a 270/280, 440/455, 112C cam in my 318, and it pulled 15+.
I think a lot of it depends on cubic inch, a bigger engine will pull more vacuum with the same cam, providing the same intake and carb is used, and also engine condition. Just one bad valve can drop the vacuum a couple inches.

Considering I bet you are running a 2bbl, or a cast iron 4bbl, you may want to consider your RPM's. Over cam will kill any engine, vacuum rule or not.

(The 270/280 cam in my 318 pulls strongest around 4000-5000, but will easily run up past 7000, still making decent power, for such a mild cam and manifold.)

The 268 comps pull nice to 5500 in a well built SB, from past experience.

I would say talk to a hughes answer man, there are lots of ways to change cam timing to get more vacuum, and they would know how to do it, if you want to order a custom camshaft.
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Old 04-08-2006, 09:14 AM
Dart14 Dart14 is offline
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Hughes tech man mentioned the variable duration lifters as the fix. Assume these are the Rhoads lifters listed in the SUmmit catalog. Others have mentioned richening the idle mixture and retarding the timing @ idle. I guess a real racer would have asked " How can I beat the 14 " vacuam rule ? Now, which cam ? I have the .454 lift or a .509 lift with 292/292 duration. Is the bigger cam too big for getting off of the corners on dirt ? I think it would be good at the end of the straights on the 5/8 mile.
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Old 04-08-2006, 11:48 AM
rklaft rklaft is offline
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Keep your duration to a minum that will pull you off the corners, Low duration
translates to high torque, this will pull you out of the turns with minimal tire
spin. As the rpm increase lift takes over and HP goes to work to get you down
the straight, your cam should be fine. Have Fun. DH
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Old 04-10-2006, 09:13 AM
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AVENGER29 AVENGER29 is offline
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Monkey, you can run a lot more cam than that and still pull the vacuum, I dont remember our exact specs, split duration Hughes cam and lift in the 540's, if i remember, have to look but duration in the 280's........we pulled 13/14 depending on weather.......

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Old 04-10-2006, 10:02 AM
340duster1 340duster1 is offline
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Are you using the mopar performance 292 .509" cam? What is the vacuum now. If you are running this cam I think you will have great difficultly pulling 14" of vacuum. I remeber getting 10" with the 284 .474" cam in a 340.
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Old 04-10-2006, 05:10 PM
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AVENGER29 AVENGER29 is offline
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we also use Comp Cam's version of a Rhoads lifter.....we run a lot of cam.....

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