Cams with agressive idle

[DrK MrK iV]

What is the most agressive cam I can get without changing out the valvesprings? I don't plan on building my motor up by any means. Just bolt ons and cams. Maybe nitrous someday, but now just minor stuff. What has the most agressive idle? Sound clips of them? I want my 04 GT to sound really mean. I already have an SLP catback. Oh, and a 70mm TB, Plenum, and K&N filter. Thanks!

 

[Mo-Tang]

While everyone wants an awesome idle, Id be leary of buying cams just based on sound. Ideally cams are going to help maximize your combination, so they can make or break you at the track. That being said, id avoid a massive duration cam. However, some the of guys swear by the VT Engines cams. Other by Comp, just do some research and youll be fine.

-Brian

 

[DrK MrK iV]

So duration gives me the idle? I thought lope did. I also heard that I don't want to go over 500 degrees with stock valve springs.

 

[krly79]

The "lope" that you want comes with the duration and lobe seperation.

 

[DrK MrK iV]

So the greater the difference between the two gives me a more agressive idle (and a more agressive cam)?

 

[nickthegenius]

So duration gives me the idle? I thought lope did. I also heard that I don't want to go over 500 degrees with stock valve springs.

First off, a quick lesson in camshaft lingo.

duration- measurement in degrees for how long the valve stays open

lift- measurement in inches for how far open the camshaft is lifted away from the valveseat.

lope- just a term to describe a choppy idle

With that out of the way, there are only 360* in a circle. 500* of duration would call for some creative grinding.

What you are looking for in a cam that can use the stock valve springs is something that stays around .500" lift. The stock PI cams are actually higher lift than that, but most of the aftermarket camshafts for the 4.6L are either right at .495"-.500" lift or .550"-.560" lift depending on whether they are intended for NPI or PI heads. What you could do, it get a set of camshafts custom ground with the stock PI lift numbers (which are just north of .500, but can't remember exactly) and get more duration and get something like a 110*-113* lobe seperation angle.

So what you could do is get someone like Comp or T&J to grind custom some cams with specs like:

230*/234* duration @.050
113* LSA
.517"/.525" Lift <---PI lift specs are something like that

That way you have the benefits of more duration and get to retain the higher lift of the PI cams instead of short-changing yourself with NPI-style .500" lift cams.

 

[Red2000GT]

Nick you're totally correct but there's one more thing that you have to consider. To get the valve to open up sooner without causing unreasonable overlap it must open faster. Lift rate is as big a factor as total lift for causing vavle float. You can really only go slightly "bigger" than factory without changing the springs. They may work on a low mileage motor for a while but eventually you will bounce a valve off a piston.(within 2 weeks to 2 months i'd say)

 

[nickthegenius]

Nick you're totally correct but there's one more thing that you have to consider. To get the valve to open up sooner without causing unreasonable overlap it must open faster. Lift rate is as big a factor as total lift for causing vavle float. You can really only go slightly "bigger" than factory without changing the springs. They may work on a low mileage motor for a while but eventually you will bounce a valve off a piston.(within 2 weeks to 2 months i'd say)

Yeah, I never thought of it that way. I did change my springs, but I was thinking of keeping the lift within OEM spec. I guess the ramp speed of the lobes would probably affect it too.