Why do they even have "advertised duration"??

[deathmunchy]

well when does the valve sit back on its seat? Would this be at the advertised duration or the duration at .05? I realize that you won't get as much flow at advertised but looking at a few of the cam PDF's the advertised duration seems to be at .006" lift. But would it be exaxtly 0 before its back on its seat? Or different. Google has yielded many search results and answers and the performance books I've acquired seem to not indicate this either. I would assume exactly 0 but valve train is never that accurate or so it would seem. If the advertised duration is from exactly point of open to point of close I could see how it would be useful.

 

[dubs74camaro]

Well I have decided to make this easy on myself. I guess there is a guy out there named Chris Straub. From what I have read, he is an absolute camshaft genius. He doesn't seem to be on this board or he would have jumped in by now but he is on every other one. Never an off the shelf cam. Everyone of them seems to be a "one-off". It's going to be expensive but if you just google "chris straub cams", all you will find is guys on other boards with serious motors praising him. Funny thing is I can't find ONE person that has a negative thing to say. He is a long ways form cheap but at least my valvetrain will be perfect for my application.

 

[AJ_72]

\AJ,not to harp on the DD2003 thing, but the xe274 would be the cam to compare the 280 magnum to since they have the same intake duration @.050.

I compared what I did because the topic is about the advertised duration. The advertised duration of the exhaust of the of the XE268 and the Magnum 280 are identical, as well as the lift at.050" duration.

I used DD2003 as a comparison of the effects of what RPM the HP numbers fell in relation to the two cams, not the overall HP. I never even gave HP numbers. They're irrelevant. I was informing everyone of what the difference is between the two cams because of the change in the advertised duration and .050" duration of the intake valve, since we're talking about advertised duration. That's it. That's all. It's about where in the RPM range the numbers fall. It's not about overall HP. If it was about HP I would have posted the HP numbers.

I thought this would have been obvious when I posted that even Comp Cams specs them at different RPM ranges.

My other point was, Comp Cams uses "advertising" (notice the similarity) to sell some cams that aren't all that different than the stuff they've been selling for the last few decades.

 

[dubs74camaro]

......and to top it off, my ramps aren't even going to be the same. Guess it's an A symmetrical lobe. All I know is I really don't care about advertised duration anymore. I paid Chris good money to make one that will work. He said I can put it on a dyno to check his math but swears I will be right at 650/650 at 6,300 rpms.

 

[sooner]

It's funny because I had a really good talk with a guy at Lunati yesterday and he sounded like he had been around awhile. He laughed and complemented Comp Cams. They are the biggest in the world because they know how to market camshafts. I mean come on.......they went and figured out how to make a cam that would F**K up a motor by shooting the compression stroke out the exhaust and make it sound "healthy"..."wicked" or whatever and they call it the THUMPR! Well also want parts in our cars that have names like "Xtreme Energy", "Magnum"...etc. Just go to the Jeg's cam page and comp takes up 3/4's of the damn thing. They even have sounds bites that are worthless as all get out!

Thread digging here, but I find it odd that you found it necessary to try and bash thumpr cam's, yet I just read the specs of your custom cam over on the truck board and it just looks like a thumper grind with a little added duration and lift.

Big mutha thumpr bbc specs:

243/257@.050 .570/.554 lift with a 1.7 ground on a 107

Your custom cam specs:

248/262@.050 .665/612 with 1.7? Ratio rocker and ground on a 107

I haven't seen you post advertised duration, but I'm going to take a wild guess and say its around 304* on the intake side.

With a 1.8 ratio rocker on the intake, and 1.7 on the exhaust the comp would yield .603/.554 that's .049 difference in I/E lift. Your cam has .053 difference in I/E lift while packing 5* more duration on both sides than the biggest thumpr.

I'm not knocking your cam by any means, but I'm pointing out that it is a custom cam spec'd for your motor by a guy with a great reputation.....and its basically a 5* bigger thumpr grind, with a 1.8 ratio rocker "ground in" to the intake side for lack of a better explanation
.

 

[dubs74camaro]

I'm not a cam guy by any means but I'm sure there is a reason why guys trying to build power don't buy the thumpr's and run a 1.8 rocker. Probably more to it than that though I'm not in my arena. All I know is I can't seem to find anyone with anything good to say about them including the guy that came up with my cam specs. You get the right guy and Comp and they'll even tell you to pass it by.

Why is 1.7 the norm? Why aren't more guys running the 1.8's? Is it a geometry issue? Point is my friend was going to run it with a 1.7 ratio and all he wanted was to make some noise. He has since sold the Thumpr and is running a steel billet full roller.