I ran the numbers comparing the 847 to the XFI and they are almost identical
up to 5500, after 6000 they both fall off big time( with 1.6 rockers) with 1.5 installed it picks up 30 horse and still climbs to 6200. I know its just a computer program but it has been fairly accurate. I was just looking for some quick advice if someone had experienced a better cam than the 847. my car has 3.89 9" and should be in the 3600 lb range. I'm just trying to build a nice street car that runs 11's w/o the spray. I agree that bigger is not always better.

 

Yeah, just cause I make money on custom cams that means I can't say anything without it connected to my pocket book. I'm not a Wall St analyst here..... I actually CARE about what the customers are getting, advice or parts. Even if he's not coming to me, I want to point him down the RIGHT path.

Actually I tell a number of customers a day that I can't get them were they want to go because I don't throw the biggest cam in the book at you just because the specs make you happy. The results of the cam are what's important.

Mike, that post has been coming out of me to you for about a month. I wanna see you give me a dyno chart with a XFI cam that peaks over 6000rpm on a stroker LT1 and doesn't fall on it's face from valve float. You know what, it's not going to happen. The other issue is if you do throw enough valvespring at the setup to do this, it's going to need $450 lifters and a billet core cam.

Your area under the curve, or lobe area doesn't play into ANYthing having to do with valve control. The problem with a hyd roller setup is that valve control is the number one thing you have to get right over 6000rpm or the setup will flat out just not run. When you have as much accerlation and jerk over the nose as those lobes have, good luck doing that reguardless of the spring.

You would figure a "ENGINEER" would have a idea on the physics pricipals behind JERK and ACCELERATION. There is a lot more too this then just grabbing the NEWEST cam lobes out there that look good to you and throwing them in a motor. You have to understand what you are getting.

Jonesy,

Look around here on the things I've done for Lloyd Elliot and his packages, call him up and ask him for a cam I'm sure you will find some good examples of stuff not falling off after 6200rpm.

Bret

 

thx Bret, didn't mean to open Pandoras box (lol)

 

So is it normal for a business-man like yourself to hand out unsolicited attacks on the internet? I never read any of the threads with you and Joe Overton bickering, but now I'm beginning to understand why they occur. I never took sides before, but I'm starting to. . .

I do have a dyno chart of an XFI cam that remained stable to 6300. However, with only 224 deg of duration, I wouldn't expect it to peak over 6000. It also had the disadvantage of 20 psi boost and 40 psi backpressure reducing the effective spring pressure. It worked with stock lifters but alot of seat pressure.

Yes, been there, done that, in Machine Design II. I have actually designed lobes myself. And, yes, I've played with the Cam Pro Plus also.

While I posted my question about XFI lobes in Advanced Tech, I was also checking with my other resources. Sure is nice to be friends with people like Geoff Skinner and Ronnie Rogers. With a carefully set up valvetrain, the XFI lobes will go over 6000.

Also, keep in mind that it doesn't have to go much over 6000. Back when I had my 11/1 383, AFR 210's, Victor Jr., and 847 cam (296/304 adv), the power peaked at 5800 and I shifted at 6200. I would expect the XFI 242/248 to have a very similar power range.

Mike

 

Exactly, he makes money because he knows what he's doing, not because he just throws out cam specs out of nowhere.