I sure hope we get mine ironed out bret!

 

Good point on the lash ramp. I have personally seen hydraullic rollers run on a mild solid grind just for the purpose of fitting into a particular class at races. The valvetrain is normally set up with roughly .005" cold lash and will run w/o issue. The thing to watch is how aggresive the lobes are... the more aggresive the profile the more likely it is that you will have to modify the base skirt of the lifter body to avoid it contacting the face of the lobe. You'd be very surprised at how many people have actually run this set up, LOL.
Steve...

 

Bret,
Build him an extra special intake and cam so he don't have any excuses.Heeee Heeeee

 

I already have his cam and intake Q u e e r

 

Who's cam and intake?

 

Duh, Brets

I thought You knew everything man?

 

Not enough knowledge here to know what you do. My crystal ball broke.

 

Your screwed then! The car will never run now......

 

Maybe not!!!!

It will probably run OK.

 

Yes, we do have patients like that. What they need most is a different doctor When I or my family needs medical care, we pick doctors we can trust and do what they recommend. Seems to work out fine.

Same with cams, pick someone you trust and go with thier recommendation. As far as the tech lines at the big companies, I would not rely on them unless as has been suggested, you know and trust a specific person there. When you deal with a small operation, you often get the boss and you can get a LOT of valuable info. Perhaps opinionated, but based on experience and real world results. Some examples recently included Manton pushrods, where I spoke with Manton himslef and learned a LOT. Worth 10 times the price of the pushrods I ordered. When you call Rossler for a tranny, you usually talk to Carl directly and can always ask for him. I have also found the folks at Callies to know their stuff, though I have idea if there is a "Mr. Callies" to speak with I have never felt the need and I always ask for the same person (who I met at PRI). Similarly, the tech at JE is good, though I do not know a specific person there. Comp has some true experts, but from my experience they do not answer phones! Do the following experiment: call Comp on a few different days and ask the same question. If you don't get the same answer, what does that mean? Closer to home, when I needed some cam advice I dealt directly with Bret. Worth every penny, in fact, I would gladly have paid more for his expert advice.

Rich

 

i would like to know about the radically unsymetric designed cams. like the stress they put on the valve train.

and also, off the top of my head, is there such thing as a step-up cam?

 

One use of highly assymetrical cam lobes might be to get more lift for a given total duration by spending say 60-65% of the duration on the opening portion of the lobe and 35-40% closing the valve. You might say you were droppin the valve of a cliff to close it and then just catching it near the seat.

The maximum aggressiveness of a cam lobe, especially a flat tappet lifter is determined by lifter diameter and the slope of the lobe flank. At some degree of steepness (slope), the edge of the lifter will dig into the cam lobe. You can't go this far, so the amount of lift per degree of cam rotation is physically limited. Because this is a distance divided by "time", you could call it cam velocity even though rpm isn't part of the equation. At 1 rpm or 10,000 rpm a given cam/lifter combination has the same cam velocity or inches of lift per degree of rotation. Valvetrain loads are proportional to valvetrain acceleration which is proportional to rpm, so higher rpm = more loads. (Load divided by area it is acting on is "stress", so effectively stress is proportional to load.)

With roller lifters you don't have the same digging in problem, but you have side loads on the lifter bore that you don't have on a flat tappet system. Visualize a line from the contact point of the lifter roller on the cam flank to the center of the roller axle. As that angle approaches 90 deg. due to agressive lobes, the component of the force trying to lift the lifter approaches zero, so there is a limiting cam velocity for rollers also. Also the side loads on the lifter and lifter bore get very large at the same time as the loads along the pushrod approach zero due to the angle.

You probably couldn't use all of the limiting cam velocity on a flat lifter Nextel Cup 9700+/- engine on the opening side and make it live the million+ revs it runs in a race. However you might be able to more closely aproach the limit on the closing side because the lifter might be almost unloaded as the valve, which might have lofted at the top of the lobe, is trying to catch up with the closing flank of the camlobe. In this case, you could get more lobe lift with the same total duration and still live. IOW, if the lobe were symmetrical, you would need more duration to get the lift, and that might not be what the airflow wants. The same thing applies to rollers. Hey, there is no free lunch.

What's a "step up cam"? The only context I have heard that is one cam might have more lift/duration that another and is considered a "step up" from the original. Are there other meanings?

 

you typed all that for me?
i don't know how to describe what i would call a step-up(i don't think it actually exists). i was thinking along the lines drawing a lobe out on paper with alot of duration and not alot of lift. then ontop of it drawing a lobe with very lilttle duration and alot on lift. i was thinking it could let the car keep the low lift a bit longer at low rpms and at higher RPMs it would float over like whats shown in red. i'm guessing that that would just break stuff though
here is a drawing
http://img18.exs.cx/img18/2207/gogogo4mk.png

 

Yeah, it would "break stuff". The idea has merit, but the execution probably doesn't. Look at Honda VTEC variable lift/duration. Of course they need to do it on OHC, but basically they change lobes at a certain rpm.

Of course there is always the old standy, the RUBBER CAM LOBE. You put a little heavy metal inside the rubber lobes near the max lift point and as it spins faster the lift increases due to "centrifugal force"! If you asymetrically loaded the rubber lobes with heavy metal, couldn't you get asymetrical valve motion AND variable duration?

JK, of course!