MILD THUNDER

iTrader: (3)

Got a couple cam questions, or basically looking for some results from some of you guys. I noticed the trend lately with some guys is Lift is increasing, spring pressures are increasing, rpm's are increasing etc. Recently been seeing some of the spring pressures of 550-575-600 open on hyd roller setups.

I had always thought, that increasing lift, netted a penalty in spring life, guide wear, etc. Not long ago, it seemed as if you were running a bbc cam, with .370 lobe lift, that was considered a substantial amount of valve lift (.630 with a 1.7 rocker). Now, I am seeing custom hyd cams going in pleasure offshore engines, with lobe lifts of .400 or even larger (.680 lift).

The understanding to me was, that for endurance stuff, as duration grows, so can valve lift. But, short duration cams which we often run in boats, with high lobe lift, make for a very steep lobe. When the lobe becomes so steep, you now have the concern of lofting the lifters over that steep nose. To prevent that from happening, you need lots of spring pressure on the open side to control the valvetrain. So that may explain these nearly 600lb over the nose hydraulic setups I've been seeing, and the demand for very rigid pushrods, and lifters that can handle all that pressure.

I've been paging thru master lobe catalogs, and there is certainly not one lobe design for all applications. In other words, a profile that works well in NHRA, certainly may not be the profile you want in your marine engine hoping to get 300 hours from your valve train. Aggressive lobes can obviously make great dyno numbers, and open and close those valves extremely fast, but, at the expense of beating the crap out of the rest of the valvetrain. That is certainly something I am not interested in for my engines.

Is there anyone running these .400+ lobe deals with 250-300 hours without issue on a typical bbc journal with .842 lifters? My next cam's I am considering going with more lift, but not sure I want to accomplish that with a larger lobe, or a smaller lobe cam designed for 1.8 rocker ratio, and possibly not need solid roller type spring pressures for a 6,000RPM endurance build.

14 apache

iTrader: (1)

Best thing to do is call some cam grinders maybe ones with spintron machines. If it was me I would run a solid roller I think with less moving parts might make it more reliable plus you can monitor part failure like a lifter wheel starting to go south. And you have more choices of lifters to go with maybe a .937 lifter for long life. And a 55mm cam core. This is just my thought.

Black Baja

iTrader: (2)

Joe, you really aren't going to gain much with the smaller cubic inch blower stuff moving up to a larger lift cam. Why not just speed up the blower a little and make more power. You are 100% correct more lift = more work for the valvetrain which means more maintenance. I've spoken to a builder that has an engine package with over .800 lift and they have nailed down the valvetrain maintenance to valve springs and lifter inspection at 120 hours. This is using a big cam core and .937 lifters which drastically reduces the pressure angle on the lifter. A 1.8 ratio rocker on a BBC is a bad idea in my opinion. What ends up happening with the higher ratio rockers is the pushrod, lifter and cam loose the leverage from the rocker arm this in return puts an immense amount of pressure on the cam side of the valvetrain. I had the numbers months ago it would blow your mind just how much more pressure it puts on everything. It's always better to have more lift at the lobe than stepping up to a higher ratio. From what I've been told when it comes to a BBC valvetrain guys usually over spring on the seat and under spring over the nose. My new cam has a .462 lobe we are trying to get an oppointment for the spintron right now. Was told with my setup we should end up somewhere around 160 closed and 675 open. This is a solid roller setup.

Rookie

iTrader: (4)

Joe, Obviously I am no expert and I know I will get flack for saying this. But, first thing I would do is get your heads on a flowbench and see how they perform and what they like. Use someone that you trust and knows how to interpret how the heads react. (I know a flowbench is an archaic tool and has no relevance in the modern era) If you flow 380 cfm @ .0630" and 382 cfm @ 0.680" is the extra lift worth the 2 cfm and maybe cost valve train stability. I know when my heads were ported they were ported to to get the most cfm of air around 0.650" (404 cfm on ~310cc heads). I have seen similar heads flow 420+ over 0.700" but that is not in the usable lift range that I wanted. That engine runs a mild HR cam with 1.85 intake rockers and 1.80 exhaust rockers and has over 200 hours on the engine.

Just my uneducated $0.02

Also, I run 1.8 and 1.75 rockers on 0.380" lobes with solids on a HR cams. I do all things wrong...

Rookie

iTrader: (4)

Your build just seems wilder and wilder every time I read about it. This is going to be cool when complete.

Bawana

Joe. who is running 600lbs on hydraulic lifters? I was told anything over 500lbs will sink the best of them. I was always told that; more then needed spring pressure = short valve train life, and will rob power.

MILD THUNDER

iTrader: (3)

What I have heard, in regards to lift, mainly on the intake valve......and it may not be true, but

lets say your heads only flow 400cfm at .700 lift, and 402 CFM at .750 lift. One may assume that there is no point in going with .750 valve lift, because the CFM gains arent there on a flow bench. However, on a running engine, the valve is only at peak lift, for a very short period of time. So, by going with the .750 lift , you will see a power gain, because now the valve see's a longer duration of time, around .700 valve lift. This is sort of why low lift numbers are just as, if not as important as peak lift numbers. This is where the flow bench vs running engine gets fuzzy as far as picking a cam...

I think it is pretty rare, to see a power loss, on a bbc with good flowing aftermarket heads, by going from .630, to say .700 lift on the intake. Of course if you got some old truck peanut ports, thats a whole different story. Exhaust, not as important when it comes to lift. This is why, the trend has been going with cams with more intake lift, than exhaust lift, and why usually most bbc's respond better on the dyno, with a higher ratio on the intake only.

Another area of camshaft stuff I am learning, is that there are many factors that can go into designing a lobe. A lobe should be designed with the rocker ratio, lifter body diameter, lifter wheel diameter, as a package. As well as, the application it will be run in. The way I understand it, as far as lift vs duration goes, is a lobe with .400 lift and 240* @ .050, will be a more aggressive lobe, than .400 lift, with 260* @ .050. Theres obviously alot more to a cam design, that just .050 numbers, lsa numbers, and lift numbers.

For a guy like me, with a small cubic inch deal, a 260* duration lobe, just doesn't fit the bill for an engine that isn't going to exceed 6000rpm. . So, if I was to go with a 236ish lobe @.050, and wanted a .400 lift lobe for a 1.7 rocker, I'd have a very steep lobe, and need more spring pressure to control the valvetrain. Seem's to make more sense, if I went with a lobe with less lift, and 1.8 rocker ratio, I'd be able to run less spring pressure because my lobe is gentler, and have a setup that's easier on the lifters, less side loading of the lifters, etc etc.

Black Baja, I get what you're saying about mine just turning the boost up a bit. This question is more along the lines of , when I tear down, if I am gonna be buying cams, or making changes, just like any build, we all want the best power and best reliability. Plus it also pertains to some friends stuff I am always involved in. What I don't want, is a drag race profile, that beats my valves off the seats, excessive spring pressures, and a valve train that barely can make 100 hours, but looks good on a dyno. I was under the impression from what some of the nascar car guys are doing with extreme rocker ratios, is that less lobe lift and more ratio takes stress off the pushrod side of things, allows them to turn serious rpm with minimal spring pressures, and still get their big valve lift?

Good tech talk guys

Rookie

iTrader: (4)

I understand what you are saying. It gets into piston speed, time at each lift interval, dwell and other stuff. I know mid lift #'s are important but all of that other s#it plays a role that I leave to the experts. I love this engine build stuff, but I am a polymers engineer and deal with the flowability of non-newtonian fluids not air. lol

14 apache

iTrader: (1)

I think nascar is limited to flat tappet camshaft that's why the will run around a 2.0 rocker ratio they can not get a lobe to do what they want in a flat tappet.
What kind of power you make now at what rpm CID?

Black Baja

iTrader: (2)

Joe, if you can get your hands on a 1.8 & 1.7 rocker. Hold them up next to each other. Where the difference in ratio comes into play is the pivot point of the rocker. The higher the ratio the closer the pivot is to the intake side. Try to think of the rocker as a pry bar. When you pry on something in order to get more leverage you need the pivot point closer to whatever you are trying to move (in this case the valve) the closer the pivot point is to the valve (1.7) the more leverage the cam lifter and pushrod have. 1.8 rockers on a BBC with a hydraulic lifter are a nightmare (for me) my hands are so beat up calissed up it's difficult to get any feeling on the pushrod. With a 1.8 rocker the pivot is so far back to the intake side you really can't even get you fingers on the pushrod to spin it and feel for resistance. It's not bad with the intake manifold off but with it on good luck. Also when you move to a 1.8 you have to machine the pocket on the guide plate deeper (exhaust if I remember correctly). Just some words of caution and things to think about. If you really want reduced pressure angle stepping up to a 55mm cam is the way to go. The larger diameter lifter with bigger wheel helps but only a couple percent compared to the larger cam core. With the larger core it puts the lifter up in the lifter bore and keeps it there very well supported. I was wrong on the lobe lift in my last post of my cam it's .472 [email protected] with the .937 lifter .850 wheel it gives it 3 degrees of duration. So the intake would actually be [email protected]. This is for a 632ci motor. As the cubic inches and air volume demand increases so does the ideal lift of the cam. With AFR 385's the motor actually wants .941 lift at the valve. I don't know about you but that scares the u know what out of me and with the 55mm cam and any more love lift on the cam I don't think I would have any connecting rods left on the even side of the motor. I had to get into the rod bolt pretty good to get the rod to squeeze by the cam and that was using rods designed for extra cam clearance. My buddy that builds very large cubic inch motors always told me its not a real motor unless you have to use an angle grinder to build it.