I would add to that 'if the engine is being somewhat cam starved, then it would be important not to disregard low and mid lift numbers and how the area under the curve helps the cylinder fill' If one is on the other end of things, head limited and using more cam yet to achieve goals, then killing off low lift flow for higher mid and max lift gives the combo much needed margin from an over cam situation in which the induction flow is stalled from too early of a valve opening and/or too much low lift flow.
They have to be pretty serious cams to exceed the action of a solid with a high rocker ratio. As a comparative...I don't consider sbc rollers over a solid until .050" duration gets to the 265-275 range and over .600" lift, but that is largely because I have the luxury of getting what I need from the port. Frankly...I'd rather see a portion of the costs of the roller go towards the head porting and end up with a better 'working engine' (more responsive, better driveability, mileage, etc.) knowing that the cam is a smaller part of the behavioral picture than the head. Beyond that point (cam duration increasing) you are wise kill the 'off the seat to low lift', similar to how a 50* valve job would and negate the effects of the seat to seat duration being so much.
Is there a downside to a lot of ratio with a roller rocker? Since Tom's rockers will vary the ratio depending on the pushrod length, you could theoretically have the same lift/duration/open-close rate AT THE VALVE by either using a more radical cam with a 1.6 ratio rocker, or a milder cam profile with a 1.9 rocker ratio. The valve would see the same action with either setup. But would the required valve spring be different for the two setups? I'm thinking having the higher lift in the cam would throw the weight of the lifter around more (increased kinetic energy) and would require a stiffer spring than having a higher ratio rocker do the work. And which setup would produce less wear on the cam lobe.... The force of a softer spring multiplied by a 1.9 rocker ratio, or a faster rate/higher lift cam lobe pushing a stiffer spring thru a 1.6 rocker ratio? I'm leaning towards using the higher rocker ratio but I'm not aware of real world problems with this option.
for high lift solid rollers on the nail head, they will need the heads to support the high lift. on smaller size roller cams a flat tappet offers as good or better area under the lift curve. the fast ramp flat tappet will have higher acceleration rates on initial opening and closing. where the roller shines is in high duration cams and engines needing high rpms. over 6500 rpms i would think the roller comes on. if i needed high lift and high rpms the extra cost of a roller would work.
Walt, great Q's. I haven't studied those limits or been subcon'd to develop valvetrain beyond a small batch (not intended to be mass marketed). The things I've worked with...have worked for their application. Not sure if we'd ever see the downside to any of those things, the nailhead isn't going to be used in an extreme enough environment to push those limits, if learning from other engine families and where they have failures. One reality is that you can only go so much lobe lift on the cam core before having to bore the cam tunnel. There seems to be plenty of examples in the automotive/industrial world in which one method or another is employed as a measure to either overcome some original design limitation or for ease of production/cost reasons. They might just use one method because it works nicely for that application. (I recall reading something about the original racing roller rockers being made that way because of the inability of whoever to harden the tips properly on the shoe style??) I have boxes of rocker sets from 1.8-2.0 ratios that are intended to exceed 1.5M(?) cycles, 9000 rpm for 3 hrs straight... Industrial engines equal a million miles or more with various slider/roller mechanisms and although run at slower speeds, may have more travel to each cycle than a hot rod engine. Engine Masters entries (high ratio trend) have been hit and miss for valvetrain control and possibly demonstrate what the hot rodding world faces most often...lack of R&D and consumer confidence in unproven methods. Gsgtx, other engine types that are already head restricted benefit from the roller by providing more degrees of engine rotation at the higher valve lifts, which is beneficial to street driven vehicles due to the smallish induction system's keeping responsive and the fact that cam events intended for higher rpm do not raise the peaks beyond the induction system's velocity limiting speeds. It doesn't matter which engines you prove this on, it's been long proven. This stuff is well accepted and proven, not the opinion of some guy on the net (BTW, that's the same strategy as using a solid with more ratio...it isn't the lift we are after or how the head flows at that lift. It's holding the valve open longer while it's at peak flow [square lobe thinking] ). Nailheads just haven't had people show many dyno sheets because there aren't products being made that require that type of 'proof' to market themselves. Most Nails are put into nostalgic rods for reasons other than extreme performance.
I am going to be running the same cam gsgtx is running in his big engine. Right now I have a set of toms rockers and 8.75 length push rod gives me .515/540 lift. My 8.85 push rods gave me .545/570 ish lift. My goal will be to run about 575/575 with this same cam, it's on a 109 lsa. 230/235 at .50.... That's as big as I would like on the street. Will be finishing my new set of heads this winter for next spring. They will have a little more air across the lift at every lift. They flow somthing like 77/140/182/215/233/246..... That's on a 4.00 bore adaptor. They are a 2.0 Mcsa almost straight through .1.94 intake vale and 1.50 exh. My concern is keeping my compression up and if they will be lazy or not. The engine is 430 cubes. Got 3.73 gears and 2004r tranny. That will be next spring. Also the 4.00 is the bore adaptor, on my phone and it won't let me go back and change it. The cam is going to really wake up with the longer push rod to get that lift. The ratio will be around 1.8 or something . Wondering if a lot of duration would help?
Also that 575 lift put about 225 cfm to the valve with the intake on the head when flowing them. Not much more at a full 600 lift
Cool! Now you are getting to a point where the sims would show potential shape changes to the torque curve relating to matching compression to duration. I'd been thinking that you might just be trading numbers around the curve without a significant change. Thinking that you weren't raising compression then you could only go so far with duration, but keep in mind you have enough flow with the new heads/top end for over 500hp. A drastic change in duration would make a really different engine out of this. I guess how far you wanted to go would depend on how much idle to wake up point you don't care about. Some like more of a gentle broad curve with it barely getting to the number making it forgiving to tune and drive, others don't mind pushing things a bit for the 10% more intense powerband you get with more overlap and duration. It's quite do-able to keep a cantankerous idle and sharply stepped powerband and still have plenty of grunt down low. That's the gift of a small CSA induction on decent sized cubes if you don't go way too far. Rougher idle in these cases doesn't automatically equal lower response or torque, they wake right up stronger than stock with smooth idle anyways.
My whole goal is to peak around 5300 and try and hold that till about 5700 or 5800. The 2.00 Mcsa . For those that don't know there is no push rod pinch in the intake runner .the 2.00 might make that a little higher. I am not interested in this engine reving higher than that. I would like it to come on hard and fast, that's always fun. It is nice to be able to adjust the lift of this cam with toms rockers by length of push rods. This should be fun,
Heavy overlap raises the curve sharply and it drops fast after peak, the danger always is drawing too much, but not really... I personally don't think there are any off the shelf cams able to do that here. The direction Nascar and Prostock took to get to where they are now was to go 'too far' on overlap and then shrink the exhaust side down while increasing the intake side. Reducing the overlap reduced the VE because of how it initiates the intake tract earlier in the cycle. I think this can be applied nicely on a Nail because the exhaust side is weak and I'd challenge anyone to see evidence of too much overlap hurting things. I also think most mis-apply what works for other makes, such as LSAngles and behavioral interpretations, and the reasons for those specs. Working with 2.0" CSA at face value and no measurements, a quick and dirty calc puts peak torque via the port hovering 3750 (425fps), peak hp near 5300 (600fps). [Tough to stretch past that but the long rod or wider LSA would help it hang on past peak] One thing I'd question right off the bat is the velocity observed in the corners of the port on a Nail. I thought I'd read elsewhere that you had done some probing in those particular ports, so maybe shrink the number used for the calc enough % to get a more realistic rough starting point for the effective flow area. [Tangent...using the valve to guesstimate wouldn't be realistic as a 1.940" would range from 2.28-2.44" in2 based on 88-91% throat, obviously the port itself is more of a choke.] Based on the architectural limitations of the Nail's port it should be expected that the effects of cam would serve to swell the torque curve around those choke points, rather than the (very misleading at times) simulations based on valve size and CFM actually moving the peaks so drastically based on cam events. Having greater CFM potential than the intended power goal usually just helps raise the VE ...if it actually gets into the engine due to cam restriction or if overcammed greatly to the point that it stalls the flow. (you won't with these small cams, look at how much valve opening you have when the rod and crank are at 90*...if you aren't already noticing a dead range at the bottom of the powerband due to excessive cam duration stalling the flow, then you are still restricted by cam.) That being said...more ratio, more degrees of rotation at max lift, roller profiles, and more importantly...the ability to feed a starving cylinder at max piston demand, gets you what you are looking for without shifting the entire curve up. I loosely recall your previous dyno curves and strip tests already doing just that when you factor out the conditional variables and the BS numbers they gave you. Even if it still pulls past the rpm you have in mind, the goal is to have more output along the way. Short rod and more stroke looks more attractive now, doesn't it? As far as low lift flow...once you are worried about over camming the powerband the idea is to kill off low lift flow. continuing to go bigger in valve diameter beyond the port's restrictions (which helps low and mid lift) or using valve angles and geometry conducive to off the seat to low lift flow will exacerbate this condition, especially with an overlap strategy serves to keep the depression strong that pulls upstream to the carb. That's how you can use an aggressive profile AND keep a strong bottom end. If the cam is restricting the powerband low lift flow helps, but it's begging for a more aggressive cam. Both strategies work.
Lots of good info and opinions f85. I can say this cam thread does need head work discussion. I all ways read more rpm can mean more hp. So when joes stroker was running a 12.87 and peak hp was at 4500 with the comp cam he sent me the heads. They had been ported and I looked at every intake runner and only one was even close to what was claimed. Knowing they did work good I didn't want to ruin them so I evened them up with the best runner as I could and opens Mcsa a little . We were wanting more rpm. Ended up running 1257 and peaking at 5200 and holding on awhile. To tell the truth I thought we would gain more hp up top. Only added 5 to 431. Did drop tq. Who knows if the dyno was right. Heads do help control cam
The heads dictate the end results, the cam influences it. I'd say your work on those heads illustrates my above comments and estimate of port velocity limiting power peaks nicely. FWIR discussing this on another forum, the later dyno #'s you were comparing were inaccurate but I can't recall if there was any effort into a guesstimate of how much. Using time slip data with mph and factoring out DA might suggest the real difference. Either way...the time spent at peak hp is much less than below that. Gains from shift recovery up past peak torque would certainly influence drag strip results. Comments on longevity with more lift, etc.... I know for a fact that a .580" flat tappet cam can go 125k miles with a stock type BBC spring and valve, no rotator. This is with significant time over 6000 rpm, countless times a day but in a street driven or road course type manner. Not Drag only. The springs themselves should be replaced every 50-60k at that abuse level. I would estimate a beehive or better quality spring would do better but at the same time I'm going to say that there would be almost no way to duplicate that level of torture and still hope to have a drivers license or stay out of jail. Anyways... the Nail valve is lighter along with the spring so you'll have to consider that.
Lol, sorry gsgtx. A cam thread will lead to head talk. Let's get back to the cams. Just waiting for your new cam
It's tough not to impart relevant induction info in a cam discussion. The point of the cam's events is to time what the heads do. All it takes is to plot out the engine's rotation by degrees to study average out the flow across the valve's opening to see that simple changes to the port would have a greater effect than the cam, which is what 'behavior' is all about. 2 different valve jobs could have as much effect as a minor change in cam specs (different ports on the same engine even!). From that...I wouldn't purchase a cam very similar to another and spend the time swapping to tweak some effect on a mostly street driven car such as a couple hundred rpm. A bit of planning to arrive at the final destination saves tons of time and $$. Greed and how far to go are different issues altogether. An induction guy is always going to rearrange the questions a bit.
I'm running a Poston NH600 in my 66 401 with stock rockers, stock porting, and adjustable pushrods. 108 lobe center, duration intake 310. duration exhaust 320. intake lift .520 and exhaust lift .523 and I was making good power to atleast 5,750 RPM before Bobs head work and roller rockers. I do sacrifice some low end torque but she wakes up real quick at 2,800- 3 grand then revs like a cutoff wheel. I'm hoping to pick up roughly 500-600 RPM when I get my heads back from Bob and install the roller rockers. Before the rollers and head work it idled at roughly 900 rpm in park and 750-800ish in gear. I can easily drive this cam on the street with the 3,500 stall converter (definitely not a smooth idle though) She smooth's out at about 1,500 ..Double roller cam advanced 2 degrees as well. 66 buick guy Mike
