Rev Kit Please Answer Question!

Discussion in 'High Tech Retrofits' started by lluciano77, Jun 25, 2006.

  1. camdoc

    camdoc Veteran Member

    Messages:
    452
    Likes Received:
    0
    Joined:
    Nov 16, 2002
    Location:
    Bangor, Maine, USA
    What is float?

    The lifter supplies the motion from the cam to the remainder of the valvetrain. If the opening NEGATIVE accelerations are too high, the resulting motion is valve loft, and can be desirable in some situations.

    Valve bounce can occur as a result of valve loft, or because you are trying to run a lobe faster than it was designed for with a given spring package. Sometimes valve bounce will get worse as you increase spring load due to valvetrain deflection.

    The valve spring is the only member returning force to the camlobe. Remember Newton? F=ma ? Basically, the spring is there to supply the F, the valvetrain mass is the m (although you can't simply add all of the masses up because the pushrod and lifter are on the other side of the rocker arm) and the a (acceleration) comes from the cam profile and is the main design focus of the designer. (Jerk, "snap, crackle and pop" make for more elegant acceleration curves)

    Saying that valvetrain no-follow (bounce, float, loft or whatever metric you wish to use) is only defined by valve bouncing misses some of the more important issues. All motion is initiated at the lifter foot, and gaps in any of the valvetrain linkage will result in undesirable valve motion.
     
  2. Tokyo Torquer3

    Tokyo Torquer3 Veteran Member

    Messages:
    2,187
    Likes Received:
    3
    Joined:
    Oct 14, 2003
    Location:
    NJ
    I have already been thru a valve float issue and I will tell you a rev kit did absolutely nothing for me. This is what I learned..

    -In my case, the valve was bouncing off their seats.. the faster you open a valve, the faster it closes. Neither AFR nor Comp realized that I needed more spring to account for the 12-14 pounds of boost on the back of the 2.02 intake valve. That's about 30 pounds of pressure on the valve effecting my seat pressure. I had bad valve float at 5800-6000 rpm with my tiny roller and it would pop and run rough until the hydro lifter pumped back up again.

    -With a hydro roller, always go with the highest seat pressure a hydro lifter can stand regardless of the rev kit; 140-150 pounds. I went with 145 on the seat with spring presure very similar to what they are recommending for you for seat and open (140/360). This cured my valve float and I rev to 6300-6400rpm with no sign of valve float, but wouldn't push it any further.

    -SEAT PRESSURE is your key for most mild/ average hydro roller cams! Our cams are not big enough to launch the rollers off the lobes of the cam and require a rev kit which holds the rollers on their lobes.
     
  3. Tokyo Torquer3

    Tokyo Torquer3 Veteran Member

    Messages:
    2,187
    Likes Received:
    3
    Joined:
    Oct 14, 2003
    Location:
    NJ
    also, I only use 1/4 turn pre-load on lifter and no more.. that helps too.
     
  4. camdoc

    camdoc Veteran Member

    Messages:
    452
    Likes Received:
    0
    Joined:
    Nov 16, 2002
    Location:
    Bangor, Maine, USA
    If you are using GM lifters, you would be better off driving the plunger all the way down to the stop, then unloading it 1/2 turn. The less oil you have in the plunger cavity, the better.

    Good post about boost and spring pressures. I'm a bit suprised that Comp didn't give you the right advice, that's the danger of tech line "experts", some are good, others are still learning.
     
  5. jakeshoe

    jakeshoe Veteran Member Lifetime Gold Member

    Messages:
    8,884
    Likes Received:
    21
    Joined:
    Dec 8, 2000
    Location:
    Republic of Texas
    Goat,
    I'm not trying to run you off. Don't take offense. My last post was probably too smart assed. (Full time work, full time college, too many projects, wrecking the Chevelle last week, etc makes me a grumpy dude). Sorry if I offended you.

    Back to the numbered response system we had going.
    First me say i think you understand what's happening but you're oversimplifying it in your initial post and in doing so you're making an incorrect or maybe a better word is incomplete statement. Let's assume our discussion will help someone learn.

    #1. The valvespring must control valve motion. The "normal" definition of valve float is that the valve bounces off the seat. Since this is the normal phenomenon the primary thing to control is the valve. If you control the valve, all else SHOULD follow as it is more or less a linkage as you stated.
    So in effect it does keep the lifter on the cam but only because it SHOULD be controlling the valve.
    If the lifter is the cause of the uncontrolled valve motion and the spring is keeping the valve and associated valvetrain parts linked together, then yes a heavier valve spring would solve the lifter "lofting" issue but isn't a realistic option on a hyd roller.
    My main point was that you shouldn't look at the valve spring as primarily controlling the lifter, because the lifter isn't usually the primary cause.


    #2 Stating the valve doesn't care is in my mind saying it's not really a factor, that the lifter is. it goes back to #1. Obviously the valve has no "feelings" :)
    If we werecomparing an overhead cam engine with no pushrod or lifter to control, I don't think the spring requirements would change much for a given valve assembly weight. I'm sure that the spring requirements are pretty well known for a given valve weight and velocity. Tokyo brings up an interesting point though with the greater intake pressures.
    Summarizing this, I believe that the valve is the harder element to control than the lifter or other valvetrain pieces. The lifter has to accelerate and decelerate, however it has ramps to do so. The valve accels/decel's quicker due to rocker ratio and when it comes to a stop, it's pretty sudden..Smacking a valve seat with an aggressive profile at 6500 rpm has to be a tremendous amount of shock/bounce. If you've ever ground valves and just dropped them on the seat from a nearly fully extended position, they bounce...
    As I stated earlier, hyd rollers weight does become an issue at rpm so controlling the valve may not be the issue.

    #3 Indirectly, it exerts force on the lifter through the valve. Back to #1, if the valve isn't controlled, nothing is. So yes it does exert force on the lifter if everything is working as it should. You mentioned in a previous post, what were you missing, because you had a 400 lb spring, reduced by 100 lbs, then added the 100lbs of tension back with a rev kit spring. Simply pointing out that the missing part of your equation was the rocker arm ratio.

    #5 Yes the forces add up, but not as you originally showed, and not what I would phrase in parallel due to the ratio multiplying. It all goes back to #1 where the problem becomes not having enough valvespring on the valve. If you control the lifter, but not the valve, in a case of valve float, you potentially lose the pushrod. Ruined pushrods and rockers result. I would rather play it safe and keep adequate spring pressure on the valve here.

    #6 My response was to your reasoning that valvespring pressures could be reduced and compensated by the rev kit spring. Back to #1 again. If the lifter is the issue (which it could be, but usually isn't) then this would work.
    However the valve requires a certain spring force to control it. No matter what you do to the rest of the valvetrain you can't controll the valve unless you positively attach the parts together so that the rev kit spring would contribute a force to the valve.

    I can definitely see a rev kit helping an aggressive hyd roller setup gain some usable rpm, however if you are using the correct components the gains seen would be in the rpm range where you typically would start looking at other options.
    If you are taking the motor to 7000 rpm often, you probably need to step up the maintenance program anyway, so lashing valves shouldn't be a huge issue.

    I'm cool. :)
    On a side note,
    anybody that needs to install rev kit springs can use a door spring installer tool, about $8-9 and works great.
     
  6. Tokyo Torquer3

    Tokyo Torquer3 Veteran Member

    Messages:
    2,187
    Likes Received:
    3
    Joined:
    Oct 14, 2003
    Location:
    NJ
    Cam Doc,

    That is the first time I had heard that recommendation, but it sounds like the same theory as the newer Comp race lifters with limited travel, kind of like a cross between a hydro and a solid lifter. I would think that if you tried to do that with stock lifters, the geometry would be all screwed up with it cranked all the way down and that a different length push rod would be necessary. I would also think that it would make for a noisy valvetrain (I hear the comp limited travel lifters are a bit noiser) and that there would be many cases where you end up with valves not fully closing as it is not uncommon to have a valve hang upon when someone over adjusts the rockers, and it is fixed by backing off the adjuster nut. Does this work well in practice?

    I no longer have faith in tech line experts, especially the ones at Comp. Bad info can be an expensive and frustrating proposition in our hobby and there is too much of it rampant in the engine hotrodding world. I have had to learn the "hard way" too many times than I care to recall.
     
  7. lluciano77

    lluciano77 Guest

    I have heard those race style hyd. lifters wear out the cam faster. If I am not mistaken they are not recommended for the street due to wear.
     
  8. Rick WI

    Rick WI Veteran Member

    Messages:
    10,400
    Likes Received:
    1
    Joined:
    Jul 9, 2001
    Location:
    Madison, WI
    As amazing as it may sound at Companies like Comp, Edelbrock, Crane and almost all other large organizations there are many many competent people that know way more than most of us in their given field. The problem is that those people can't answer the phone all day with 99.9% of those calls being pretty meaningless drivel. Like, can I run a 292 duration cam in my stock 305 that burns oil.

    If you really have a situation that is a real issue with a companies product ask to be put through to Engineering or R&D. When you are a dealer there are lots of advantages when it comes to tech support. One of those is not having to talk to the same folks the average joe does. The 1-800 number goes to a persons desk, not a call center.

    Now your other option of course is to discuss this with the company or business that sold the part to you. They buy the product at a discount, put a markup on it and sell it to the customer. They should be the first call. If it's Jegs or Summit that's the downside of ordering through them. Not quite ready for prime time tech support.

    Your other option is at some of the large trade shows and events like Power Tour most of the heavy hitters from the Comanies will be there. Get to know them and get their cards for future reference. On Power Tour last year we BS'ed with Scooter from Comp for over an hour and 3 beers. Learned more about lifters, cams, plans for RHS and the industry than I thought I'd ever know. Plus made us a hell of a deal on our Jobber program.

    The people are all hiding within the walls of the Company that can solve most any problem I have seen on the board. You just have to weave your way through the gatekeepers and get to them.
     
  9. Goat

    Goat Veteran Member Lifetime Gold Member

    Messages:
    1,913
    Likes Received:
    44
    Joined:
    Jun 7, 2001
    Location:
    moncure, NC
    Jake, no problem. I too get a little frustrated trying to communicate on the internet sometimes. It's not like you can stop someone in the middle of a sentence to correct a misunderstanding. Like anything else, you learn to pick out the stuff that's beneficial and disregard the rest (try to anyway:) )

    You're cool with me.;)
     
  10. camdoc

    camdoc Veteran Member

    Messages:
    452
    Likes Received:
    0
    Joined:
    Nov 16, 2002
    Location:
    Bangor, Maine, USA
    An OEM GM lifter will collapse before it pumps up. Topping of the plunger to avoid pump-up does not apply to the GM style lifter, but, the column of oil and entrained air captured under the plunger acts like a mini-spring. If you minimize the volume of oil under the plunger, you effectively make the lifter "stiffer", and it will run to a higher RPM. You're correct, you still need to check for proper geometry.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.