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Hyd roller VS flat tappet

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  • Hyd roller VS flat tappet

    On just about every forum this topic comes up and usually gets peoples bowls moving. Let me start of by saying I don't claim to be an expert but like to follow along on this topic and enjoy reading people's opinion. What me feeling on the topic is this. I'm not convinced to spend the money on a hyd roller. As I understand, the big problem with them is their weight and somewhat limiting RPM to slightly above 6,000 RPM. It would seem to me that despite the advantage of a roller tappet to follow more agressive profiles, it's usable profile is going to be determined by the RPM limit due to the roller tappets increased weight. Sure there are 5.0 guys spinning a lot faster with hyd rollers but that's a whole different story IMO.

    One can argue that you can install stronger springs but again from my understanding this has a negative effect by the spring's pressure trying to collapse the tappet, reducing net duration and lift. According to an article David Vizard publishe in PHR a few years ago, a flat tappet actually has the advantage in duration VS lift over a roller up to about 280* advertized duration at which point the roller has it. As I see it the roller can make more power then the flat but up to a point. With modern valve springs, a fla hydraulic tappet can really be buzzed without valve float or harmonics effecting the springs and valve seal. Since the flat tappet either solid or hydraulic has lighter mass, it has a much higher RPM ceiling, hence making more power then a hydraulic roller since more RPM equals more power.

    I think the difference in cost between a hydraulic roller and a hydraulic flat tappet is substantial, the savings could be used elsewhere to offset the hydraulic usuable range advantage, such as going towards a set of heads. My feelings are this, if I were to go use a roller cam, I'd go for a solid roller where the added spring pressure needed to follow the lobe is some what of a non issue since it's not going to collaps a tappet.

    The OEM's such as Ford started using hyd. rollers only because they offered less friction. But in my opinion this is true when comparing net lift cam timing at the valve where both the flat and hyd roller would have exactly the same numbers. The main purpose of a roller is to follow more aggressive profiles that a flat tappet can't, not for reduced friction as I see it. I recall reading on another forum or someplace where Ford tested the 82-84 Mustang cam agasinst the 85 & up roller and both were almost exactly the same.

    While harking on friction, just how much less friction does a hyd roller offer compared to a flat tappet of similar specs? I recall a rebutal from a Pontiac engineer once wrote about the friction difference between a 400 & 455 main bearings since the 455 usess a 3" journal and the 400 uses a 2.5" IIRC. He said the difference was negliable. He went on to state if I remember correctly that the piston and ring pack of a typical engine accounts for about 50% of friction, bearings were about 25% and the cam, valvetrain was about another 25%. If I were looking to reduce friction, I'd be focusing on the pistons by using metric style rings and a coated piston.

    I'm not trying to come off sounding like an internet expert but rather my own personal reasoning why I would or would not use a hydraulic cam. Sure, I believe that a hydraulic roller will make more power over a hydraulic flat tappet but I believe that is with in a limited range. I think it would be interesting to see a back to back test with all things otherwise being equal which make more where. Could a hydraulic flat tappet with a right set of springs that allowed it to spin to 7,000 make more power then a hydraulic roller? Especially with Chrysler, Ford or AMC's that use a larger .904" diameter tappet to that of a GM's .874".
    Tom
    Overdrive is overrated



  • #2
    Re: Hyd roller VS flat tappet

    I have a hyd roller that I spun 7000-7200 every time. I don't think the hyd flats will make anywhere near the same power. btw, i set mine at 0" preload. it's even been suggested to use .006" lash but I passed on that.

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    • #3
      Re: Hyd roller VS flat tappet

      I am a rookie. That being said, I will pretty much only run rollers from now on for durablility reasons. I might run a flat-tappet hydraulic in a stock rebuild. However, in the past couple of years I have wiped out a number of flat-tappet cams (hydraulic and solid) and *wimper* don't like them any more. I feel the extra cost is a worthwhile investment, and flat-tappets are high risk. Furthermore, solid rollers with proper poly-locks seldom need adjustment, in my limited experience.
      The official Bangshift garage door guru. Just about anything can be built using garage door parts, trust me.

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      • #4
        Re: Hyd roller VS flat tappet

        I'll take rollers when I can get 'em (I'm really happy with the Comp in the 'Stang) but this was not an option on the six. So I'm going with flat solids. I've been following the thread on proper zinc-laden oil in the HR forum a few weeks back, and that seems to be the key to keeping them alive. I'm guessing I should order a case or two of Brad Penn (I think they said) which has the old zinc content. This oil deal may be why your flat tappet cams failed. Evidently, even Rotella T has had most or all of the zinc removed.

        Later
        Dan

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        • #5
          Re: Hyd roller VS flat tappet

          Rollers probably have the advantage after a certain point. If it's a mild motor, say 220 at .050, you'd be wasting your money on a roller IMO, other than for reliability. Rollers of course cost more than flat tappets. I donít think ramp rates and spring pressures for mild cam motors will kill the cam too quickly, not taking into account poor cam manufacturing. For motors with more thump, and assuming the person opening the wallet has the cash, a roller would surely make more power. Maybe 20-40 horsepower comparing similar grinds, flat to roller??? And you can get a motor to rev with rollers, especially solid rollers, IMO. I personally stick to flat tappets. Mainly because I donít have usually have the cash to hand out and Iíve made good power with flat tappets.

          Furthermore, solid rollers with proper poly-locks seldom need adjustment, in my limited experience.
          In my limited experience, this is true. And, furthermore, solid flat tappets rarely need adjustment as well. At least in my limited experience. 8)

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          • #6
            Re: Hyd roller VS flat tappet

            I think flat tappets can have a quicker starting ramp than a roller but can't ramp them up to max lift quite as fast. If you want a lot of lift without too much duration, a roller is a great option. I agree at anything under 220 @ 0.050 and 0.5 lift, the benefits of a roller aren't too significant. If you're heads flow a lot more at .6 than .5 lift and you don't want 3K+ stall (or a lot of duration), a roller can be a great option. A solid roller helps the max rpm limitation, but if your valvetrain is setup right, you can rev 7K without problems with a hydraulic (I hit my 6600 limiter hard and often with a relatively mild hydraulic roller).

            Tampa, FL

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            • #7
              Re: Hyd roller VS flat tappet

              Ditto.


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              • #8
                Re: Hyd roller VS flat tappet

                on the zinc thing i found 10-40 oil at wall mart that meets spec sf 1989 and older excell oil or such cheep 1.29 qt wont use in a race motor but in my D D junk.

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                • #9
                  Re: Hyd roller VS flat tappet

                  spend the dough on a roller
                  you can get roller lifters in the junkyard

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