I've seen this done many times, and I don't get it. If you need more spring pressure at the seat, why not just add spring pressure? To me, the extra weight of the rev kit adds is a big negative, and should be avoided.

What am I missing?

 

the extra weight of the rev kit means nothing it makes for a much more stable valvetrain at high rpms. too much spring pressure is bad for the valvetrain. thats basicly what the revkit is for.. so you dont need high spring pressures.

 

and if you break something your lifter wont come out, therefore losing oil pressure

 

IIRC, the rev kit is so you don't need so much spring pressure that you collapse your lifters at high RPM.

-Rippin

 

a small investment in the grand scheme of things. i am considering doing it before i reassemble my motor.

 

Solid Roller Lifters don't collapse.

It's not all about seated spring pressure, it's about security.

If you are running the motor hard at high RPM and something breaks, a valve, a rocker stud, rocker, pushrod, lifter etc..... then the Rev kit can help save the setup from completely destroying the engine.

The weight of it is added to the lifter end, which is not as important. More weight means more spring is needed and the rev-kit does enough to more than offset it's added weight.

High spring pressure is not bad, too much can break parts and too little can cause valve float and banged up parts.

Bret

 

Max- I disagree that the weight "makes no difference". I'd guess that the mass of a rev kit is every bit as much as the difference between Ti valves and Stainless... though it doesn't have the multiplied ratio. Still, weight is always an issue.

Rippin- a solid lifter doesn't collapse.

Taner- Budget doesn't come into the equation at all on this one. The motors I'm talking about are 40-50k.

Bret- So, the rev kit is there to hold things in place if what lets go? Pushrods broke, there's no way a rev kit is holding that lifter in, is there? Rocker arm breaks, pushrod flies out the top or bends. Valve breaks, it's game over anyway.

How much spring pressure is a rev kit? The ones I've installed (Crower, Crane) have marginal pressure, as I can compress and install them by hand.

I understand that weight on the lifter side has less effect than weight on the valve side, but still... as you know high end engines go to great lengths to lighten the lifter side. Aside from light materials, I've seen slotted lifter bores without bars, and lots of shops put Chevy lifters in sleeved Fords for the smaller diameter and reduced weight. At the end of the day, the margin of safety offsets the weight penalty?

Don't get me wrong, I not saying you are wrong, just that it still doesn't make sense to me.

 

NOSFED,

I'M unsure as to what type of race engines your are looking at? I would guess your probably looking at circle track motors or maybe some small block drag racing engines because honestly these are probably some of the popular engines besides a hot street car using a hyd roller. Some engine builders are very fond of the use of these kits if the motor is going to see some rpm's over and above 6500+ with either the use of a hyd roller or flat tappet. I know other engine builder do not like them because these rev kits have been know to show a loss of power on the dyno at lower lift.

Hydraulic Roller Cams (as do Mechanical Roller Cams) have an important advantage over their flat tappet Hydraulic & Mechanical. Their maximum velocity (max rate of lift per degree of camshaft rotation) is not limited by the available lifter diameter. You'd wear out a flat tappet cam trying to make it as radical as a roller simply because the lobe would be trying to reach out over the edge of the lifter!

These higher lifter rates translate into more potential area under the lift curve and subsequently more power. Quicker lift rates can also result in lower "seat to seat" duration numbers and somewhat improved throttle response in the lower and mid RPM ranges. All this is very well and good, however, it comes at a price. Hydraulic roller cam kits are roughly 3 times the cost of a comparable flat tappet hydraulic cam kit and have one other potential area of concern, RPM. Those quicker rates of lift demand higher spring loads (increased pressures) to keep the valve train out of "float". Sometimes this can be remedied as in the case of a small block Chevy, with the aid of Camfather Ed Isky's invention of the 1950's, the "Ultra Rev Kit" or "Rev Kit" as it is known as today.

Small blocks can usually benefit some 400 - 600 RPM or more with the aid of a Rev-Kit, and the Rev-Kit is preferable to simply adding more valve spring pressure because the latter increases the load on the hydraulic piston assembly, and this can lead to quicker leak down (bleed off) rates which are in themselves RPM limiting.

Big Blocks however are another matter. Because of their canted valves and subsequently severe pushrod angles coming out of the lifters (especially on the exhaust side) it has always been a difficult proposition to construct a Rev-Kit for a "Rat Motor" that would be in the long run a trouble free installation. Usually they entail the use of a spring and retainer affixed via keepers to a grooved pushrod. If a conventional Rev-Kit has acquired the reputation for being difficult to install, it is not hard to understand why most people feel thumbs down about these.

Regarding big block, depending on valve spring loads and how aggressive the hydraulic roller cam is (extreme cases in a big block have been known to float at roughly 5900-6000 rpm) you could conceivably get a maximum of 6200 - 6400 Rpm out of your installation. On the other hand, you could with the proper valve train (i.e. Properly dampened dual Valve Springs & Anti-Pump Up Hydraulic Lifters) achieve 6800 - 7000 Rpm or possibly higher with a flat tappet Mega Hydraulic Series cam.

I following most people would that I know and at least two friends of mine that have purchased high end motors did not have this item Rev Kit in use. The one friend purchased a 706ci Schmidt BB Chevy Nitrous Motor. The other guy purchased a Sonny Lenord 762ci BB Chevy Nitrous motor, now I know out side of a turbo motor a person probably can't get much better then these two engines nor could ya spend much more.LOL!!! Neither of these engines used a rev kit but both did use some HUGE valve springs and if my memorie serves me correct the valve on the seat was like 1200 to 1500lbs and both cams are over 1" lift. That's like saying you run a cam with a 1000 lift! Needless to say valve springs get changed and relashed often at the track. That's how I learned to adjust valves on a engine is less then 15 minutes. You for the most part would adjust them ever three runs but would check them after each pass.

Maybe that clears something?

 

Nosfed,

Couple of things here. First, I think what Bret was trying to say is the extra spring pressure added by the rev-kit more than offsets it's weight.

Secondly, to answer your question earlier. If the pushrod broke, the rev kit WOULD keep the lifter in it's bore. You are correct that major damage would still occur, but by not losing oil pressure, expensive bottom end parts could still be saved.

Lastly, one thing I've always liked about rev kits, other than the extra insurance, is the fact that they keep pressure on the roller lifter. By pushing the lifter against the cam at all times, even on the base circle, the roller continues to turn, so when the cam comes up on the lash ramp, the lifter is already turning and is "preloaded". This reduces the shock seen by the roller's needle bearing, and eliminates "flat-spotting" of the roller due to it not turning on the base circle. Of course, this is only applicable in a solid roller environment where there is valve lash. Just some thought not mentioned yet.

Shane

 

Ok, theres a couple things I can see making sense here... namely keeping the roller in contact. You probably know, but road race motors see more torture in a weekend than a drag motor sees in a lifetime, so we replace things like lifters as routine maintenance. Do the rollers really slow significantly at 9500 rpm?

However, what I was getting at with the weight issue is the parasitic loss. If we have extra weight (a negative on performance) and we offset it with extra spring pressure (yet another negative) how can the net effect be anything other than negative?

I guess the lifter staying in might save a crank though. When our valve broke at Hallett, several builders told me not to reuse the rods, as they could be weakened, even though they look fine, as with the crank. In the end, the entire rotating assembly was scrapped, as well as the block.

JWINN- Heh.. I knew the things you mentioned, but thanks for the input. The motors I'm talking about are CRD and Katech Trans Am pieces. Rev kits have no effect on the rpm limits of solid rollers, though afaik. Much of what you were talking about is hydraulic stuff, and I'm obviously talking about solid rollers . For a hydraulic setup, especially a hydro roller, rev kits make a lot of sense, but that's not in question.

And the reason I'm asking is that we're probably going to have the budget for a real motor this winter. It looks like we're going with Crower ultra light crank (38lb) and Crower Ultra light billet rods, along with Crower pistons(dunno who makes those). My buddy just got back from SEMA, and we're going to get a killer deal on the rotating assembly.

We have several rev kits, but I don't think I'm going to install one. In my experience, when these things let go there's nothing to save below the deck, so why give up the hp?

So, my next question is about the slotted lifters. Has anybody run those?

 

Funny you should ask because I know all to well about slotted lifters. At least in my experience was with using them them pertaining to big inch motors with camshafts over .950 lift. A slotted lifter is supposed to allow oil to still reach the lifter oil orifice in the lifter body when the lifter approaches max lift and keeping oil up to the pushrod. You see with some very large lift cams the lifter will actually lift beyond the oil feed orifice in the lifter bore and at that point the oil orifice in the lifter body does not get oil causing a lack of lubrication to the pushrod tip at the rocker.

We found this out the hard way one season and only after eating up three sets of $550.00 Smith Brother pushrods and destroying three Jesel pedastal rockers, these where pretty cheap also to replace especially when you have to get them for Big Chief Heads. The pushrod tip at the rocker tip both where getting destroyed in less then 1 maybe 2 minutes just at a idle.

What was worst yet was the fact the engine builder whom built the engine a very well know name I prefer not to mention failed to inform us of this little trick that must be done still yet even on slotted lifters because of the extreme lift. We had to replace the lifters that came in the motor one year and figured the $600.00 roller lifters would be good to go, well that wasn't the case. We had to slot them even more with a dremel after that all was OK. Funny how these little tricks that help to either make power or are part of a particular engines combination sometimes don't get mentioned because the engine builder wants the engine to come back to him for repaires or work. I guess thats what ya get when ya pay $38,000.00 for a complete engine. Secrets must be extra cost which is priceless.

The way to go is purchasing Jesels new 1" dia lifters that ride in a bushed lifter bores with a built in key slot cut in to the bronze bused lifter bore and the lifter has a key built into the body that fits into the lifter bore groove.

 

Extra weight is bad, yeah that's true but all you need is more spring pressure to control it.

The extra pressure is not a bad thing in my book. Everytime a lifter is going up against the spring pressure another one is going down.

I have never seen a motor lose power from adding spring pressure. I usually gains power and wears out parts and valve seats faster.

Spring pressure is our friend not your enemy, but you have to use it the right way with the right parts.

As for Hyd Roller setups, you can either run a rev kit or $500+ lifters, take your pick. I'm going with the rev kit.

Bret