thanks for the specs and info.:gp: ---------- Post added at 09:44 AM ---------- Previous post was at 08:28 AM ---------- yes lots of good reading, i cant understand a lot of it myself, but it does say i think, that the smaller the base circle the more pointed the lobe nose and the more it will wear.do i have that right? like i said in my post #38 the nose was rounded down about 10 thousand, the good thing it stays the same after rounding off and does not wipe out the lobe, nitride the cam might cure that.
"Fast Ramp" is a generalization. One must spend the time to cam doctor multiple cams, and get a fix on lifter acceleration rates. Then, that same person has to spend considerable dyno time, evaluating what combinations will "work" and the benefits of said profiles. This work has been done to some extent, for the high volume engines by the cam companies and builders. It has not been done, to my knowledge, for the Buick 455. So before we start saying "so and so runs a fast ramp cam and it works for him" my question is going to be ... how fast?, what lifter accel rate? Where is the borderline, what components are required? And just how much is it worth? How about long term wear issues? All of these things need to be scientifically quantified, documented and reported. Long ago I wrote off "fast ramp cams" as a sales gimmick by the cam companies, with very little upside, and a whole lot of downside. The best "fast ramp cams" have wheels on the bottoms of the lifters. And they are available to us now for all applications of the 350 and 455. JW
My guess is the lifter crash is caused by a lifter that is bleeding off, it might just be a matter of using a good lifter with the correct spring rate. Would you call this a fast ramp cam? I know its not a HYD cam but. Its a solid cam that uses a .874 lifter are 455's Buick 455 cam. Intake Duration (gross): 296 Exhaust Duration (gross): 304 Intake Duration (.050): 262 Exhaust Duration (.050): 266 Intake Valve Lift*: .616" Exhaust Valve Lift*: .612" Lobe Separation: 112 Intake Valve Lash: .020" Exhaust Valve Lash: .020" RPM Range: 3400-7000 *Based on 1.6 Rocker Arm Ratio
Some more info to add on to what I said in an earlier post. I wouldn't say Scott Brown cams have no problems. One of the cams I was having problems with was a Scott Brown cam, 226/238@.050" from the late 90's/early 2000's. Once I took care of the problem with the Pro Magnums and very little preload it worked fine. In fact I was still running it in my '76 into the 11's when I finally switched it out to a custom Mark Remmel Erson cam with slower ramps just 2 years ago. Only a slight change in specs to 229/235 but I did pick up some power and it revs above 5700+ smoothly with regular lifters compared to the SB cam which needed the Comp Pro Magnums to get to 5700 where it pretty much stopped revving. Please note I said "PRO MAGNUM". Comp also used to make "MAGNUM" lifters which were their regular "Hi-Rev" anti-pump up lifters a step up above their "Hi-Energy". The plain "Magnums" don't operate like the "Pros" which are run like hydraulic versions of a soild lifter. They are meant to to be run at very, very little preload. The pushrod cup can be run right up close to the retainer because they are very strong so they don't push through so they can't "pump up". As far as "pumping down" or collapsing these lifters are probably the strongest for keeping the piston from collapsing I've every used. They just don't collapse. If anything they make great lifters on mild cams if you run a normal .030-.040" preload. They don't make startup noise because the lifters haven't collapsed after sitting. If you have a cup almost pushing into the retainer so it can't go any higher and a piston that won't collapse that about equals what a soilid lifter will do. One of the other cams which really caused problems was an early version of the "Popular Mechanics" cams from the GSCA, 230/245 @.050". I had it in my 455 Buick powered TA and with 3.73 gears and 25.5" tires in the back it would be hitting 5400 over 100' from the finish line and you could just feel the car stop accelerating. It wasn't that noticable down low because I would just shift at 5350 just before it kicked in. The other reason I really wanted to get to 5700 was because I had the 700r-4 in it and with the wide spread of gears you needed to shift at a higher point. When they first came out with the Pro Magnums I installed a set with little preload and that got the tach to just about touch 5700 where it would hit a big wall but that is all I wanted. It wasn't making any more power by then anyway. Cams in that range of duration are all on the downside of the power curve by that rpm but you do want to get there smoothly. I also drove both those cams for thousands of miles on the street with no abnormal wear from the minimal prelaod so that isn't a concern as far as I can tell.
Try this formula in the post below, see if this works for you if you have a known fast ramp cam. What was the installed valve tip height with the SB cam? I might dyno test with my custom ground cam I mentioned above this summer if I can make it to the dyno with one of my own engines. The idea behind that cam is to increase the base circle hence the bigger lifter which will make room for a faster ram which should = dyno results. Here is a tech guys thoughts on the subject at hand here: If by "ramp speed" you mean how fast the lift occurs or how "steep" the cam lobes are, it's called "cam velocity" and measured in inches of lift per degree of cam rotation. It is independent of cam (engine) rpm, which isn't always ovbious. Cam velocity generally is the basic limiting factor in lobe design; the cam/lifter interface can only handle so much "velocity" and live. With flat lifters, lifter diameter determines it; if you try to get too much velocity, the edge of the lifter digs into the lobe. With roller lifters, it's things like side loads on the lifter bores which limit the durability. Do cam manufacturers usually quote these numbers? Rarely, if ever, in public. One reason is that many end users don't understand their significance, and various other things also enter into the picture. You can compare the relative 'velocity' of cams crudely by dividing the lobe lift (valve lift divided by rocker ratio) by 1/2 of the .050 duration. For example, a 224 degree (@.050) .380 lobe lift cam would calc out to ".0034" while a 244 degree (@.050) .380 lift cam would calc out to ".0031". Therefore the 224 cam would have a higher velocity and would be a more aggressive lobe than the 244. It gets the same lift with less duration. More aggressive lobes usually give more power with less duration, but they are harder on the valvetrain and often need stronger springs, pushrods, rockerams, etc. and are restricted to lower rpm for good durability. Ot the outer edge, ProStock valve springs may have about 8-10 seconds of life at racing speeds! It's even hard to get a dyno pull on a set of springs. That's BIG time velocity!
Can't really say other than it was the same for the SB cam and the Erson cam I installed after it and only had to use regular lifters to rev past 5700. JW had a nice writeup a while back in a thread about the tip height affecting crash and at that time I looked into mine and what ever it was it fell into the OK height where it should not be a problem. Just off the top of my head I'd have to say that cam you're installing doesn't really relate to the problem that is going on here. It is big by large compared to the cams the OP and I were using so it has its own problems keeping the lifter on the lobe. I could see where a solid lifter may be the way to go with something that big and the spring pressures needed to do so. From what I understand the Chryslers use a larger diameter lifter and can get away with faster lobes than the GM's.
OK for the record even roller cams have fast ramp set ups and depending on how fast the cam velocity is will cap the rocker ratio. The 3 common flat tappet lifters are (.842 GM, chev, BOP, and caddy (.875 Ford) and (.903 Dodge/Chrysler, pretty much every thing from 1958 up) The reason for a fast ramp cam is to give more mid range lift/air flow. That custom fast ramp cam I have uses the ford .875 lifter, if you were to use the buick .842 lifter on that cam the lifter would dig in on the side of the lobe and poop the bed so you have to find a block with thick lifter bores and enlarge them to except the .875 lifters. I here what you guys are saying but to say a fast ramp cam doesn't work in a Buick is short sighted and not true. It is the same with all the brands, too much of anything is often not a good thing.
You must be talking about those other guys because I'm the guy that has run the fast ramps cam since the 90's. They worked fine in the rpm, power range, and idle quality I wanted but they did need extra help in getting them to work. When I needed a few more HP I moved away from them that's all.
It was a general statement. I do find that people all to often give up because they can't make something work and assume it doesn't work or work as good as another set-up. I am booked at the dyno with 2 SB cams and I will post the results on my cylinder head thread. :TU:
what i dont understand, is if you run a fast ramp roller cam you should have the same lifter problems of bleed down ,maybe more so because you have to use even more spring pressure and the lifters are more heavy too with a roller.
Certainly there are issues with overly aggressive hyd roller grinds Give Cliff Ruggles a call, besides being the Q-jet guru, he is a big time Ponitac racer. He uses solid roller lifters on aggressive hyd roller grinds, to combat exactly this problem. He is passionate about the dis-believers on this issue, so be prepared for an earful. He has extensive experience, they went thru a much worst deal with this on Pontiacs. Because the major vendors were stuffing these down everyone's throat there for a while, and most Pontiac guys are buying from major vendors, unlike us Buick guys who mostly buy from a smaller guys like TA and Poston, when it existed. JW
Jim, I think It would be interesting to do some lifter testing on the dyno to see which lifters are bleeding off or maybe we are just expecting too much out of are HYD lifters. Its seems to be all the different brands talking about the same thing we are here. I find that some times we get comfortable with the parts we use not thinking that are suppliers are having to change there suppliers from time to time as these old chunks of iron are getting harder to find good quality parts for, speaking of that :laugh:I will know this week if the new solids fix the O/P problem I was having ou:
New Pro Magnum lifters on the way I will post results ASAP. I'am going to leave the .030 shims under the springs that way we can see the before & after results of the Pro Magnum lifters , I just hope the lifter to cam break in goes well. Thanks, Mark
Something else that should be looked at/tested is the possible effects that oil pressure might have on this problem. Anyone have any dyno #s on the KB107? That is a fast ramp cam.
Sounds like a good test. Do you know the internal lifter construction? I.E. johnson-type with disc check valve or delphi ball-type check valve?
Scott, I am not shure of the valving I will check when they get here. I would like to say that in some of my earlier posts I had refered to the Poston HI REV style lifters as the Johnson (reed type) this was later found not to be true ,they were ball & seat all I can say is they were much quieter than the Delphi lifters but because they bleed down after setting I removed them before ever takeing the car out for a rpm test . Thanks , Mark
