I ran Rhoades V-Max lifters when I used a TA 413 cam. It would rev like crazy. I am talking 6500 rpm. Also have TA roller rockers and a good set of pushrods. The valve springs were TA stage ones that were pretty light, about 100 pounds.
I have had this problem myself. It turned out that I had to much spring preasure causing the lifters to have a float problem. After shimming my springs properly they did not float anymore but it did run flat at 5100 rpm as you said. It had a crain cam in it that was 460 intake and 480 exhaust lift with 284 - 292 duration. After a lot of tunning and finaly taking the motor apart. We put the heads on a flow bench and found that after .400 they did not flow any more air than they did at .600 there for making the motor run flat at high rpm. I now have rebuilt my motor with TA SE stage one heads with a level 3 port job and the 290 - 08hl cam with spring preasure @ 125 closed and 290lbs. open. The heads flow great with gains up into the .800 range and the motor pulles very strong up to the 6,000 rpm shift piont of the cam and will fly by that if you dont shift fast enough. Just some exsperiance with this isue.
I'm sorry, I misunderstood, or somehow drifted off-track with Larry's mention of the Voodoo series of fast ramp camshafts. Unfortunately, I haven 't been able to find any driving impression or dyno run-related info on the Lunati Voodoo 68002 that I purchased, just the more aggressive #68003 that JW tested. Oh, well... It looks as though I'm going to have to bite the bullet and go to Tri Shield or TA Perf for a custom grind. Thanks for your response, though.... And good luck on your project.
Dan I would also look into Scott Browns camshafts ,my problem is NOT the norm with this camshaft & it has many rave reviews by other Buick engine builders & Buick customers . I have no problems with the power & driveabilty of this cam ...just short a few rpm & this could very well be some other area causing the problem .... I base this on the fact that so many people have used this cam with out any rpm issues . Mark ---------- Post added at 03:53 PM ---------- Previous post was at 02:58 PM ---------- Thanks ick
Lets look at lifters Comp Magnum , Delphi (check ball & spring) the other style Johnson style (reed valve) The johnson style bleeds off more oil @ high RPM ? & the Delphi lifter stays pumped up @ higher rpm ? Wouldn't the Johnson make the lifter crash worse ? Is lifter crash the right term to describe the condition we have been talking about ? Bottom line are the lifters bleeding down ? If this is the case then the higher spring pressures would make things worse & the use of a mech lifter lashed .005 would prove that the lifter was at fault & was bleeding down ? I wonder if anyone has ever givin thought to a double chamber type oil lifter body ,like a gas shock design. ick
No, it's not bleed down at all. That's because there is so little time spent on the cam nose at high rpm (on the order of 16 to 20 msec). Not enough time for even a worn out lifter and plunger to bleed down appreciably. This "lifter crash" is about the dynamics of the check valve operation. High lifter accelerations cause the check valve not to function correctly. A Johson (or old Stanadyne) lifter with the flat disc check valve "should" be better with crash than the heavier (Delphi, Eaton) check ball valve.
Well you can only ask so much out of a shock absorber, a.k.a., hydraulic lifter. Perhaps going to solid would be the answer and less headache? Seems if you've got a hot cam and all the accoutrements that come with it, solid would be the no-brainer to me. You get more performance out of them anyway. Not meaning to offend or disrupt anything here, just adding my 2c. G
Well it's not so bad is it? If you have an adjustable valve train anyway, you have to adjust it whether you have hydraulic or solid, why not go with solid? If I had adjustable rollers I'd damn sure be putting in some solids. Why else use hydraulics unless you just wanted a weaker running engine? A hot engine is going to make a little noise anyway with looser fits and forged pistons, plus with loud exhaust you may not even notice the solids much. And you get all the benefits of solid lifters: wider power band and more power throughout that band. I see a win/win scenario here. Hydraulics are for us cheap ass sissy stocker folks who want maintenance free performance anyways. All the best wishes to you and yours and your project. Cheers! G
How come some people run these fast ramp cams with out any issues? Could it be base circle run out? The entry to the ramp is Very important. Could it be poor valve train geometry? Go to this link and read from page 65 on, and you need to read all of it. It might help you guys understand more about what might be causing this problem. http://books.google.ca/books?id=Ulv...e&q=are fast ramp camshafts a problem&f=false
What would be the long-term downsides of using solids with a fast-ramp hydraulic cam, other than occasional clearance adjustments? Accelerated cam and/or lifter wear? I'm thinking along the lines of a street car that only sees occasional strip time. Wa-a-a-y back in the old days, when I first got my driver license, many of the used cars priced within my meager budget range were equipped with solids. So, it was no big deal. Of course, we didn't put many miles on our cars (to/from school and after-school job, etc.), and we were dealing with "slow ramp" cams in those days.
From what Jim W and others have found, it seems to be a problem specific to Buick engines. He has theorized that it may be due to the small base circle of our cams - we have one of ( if not the) smallest lobe sizes of any modern engine manufacturer (size "A", according to Crane). This may mean the issue lies in how our cams are manufactured - for example since they are smaller, it may be tougher to hold accurate tolerances when grinding it. Or it could be an operational issue - the small size leads to higher accelerations or loads when running.
Isn't the reason for the improved performance related to the use of solid lifters due to the grind of the cam, itself? Would you really see a measurable performance improvement simply by replacing hyd. lifters with solid lifters on a cam profile designed for hyd. lifters? I'm under the impression that it's the cam itself that makes the real difference.
Its not just buicks that has this "problem" I know of some hard charging buicks with fast ramp cams. There could be a number of things causing this and chances are it could be self induced ie: spring rate is different on these cams or could it be base circle run out and as it enters the start of the ramp? How many of you guys check your cams for base circle run out when you degree your cam? Here is another link worth looking at http://ls1tech.com/forums/generatio...ffect-do-ramp-rates-have-how-engine-runs.html Did anyone read the link I posted above? It is a old book but it does offer great info. Fast ramp cams are not new they have been used for many years.......
According to what I've heard and read, one of the easiest ways to wake up a sleepy/problematic top end hydraulic cam is to use solid lifters. I'm not a pro on this subject by any stretch of the imagination. All I'm doing is sharing what I've learned myself. What good is the cam if it can't realize its full potential? Solids will wake up the top end past 5300 or so, on pretty much any cam that's ground to pull past that. The lifters are the issue here, not the cam. Here is an excerpt from TA's catalog: "Hybrid Solid MethodNeed a little more out of that Hydraulic cam? Have a good combination but for some reason, it starts to fall off after 5300 RPM? Well, you can onlyask so much from a shock absorber aka hydraulic lifter. Faster ramp cam profiles, higher rpm combinations and roller combinations with hydraulic liftersare always a compromise. Replacing the hydraulic lifter with a solid lifter will breathe new life into your combination without having to re-configure it! TheHybrid Solid Method is easy to do and well worth it. Just as long as you have adjustable rockers or adjustable pushrods you can switch to the solid lifter.When putting the solids on a hydraulic profile cam, you will only need minimal lash, approximately .005. Most combinations will only need infrequentadjustments in the future. Ask a TA Tech for additional info. "
on holding accurate tolerances, i used 4 different fast ramp cams from comp cams all were with in 1* specs (1*retard). 2 were in my 340ci no noise revs to 6000 rpms with power. 216-224@.050 never would know they were fast ramp. the other 2 on the 446ci nailhead were both noisy more so at idle on low rpm, the lifters bleed down because of the small base circle i was told..( i think the 340 has a bigger base circle does any one know for sure?). the 224-231@.50 in the 446ci makes good power to 5500 rpms with no valve train problems, but power drops off after 5500 rpms maybe because of the small valves and head design, not sure why.the cam in the 446ci was not nitride and the tip of the lope is now worn down 10 thousands maybe because of the high spring pressures and the pointy lobes. the more i read the more i dont know theres a lot of grey area with fast ramp cams it seems. am going to a solid cam and lifters for the nailhead, i will post in a few weeks.
I looked up the cam journal sizes for 215/300/340,and for the Nail Head engines,the journal sizes are the same,from front to back; 1.7850"/1.7860" 1.7550"/1.7560" 1.7250"/1.7260" 1.6950"/1,6960" 1.6650"/1.6660" Housing bores are the same also,the oil clearance is slightly different,but very similar,and the bearing widths are the same except the sbb front bearing is .010" wider.(hell,in a pinch they look like they could be interchangeable,if the oil holes are the same,the book doesn't say how they're clocked) Anyway,comparing this information,it would be logical to assume the base circles would be the same,or very very close. The factor that would make the Nail Head cam less stable would be the fact that it is a longer cam,which would let it flex more.(215/300/340 bore centers are 4.24",and the Nail Head is 4.75") So that would be .510" longer center to center of each cylinder,so the cam would be approx. 2.550" longer the length of the block than the sbb version?(estimated) Now here's where this info pretains to THIS thread,sbb 350 and bbb 455 use the same cam bearings(different than the above 2 different bearings),so the base circle would be close,or the same with both the ssb 350 and the bbb 455.(camshaft journal size of all the journals is the same as the front journal of the above example,1.7850"/1.7860") So the issue here could be the camshaft itself is more flexible than others with similar grinds,the heat treating might not be as good,or the cams material differs from the people that have a fast ramp cam that revs much higher? Something to consider,if all else fails. With the shims installed the higher pressure would make the cam flex even more at higher rpm catapulting the valves making them float? Another thing to consider would be a beehive valve spring that gives more valve control with less pressure? For comparison sake the chebbies sb vs bb cam journal dia.,a sbc dia. is 1.8682"/1.8692" vs the bbc 1.9487"/1.9497",so with the GM .842" lifter dia. disadvantage,Buick has a small base circle disadvantage also,even more so with a bbb,because it is longer.(same bore center as a Nail Head,4.750") If anyone is wondering the relevance of cam journal size vs base circle,is that the lobes can't be higher than the cam journal,or it won't slide in the block,so that limits the size of the base circle so it will fit through the cam bearings.And with a smaller base circle,the ramp rate is going to be faster to begin with,because of less surface area of the entire lobe vs a larger base circle with the same profile ground on it(like riding on the diameter of a spinning quarter vs a dime,takes the same amount of time to make a full circle,but with the quarter theres more area to ride on) . Now a "fast" profile is ground on a small base circle cam that a regular profile is faster on already,and things get really fast.:Brow: This post probbably won't solve the OP problem,but is a piece of the puzzle that is Buick. I hope this was helpful,goodluck.:TU:
Well that makes a lot of sense ... small cam bore ,limited base circle size = faster profile ramp. Has it been proven? Great input ..... food for thought ick
