Aggressive/Extreme cams?

87GN_70GS · Apr 27, 2016

BuickAl said: ↑

Mushroom lifters......interesting and the first I've heard of and seen them.

So your comment about lift rate suggests to me that the bigger the diameter of the lifter, the greater the lift rate can be? Conversely, smaller lifter diameter means less left rate is acceptable. I assume roller cam setups by their nature don't have this limitation.

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Roller lifters are limited by pressure angle, which is basically side loading of the lifter. An aggressvie lobe pushes the lifter sideways as well as up

87GN_70GS · Apr 27, 2016

Bluzilla said: ↑

Interesting old thread! Like Cliff said, "there is always someone who runs good with this stuff". I have a XE274 in my small block '70 Corvette and love it. It's quiet, pulls strong from idle through 6000rpm. Just finished a build for a customers '67 396 Chevelle with that cam...same results. I like it so much that I installed one in my '68 Tri-Carb 427 Corvette Roadster, but haven't finished that restoration yet. It's too bad the Pontiac and Buicks are not sharing the same results as the Chevys, but after reading the thread I can understand why.

Larry
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SB Chevys have lower rocker arm ratio at 1.5

BB Chevys also have bigger cam journal tunnels than Buick. Buicks have some of the smallest of all cam journal diameter. This limits the lobe size (it has to fit thru the tunnel to install it). The small lobes (and conversely, small base circles) affect what kind of lobe profile can be used. Too aggressive of a lobe and you run into inverse radius of curvature (for rollers) issues. The small lobe size also affects the precision; it takes more accuracy to grind a small lobe correctly

BuickAl · Apr 27, 2016

pmuller9 said: ↑

Yes, that is correct.
When you look through a Cam Lobe Master catalog, each flat tappet lobe specifies the minimum diameter lifter to be used. Here is Comps lobe master catalog. Have a look.
http://www.compcams.com/Technical/Catalogs/CamLobeMasterCatalog.pdf

The same actually holds true for the roller lifter.
There comes a point where the minimum roller diameter is specified and the lifter diameters have to be larger to fit the larger wheel.
You don't usually see this until you get to the bigger solid roller cams.

A .842" roller lifter has a .750" wheel.
We use a .936" diameter solid roller lifter with a .850" wheel.
Then there are roller lifters with over 1" diameter bodies using .900" wheel diameters and over.

The classes that restricted the cams to flat tappet only eventually restricted the body diameter making mushroom lifters illegal.

Paul
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Wow. Totally learned something new today. Thanks for the new knowledge. I had no idea that flat tappet cams had specified minimum diameter lifter that had to be used.

Thanks again!!!!

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Thumper (aka greatscat) · Apr 27, 2016

BuickAl said: ↑

Mushroom lifters......interesting and the first I've heard of and seen them.

So your comment about lift rate suggests to me that the bigger the diameter of the lifter, the greater the lift rate can be? Conversely, smaller lifter diameter means less left rate is acceptable. I assume roller cam setups by their nature don't have this limitation.

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At one time Kenne-Bell used to have a mushroom cam. Lifters had to be installed from the bottom up.
gary

8ad-f85 · Apr 27, 2016

Something I've done to repair otherwise junk GM blocks without the expense of bushing lifter bores is to bore/hone them to the Ford size.
I've been able to run some fairly aggressive cams/rocker ratios without problems.

BuickAl · Apr 27, 2016

So why did KB stop making them? Did they perform well?

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rtanner · Apr 28, 2016

BuickAl said: ↑

Ok. This is an old post, but I have a question about fast ramp cams. If my understanding Is correct that the angle of the lobe on a fast ramp cam is steeper than a non fast ramp cam, wouldn't the cam lobe more directly contact the edge of the lifter, which I would t think is a good thing as the edges are sharper?

Sorry if my lack of knowledge has resulted in my asking a really dumb question.

Really, from my exp, since I bought my first comp 268 high energy, back n 1979, all the way up thru todays xtreme energy cams, and after dozens of builds, and lots of street miles, w constant track outings, if you want your engine to have a sewing machine sound coming from the intake and valve cover area of your engine at idle and low speed, go with high energy/xtreme energy, If you don't, and like going fast, and getting long life out of your valve train, don't, its really that simple,
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buicksstage1 · May 1, 2016

Cliff R said: ↑

We have been following the Comp XE cams for some time, and even installed and tested one several years ago. My own test was a Pontiac 400 cid engine, about 10 to 1 SCR, 240cfm heads. We chose the Comp XE268 camshaft, which sports 224/230/110 specs and 268/274 degrees of off seat duration.

Prior to this, we had been using either the Crower 60916 (221/229/112) or the Crower 60243 (228/235/112) in these engines. Either one of the Crower cams will tear your head off to at least 5500rpm's, both have a LOT off off seat duration, they exhibit a choppy idle, strong mid-range, broad power curve, etc, complimented by a strong top end charge to well past 5000rpm's.

Right on the dyno we made 417hp/453tq (5500rpms peak), and 424hp/465tq (5800rpm peak) using those cams in a 400 cid engine, 10 to 1 SCR, unported heads.

Not ever being completely content with anything, I chose the XE268 cam mentioned above to see how it would do in a well prepared 400 engine.

The opportunity to dyno the engine never presented itself, so we just installed the engine in the car and did some street testing. Immediately, I noticed that the engine had no "lope" at idle whatsoever, somewhat "noisey" valvetrain. After break-in we did some street testing, and the engine was a TURD. Yes, one more time, TURD. It pulled OK off idle, and decent in the mid-range, but all DONE by 4800rpm's if not a tad sooner.

I ran the timing/fuel curves all over the place, ran better before I touched anything. The initial results were so poor, I never even attempted track runs with that car to see how much power it really wasn't making.

Jump ahead about 4 years. In my own 455, after having my engine and car in HPP and Popular Hot Rodding's Engine Masters addition, we decided to do a cam change.

The engine (very basic 455) had made 494hp on the dyno and pushed my car to 11.64 @ 116mph at the track. The cam we were using was a Crower 60919 (304/314/113), basically a copy of the "old" Pontiac RAIV cam. Yes, an old design with tons off off seat duration, and slow/lazy lobe profiles.

The cam chose to replace it was from Comp, custom XTQ lobes (very aggressive), 240/248/112. It sported less advertised duration, but .060" more lift than the old RAIV copy.

We figured it had to make more power, right? WRONG, we lost 10hp and 22 ft lbs torque, peak number, and a LOT of average power. The engine went "dead" right at 5200rpm's.

I tuned and tuned, even changed intakes and carbs, MSD billet distributor with locked out timing, etc, it made more power on the very first pull, every single thing I did just made things worse.

The cam came out, and a custom hydraulic roller cam was installed, 230/242/112, with .361" lobes. It made 514hp and 587tq, and improved by cars performance at the track from 11.64 to 11.52, almost exactly what the power difference should have.

OK folks, I'll add a couple of more examples, then tell you what I'm pretty sure is going on here.

455, 232cfm heads, XE274 camshaft, 414hp/487tq, DONE at 4900rpm's.

Another 455, 230cfm heads, XE274 camshaft, 412hp, 457tq, DONE at 4900rpm's.

Yet another 455, XE284 camshaft, head flow unknown, 400hp/499tq, DONE at 5000rpm's. (Yes, the bigger cam made LESS power).

I could list another dozen or so examples, but by now we should be able to see a "trend" here.

For the past 5 years or so, we have avoided the XE or any other "fast ramp"/short seat timing/more area under the curve flat cam like the plague.

All the while I'm thinking that the short seat timing is not allowing enough air to flow thru the engine to make up what the long duration lobes can do. Not so, the problem is actually caused by the ultra fast seating velocity of the lobes. This causes valve bounce and instability in the valvetrain ("lifter crash"), which not only limits upper rpm power production, but kills off power in the upper mid-range as well.

Jim Weise and I have spoken on this topic on several occassions. My conversations with him prompted me to contact a cam design expert, who fully explained what is going on here.

All the while I'm thinking the lobes are just too "small", when they are actually really good lobes, as far as technology goes, but just don't work very well in actual use.

Anyhow, I've taken considerable critisism for releasing this sort of information. There is always someone here and there that runs pretty good with this stuff, like most anything else. There are always a few that get "territorial" about parts that they use, whether they work all that well or not, anyhow.

I try to stick to facts, and the facts are, that I keep seeing folks running near identical combinations of parts as I do, but using these sort of cams instead, and coming up WAY short of the power we are making, and the track numbers we are running.

As a disclaimer, I've seen a few exceptions. Most recently, a customer of mine used the XE274 cam in a 455 for pure stock, and he must run the stamped steel rockers. He installed really light retainers, and pretty strong springs, along with stiff thick-wall pushrods, with perfect valve train geometry. His engine made up near 480hp, and his car runs much better than any other set-up I've seen using that particular cam. He may be onto something there, not sure?

In any case, I apologize for the long post, although I left out about 20 pages of specifics, etc, just wanted to let the Buick folks know that quite a few Pontiac engines have not responded well to this sort of cam technology.....Cliff
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Would you mind posting your dyno sheets for these engine Cliff?

stage2man said: ↑

Scott Brown cams do not have this problem! Used your same cam in my '71 which liked to shift right at 6,000 and in another local guys stage1. Both cars sounded great. This cam is well known as the big car performance cam for it's huge torque figures. Scott's cams are asymetrical profiles, fast open, easy close. The mopar profiles seem to run great in the 455.
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You are 110% correct. How ever so far I have had 4 or 5 fast ramp cams that fell on there face up top on the dyno HYD and solid and everyone of these were fixed on the dyno by adding more valve spring shims. The cam cards recommendation for valve spring pressures were incorrect. There is a solid flat tappet SB cam that I have used a few times (love it) that is in the .580 lift range that was marked as 350 lbs over the nose and the cam card is now revised to 380lbs now. I am using LS springs now on a lot of these with great results and there is a lot more retainer/valve spring to rocker arm clearance with these springs so its a win win.

buicksstage1 · May 1, 2016

8ad-f85 said: ↑

Something I've done to repair otherwise junk GM blocks without the expense of bushing lifter bores is to bore/hone them to the Ford size.
I've been able to run some fairly aggressive cams/rocker ratios without problems.
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I have a brand new one of these cams designed to use the ford lifter in our 455's on the shelf.

gmcgruther · May 2, 2016

Here is what's funny, Fred has and still use's a solid flat tappet cam. The lift is past 0.680 lift and a bunch of duration. He ran 9.38 E.T. at 154 MPH. Whats wrong with that? If you build your engine right or have a very compotent engine builder. And have very well known cam make tell you what need, not someone that really isn't,never mind. Call LSM System Engineering or Shinader cams (spelled wrong sorry) they know more then anyone in here. They will discuss very important things you need to know. Like what actually works and what don't. Thats why Im listen to Fred Carlin. He only been doing buick engines for 61 yrs that's all. More dyno time then most people in here and ran most of Kenne-Bell's experimental stuff. Also raced for them. Dyno, plus drag strip proof is his motto,not guess work. Just think, 9.38's with cast factory block with oiling mods and cast iron stage 2 factory heads using a Kenne-Bell's wildcat single plan intake. Hmmm, what's everyone's excuse.

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Aggressive/Extreme cams?

87GN_70GS Well-Known Member

87GN_70GS Well-Known Member

BuickAl Well-Known Member

Thumper (aka greatscat) Well-Known Member

8ad-f85 Well-Known Member

BuickAl Well-Known Member

rtanner Well-Known Member

buicksstage1 Well-Known Member

buicksstage1 Well-Known Member

gmcgruther Well-Known Member

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