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
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
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!!!! Sent from my iPhone using Tapatalk
At one time Kenne-Bell used to have a mushroom cam. Lifters had to be installed from the bottom up. gary
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.
Would you mind posting your dyno sheets for these engine Cliff? 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.
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.
