For those unfamiliar with them, they are hydraulic lifters modified with a groove on the inner piston that allows them to collapse slightly at lower rpm. This cuts the lift and duration at low rpm. At higher rpm, they pump back up and give full lift and duration, mostly. So you get the benefits of a big cam at high rpm, with milder idle/low rpm torque of a smaller cam.

I actually used these back in the day (anyone else?) with a flat tappet cam in a 350 with a Crane Blazer 230* cam. Worked well, it idled/ran like a 214-218* cam, had no problems with a stock torque converter behind it. 2 small issues. It sounded like it had a solid cam at idle due to the lifters pumping down, and it would idle like a 230* cam when it was really cold. This was due to the oil pressure kicking up due to the oil thickening (ran straight 30 back then), but once warm, it would idle fine.

Well I read in the August issue of Hot Rod that they are now available for GM roller cam engines, LSx included. They did a test on an 04 Vette LS1 with a big cam, 236/241 .050". This cam idled with 10" of vacuum @ 800 rpm with factory lifters, made 461 peak hp @ 6,100.

With Rhoads, it idled with 15" of vacuum, average torqe output from 2,400-5000 rpm incresed from 374 ft/lbs to 397 ft/lbs, but it lost 4 hp at peak, lost 35 hp @ 7k rpm. That was with the preload settings recommended by Rhoads. That brings up another issue, you need adjustable rockers, no problem on classic sbc, but on LSXs, it's an extra cost.

They messed with the lifter adjustment and lost a few peak ponies, but improved average power over 5k. It also had the most area under the curve from 2,400 to 7,000, an indicator of best potential real world performance.

They then reflashed the computer with a TPIS level 4 tune. The 2,400-5,000 avg tq improved to 426 (?!?). Hp avg went up from 268 hp over the same range with the stock lifters/tune to 346 hp. And it made 462 peak @ 6,900.

So looks like with these lifters you could run a 224 cam and have it idle/make low end torque like a stock cam, or run a 230 cam and have it behave like a 218 cam until you hammer it and have it pull up top like a 230 cam, until it goes past 6k with the stock tune.

Only concern would be the lifter noise @ low rpm. Like I said, these lifters on a flat tappet cam sounded like you were running a solid lifter cam, not a loose lash cam like the 30-30, more like a tight lash .015" aftermarket cam. By about 2-2,500 rpm the sound went away. Don't think they would be picked up by the knock sensor, and HR didn't mention anything, but I wonder???

edit: http://www.rhoadsproducts.com/

 

very cool, I ran these in the old school blocks and they work really well, had great results with them. I've been wanting these for the newer engines but always heard it would trigger the knock sensor. I called up roads and they told me that Hot rod didn't have any problem with it triggering them, so we shouldn't have a problem. The guy also said that we can use the non variable type since we don't have adjustable rockers-the price he thought from memory was 200 bucks. He said that it should reduce a cams duration by 10 degrees, good news for those looking to pass emissions with bigger cams. So California guys could run a 230 cam and pass as though they had a 220 cam. if I'm not mistakend you must pull the heads to change the lifters on these engines-so thats alot of work unless your doing port work on them.

 

I emailed Hot Rod about the knock sensor issue, see if they say anything.