Just wondering what lobe types you guys are running, XE, XER, etc.?

Also tell why you chose that lobe?

Any gains going from XE to XER or other?

 

bump.....

 

I am using the Xtreme Street Roller lobes on a solid roller for general excellent performance and the best hi-end control and power, just when you need it with a centri. I do have a SBC, not an LS motor but that shouldn't make a big difference.

Jim

 

Depends on the setup but most are XER.

 

I'm not using Comp at all!

 

Well, damnit, you should be

Jim

 

LOL-figured I would stir the pot. I've been doing alot of research recently and I'm really leaning away from the aggressive lobes.

 

Without an agressive cam it's like having a toilet with a slow-opening lid - you want that thing out of the way fast... And when you're done, you want it closed fast!

Jim

 

Thats a good one! I agree though!

 

Sure if it's solid roller, but imagine hydrauilic roller, plunger and all, with a super aggressive cam at 7000 rpm and watch how that lifter is rolling up and down that cam profile and see how it keeps up with **** spring and only 150lbs on the seat while still trying to keep 20lbs of boost in it.

Go check out the .50 thou, .006 thou and advertised duration of the guys running 8's on a hydrauilc roller and you'll see the point.

 

Hey Bro, just a little bit of your conventional wisdom Please

 

LOL-okay let me see if I can explain this better. We have XE, XER, and now the LSK lobes. Each one is more agressive than the other. Basicaly we have a wheel the roller on the lifter that follows the cam lobe. Just imagine at 7000 rpm how fast that lobe on the aggressive cam is moving and how that poor roller wheel has to follow it.
The more aggressive the lobe the harder it is for that wheel to stay in perfect contact with that lobe.
Next point is the springs-the typical dual spring is rated at 130-140lbs on the seat. that's fine for N/A but stuff 20lbs off boost in the cylinder and then ask that spring to stay seated-it's alot harder. So we can shim the spring to build more seat pressure-to a point. Most of the duals are only rated for .650 lift so how much extra seat pressure can you get if your cam is already over .615 lift-with a XER lobe?
An XE lobe which has easier on, off ramps all are under .600 lift so we can still shim the spring up for big boost. But not too much as you'll over power the lifter.

Bro-your cam for example is on the XE lobes-I bet you wouldn't make a drop more power if you went to XER lobes-but what you would pick up is a noiser valvetrain and shorter spring life-so if the more agrressive lobe doesn't offer greater power gains, but requires you to change springs more often and listen to that sewing machine what would you choose?

When I test the LS6 versus the VicJr I hope to buzz the the motor past 7000, the cam(S) i have picked are both non-aggressive lobes so I can get extra pressure on the springs so they don't float and the power goes flat. I've got some trick pushrods and rocker arms I'll be using as well-and best part is none of this stuff will break the bank. I'm not just looking for big peak numbers but a nice fat curve that doesn't fall off a cliff after peak.

Of course when i'm all done i'll give you guys exact specs and part #'s as always!

 

Thanks Arun! ...I understand about the roller lifter following the lobe profile but are you also saying that additional lift (XER lobe) in FI application would not yield more power with all other things remaining equal (duration-LSA-advance) ?...Still a little confused on that issue

 

I'm running 160 lb seat pressure and I've heard of folks going as high as 180 lb on stock lifters. The trick is to run alot of seat pressure and keep the open pressure down, so you have to carefully choose the spring.

I'm running Crane 99893 springs, which when shimmed to 160 lb seat, gives me a tad under 400 lb open and don't bind until almost .700". I could run up to .650" lift on these and still be ok from both spring pressure (420 lb) and coil bind (.050 margin) perspectives.

Mike

 

Having switched between XE and XER lobed camshafts and nothing else I think the possible slight valve float at high rpm I saw was an ok tradeoff for increased overall power (3-4mph in the 1/4). It still pulled clean to 7350rpm though, nothing you would feel but by the a/f I could tell something was up above 6900 with the bigger blower. I have 150lbs on the seat and I'm hoping the caddy lifter will help that a little on the new engine, be a while before I put the F1A back on so I wont know.

 

A 2" intake valve has an area of 3.14 square inches, so at 20psi of boost, there is a max of 62.8 pounds of pressure on the face of the valve. In reality, that number drops anytime the valve is off the seat as air starts going around the valve. So your most dangerous time is when you are just about to lay the intake valve back on its seat. You get a quick ramp up to the 62.8 lbs of pressure trying to keep the valve open. Even a tiny amount of valve bounce can show up as a noticeable decrease in torque.

The effect of boost psi at full valve lift is much lower than the max of 62. If you have good cylinder filling it is almost zero because the cylinder is at almost the same pressure.

So you need to spec your springs to plan for that, and it's the seat pressure & and very low lift spring rating that most affects that part of the cycle.

IMO, the exhaust spring is almost unaffected by boost except for possibly taking a turbo setup's extreme backpressure into account during the very last part of the exhaust closing cycle. It wouldn't affect a SC setup.

Jim

 

Dave@CDNperf convinced me to put Morels in my 402, where also getting some 5/16 .110 wall pushrods made up as well, I wanted 3/8 but that would require some clearancing on the head-problem is the heads are already bolted on so that will wait until next season. My new cam has .595 lift on both sides so I can play with some different pressures on the springs to see how it affects the curves.
With Vette all i'm trying to do is keep the power soft on launch but come on strong ontop-so if I can make the same power/torque as the 347 up to 3500 I should be good. I know it's not great but it was getting 1.47 sixty's leaving off idle with the 347.
With the same cam as the 347 in the 402, it blew the tires off on the dyno at 4500 rpm with no timing in the car-hopefully the new cam will shift the power curve over abit!

 

Another thought...On factory LS7 engine, cam lift is .56? intake & exhaust, but with 1.8 rockers lift is I believe .59? in/ex. With the LS7's 7K redline (7200 rpm rev limiter) it appears GM was playing it safe with lobe profiles while using rocker ratio for more lift. I have read of many who don't like some of the 1.8's because of valvetrain instability issues, but IMO if GM can do it on the LS7, then I would think an experienced engine builder could do as good or better with high quality aftermarket parts. Just my $.02 theory, now somebody bust some holes in it

 

We run XE lobes, 190-200 on the seat, comp stock replacement lifters, stock rockers w/harland sharp bearings, stiff pushrods and see 7,500-7,700rpm.

 

That's a nice combo of parts!