bigdsz

iTrader: (1)

A couple of my friends are running Comp 224/228 .581/.588 114 lsa. I've got AS 5.3's Stg 2 61cc 11/1 CR. Is there any reason I shouldn't run this slightly larger XER lobe cam? Will it be too harsh on my CC978 springs and will I have to replace them every 10-15,000 miles? My car is a daily driver in addition to the track.I'm a M6.

Blue02Ws6

iTrader: (3)

The 978's are rated at .600 lift so that lift on that cam would be working them pretty good, I would change them pretty often from what I have read on here. Then again think about how the cars are driven by people that don't use them as daily drivers, they put low miles on them, but those miles are tough miles, when you are going back and forth to work you aren't reving to 6700 rpm are you? When they wear out they will lose seat pressure and you will experience valve float at high rpm's which you can and will notice so that is a good sign of when to change them if you wanted to press your luck. I have seen people running 918's for well over 20-30K miles and still performing great, I think changing them so often is kinda like people changing their oil every 1K-2K miles with synthetic it isn't nessesary but they do it out of fear or just precaution.

bigdsz

iTrader: (1)

You're putting out 385 rwhp without heads and I'm putting out only 403 rwhp, 390 rw tq with heads, that's why I gotta go bigger.

fnbrowning

I've owned Pontiac Firebirds for >25 years. I've never had one of my cars on the drag strip, and probably never will. I enjoy driving fast on the highway. I enjoy high performance.

But time spent in the aerospace industry has taught me that engine power can never come at the expense of reliability. With good maintenance, the engine internals {crank, rods, cam, lifters, springs, rockers, etc} should run without requiring replacement until cylinder leak down due to weak rings necessitates an overhaul. {This does not include water pump, timing chain, seals, accessories.}

My research so far:
I'm rejecting the Thunder Racing cams and their type with the fast/aggressive ramp rates due to unnecessary valve train noise and early fatigue with respect to valve springs. Again with respect to valve springs, I'm thinking that anything over .560 lift is too stressful for long term longevity.

Duration and LSA are 2 very important items in clueing you into how a cam will idle and drive, however, the right LSA can also mean more power and you get it sooner in the RPM range to boot.

From my research, it appears that an LSA of 114 degrees will make good power throughout the band and provide an ear pleasing idle.

There are cams out there that I consider to be well balanced, with 220/220 .551/.551 and a LSA 114. But they have that extreme lobe profile.

There are other cams with 220/220, but with .581 lift, or they have an LSA of 112 that means more lope, gas smell, and drivability issues...

Research continues. . . .

bigdsz

iTrader: (1)

You make some good points, I myself have been in somewhat of a quandry as which way to proceed. Originally my thoughts were moderate lift and moderate duration, I had a Comp 216/220 .525/.532 114lsa for a couple of years. It put out 390 rwhp with AS 5.3's. The cams on balance just kept getting larger and larger, so I felt the need to go bigger, which I did with the 224/224 .563/.563 112lsa. I only picked up 13 rwhp although the peak is at 5,700 rpms, I need to retard two degrees to bring the power peak to 6,1-6,200 rpms.

Now I have to open the engine up for a lifter change so I feel pressured by my peers to go even bigger, where does it stop? The question is do I go with a ramp rate of about 53 on a XE lobe and keep the lift in the mid .570's or do I get more agressive with the XER and a 49 ramp rate with lifts in the md .580's and mid .590's? I may stay in the .570's unless I get some real good arguements to go bigger.

Also, three weeks ago I had a 9" with a Detroit soft locker installed, and it is begging to be run and run hard.