Muskys SS

Does the power really drop off fast at high rpms???? I've heard a couple people talk about how the steeper XE cam lobes drop off in power at higher rpms. Is this true? Is it the cam that causes this or could it be that the spring pressures people use aren't strong enough causing the valves to bounce upon closing at high rpms?

bunker

Shawn didn't you ask Payam this question like a million times?

If you want an answer call me or search under "bunker" in the LT1 tech section, I made a write up of my findings a long time ago.

The weird part is valve float feels a lot different then when the XE cam just runs out of breath at high rpm simply because the cams seems to be small in general when it comes to overall durration, they durration at .006 (seat timing/advertised durration) is much smaller then your general soft ramp cam, so it just feels like it dies off instead of floats the valve (which is what you would think of first as the cam is agreesive, think though that although an agreesive opening, they still close relatively slow to prevent bouncing off the seat).

When floating the valves the car just dies makes a louid "waaam" sound but goes no where, with xe cams you just feel that you are not accelerating anymore, kinda like a small cam runs out of breath up top because it doesn't have enough durration, however I am sure that some of it is because you might be starting to float, so more vale spring pressure/lighter valve train should definetly help in the long run.

Again read up my write up and keep this in mind, the XE cam at .050 durration may look big, but this is only because it wastes no time opening and although may have relatively long durration fully opened, it has no durration over all when it start off, so it is generally a small cam in perspective to a slow ramp rate cam.

I can not remember, but if you check as I am sure this makes sense, but the IC is sooner too with an XE cam bringing your peak power down but keeps DCR higher making more power down low and at idle preventing reversion etc.. all effects of the valve being seated while the other cams of same .050 durration and slower ramp rates may have hanging still.

Muskys SS

No?? I remember you telling me about this a while ago, then Payam mentioned it earlier this week. I just wanted to get some more info. Is there anybody on here that is running a XE cam and noticed a drop in top end power versus a cam with a less aggressive slope.

bunker

do a search for dyno numbers, from what I've seen my theory makes 100% perfect sense and all the dyno numbers seem to reflect it, you wanna know how my spring pressure I'm running shawn? hmm... 400 lb open with comp R' lifter and a hydra rev kit adding 80 lb open at the lifter, you do the math. Plus 150 on the seat or so and whatever the hydra rev add's on the lifter when the valve is down.

I've got really agreesive lobes on my cam, but I make up with tons of durration.

Denny McLain

The absolute truth is I'm giving Xtremes ginds the benefit of the doubt, but I had a horrible experience few years ago when they first came out. I found as you mention, they hit the wall and dropped like a rock. With a bunch of playing around you could get a decent peak hp, but the power curve sucked big time.

I reported this on the F-body list back then and caught all kinds of static from Xtreme owners.

That's OK.......... Let them keep using um. I'm happy with other profiles.

Smoke um, if ya got um, but I'd rather not go to the extreme!

Juiced Impala SS

Power does tend to drop off quickly. My cam (see sig) makes GOBS of torque everywhere but peaks at 6200/6300 with a rev kit and good spring pressure.

OneFlyn95z28

heck we reported that 6 years ago

bunker

Yup, you have to custom build a cam IMHO, if you don't, stick with traditional soft ramp cams as I've yet to see an off the shelf XE cam make any good power as apposed to a soft ramp cam like cc306/gm847.

rskrause

I like the XE lobes, but they are not "plug-n-play". They need excellent supporting parts (such as springs) and no matter what are not well suited to a high revver. They work GREAT on blower cars, however! Just don't plan on more the 6,200-6,500rpm though.

Rich

mastrdrver

Correct me if I am wrong, but I think it would be better to run 977s with the XE cams to help control the valve better then with a 986/7. The problem runs into if you don't run the right lifter and spring height, you can colapse the lifter.

How does the XE ramps compare to the cams from Crower? I have noticed that their ramps look just as fast as the XE ramps(from the adv dur numbers).

Also, given the same valve timing events at .050 duration, how will a softer ramp cam compare to the XE ramps? I would asume it would lack some power on the bottom, but catch up to it on the topend.

Muskys SS

6200/6300rpm seems about right for a 224/230 cam doesn't it??

bunker

Umm... Musky are you reading anything at all or are you reading only what you want to read? That cam will most likely die at 5700-5800 if its an off the shelf 224/230 XE on a 112lsa.

The 236/242 XE's make it to 6200rpm, 6500 maybe if you ran real strong springs like I'm running and thats drawing the line, my 236/242 fell on it's face at 6100rpm with lesser springs but they were still Crane 10308 kit springs with 130 lb on the seat and a hydra rev kit with steel retainers.

The 224/230 will most likely not make it there but who knows, comp's cams are all different, some break upon start up, some make more power then others so who knows.

Isn't the advertised durration of the 224/230 at .006 274/286?

Then you have the cc305 with 276/290 duration at .006

So its smaller there then the cc305, however who knows, the only way to find out is to put it in Shawn, you prolly already did that anyways

Juiced Impala SS

I have done quite a few dyno sessions and my peak HP is at 6200/6300 pull after pull. Considering the 383 stroke should bring the peak HP a few RPMs, getting to 62/6300 is quite good. I've revved ti to 6700 and seen a drop of 30-40 HP.

My cam is 224/230 .605/.622 w/ 1.6, 114 LSA, AFR rev kit, Comp 914 springs Schubeck lifters....

If your BIGGER cam fell on its face at 6100, then you have other issues, IMO.

rskrause

I have used the 224/2236 high lift XE lobes an made peak hp at ~6,200.

Rich

AdioSS

I'm betting that if you had better flowing heads, lighter valvetrain and/or a smaller cubic inch engine, the XE lobes would be able to pull to a higher RPM. Noel's heads are pretty darn good, and I'm sure his fairly hgih compression doesn't hurt the higher RPM output.