1998chevy1500

I apologize for the less than witty title, it was the best I could come up with. Looking at the following cams.

Comp Cams XR259HR...206/212 .515/.522 112+2LSA
Comp Cams XR265HR...212/218 .522/.529 114+2LSA
TR Old Man Truck Cam 214/220 .600/.523 115+2LSA

The truck: 2002 1500HD LQ4 6.0L 4l80e stock w/ Bassani mid-length headers.

The goals: More pull from idle to 6k. Mainly focusing on the idle to ~4k area. No plans to change out the stock converter, so low end torque is what I am looking for. I will probably be swapping out heads for a set of 243s at the time of the cam swap. Should bring the compression up to the same as a LQ9. Also, for longevity I would really like to run LS6 springs and never have to change them out over the next 100k+ life of the truck.

My thoughts: My research thus far puts even the XR265 as possibly a little big for my needs. See this post. Although the SSS runs a 4l60e which has a slightly tighter converter than the 4l80e from what I have read.
The XR259 will probably be too small by many peoples standards for a 6.0, even for what I want I am worried about it being so small that it wouldn't be worth the swap.
The Old Man Truck Cam. This one is a bit of a wild card, my research and a few assumptions would place this cam in between the above two, despite its larger duration than both of them. I will explain...
Most of this is taken from the Performance Trucks Cam Thread. Both Comp cams run XE lobes, that equates out to the .006" duration to be the .05" duration +53*. So for the XR265 it is 265/271 and XR259 259/265. Both of these numbers are available on Comps cam cards for these cams. The Old Man Truck Cam, however, is a much more aggressive lobe, well we do not know how much more, we will assume for now that it is a XE-R shape which is +49* (it may even be more aggressive, who knows). So for the OMTC we have 263/269 which would equate to a slightly higher DCR than the XR265 which should help keep more bottom end power without loosing any on the top end like the XR259 would.

My Concerns: With the aggressive ramp rate and .600" lift on the OMTC I doubt that the LS6 springs would survive for very long. I believe .570" is the max lift for LS6 springs. Also the max exhaust lift for the OMTC is lower than either Comp cam, no idea why or what the advantage would be. Also I have read that a tighter (smaller) LSA helps to move the power band down in RPM, yet the OMTC has the largest LSA of the 3. Advance helps move the power band down as well, but all three are +2 advanced.

Final thoughts: Custom version of the OMTC where the max intake lift is taken down to a usable LS6 spring size and the LSA is tightened up a touch. Maybe just settle with a XR259 and wonder what could have been. Or get the XR265 and wonder if the XR259 would have given me more power in the bottom end. So many variables.

Thanks all, sorry the post got a little long.

ap2002

iTrader: (8)

i would definately go with the 212/218, like mentioned with looser converter of the 80e, it is going to put you in the power range perfectly.... im looking into the same one for my 2500hd myself...

1998chevy1500

You are probably right, it seems to be the cam I keep coming back to after looking at other cams in comparison.

My reasons against the XR265: The max lift is a little small, the LS6 springs are good for ~0.580" (went and looked it up) and the LS6 ran the following cam in them from 02-04 GM P/N12565308 204/218 .555/.551 117.5 So I feel that I should be running something with ~.55x" max lift on it. Maybe lift doesn't matter than much for what I am looking for, haven't read up to much on lift pros/cons. Also, the ramp rate is a little slow, meaning I could get more power under the curve if I chose something a little more aggressive like the TR cam lobes. (Just don't want something so aggressive that it sounds like a little old lady is sewing curtains for the old man cam)

My reasons for the XR265: Low lift means the LS6 springs should last forever, although if GM went w/ .55x" lift on them stock then they should be able to handle it for 100k+ with no problems so that shouldn't really be a reason for it. XE lobes=quiet valvetrain. Respected company, off the shelf product.


Maybe I will have to just talk to TR and see what they can grind up that will compare with the OMTC with 0.55x" max lift and maybe a slightly tighter LSA (although I though I remember reading that a tighter LSA=worse idle) Ugh, decisions, decisions, decisions.

1998chevy1500

More thoughts to ponder. It appears that the gains in flow from more lift drop off dramatically after 0.500" of valve lift. There is very little to be gained by jumping from 0.500" of lift to 0.550" of lift, at least according to the info posted here. And even less to be gained from 0.550" to 0.600".

What that means for me, the lift of the Comp XR265 is sufficient enough to give me near max flow into the chamber without opening the valve anywhere near enough to begin stressing the LS6 springs. This should equate to a very long valvetrain life.

Now the only question is if I should be looking at a more aggressive lobe profile than the XE to give me more power under the curve, and also if tightening the LSA a little bit would be worth it for moving the power down lower.

1998chevy1500

More reading, more research. It appears that while a tighter (smaller) LSA moves the power curve down in RPM, it also affects the idle. It does not do this directly, it is the overlap that does this, but overlap is a byproduct of LSA. Take the following equation.

OL = Intake Duration + Exhaust Duration/2 - 2* lobe seperation angle(LSA).

A overlap value of -10* will give you a almost stock idle. A value of 0* will give you the chopy idle you like.

(this equation and comment on overlap value was taken from here)

Using the above equation we find the following (assuming that the duration is the 0.05" value, I do not know if that is the one you use for the calcs)

LQ4 01-04 196/207 .467/.479 116LSA -30.5OL
Comp Cams XR259HR...206/212 .515/.522 112+2LSA -15OL
Comp Cams XR265HR...212/218 .522/.529 114+2LSA -13OL
TR Old Man Truck Cam 214/220 .600/.523 115+2LSA -13OL
LS6 02-04 204/218 .555/.551 117.5LSA -24OL



Really, I am probably just going to have to get a custom grind made, so most of this is just research for what to ask for in a custom grind.

Next thought to ask. I know the XE lobes of both of the Comp cams are mild enough to give me plenty of valvetrain life, but what about the XE-R lobes, or the Thunder Racing (TR) lobes? I know that at higher RPMs neither would fair well with LS6 springs, but I am talking 6k for a max RPM, would they still be too much ramp rate?

sonoma43

iTrader: (1)

The TR lobes are just shy of the XE-R Lobes as far as being that aggressive, comp grinds TR's cams and they agreed to have something a little "different than the XE-R lobes, but not that much different" that is what a TR employee told me.
on a side note, the LS6 springs are not meant to handle the fast ramp rates of after market cams. although many people have had success running them for long periods of time, they to also wear out.
IMO it's not worth building it if your going to run a spring that is meant for a stock setup. its worth the $160 or whatever to run the PAC springs, they too should last a long time with the cam's you are looking at

1998chevy1500

Good to know when it comes to the shape of TRs lobes. I had read they were actually ground by Comp.

Well poo on the LS6 springs idea. I was really hoping that I could use a GM part for this. Oh well, whats a few $100 for piece of mind.
Now, to grill you on the PAC springs. As you saw above, I want this to all be working like the day it was installed in 100k miles, so aftermarket springs that begin to have trouble in 30k is just not going to cut it. What will the PAC springs hold up to in terms of milage/ramp rate/lift?

I saw this post a few weeks back, seems to be the best deal on their springs. PAC says the 1518 is rated for 0.650" lift. That said I would still probably try and keep my lift in the 0.55x" range, 0.57x" would be pushing it, as the flow gains above that are minimal.
How will the PAC springs hold up to abuse? I have read that many of the aftermarket springs need to be brought up to operating temp before you can do much revving. I don't know if I want to deal w/ having to warm the engine completely up every time I plan on going over 2k. Brittle springs will be no good for me.

Is there a particular PAC spring you would recommend? Looking at their catalog I see the 1218 1215 1518

sonoma43

iTrader: (1)

well, I actually run comp 918's and I have no worries about them breaking within 100K with my cam it's not exactly pushing the springs to their limits.
The Pac springs that are rated to .600 or .625 whatever it is will suffice, or if you want the comp 918's will be good as well, I have actually heard that one of the PAC springs are the exact same as the comp 918's but thats specualtion.
as far as a warm up period, I just wouldnt start it up and go crank it up right away. let the engine get to operating temp before stomping it. I start my truck and run it up to 3500 in the morning some times with no worries when it's cold, just not 6k. it's good to let the engine warm up anyway even if its bone stock. it only takes 10 minutes or so to get the engine to full operating temp anyway.

1998chevy1500

My reading thus far says that the Comp 918s used to be made by PAC back in the old days. PAC P/N 1218 to be exact, however Comp decided to ship the 918 production off to Brazil or Mexico or something, since then people have had problems with both the 1st and 2nd foreign design. I don't want to take that risk.

I would be very happy with the PAC-1218 as they would do everything I want and more, problem is I can't find them for sale anywhere but PAC, and their price is high enough that I could just get the Lunati 75818 for another $30 (the Lunati 75818 is actually a PAC-1518) and have some of the better beehive springs out there.

As for the warm up period, if ~3500 is OK on aftermarket springs without warming them up I am fine with that. I don't like revving the motor up too much until it is up to operating temp anyway. All I really want to know is that I don't have to drive like a little old lady until the springs warm up, 6k on a cold engine is just asking for trouble.

Check out this post from another forum, I believe that this guy works for PAC however, I have not seen any definite proof of that.
http://www.ls1gto.com/forums/showpos...3&postcount=16

GMCtrk

iTrader: (27)

I would only run double springs with the old man cam. It has a very aggressive intake lobe. Also, I read a post on here that two trucks, basically identical other than 1 had the 212/218 the other had the old man, and the 212/218 out ran it every time. I'd go 212/218 myself.