I have a 99GMC Z71 that I am rebuilding the engine on. Lots of mods. My question is this. Does anyone know what the steepest angle lobe ramp is that an LS1 engine with rollimg rockers and rolling lifters can take?

I bought a Dyno 5 Sim program and have loaded in all my mods and I am able to simulate dyno runs on any cam specs I desire. For instance, a cam with
250/260 at .006 and 218/228 at .050 with .6/.550 lift and a 112 LCA yields a 31 degree valve overlap and is rated as a medium ramp rate cam. It also gives impressive torque in the 1000 to 5000 rpm bracket with HP peaking out around 423 at 6000 rpm. Since this is a truck I am more interested in the high torque figures.

Will my double roller application handle this cam? Can the cam be made? Who would grind it without charging three grand?

Thanks for your input.

 

Comp's custom grinds cost the same as their off the shelf cams, usually between $375 and $400ish. The specs that you listed are actually very close to one of Comp's most popular 5.3 cam choices, which has been proven to provide nice torque and horsepower gains throughout the RPM band. The cam in my sig is also a nice improvement over stock and works well with the stock torque converter. If you wanted to go a little bigger, the Vinci Trucker is also a well known performer, especially in supercharged applications. (Vinci Trucker = 216/224 .551/.551 115). Once you start getting more duration like the Trucker, you're going to want a higher stalled converter to make up what you may lose down low...I'd use a 2600 for the Trucker in a 5.3. A wider LSA, like 114 or 115 will provide a longer flatter torque curve than say a 112, which may bring the torque on a little sooner, but will have a more peaky torque curve. Also, if looking for torque, keep the duration lower, under .220 IMO, to help keep the powerband where you want it

 

Thanks for your reply.
Can you provide me the full specs on the cams you mentioned? I need the .006 duration and the .050 duration to get a full comparison.

My rebuild has forged pistons with .165 and .104 valve reliefs for intake and exhaust. I would like to take advantage of these reliefs and reap the gains of higher lifts. I have room to go higher than .630 if I choose to.

I am running a .581/.581 with 114 lsa now and find it lacking. The .006 numbers are 269/271 giving an overlap of 42 degrees.

Comp cams did this grind and it is a custom in their eyes. As long as you pick a lobe from their catalog they will grind it for the fees you mentioned. However, if you want a grind outside their catalog, a $1500.00/lobe engineering set up charge comes into play.

The degree between the .006 and .050 values is what determines how fast the valve opens ( ramp rate ) and also determines how much volume is under the curve. The proposed cam I have has 32 degrees difference between the .006 and .050 duration figures. Does anyone know what the fastest ramp rate is a roller with roller rocker valve train can handle without compromising life expectancy?

The cam configurations in the Dyno simulation program I am using have torque profiles that hit 333ftlbs at 1500 rpms and peak at 418ftlbs at 5500rpms. This is well within the operational rpms of my trucks intended use. Moving the LSA out to 114 pushes the torque peak down by 5 ftlbs and back to 4500 rpms with a 14HP loss in peak HP and 4 ft lbs increase at 1500rpms.
Total average gains are better at 112 LSA.

The ramp rate question and a custom grind cam shop are the two areas I am in the unkown zone on. If anyone knows where I can find answers please chime in.

Thanks again.

 

Unfortunately I don't have the answers that you're looking for, but here's a link to one of Comp's catalog pages, which includes the advertised durations as well as duration@.050. the XR265HR is the ever popular 212/218 that many, many guys have run with great results. A search of both this section and the GM Engine and Exhaust Performance section will yield enough threads to make your head spin lol. It's offered off the shelf as an XFI RPM low lift version (.522/.529 114 lsa), as well as XFI RPM Hi Lift (.558/.563 115 lsa).

http://www.compcams.com/catalog/COMP...g_2010_190.pdf

Here's the specs for the Trucker as copied and pasted off of Vinci's website ( www.vincihiperformance.com ) ...they don't have the specs listed for .006, but have them for .004 instead...

DUR @ .004" 278*/ 286*
DUR @ .050" 216*/ 224*
LIFT .551/.551
OVERLAP 53*
LSA 115*