Hi everyone. I just joined LS1Tech to make this post and start my build journey.
I’m looking for guidance regarding camshaft selection for my LS build. I want to take advantage of the extra cubes with a proper camshaft. Below are the details:2002 GMC 2500HD 4x4 6.0L LQ4 with 4L80E and 4:10 gears, G80 locker, and 33" tires.

Build plans:
The objective is good low-end/mid-range torque for fun DD use and occasional light towing. I'm not looking for a hot rod per se and will probably never see 6k rpm if I can help it.

• LQ4 block (stock bore if the cylinder walls clean up with a dingleball hone)
• 4” stroker rotating assembly (with 6.125” rods and -8cc dish pistons)
• ????? cam kit (upgraded springs and 7.400” 5/16” pushrods)
• 706 or 317 heads (both unmodified - I should have 10.06:1 SCR with the 317s and 11.18:1 SCR with the 706s; I don't know what would perform best for my setup, but running up to 93 octane is not a problem.
• rocker trunnion upgrade
• stock intake, TB, and MAF
• stock 4L80E and converter
• fresh timing chain set
• 36# upgraded injectors (with adapters to use my stock fuel rail)
• stock fuel pump
• Melling oil pump (10295)
• Fel-Pro fasteners
• Fel-Pro gaskets (likely .051” for heads)
• A set of 1-3/4” long tubes
• undetermined exhaust setup but most likely 2.5” and X-Pipe
• MSD spark wires 32829
• NGK TR6 plugs 4177
• 190* thermostat
I have already reached out to a few cam manufacturers and this is what I got back. This is by no means an exhaustive list, it's just what I've gathered from emails.

Tick Performance: towMAX Stage 2 TMX002 (the email originally stated TMX0013 but I assume that was a mistake because it was for rec ports, not cathedral). 214/224, .571"/.561", LSA 114+4

Texas-Speed and Performance: Stage 3 Low LiftTruck Cam 216/220, .550"/.550", LSA 112

Comp Cams: LSR Cathedral Port Roller Cam 54-456-11. 219/227, .607"/.614" LSA 112

Brain Tooley Racing: They haven't responded but they have a 4" Stroke Cathedral Port Truck Cam. 219/239, .553"/.553", LSA 115+0. They also have a variety of other "truck" cams that are popular among LS builds I've seen online.

Cam Motion: They haven't responded yet but they have a Torquey Stroker LS Camshaft for Cathedral Port. 235/242, .621"/.604", LSA 114. They also have several "truck" and stroker cams available but I don't know which one is ideal for me.

Anyway, if you have time, please have a look and maybe respond with some feedback. I greatly appreciate it!

 

The Tick and TSP would be in the ballpark. You can also check Summit and Vinci. Look at something in the 215 - 220° on the intake, no more than 10° split toward the exhaust, no more than 114° LSA, plenty of lift like at least .550". That BTR looks almost like a nitrous cam for rect port heads, if those specs are right; that CamMotion is a high-RPM racing cam for a light car, just altogether wrong for a towing type build for a heavy truck especially with stock converter and larger than stock tires.

I'd go with the 317s, or 243/799 if you want more compression. 706 is probably inadequate for that many cubes. The small valves in them would probably become the limit to the power output at a lower RPM in the larger motor than they would in a 5.3 or 5.7.

Don't hallucinate that you can order push rods before you build it. Buy an adjustable push rod and measure after it's all together.

It goes without saying that you'll need a tune.

 

So that’s a +1 for Tick (I was unsure if the timing advance would be detrimental to tune-ability and low/mid range power band).

You are correct, I have a guy that uses HP and he’ll be live tuning after the install.

Also, you make a valid point about the pushrod checker. I will either buy one or borrow from the neighbor)

 

Advancing a cam usually benefits lower-RPM properties generally. Retarding it favors higher RPMs by leaving the valves open longer, esp the intake, and taking advantage of the inertia of the air in the int tract rushing into the cyl, to fill the cyls more than they would otherwise; at the expense of leaving the int valve open past BDC which causes reversion into the manifold. So no, I wouldn't foresee a problem with that.

For that matter, if whatever cam you end up with doesn't have enough advance ground into it, you can use an adjustable timing set to advance it yourself.

I think the TSP would probably be better than the Tick for your situation but either is OK.

 

ah ok. What makes you lean toward the TSP? The lower lift? Tighter LSA? I’m trying to learn

Oh, and what were your thoughts on the comp cam recommendation??

 

Think the 317s would be a good choice for that combo as well. Check into the Summit SUM-8720R1 218/227 112+2 .600/.600 (also available as a complete kit). For a 402 with 10:1 in a heavy truck that won't generally see past 6k it's a good fit. Consider upgrading the intake and throttle body with a NBSS truck cathedral port and 90mm.

 

thanks man! Is .600 lift on the upper end of what I should be looking for? Also, will the additional lift (~.550” > .600”) suffer if I DON’T upgrade the intake and TB right away? Those are both upgrades I plan on making in the future, just don’t know if they’re what you’d call make or break components considering my budget limitations.

 

I think a large int/exh duration split will reduce torque without any benefit since you're concerned with low RPM.

The Comp looks like a rect port cam. The large int/exh split favors those heads: the int flows considerably better than cathedrals, but the exh is about the same and therefore needs some help.

With stock unported ports, the valve becomes no longer The Bottleneck, past some given lift. Instead, the port is The Bottleneck, meaning that no matter how far you open the valve, it doesn't flow any more. In fact it's possible to get into a situation where adding more lift actually decreases the flow. While a higher lift cam will have to have more aggressive ramps, and therefore opens the valves more at all times even when it's at lower lift parts of the ramps, you get to a point where the bigger springs, higher stresses on everything, etc. don't give enough "more power" to outweigh the hassle. Diminishing returns. For a DD, aim more for reliability than maxing everything out: leaving 2 or 3 HP or ft-lbs on the table, is preferable to breaking valve springs or bending push rods or wearing out rockers every few thousand miles.

LSA is the angle between the int and exh lobes. All valve events are measured off of the int lobe center; which may or may not be the peak lift, if the ramps are asymmetrical (many are: usually, steeper on the opening side, and more gradual on the closing side). But however that may be, the single most important valve event, is the int closing point, because of the "ram" effect of the air in the ports. If the engine ran at a very low RPM all the time, or if air had no mass (inertia), then you'd want the int to start opening at TDC, and reach fully closed at BDC; and you'd want it to snap open, from zero to max, as near instantaneously as possible. But for any higher RPMs than a couple of hundred, that won't work; a cam ground like that would make it run like a tractor. So, the int always starts opening a little before TDC and closes after BDC. The later it closes, the more lower RPM power it gives up, in favor of upper RPMs. Similarly, the exh could open exactly at BDC and close at TDC, but again, this would put an extreme cap on the RPM range. Opening the exhaust earlier lets the cyl start to "blow down" before the piston reaches BDC, allowing more exh gas to escape during that stroke, which empties the cyl better to prepare for the next int charge to come in; but by doing that, the last few degrees of power production are sacrificed, since the cyl pressure goes to zero instead of continuing to push the piston down. Both exh duration and LSA affect this, as well as intake lobe center (cam adv/retard).

Remember that lobe duration is given in crank degrees (there's 720°, 2 revs, per complete engine cycle, which is 180° per stroke). But LSA is given as the # of cam degrees (360° per engine cycle, or 90° per stroke) between exh and int, and since the exh stroke comes right before the int, a high LSA means that the exh opens early. 90° would be the "theoretical" zero-RPM difference between them, and each would have 180° of duration. This is why lobe durations might be in the 200 - 220° kind of range for a truck on the street, and LSA is usually a bit over 100°; those #s are slightly larger than 180° and 90° respectively. Your stock cam is something like 191° with 116° LSA or some such.

Tight LSA tends to make a motor's peak torque and peak HP RPMs closer together, mostly by lowering the peak HP RPM; and tends to make both peaks higher and narrower. Wider LSA tends to kind of "smear" the curves in the higher RPM direction, and lowers both peaks; the net effect is to also move their peak RPMs apart. The area under both curves stays about the same no matter the LSA, they're just shaped and located differently. Wide LSA thus favors a broad RPM range of power, which is usually better for street DD type use. But for highest low - mid RPM torque, you don't really want either a real big exh lobe compared to the int, or a wide LSA.

When you install the cam, YOU control the "advance", by way of the timing set. Advancing the cam, i.e. making ALL valve events sooner in relation to the crank, moves the int closing point earlier; doing that raises cyl pressure (torque) by not letting any intake charge escape back to the manifold during compression. But at the same time it reduces the benefit that can be obtained from the airflow inertia effect, and also has the downside of raising the potential for spark knock. Which is why it moves all the RPMs of everything, downward. There's no absolute standard for what "zero advance" is; it's really kind of up to the cam designer to determine that. When a cam spec says +4 or whatever, think of it as designer shorthand for "I put this lobe that many degrees from wherever I would have put it if I wasn't optimizing it for this application". But you can then put it wherever you want.

 

Stock 317s don't stall until somewhere above .600", so keeping the duration modest while using the full flow potential of the head makes the best torque curve across the full rpm range; with little to no penalty to part throttle driveability. For the rpm range you indicated, with the 402 you don't need much more intake duration than that; it'll just swap low end torque and part throttle for peak rpm beyond what you intend to run it. It has a modest 9* pattern split which is good range for cathedral. It's -2* overlap is enough that you'll get some benefit from the exhaust charge pulling in the intake for mid and top end power. But with the larger displacement, it's still conservative enough that the light-to-moderate loads will make plenty of torque. The 65* intake closing @ .006" puts the DCR ~8.2:1 which can run on 91-93.

The .600" lift will help the GENIII intake & 78mm throttle body. The NBSS intake pretty much makes better power everywhere so it's a great upgrade, and of course mated to it's 88mm stock TB it breathes even better in comparison on the upper rpm range. You can certainly wait until you upgrade, but they're not all that expense to buy used. Biggest cost will be a decent aftermarket TB. Do a search on here and you'll find which brands work, and which ones cause tuning issues. You will have to re-calibrate of course, so unless you do that on your own, it might be smarter to do the upgrade first; so you don't have to go threw multiple tuning iterations with the change.

 

Is there any functional advantage the 8720 has over the 8728?

 

The 8728 would be an absolute stump puller on the low end, but with a 10.2 402, it'd push the limits for pump fuel (especially in a heavy vehicle). The 8720 would have more margin and pull harder in the mid and upper rpm range. keeping the IVC @ 050" in the 36-40* range make the best mid to upper (upper in your case being only 6k). At the same time the IVC @ .006" in the 60+* range will keep it pump gas friendly. If you kept the stock stroke, the 8728R1 would be better for your particular goals.

 

Can you expand on your comment on pump gas limits, please? Are we talking like 93 not being enough for towing or like 87 not being enough for DD use?

 

A "bigger" cam, since it opens the valves at times outside of their appropriate strokes, "bleeds off" considerable cyl pressure at low RPMs, which greatly reduces the tendency toward spark knock. A "smaller" one doesn't do this.

Check out the idea of "dynamic compression ratio", that's kinda what it's all about.

 

Oh so that’s why these long duration cams have poorer performance on the low-end? What you’re saying made some things click that were kinda fuzzy before. With DCR in mind, and at 10.06:1 (best estimate) SCR, do you know if 68Formula was referring to 93 not being enough even for towing or so bad that 87 won’t be enough for DD? If it’s 87 not being high enough for DD I can live with it and use 91. But, if 93 isn’t going to be enough to tow 5-8klbs, then that’s a problem.

 

Hard to say for sure. Plug that cam and your static compression into a DCR calculator and see what it gives. And yes, that's exactly why a bigger cam causes poor low end.

 

As it turns out, many cam manufacturers don’t like to publish their valve timing events. Trade secrets I guess?

In response to you and 68Formula, I plugged my basic info into a SCR calculator and got 8.97:1 using 39* IVC @ .050” on the 8720R1. From what I gather, this is still way too high even for 93 octane, much less 87-91. *The only liberties I took when calculating were an estimate of .005” deck clearance, simply because idk what it will be and can’t find any info only about this exact stroker kit. I also ran the numbers on the 8728R1 and it was crazy high DCR, so y’all called it. To get an 8.5:1 SCR I apparently need an IVC at 47-48 degrees. Sound right?

calculator entries:
4” bore
4” stroke
71cc head chamber
5cc dish pistons
.005” deck clearance*
.051” gasket thickness
4.020” gasket bore
6.125” rods
39* IVC @ .050” (Summit 8720R1)

If this is the case, I’m not sure how other people cam their strokers for actual truck use. I understand from you guys that I could go with a more aggressive cam to cut down on SCR but to do so would mean a penalty in bottom end torque. Am I overthinking this loss to low end power? Surely there are people running 87-91 octane out there on 402-408 strokers that actually maintain strong low-end torque, right?

Sorry if I’m all over the place, and thanks for the continued conversation. Trying to work and crash course timing/cam knowledge over the past few days is doing my head in.

 

DCR should be done using .006" lift. Summit posts both .050" and .006" lift, so you can calculate it properly. You should end up around 8.64 DCR with the 8728R1. While DCR is a guideline and not an end all be all definitive answer, you're on the very high side for pump gas. Usually cars running this range are 3000-3500lb vehicles. With your heavier truck and any light towing it's going to produce more heat and more likelyhood of knock.

If you don't have the .006" lift numbers, then as an estimate add 25* to the .050" IVC and be close. Some are a little more, some are a little less. For example Cammotion is typically 55* more duration @ .006" than @ .050", so the IVC @ .006" is 27.5 more. Factory cams tend to be even higher. But most aftermarket tend to run in the +48 to +50* @.006" duration.

The valve events (@ either lift) can be calculated if you have both durations, the lsa and advance. Just plug it into Summit Calculator. https://www.summitracing.com/newsand...ing-calculator

Some, do try to hide there specs. Pointless IMO. If someone has the means to make copies of it, then they should also have the means to measure the full lobe profiles too. So all they need is to order one. If a person just wanted one for their own use, they'd buy the seller, not take the specs and give them to a custom grinder that would just cost them more.

 

I used a different calculator this time and input IVC at .006” (57* for 8728r1 and 65* for 8720r1). Now I see that DCR for the 8728r1 is 8.81:1 and for the 8720r1 it’s 8.33:1. Again, I’m assuming .005” deck clearance here. From what I understand, I may be able to get by running 91 (doubtful on 87) with 8.33:1 even while towing light to moderate loads.

With that sorted out, I feel much better about the 8720r1 from your original recommendation. Thanks a bunch man!

 

Ok guys, I’ve narrowed it down to three contenders.

Summit 8720R1 ($320)
218/227 .600”/.600” 112+2 LSA

Tick TowMax TMX002 ($390)
214/224 .571”/.561” 114+4 LSA

Vinci Custom ($460)
218/226 .570”/.578” 113+5 LSA

If it was your truck, which would you go with?

 

Those choices are all going to be very close, but I would go with the Tick. It will be very slightly easier on your tuner than the other two, and we are really splitting hairs at this point. If it was my truck I would put in a higher stall, trans cooler, bigger cam, and turbo, so that point of view is a bit irrelevant. For your stated build goals it is almost a coin toss between the Tick and Vinci. So close I would not spend the extra $70 for a difference I would never feel.