So my thing is I can't find accurate intake runner length and especially the min cross sectional area. I haven't used some of the other engine sims like EngMod and some of the other less user friendly, and probably more detailed ones, but with DynoSim the developers have decided that basically head flow (vol/time), min intake cross section (in^2), and intake runner +intake port length has been enough information to accurately simulate what they need.

I attempted to model my GEN V LT1 which Corvette team posted the runner lengths in a power point, but I still had to estimate the min cross section using snap gauges and trying to sketch out the port with splines in CAD. Given that it's an area slight miscalculations are going to have a large effect in error.

I just don't want to have to tear my engine apart just to try to get specs and even if I do it's still really hard to measure. I could maybe try to get a digitized measure with the CMM machine at work though if they let me.

And on the cam profile estimation, I have used the DynoSim built in estimator which just looks like it tries to best fit the spline curve and maintain tangency, but it appears to over estimate the seat durations compared to when I degreed my cam inside my engine. I don't know if I can trust it and it's surprising how much of an effect the extremely low-lift right off the seat areas make a difference.

 

Sounds like you have the newer version than I did. Mine only had a drop-down list for intakes. To sim the GENIII truck intake, I used the stock LS6 (not ideal for true low end, but okay as a relative comparison) and an flow rate estimation for the 78mm TB. And then for sim of the TBSS/NNBS GENIV I found the "ported LS6" manifold drop-down and higher TB flow rate for the 87mm inlet. Cam had the option of inputting 0.050", 0.006", or both. It could infer one or the other, based on a "aggressive estimation" of the lobes, but then accuracy of course is reduced. So it worked best when you had both specs for that particular camshaft. Also doesn't take into account asymmetrical lobes, but that usually only shifts valve events a degree or so at advertised.

 

cam motion also cuts many of BTR's grinds, if i remember right.
but for a 4.8, there ain't much worth doing below 2500 anyway because it's just so little.

 

I agree with the above.
larger than stock cam to make more low end power with a 4.8 isn't going to work.
in my past experiences boost is about the most simple way to add power all thru the rpms.
I use to tow alot with a stock 6.0 and turbo. It made a substantial difference at 2000 rpms. I could set the cruise control and never had it unlock the torque converter or have to downshift pulling long hills towing 6000#+
when I took the turbo off I made a short trip to tow a Suzuki sidekick with a 16' trailer and it was miserable compared to with the turbo.

 

When calculating for dynamic compression you're supposed to use duration @ 0.006 not the @ 0.50 on the cam card. Some online DC calculators tell you to subtract 180° from the cam card duration at 0.050" and then add 15° to get the 0.006 numbers. It's not a 100% solid way because of different camshaft ramp rates. The ramp rate is probably what grinders are trying to hide from us lol.

 

If the OP is lacking bottom end then he needs gears not a cam for that 4.8, if you want power in that range then large cubic inches or get a diesel.

 

besides forced induction, anything you do for that 4.8 is going to be lackluster. I recently put a 6.0 in due to a broken spring dropping a valve and destroying no 7 chamber and piston. I used the same heads (799 and 243) nnbs truck intake, BTR truck 2 cam and the torque increase from the 5.3 to 6.0 with .4 increase in compression made a huge difference. The stock stall is great now where as before I wanted a 1800-2000 stall

 

So there is a lot of stuff I need that I don't have to get the accuracy we need. You can tell the torque curves generated by the sim don't match the typical LS double hump below 3600, they also don't peak at 4000 rpm like a LS should but instead remain flat from about 3200 rpms, which is way to optimistic. What we need is the proper lengths of the intake manifolds, GEN III intake, TBSS Intake, etc. and we also need the taper of the intake which I estimated at 1deg/in, I got this from a old hot rod article interviewing the GM team that designed the LS1 at its introduction. I also ran this with the "FE" sim, I could use the "Wave Action" sim, but then it would be more critical that I know the lengths of the exhaust manifold runners (running the wave action might be less accurate if you are running stock manifolds versus long tubes), and I would also need the correct length of the intake runners again and additionally need the smallest intake and exhaust port cross section.

I set everything up best I could for a bone stock (stock exhaust/stock intake/stock TB/stock everything) 4.8 and then compared it to the BTR and Summit cams with the only change being the cams:

 

I am also missing the advance on the cams, I know the BTR says its +1 degree advanced, but the curve is not determinate with just advertised and 0.050 duration, lift, and LSA. I think you still need to know one of the cam centerlines to locate the advance retard, if the BTR cam is one degree advanced, its one degree advanced from what baseline?

Although I don't think this explains the stock 4.8 torque peaking at 2900 rpms, there is something else I have put in wrong. I know from trying to model stock engines in the past I could never really achieve the typical LS torque peak where it should be from 4000-4600rpms, the sim would always show it peaking at 3600rpm or so as much as I tried playing with the unknown cam advance/retard and port sizes.

However with all that being said, it help confirm what everyone else was saying. There is a reason all these "tooners" and "super awesome" shops make all these ultra super "truck" "torquey" cams then start the dyno pull at 3000 rpms, they don't want you to see whats going on below that.

So if you're concern/goal is more towing, then yes low rpm torque is "better" since if you can operate the engine, for example climbing a grade, at a lower rpm instead of having to downshift and run at a higher rpm, you should in theory gain more efficiency as there will be less frictional and pumping losses at the lower rpms, along with less wear. However, its not like we are talking a huge difference here.

With all that being said again, if you took for example a LB7/LLY Duramax versus say a similar truck but with a 6.0 but you had a huge stage 3 type cam in the 6.0 to where it was making 400 rwhp while the Duramax was stock at around 250 rwhp, and you had 15k pounds behind it and you were racing both up a grade who do you think would win? Ignoring some other additional factors the 6.0 would get to the top of the hill way faster than the stock Duramax. At the end of the day if you're goal is to "race" or get to the top of the hill faster, more horsepower always wins (considering gearing is optimized and correct) weather you are fully loaded or not loaded at all makes no difference.

Now if you're goal, like I was saying before, is efficiency when towing, then yes that "low rpm torque" helps although the difference will be barely noticeable probably.

 

The BTR is a 202/202 111+1 meaning 111 LSA with +1 advance. So 110 Intake Centerline and 112 Exhaust Centerline.
The Summit 8727R is a 200/205 113+4. So 109 Int. Center and 117 Exh. Center.

Something seems very off though. What did you use for the stock camshaft specs and heads? The BTR should be higher in torque than with the stock lower than that. Even the dyno run in post #1 is showing a huge torque delta down low that doesn't reflect in your modeling

From what I've been able to find I believe that 4.8/5.3 is ground retarded (190/191 114 -2). Haven't been able to find advertised specs on it though.