Real World 383 vs Built 5.3L vs Stock LQ9

L31MaxExpress

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I have tuned several vehicles recently and gathered a unique comparison between 3 of them. Acceleration runs made in nearly the same weather and same section of road. Different vehicles and different engine setups. The data was pretty cool and not exactly what I expected, but HP Tuners time stamps the data log so it is easy to get the acceleration times. The section of road I use for power tuning is about 1/2-mile-long section of service road that is two lanes wide. It does not have any roads or driveways that intersect into it and thus relatively safe to make a WOT hit on. Once across the gravel covered 4-way intersection the throttle is matted from a slow roll in 1st gear and away the vehicles went. I choose 25 mph as the starting point since the throttles were pinned shortly prior to that point on all 3 vehicles. The speedometer calibration is accurate on all 3 at 65 mph via GPS.

The results were surprising to me because the Suburban flat out feels like a race car. The converter hits hard and that 5.3L revs cleanly all the way to the 6,500 rpm shift points. It is loud, feels very quick for what it is and the 5.3L does a pretty good job moving the Suburban with the drivetrain combination it has. The LQ9 truck is nearly factory quiet and feels strong when the revs climb into the 3,500 rpm range and it pulls all the way to the 5,800 rpm shift points they tuned it for during the dyno tune. With the 4.10 gearing it is still a solid running truck but could definitely use a mild cam and a decent converter in the acceleration department. The 383 feels tame by comparison, it is also quiet, only revs 5,500 rpm before it shifts and that tall gearing in the 4L85E makes the acceleration feel like it is lagging behind.

1st was a 1990 Suburban 2wd with a L33 5.3L. The 5.3L was rebuilt with 0.020" over flat top pistons, milled and ported 799 heads, Texas Speed Stage 3 truck cam (216/220 @ 0.050 on a 112 LSA 0.600 lift), TBSS intake, 92mm DBC throttle body, 4" air intake with a 100mm LS3 MAF, Speed Engineering C10 long tubes and dual 2.5" exhaust with a X-pipe and Borla mufflers. Built up 4L60E transmission with a Yank SSR 3,000 rpm converter, 3.73 gears and ~27" tall P295/50R15s.

2nd was a 2005 crew cab 4x4 with a Zero-mile LQ9 swapped in place of the 5.3L. It has about 5K miles on it and was dyno tuned but had a ghost cam added that was not requested by the owner and terrible idle manners. He wanted it to run like a tuned Vortec Max truck should which for all practical purposes the truck is. I fixed the drivability problems with the tune and left the WOT stuff alone. It was not how I would have tuned it at WOT, but it put down 297 HP and right at 310 ft/lbs of torque at the wheels on the dyno. It has a 4L65E in it. 4.10 gears and 33" tall tires. The LQ9 has a new Magnaflow LQ9 Y-pipe that replaced the factory cats because one was plugged up and a Magnaflow muffler. The stock air box has K&N in it. It has an Airaid modular intake tube for a GMT900 and a GMT900 water pump and GMT900 upper hose. Those 3 things were done for aesthetics and to streamline the intake tubing. Truck has factory electric fans.

3rd was my 1997 Express with the 383 I built. 383 has 6" rods, 11:1 compression, LLoyd Elliot ported 210cc aluminum heads, Comp Custom cam (271/284 @ 0.006, 218/228 @ 0.050, on a 108 LSA and 106 ICL with 0.578" lift with the 1.7 rockers). Ported L31 truck manifold with AUS 48 lb/hr spider. Thorley Tri-Y headers into dual 3" pipes to the muffler, high flow 3" cats and dual 3" in/single 4" out muffler. 4" silicone intake ducting with a 100MM LS3 MAF. 4L85E transmission with a Performance Converters of North Texas custom built converter that flash stalls 2,850 rpm. 3.73 gears in the 10.5" full floating 14 bolt and 30.5" tall LT245/75R16s.

Raw Data from time stamps the instant the MPH reading was achieved. All time values are in seconds.

No 75-mph number from the 6.0 LQ9 truck because frankly it did not make it to 75 mph with adequate room to spare for stopping at the stop sign at the end of the test area.

5.3L--------6.0L--------383------MPH

50.421------xx-------46.655-----75
48.851----62.463----45.195-----70
47.271----60.663----43.745-----65
45.791----58.763----42.585-----60
44.491----56.685----41.275-----55
43.211----54.445----40.409-----50
42.111----53.222----39.505-----45
41.241----52.250----38.789-----40
40.491----51.315----38.039-----35
39.761----50.413----37.330-----30
39.041----49.422----36.585-----25

I know that the comparisons are apples to oranges, and I am not saying one engine is better than the other, but it was cool to see how they compared to each other in real world acceleration times. 25-75 mph is a great judge for how well a vehicle can merge onto the highway. The higher speed 40-70 is great to judge how a vehicle will pass on a 2-lane road. 25-40 mph the 5.3L Suburban edges out my 383/4L85E, then the 4L60E has to shift in the suburban. That 3.06 to 1.63 gear ratio jump is hard to overcome without alot of torque and frankly too much torque especially during the shift will blow the best built 60E to pieces. The 4L80E has a taller 1st and 2nd gear but the ratio gap is much closer. Shifting at 6,500 the 5.3Ls 1-2 shift recovery rpm is well under its peak torque RPM where the 4L80E puts the 383 right back into the meat of its torque curve. All 3 vehicles have functional TQ Management and Abuse modes still enabled.

Acceleration times from 25 mph.
5.3L-------6.0L------383-------MPH
11.380-----xx------10.070----25-75
9.810----13.041----8.610----25-70
8.230----11.241----7.160----25-65
6.750-----9.345----6.000----25-60
5.450-----7.263----4.690----25-55
4.170-----5.023----3.824----25-50
3.070-----3.800----2.920----25-45
2.200-----2.828----2.204----25-40
1.450-----1.893----1.454----25-35
0.720-----0.991----0.745----25-30

Various acceleration times and speeds
5.3L-------6.0L------383------MPH
3.450-----4.032----2.760----30-50
6.030-----8.350----5.255----30-60
9.090----12.050----7.865----30-70

4.550-----6.513----3.796----40-60
7.610----10.213----6.406----40-70

5.640-----8.018-----4.786----50-70
 
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L31MaxExpress

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My take away on this comparison. Build as much torque as possible within your budget and use a 4L80E trans. 4l80E has better gearing to keep the engine in its powerband and is stronger all around. I think the 5.3L would have had better acceleration with a smaller cam. I also feel a LS needs a good quality converter to help get it up into its powerband. The stock LQ9 is begging for a mild cam, TBSS intake and long tubes to open it up power wise. Last do not under estimate what a well thought out and built small block can do. Budget aluminum heads are very affordible and can make great power especially with the longer stroke used to make a 383.
 
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L31MaxExpress

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One last comparison from a data log of a 6.0L that I tuned for a buddy of mine. It is in a 2001 S10 Extreme. Has a 4L80E with a 3,600 rpm converter and 3.42 gears. The 6.0L is a LQ9 with 799 heads. Cam is a BTR Stage 4 Truck cam. It has a Fast LSXT 102mm intake and a 102mm Nick Williams throttle body. Custom 4" air inlet. Has swap headers and 2.5" exhaust. That light weight S10 gets it. The stock 799 heads however could use some work to make the most out of the cam ands Fast intake.

Raw Data
12.850-----80
11.760-----75
10.780-----70
9.620------65
8.850------60
8.330------55
7.660------50
7.050------45
6.420------40
5.590------35
5.110------30
4.750------25

Acceleration times from 25 mph
8.100----25-80
7.010----25-75
6.030----25-70
4.870----25-65
4.100----25-60
3.580----25-55
2.910----25-50
2.300----25-45
1.670----25-40
0.840----25-35
0.360----25-30

Various acceleration times and speeds
2.550----30-50
3.740----30-60
5.670----30-70

2.430----40-60
4.360----40-70

3.120----50-70
 
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Schurkey

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Years ago, I looked down my nose at "383" SBCs; I was all hot 'n' bothered for the 377 instead. (383 = 350 + .030 bore, stock 400 stroke. 377 = 400 + .030 bore, stock 350 stroke)

And...if the world were chock-full of good 400 blocks, the 377 would likely be more popular. The plain ol' 400 is a good street engine in itself; better-still with aftermarket rods and pistons.

But the world is NOT full of usable 400 blocks. The 383 has proven to be an aftermarket sweet-spot that overachieves. I've "come around" on the 383 combo. It's the best PRACTICAL combination; one that Chevy should have been using in production vehicles. The closest they've come to that is allowing an emissions-legal swap of the 383HT into 1500-series trucks.

I'm jealous.
 

L31MaxExpress

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Years ago, I looked down my nose at "383" SBCs; I was all hot 'n' bothered for the 377 instead. (383 = 350 + .030 bore, stock 400 stroke. 377 = 400 + .030 bore, stock 350 stroke)

And...if the world were chock-full of good 400 blocks, the 377 would likely be more popular. The plain ol' 400 is a good street engine in itself; better-still with aftermarket rods and pistons.

But the world is NOT full of usable 400 blocks. The 383 has proven to be an aftermarket sweet-spot that overachieves. I've "come around" on the 383 combo. It's the best PRACTICAL combination; one that Chevy should have been using in production vehicles. The closest they've come to that is allowing an emissions-legal swap of the 383HT into 1500-series trucks.

I'm jealous.
I actually kind of kick myself for not having started with a Dart SHP 400 block. 1 piece rear seal, 350 mains and OE roller compatible. I would have also gone with a 3.875" stroke in hindsight. Would not have cost me all that much more in 2017-2018 $ when I started this 383 build. As much as I like the 383 a 415 would have been even stronger. At times the 383 has to work pretty hard moving the weight with the 3.73 gear and the 415s added torque would be nice.

I never understood why GM only decided to warranty that engine in a 1500. Its a Marine 6.3L. It is capable of running long and hard just like the HD 350. GM cites PCM tuning differences as to the reason it is not compatible. Having tuned both, neither are ideal for the HT383. The trucks that would best benifit from the 383 atleast on paper from GM cannot use it out of sheer laziness on GMs part to put it through the certification process which I doubt the 383 running on the 350 tuning truly passes anyway. GM should have had an updated calibration to go along with that engine. Its similar to swapping a 6.0L or 5.3L in place of a 4.8L and leaving the 4.8 tuning. It will run but it is far from ideal.

I have tuned 3 HT383Es. 2 black boxes and one factory 0411. All 3 were lean and had knock retard. 2 were in 3/4 or 1 tons (1 truck and 1 work van) and one was in a 2 door 4x4 Yukon. With the full torque management in place they barely make more torque then the 350 they replaced. Once they are tuned they come alive.
 
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L31MaxExpress

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Expanding more on what I was saying above. The PCMs running these engines have a torque model in place. It uses rpm, dynamic airflow, cylinder displacement, air/fuel ratio being burned and current timing advance against the programmed MBT advance in a complicated torque production model. The torque model then subtracts the friction torque needed to run the engine itself, the torque to run the accessory drive and the torque to run the ac compressor and gives a delivered torque value. The delivered torque is then used for the torque management spark timing retard, transmission line pressure, and idle routines.

When I first started tuning these I did not understand what it all did in very high detail. My L31 with a mild cam kept feeling like it was being held back as if it had a fuel delivery issue. It was not until I put the thorley tri-ys on and suddenly had about 10° of timing missing at WOT that I was able to figure it out. The engine torque output limit is capped at 300 ft/lbs delivered torque. There are also limits for every piece of the drivetrain. There is even a model in place that predicts converter torque multiplication via converter slip rpm. Now back to when I put the headers on. When I logged delivered torque and realized it was a flat line near 300 ft/lbs for over 3,000 rpm I knew something was artificially doing it. I then noticed that 300 ft/lbs delivered torque setting and upped it to 450. All of a sudden I had my timing back and far more power. I was seeing output torque values near 400 ft/lbs.

I laugh everytime I see that GM HT383E claim of 444 ft/lbs, since I know darn well the PCM is detuning it to whatever it calculates for ~300 ft/lbs. With the stock PCM tuning in place that over 400 ft/lbs from 2,500-4,000 rpm spread GM claims it makes is less than 350 ft/lbs. That being said it will pin that 300 ft/lbs delivered torque value cap from just above idle through 5,000 rpm.
 
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L31MaxExpress

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Blueprints 383 L31 is hitting the same limit I have seen. The PCM is capping the engines torque output and the torque output on the dyno ends up a wavy near flat line as the PCM modulates the ignition timing to control engine output. I bet nothing more involved then adjusting the cylinder volume and adjusting the torque limit would make blueprints 383 make ~350 wheel torque.

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