TBI vs LS replacement

**lionelhutz** · 08-26-2017

Originally Posted by Fast355

Actually the Vortec 350 makes as much as 40 ft/lbs more than a 6.0 down in the 1,200-2,000 rpm range, stock for stock. In the 2,200-2,500 rpm range it will brake stall the same converter more than 200 rpm higher. The 350 in my Express in stock form was making close to 280 hp @ 4,500 and 380 tq at the flywheel at 3,000 rpm if you go off the 25% expected drivetrain loss of a 4L80E and 9.5" 14-bolt. Stock intake & exhaust manifolds, factory 3" piping to the cats, factory muffler, factory 2002 5.7 Express 0411 tune, descreened maf, K&N filter and tb lip removed, MFI spider cranked to 66 psi to match the OEM spider. Oh I forgot I also had the EGR disabled in the tune and blocked off at the valve with a plate between the intake and valve.

I don't care at all about your numbers. You have posted enough complete bullshit to show that none of them have any credibility. Previous crap like claiming numbers that the performance magazines with their typical over-inflated tests NEVER come close to matching with or that an engine with a cold-air intake and catback can put 50 ft-lbs more wheel torque down then it's factory rated flywheel torque. Add in the fact that you hate LS engines and you have no credibility. I liked the old small blocks and still have a few around, but have no trouble admitting that the LS engines can make more power.

You are completely full of shit about the L31 making up to 40 ft-lbs vs the 6.0L. Anyone who can use Google can look up this curve.

The LQ4 certainly DOES make hit 300 ft-lbs of torque in about the 1300-1400 rpm range. Add 40 ft-lbs and you're over the L31 peak rated torque.

Any claims about how a L31 does way more than rated after you do the simplest bolt-on mods is bullshit. Tons of people have proved that mods like MAF de-screening, TBI lip removal or catback exhausts pick up very minimal power.

Any claims about how a L31 picks up a bunch of power after more serious bolt-ons or a cam and tuning would also apply to a LQ4. It's not hard to find power in a LS engine with smart modifications and tuning.

**Fast355** · 08-26-2017

Originally Posted by lionelhutz

I don't care at all about your numbers. You have posted enough complete bullshit to show that none of them have any credibility. Previous crap like claiming numbers that the performance magazines with their typical over-inflated tests NEVER come close to matching with or that an engine with a cold-air intake and catback can put 50 ft-lbs more wheel torque down then it's factory rated flywheel torque. Add in the fact that you hate LS engines and you have no credibility. I liked the old small blocks and still have a few around, but have no trouble admitting that the LS engines can make more power.

You are completely full of shit about the L31 making up to 40 ft-lbs vs the 6.0L. Anyone who can use Google can look up this curve.

The LQ4 certainly DOES make hit 300 ft-lbs of torque in about the 1300-1400 rpm range. Add 40 ft-lbs and you're over the L31 peak rated torque.

Any claims about how a L31 does way more than rated after you do the simplest bolt-on mods is bullshit. Tons of people have proved that mods like MAF de-screening, TBI lip removal or catback exhausts pick up very minimal power.

Any claims about how a L31 picks up a bunch of power after more serious bolt-ons or a cam and tuning would also apply to a LQ4. It's not hard to find power in a LS engine with smart modifications and tuning.

I guess anyone can google this power chart too and realize what a L31 with a decent intake manifold will do. Remember he said nothing of using the stock Vortec truck intake manifold. The factory Marine cam is really no hotter than the truck cam. Marine L31 is 292 HP @ 4,800 and 370 TQ @ 3,200 with more than 350 ft/lbs @ 2,000 rpm. But what do I know. I have run a stock long block L31 in a TBI application with shorty headers and a 454 TBI unit on top of an edelbrock performer rpm intake manifold. It made over 300 HP at the crank and over 400 TQ at the crank. It did 260 RWHP/330 RWTQ through a 700r4 and 8.5 10-bolt with TBI.

http://www.gmpowertrain.com/2013_pdf...ine_010713.pdf

As for your factory rated power vs wheel power. My 2012 Titan put down 398 RWTQ on a stingy ass Mustang dyno and 296 RWHP after power correction. Real power was 6% higher than the correction in 45*F weather. The truck made over 300 RWHP and 400 RWTQ un-corrected. Same truck on a Dynojet made 330 RWHP. Factory rating was 317 HP and 385 TQ. Cold air intake, muffler swap, and a Hypertech programmer was all it had. On a 60*F sunny day on a decent track, it ran a 13.98 @ 98 on a 2.01s 60' with an open differential and well worn P275/60R20 Goodyears wrangler SRAs.

MAF descreen, TB lip removal, and K&N kept my MAP sensor from dropping above 3,500 rpm on the stock L31 setup. All stock it would pull down to about 90-92 KPA by 5,000 rpm on a 99-101 KPA baro. After the changes it would hold 96 KPA all the way to the 5,600 rpm fuel kill. The descreen also leaned the over-rich WOT air/fuel ratio down nearly a full point on stock tune. It was one of the first things I messed with and had a HUGE impact on how it ran.

**Fast355** · 08-26-2017

I have also seen numerous stock longblock, stock cam, stock intake manifold, stock head 350 vortecs put down more than 320 RWTQ once you open up the horrendous exhaust system they came with from the factory. The manifolds are not the worst part of MOST stock L31 engines. My Express van just happened to have a better factory exhaust system than any other factory LD L31 GM vehicle. Most of the trucks and SUVs used tiny 1 7/8" exhaust pipes between the manifolds and the mufflers with smaller cats. The Express van came out of the manifolds at about 2.5" and stepped up to 3" less than 6" off the manifolds and ran all the way to the muffler at dual 3". Makes a tremendous difference in power even with the stock manifolds.

**lionelhutz** · 08-26-2017

The numbers I posted are for the truck L31, not the marine engine. The marine cam had > 0.020" more lift and > 5* duration so they are not the same.

Claims that a manufacturer would leave 75+ ft-lbs of torque on the table by installing a terrible intake filter or muffler are grossly exaggerated.

**Fast355** · 08-26-2017

Originally Posted by lionelhutz

The numbers I posted are for the truck L31, not the marine engine. The marine cam had > 0.020" more lift and > 5* duration so they are not the same.

Claims that a manufacturer would leave 75+ ft-lbs of torque on the table by installing a terrible intake filter or muffler are grossly exaggerated.

The last line you just said is laughable....There are plenty of engines that can gain that kind of power with OEM vs Aftermarket intake and exhaust. My Infiniti M56 is the perfect example of that. It had 2 small panel filters, intake hoses that were smaller than the throttle body opening and had accordions, and then the exhaust had a horrible 1 7/8" to 2.5" Y-pipe, 2 resonators with a 1.5" ID core, and restrictive mufflers. I gained 8 rwhp form K&N filters. Replacing the stock intake ducts with HPS silicone intake tubes gained another 12 RWHP. 30 rwhp from a 2.5" dual exhaust with X-pipe and magnaflow setup after the manifold cats. I gained 50 hp at the tires without touching the long block or the tune. At a 20% drivetrain loss that is 62.5 hp at the crankshaft on a engine that was making about 450 hp out of the box despite its 420 hp rating. Magazine testing shows the 4,200 lbs car ran about a 13.4 @ 106 STOCK. I have run a 12.4 @ 110 mph in the car.

As for your cam spec difference. Having run both cams in the same setup, the cam does not make 10-15 HP or TQ difference one way or the other. The only reason I even swapped in the Marine cam at the time is I had destroyed 2 different aftermarket cams in the engine. The Marine cam was $150 for a GM billet steel roller cam. The marine vs automotive difference is mostly the intake manifold and exhaust difference between them.

**Fast355** · 08-26-2017

For what it is worth this article almost EXACTLY matches a setup I ran on one of the L31s. Set it up for a friend of mines class c motorhome based off a 2002 Express van. Basically a .030" over STOCK rebuild with 1.56" compression height pistons, .016" steel shim head gaskets, and the marine cam. It did 230 RWHP @ 4,400 rpm and 304 RWTQ @ 3,400 rpm on 87 octane after some tuning. Using the stock L31 truck intake manifold, tri-y headers, stock cats, stock muffler, and a tuned 0411. His van probably loses more like 30% through the driveline as well. 4L80E and GM 4.56 10.5" 14-bolt full floater. I also know the HD clutch fan eats some HP off the crank.

http://www.hotrod.com/articles/how-t...l-block-chevy/