demonsmokr

Maybe I'm searching wrong, but in coming up with nothing on the interwebs.

I have a bone stock 99 Tahoe Z71. It has the 5.7 vortec, and I'm wondering if i can swap the LT1 top end onto my existing heads and block. As opposed to an entire motor swap.

What I'm wanting is a better fuel injection system. The lt1 design is more efficient than the spider crap of the vortec, I'm assuming. I'm really just trying to get better gas mileage than performance.

Would a swap be worth it? I'm not wanting a hot rod, but a stout truck. I'm wanting it to serve the purpose it was designed for, but with every bit of gas mileage i can get.

Or would it be best to go the LS route with a 5.3 or 6.0 out of a truck or van?

Again, I'm just looking to get the best mileage really. This will be my do everything well truck. Nothing fancy.

ETA: i have my hands on a donor Cadillac with the LT1, not an fbody. Got it for a swap into my 75 formula, but the brain started hurting, and i started coming up with ideas to boost my dollars per tank on the truck first.

96capricemgr

iTrader: (1)

Not going to work.
Besides spending that kind of money to save fuel is silly since it won't ever return the investment.

bowtienut

iTrader: (1)

Furthermore, you'll get zero improvement in mpg's if you were to pull this one off.
The L31 (Vortec) fuel injection system doesn't leave anything on the table compared to the LT1 system as far as fuel mileage.
If you have gummed up poppet injectors on the truck, that's another matter. In that case, your best option is to get the upgrade that replaces the pressure actuated poppets with conventional injectors on the spider assembly.

BIGsmokey10

iTrader: (3)

Absolutely^^^^ I have 257 k on my 99 tahoe with the l31 and I have a set of fresh 02s and keep the maf clean and get 19 mpg going 65 and 15 city driving. . Your not going to really swap anything that will save a bunch of gas over the l31 and like caprice said not worth the hassle of swapping a motor. ..

If you were wanting performance I could see a lt1 swap but II'd run that l31 into the ground. .. if experiencing bad gas mileage put some fresh oxygen sensors in it and clean that maf plugs cap and rotor

Paul Bell

iTrader: (9)

Here's one upgrade you can do: http://www.theautoshop.net/VortecMPFI.htm

And here's another: http://www.pacificp.com/forum/viewtopic.php?t=317

Ed Wright

iTrader: (1)

We have owned both a 350" '97 2wd pick up and a '97 350" 2wd Tahoe. Put well over 100,000 miles on each. Had several customers at the shop driving those. Have not seen one single injector change I would consider an upgrade. Keep the MAFS clean, clean the injectors (flush on the truck) every 75,000 or so, and if you notice a slight hesitation, take a look at the rotor. I recommended to my customers a minor tuneup every 100,000 miles or so. Over half showed evidence of a leaking distributor rotor. A small hesitation at take off often shows up when the rotor begins to leak. Take it off and look at the bottom. A small black dot on the bottom, near the bottom of the rotor blade indicated voltage leaking through the plastic rotor to the steel shaft. Both of ours had 3.42 gears, and both consistently beat 20 MPG highway, and beat 15 around town. Nothing but tuning. Stock exhaust, air boxes, etc. I found no trick parts to be worth anything.

94FBIRD

iTrader: (5)

ALSO... the heads and intake of the LT1 and truck 5.7 are physically different and cannot be swapped. If you swap the entire engine, then there is the computer and harness swap required...ugh...not worth it.

Fast355

The best swap on these trucks is a L31 marine intake and the best $$$ spent is headers/full exhaust and an 0411 swap + tune. For performance the factory cam is also horrible.

Fast355

I am running a 97 Express with a Marine intake, ETec 170 heads, 215/220 @ .050 custom ground cam, Thorley Tri-Ys, full exhaust, 0411 ECM, backed to a 4L80E and GM 9.5" 14-bolt with 3.73s. 19 mpg highway and about 13 mpg in town. I have a bit of a lead foot and cruise 80-85 mph.

Ed Wright

iTrader: (1)

I have tuned a bunch of those. Had some Mexican versions in the shop from south Texas. 2001 models are the newer body style, 411 box, but the old L32 350" Vortec engines. They make the same power as the U.S. Version with the black Vortec box. No more power with the 411 box. The marine intake allows injector changes. As long as you don't need to spin it over 6000 RPM, there is no reason to change to the 411 PCM, unless HPTuners is all you know how to use. The factory LT4 cam runs pretty nice in those.

Fast355

They may make the same power but an 0411 will always have better driveability. It is a much more advanced PCM with more code, more RAM and a faster processor. I personally noticed a big driveability difference between PCMs.

The marine intake allows for injector changes and removes the garbage stock fuel system from the plenum. Makes servicing the injectors and fuel pressure regulator much easier as well. I gained 500 rpm of useable RPM from the intake swap alone.



The factory LT4 cam does run nice as does an Elgin E1136. It is 210/215 @ .050", .462/.470" lift, ground on a 110* LSA, 4* advanced.

I built a F-car LT1 cammed L31 and put it in a 1999 Suburban with the blackbox. Ran great for what it was.

Ed Wright

iTrader: (1)

With the black Vortec box, there is no reason to put in a cam that would like to rev higher than 600 RPM, since that box will not rev past that. The operating systems would need re-written to enable that. I have tuned and driven them with both boxes (the Mexican trucks) if the tuner knows what he is doing, both drive the same. That box references the V.E. tables all the time, unlike LT1 & 411 boxes. Changes there are much more evident. The processor in that box is faster than you or the engine. Faster processor speeds is more for emission controls, and might help some at very high RPM. That was not the reason for it. Much more going on in the newer Corvettes, than an old truck.
I can not imagine using an Elgin cam in anything. Really? That one you mentioned should run quicker shifted above 6000.
A bone stock 350" Tahoe will beat 20 MPG easily with just a little tuning. My wife's '97, and many customer's did all the time.

Fast355

Nothing wrong with that Elgin cam, it ran great. Sure its not a Comp XFI or a Lunati Voodoo but it gave a very nice torque increase across a broad operating range and has a nice throaty idle too it.

The 210/215 makes the bulk of its power from 2,500-5,000 rpm and likes to shift about 5,500 rpm, especially with the stock intake.

I shift my L31 Express at 6,200 rpm but it has a 215/220 @ .050 cam. It has the older Magnum lobes but no complaints here either.

Maybe you can't tell a difference or feel a difference but I can. My Black box was dialed in very nicely as well. My buddy has it in his nearly stock 97 ECSB that is lowered with 3.73s and a full exhaust from the manifolds back.

Not much you can do with the L31 gains mileage other than headers/exhaust/tuning, but you can add alot of power without hurting the highway mileage.

bufmatmuslepants

iTrader: (3)

I dont know how you guys are getting such good mileage on your vortec 350s. Mine runs great as far as I can tell, and I only get 14 highway at 75. Unless my MAF is dirty or my O2s are bad, I dont know. Thats been my only major gripe with that motor.

transbird95

iTrader: (4)

Mine is the same exact way. I never heard of anyone getting that good of milage with one either. Might have to try some new things after reading this thread.

bowtienut

iTrader: (1)

It depends a lot on the weight of the truck, especially in mixed/city driving.
4WD 3/4 ton versions will probably never see 20.
My 2WD C1500 extended cab at 451,000 miles (new GM crate at 250k with ZZ3 cam) still gets 21 summer and 19 winter on my daily commute. Best ever last summer on a weekend trip on primarily 2-lane highways was 23.3 mpg.
Self tuned, but it also got 20-21 highway summer mileage with stock cam and stock tune. It's never been very sensitive to O2 sensors or dirty MAF. I typically clean the MAF every ~2 years and it's never made a difference in mpg, just slightly less fuel trim correction. I used to replace the O2 sensors ~100k miles and never noticed a difference there either. The current ones have been in there for over 200k.

Ed Wright

iTrader: (1)

When my shop was still open, many of my customers did get 20+ highway. Most with stock tuning. The 3.73 geared trucks, and 4wd trucks, of course did not. The guys putting those big-assed tires on, naturally got even worse. The 4wd trucks all showed about 20 less on the dyno as well. Even in 2wd mode, the transfer case, and larger tires they use, eat power. I see guys talking mpg gains with headers. I have never witnessed that. Ditto K&N air filters. They just dirty up the MAF. I tested that as well. While sitting on the dyno, A-B-A tested the filters. Also removed the filter. Made the same power with the filter left out. High (3.42 or 3.08) gears, light wheels & light tires correctly inflated. Many guys put those big-assed tires (like 33" to 35") on, then change the gears to restore the over-all ratio to try to get some of thir performance back. Didn't get it all, then come to me for tuning "to get all my power back". I tell them "If I could do that I could probably walk on water as well." There is this **** called inertia. It's an *** kicker. LOL

transbird95

iTrader: (4)

Thanks for the info Ed.

Fast355

My 09/96 built 1997 G1500 Express was L31/4L60E/3.42 with 235/75R15s on it. Would get 17-18 MPG bone stock crusing 70-75 mph on long road trips. Over 500 miles to a tank (usually takes about 28 gallons to fill on a 31 gallon tank when the needle hits "E"). I have made alot of changes over the years. The only mileage improvement I have seen was a LT4 cam, 1.6 rockers, LT4 knock module and tuning all lumped togather. The headers and exhaust did not hurt the city MPG, but drastically increased the low-midrange torque which helped the highway mileage. I swapped two other cams into it and even put a marine intake and Etec 170 heads on it. Roughly the same mileage regardless. I swapped a 3/4 ton driveline in it as the stock parts failed. I replaced the 60E with an 80E and shortly after replaced the 8.5" 3.42 with a 9.5" 3.73. Highway mileage was unchanged, maybe 1/2 mpg worse, but city mileage dropped 2-3 mpg in all driving conditions. For the cam that is in it, the setup is undergeared for driving at slow speeds and accelerating from a stop. 4.10s or 4.56s and a 2,800 rpm converter would wake it up considerably, maybe even help the city mileage a little at the expense of highway mileage. The biggest mileage killers I have found have been bad/faulty ignition components, low fuel pressure, and front brakes dragging due to warped rotors and rusty, sticking caliper slides and bad brake hoses as well as my size 11 lead foot. I currently get 18-19 mpg on long trups cruising 70-75 mph and still get about 16-17 running 85. I have had the cruise set at 99 mph on numerous occasions as well. The old L31s do pretty well if you keep them up.

Fast355

My brother had a 1999 Suburban we bought knocking, put a .020" rebuilt, used HD L31 from a 1-ton van in. Slapped a used OBD1 F-car LT1 cam in with stock rockers, used a ported stock intake with a MFI spider set at 70 psi and backed it up to a S10 converter and the burbs stock 3.73s. Stock sized tires with a matching HP Tune it would get about 19-20 mpg. Added Hooker 1 5/8 primary long tubes, dual 2.25" exhaust, and a Volant CAI with power core filter. Added about 40 hp over the manifolds, factory exhaust, and stock JUNK air ducting. After headers and E-fans we saw 21 mpg on a long trip with a smallblock 400 engine in the cargo area we were delivering in Colorado. It would pull the mountain passes like they weren't even there. Only issue we ran into is we maxed out the spiders at 98% duty cycle.