When my GMT400 isn't enough...

[L31MaxExpress]

as a guy with a way way over built 454 TBI burb I say swap a junk yard L94 out of an escalade including the whole computer and wiring harness, few grand and a few hard weekends work plus time messing with wiring =403hp & 417ft-lbs, or to get any power out of the TBI the motor needs to be pulled and rebuilt, shaved deck, new full performance heads, cam, push rods, rockers at the least, the throttle body and ignition really limit any top end and the CPU's are untunable so getting a chip burnt is just guess work on how the motor will function but it would do fine for towing, you'll get ~350hp ~400ft-lbs for $4000 as a guess but won't have to mess with wiring

Also a few tips if you do rebuild the 454 in your burb:

1.)don't try and fit long-tube headers on, I have them on mine, not worth it, had to drop the engine in without them, unbolt the passenger side motor mount, hoist the truck, hoist the motor to sit on an angle then pass the passenger header from below. Then had to do it all over again cause their isn't enough room to get a mini-hi torque starter in with them in & its hard to not burn through plug wires

2.)don't put tall valve covers on, they rub the passenger side firewall, I took a hammer drill to a small area on my firewall to give it clearance so it wouldn't pop the valve cover bolts out when I floor it, looks ugly but works

L94 is a dog. I used my uncles direct injected 6.2 to pull my trailer just because he raved on how strong it was. Was not impressed at all. I wouldn't use to pull a utility trailer if it did not have a positive displacement blower on it. All rev and no grunt.

TBI can be real time tuned without touching a chip. It also will not hamper top end power to any degree. They make 54mm bored TBI units and those are way over 750 cfm. If that is not enough you can go to a 1:1 linkage 4bbl throttle body with 4 x 120 lb/hr high impedence injectors. Stock small cap HEI works well past 7,000 rpm if you use a DUI module or MSD 6A box to get the coil charged with the limited dwell time available at high rpm.

Look at what Mercruiser did with the 575SCI. Dual 454 TBI units on a blower on a 502 and it had 575 hp @ 5,000 rpm and low boost. Pulley them up and add a decent charge cooler and they reliably gain 100 hp or more.

 

[andy396]

Going back to @scottydl ‘s original post, I’ll toss in another $0.02. The cheapest and easiest upgrade you can do is trade your ‘95 L19 for a ‘96+ L29 because they basically have the same value. With how old they are their value is more dictated by their condition. So I would expect a ‘96 in the same condition as yours to be worth about the same as your ‘95.

Most folks seem to be most happy with their tow rig when they’re working it to about 70% of the manufacturer’s rated towing capacity. Taking the fact that GM only rated a L29 at 10,000lbs with its 410 lb•ft of torque means that you would be looking at a vehicle rated to tow around 14-15k lbs or has about 550-600 lb•ft of torque. Working through some math (and making some drivetrain efficiency assumptions) it puts you at about 1600lbs of force at 1:1 in the transmission. That’s right where a GMT800 Duramax runs. Now looking at a L29 GMT400 to get that kind of force at the wheels you’ll be in second gear.

Bottom line, accept you’ll be pulling grades more slowly in second gear at 3200rpm or save up and buy a big diesel truck.

 

[scottydl]

^^ That's probably the most realistic option in all honesty. You're right on value, I can't really see spending $thousands on L19 upgrades when I can sell and re-buy an L29 Burb for a much smaller margin. I do find it interesting that L19 and L29 2500's both state 10k# towing limit, i.e. the improved engine doesn't increase that capacity. Must be a limitation of the chassis / suspension. The 8.1L is bumped up to 12k# towing but that's GMT800 so other improvements there aside from powertrain.

 

[andy396]

There seems to be a lot of leeway in what manufactures state as towing capacity and real world performance. For the 5% increase in peak torque and more torque under the curve that the L29 brought they left it at 10,000lbs, but with a 10% increase in torque with the 8.1L they bumped it up to 12,000lbs. Like you said, must be other factors at play. As far as pulling grades, it all boils down to force at the wheels which relates to engine torque, gear ratio and tire diameter.

You’ll likely have to search a wide radius to find a L29 burb in good condition. If you can find an 8.1L burb I certainly wouldn’t hesitate on that either. I know in the pickups you could get the Allison transmission behind the 8.1L, not sure if you could in the suburbans or not. If so, that would be an added bonus if you find one. Good luck and let us know what to find.

 

[scottydl]

Yeah it took me a good while to find mine, which was advertised as a 1997 by the grandson of the deceased original owner. And I drove a couple hundred miles from IL to IN to buy it, learning it was a 1995 after arriving and going through paperwork. Everything else matched up and physical condition was excellent as described (and still is) so I bought it anyway. Of course I didn't know there were any 7.4L differences between 95 and 96+ at the time.

 

[andy396]

Did a quick search to satisfy my curiosity:

“The 8.1L/4L85E combination was only available in the Suburbans, YukonXL, and Avalanche. These SUVs did not have any manual transmission options after the 1999 model year. Nor could you get the Allison in the big GM SUVs.”

So no Allison. the Suburbans got a detuned 8.1L and the 4L85E.

 

[Schurkey]

“The 8.1L/4L85E combination was only available in the Suburbans, YukonXL, and Avalanche. These SUVs did not have any manual transmission options after the 1999 model year. Nor could you get the Allison in the big GM SUVs.”

So no Allison. the Suburbans got a detuned 8.1L and the 4L85E.

Bummer.

Different floorpan in the 'Burban, Yukon, and Avalanche? No room for the bigger Allison? Or just a marketing decision? (VERY dumb move if it was just a marketing decision!)

 

[What?]

Sounds like you can sell your current rig and get a 96+ 7.4L.

Supercharger upgrade is an alternate

8.1 Burb also a good option, that will cost a bit more.


https://phoenix.craigslist.org/wvl/cto/d/yarnell-1999-chevy-suburban-obo/6931360244.html

Selling my 1999 Suburban C2500 3/4 ton.

Only 135,000 original miles.
454 7.4L Vortec.
Battery about a year old.
Great tires, slightly over-sized and on premium alloy wheels.

Strong motor and transmission, takes me anywhere I want to go.
Seats 8, with flat folding second row and removable third row.
AC has been professionally replaced recently.
Tow package of course.
LED headlights and new housings.
Passes emissions no problem.

I am located about an hour north of Phoenix in Yarnell, AZ just north of Wickenburg.

Any questions please ask.

Thank You,
Andrew

 

[L31MaxExpress]

Did a quick search to satisfy my curiosity:

“The 8.1L/4L85E combination was only available in the Suburbans, YukonXL, and Avalanche. These SUVs did not have any manual transmission options after the 1999 model year. Nor could you get the Allison in the big GM SUVs.”

So no Allison. the Suburbans got a detuned 8.1L and the 4L85E.

Thats weird because the GMT400 and Express/Savana vans with the 8.1/4L80E were not detuned. I compared a Suburban tune with a Van tune and very little was changed. Some torque values and the MAF table for the larger maf used in the GMT800 trucks was the only real difference. Oh and the van had alot more throttle opening at lower pedal values.

 

[andy396]

Thats weird because the GMT400 and Express/Savana vans with the 8.1/4L80E were not detuned. I compared a Suburban tune with a Van tune and very little was changed. Some torque values and the MAF table for the larger maf used in the GMT800 trucks was the only real difference. Oh and the van had alot more throttle opening at lower pedal values.

That’s awesome that you looked into the details of this. It sounds like it’s not that much “detuned” after all.