Do they really have 8.0:1 compression? If so I agree, it's begging for FI.

 

So which one is it? If it's the latter you're forged already.

L29[edit]
The Vortec 7400 L29 7.4 L (454 cu in) V8 was a truck version of the Chevrolet Big-Block engine. Introduced in 1996, it was produced for five years, until replaced by the Vortec 8100. Although introduced as the Vortec 7400 in 1996, it was basically a 454 Big-Block with a hydraulic roller cam, parts more suitable for use in light duty trucks, and more advanced technology. The engine had MPFI (multi-port fuel injection), and 2 valves per cylinder, which gave slightly more power and better fuel economy. The engine had a 107.95mm (4.250 inch) bore, 101.6 millimetres (4.0 inches) stroke, and produced 290 hp (216 kW) at 4000 rpm and 410 lb·ft (556 N·m) at 3200 rpm.
L29 Applications:
1996–2000 Chevrolet Silverado/GMC Sierra GMC Sierra Classic 2500HD & 3500 (option)
1996–1999 Chevrolet Suburban 2500/GMC Suburban 2500 (option)
1996–2000 Chevrolet Express 3/4 or 1 ton
L21[edit]
The Vortec 7400 L21 was a commercial version of the Chevrolet Big-Block engine used in the medium duty truck platform. Its design shared much with the L29 454, but with the addition of forged pistons and crankshaft, and coil near plug ignition. It had slightly reduced power compared to the L29 454 and used a different PCM. The L21 was paired with the early 4 speed Allison automatic transmission or manual transmission, depending on the application.
L21 Applications:
1998–2001 Chevrolet Kodiak/GMC TopKick/Isuzu H-Series 4500 5500
1998–1999 Chevrolet Suburban 2500/GMC Suburban 2500 (option)
1998–2000 Chevrolet Express 3/4 or 1 ton
1998–2001 Kodiak/Topkick
1998–2001 P12 HD Motorhome Chassis. The Workhorse W-20 is a clone of the P12 Chassis.

 

And how many of those have oil squirters to cool pistons?

 

Hiuh.
I figured there would be a different version for medium duty, but had no idea it would be an option for my truck. How would I find out?

 

Some do, some dont.

More modern stuff tend to do it, but not all.

it isnt as if it is an all out 50psi boost type of affair. It's still a very low power build, low stress so there should be no problem whatsoever running at at max load for long durations.

 

RPO codes are on a label attached to the glove box door.

 

I put in a stock 1998 454/4l80e in my 68' GMC truck and it got horrid gas mileage and the power didnt fell like a bbc. I put in a zz502 cam (came out of a new crate motor) put in a new converter (3500rpm) and a tune and it made a huge difference. I feel like the gas mieage may have gotten a little better but the power is there now.

 

I've been wanting to do this in my 1500hd, it has a 6.0 and 4l80e and it would be nice to have 5lbs of boost available to help it pull hills.

For long pulls, you would have to watch IATs, it would probably need a really good intercooler and possibly water/meth injection to keep everything cool, but other than that it would work.

Expect to burn tons of fuel though because at the boost afr ratio of 11:1 or so it would be flowing.

 

for low boost, it'd be daft to run as rich as 11:1

You'd be perfectly safe touching 12.0:1 with only 5psi, and at such low pressure air temps shouldnt be an issue at all, even with no intercooler.

 

Well that would be good, how much power will a 5.3 make at 5lbs of boost?

 

My car made 360 at the wheels on 5 pounds. 5.3, th400, LS9 cam, On3 76mm.

 

Well that would be a pretty darn good gain. I would imagine that combo would probably only put down around 280 or so NA. 80 hp gain and probably 120 torque would be well worth it.

Do you have the graph from the 5 psi dyno?

 

Did any of you ever build a turbo LS for towing? Or find a good source of info from someone who did?

My '77 C30 dually crew cab has the most anemic excuse for a big block in it. 245hp? Geez. Coupled with 9mpg and a top speed (comfortably) of 65 mph, it's a miserable combination for daily driving.

I've got a 6.0/4L80e to go in it. Trying to decide on N/A or Turbo. I'm an old Turbo Buick guy, so having power when you want it, is very appealing to me!

 

I have a turbo 4.8 in my tow rig, was a 6.0. It does pretty well for what it is. My buddy has a 2011 cummins with all the deletes and a tune, my truck will outrun it in a race but it does not pull as hard with a trailer behind it. I've pulled 14k and it wasn't an issue at all.

 

You put an NA 6.0 in that thing and you will miss that big block very quickly. Stocl smog motor or not. Your a set of heads, an intake and cam away from very good, usable power. Wait until you have to get past three grand to get and meaningful torque with an LS in a truck.

Ive got a 5.3 Silverado and a 396/TH400 Suburban. Newer LS truck will win in a drag race hands down, all day. The old school big block FEELS faster in daily driving and makes power where you want and need it. It is by far the better truck to drive drivetrain wise.

 

If I did nothing but pull a heavy load with it all the time, I'm sure that'd be true. Since I only tow my boat with it a few miles (<5 miles) about 20X a year, I'll have to respectfully disagree. I sold my '05 1500HD Crew Cab 4X4 recently. That was my "tow pig" before the dually. It had the same drivetrain (stock) that I'm putting in the square body.

Sure, I could dump $$$$ into the BBC and make a decent motor out of it. I was actually leaning that way for a while. Even with adding an FiTech or Holley Sniper ($1300), it's still a BBC that'll get 11mpg on it's best day with a light foot.

The specs on the 6.0 and 454 (stock vs. stock)
LQ4 6.0 - 300hp at 4400rpm, 360 lb-ft torque at 4000 rpm
454 - 230hp at 3600 rpm 360 lb-ft torque at 1600 rpm (<--your point)

Like I said, If it was a "Tow-only" rig, it'd be an easy choice. But dollar-for-dollar and long term enjoyment of the truck, I believe the 6.0 will make me happier.

Now, Turbo or N/A.....that is the question at hand.

 

I'm just telling you - and there are plenty of threads about this - that a LS motor in a heavy truck is a bad idea. Livable when not towing, awful when towing. They just don't make the torque low enough. And yes, it's more noticeable when towing. There is an absolute light switch that gets flipped at 2,800-2,900 rpm. Before that it will not accelerate or maintain speed on hills. Past it does great. And it is still there to a very noticeable extent when unloaded. So much so that I put a 3,200 rpm stall behind my bone stock 5.3.

I get 12.5 mpg in my new-ish truck. Unloaded. LS motors can make crazy power. But not the kind of power that is conducive to heavy trucks.

Your 454 has ridiculously low compression. Problem number one. Tiiiiny cam. **** heads. Get your compression up to modern standards, put a nice truck cam in it (what I have) and it will be night and day. My big block Suburban gets 11mpg and I have not touched the carb. Just threw it on, adjusted the idle and that it.

 

I understand what you're saying. I towed my boat (#8000) from Daytona, Fl to my house in Mississippi with my 1500HD 4X4. Big tires and stock gears had it down on performance already and it returned a whopping 5.9mpg all the way back!

My point is, I don't tow very often or very far. The 1500HD was fine unloaded and got around 13mpg.

I just have no affection for the big block other than it "looks right" in my restored 40 year old truck.

I've got the 4L80e and could put it in there behind the 454 and add EFI to the motor but....it's still a gas sucking big block. I don't know, everytime I have this conversation I go back to considering the 454/4L80e combo. The motor burns oil considerably despite supposedly having a recent rebuild. Appears to be the valve seals or the intake is leaking. Compression is good on all 8.

 

It looks right because it is right. And you talk about a gas sucking big block. Your driving a crew cab dually. You're never going to get great mileage. Your driving an enormous, heavy brick shaped vehicle.

Compression may be "good" meaning the rings are ok, but trust me, if it was built back to stock specs it's probaly about 8:1. Which is G awful for performance AND economy. I think a decent set of heads like Edelbrock Performers, a cam and maybe an FItech (I have on e sitting in my garage waiting to go on) would solve a lot if not all of your problems.

This is coming from someone who currently owns and drives both types of trucks. New vs old. I belong to another forum for old trucks and everytime I start going through a build thread and see an LS motor my heart sinks a little. Just my 2 cents.

 

An s369 on the 6.0 will walk all over That big block in all situations. Almost instant torque.