454 (7.4L) swap / repair options - 1999 Suburban K2500

[Carlaisle]

The fuel injection system works pretty well on these engines, so unless there is some compelling reason to delete it, I would leave it alone. Just swap in some good injectors and you're done. Most likely won't even need to retune if you use the right ones.

A crate 454 would be by far the easiest and most economical option. For every day driving the 6.0 will outrun the big blocks. The big blocks will both easily out tow the 6.0 hauling heavy if that's a deciding factor.

Not sure why you think you might have a broken valve spring/rocker. My experience with expensive-sounding valve train noise in these engines has always revealed the lifters to be the culprit. Severely eroded camshafts crop up sometimes, too.

The L21 gives a more reliable and smoother engine by getting rid of the distributor and associated components. Stutaeng has the conversion process about right. Need to convert to a 411 PCM to run the individual coil packs. Can't remove the distributor - need it to drive the oil pump. A few other details, but it's not terribly complicated. FYI: the L21 has the exact same crankshaft as the L29.

 

[L29Sub]

L29s are tough on cams. But they generally go further than 150k. A curious noise at valve speed could be a loose rocker stud. They are simply bolts. They'll back out and sounds like a flat lifter...but still runs ok early on. As OP dedcribed head gaskets and such..who knows.
An 8.1 is an expensive item if good, known low mileage. But. It's a heavy turning truck engine designed for towing at low RPM.
For some, working out a '411 would be doable. An 8.1 will be a really tight fit into his '99. All custom plumbing, exhaust and radiator. 8.1s are rare.
We part company on Vortec factory FI. Those things are a crap shoot. All the plenum wiring is brittle and about useless. The injectors, if new ($$$$) quality brands are OK. But they are a ***** to access. Regulator is same. BB vortec distributors are crap. Quadrajets are good.
If going budget, the 454 base is ideal. Unless OP has huge funds and a lot of fab and electronic skills, neither the 6.0 or 8.1 is a good option. 6.0 is much better daily driver and quick feeling, it would require fabbed mounts and the same wiring mods as the 8.1.
I have no problem with being proven wrong...
One thing good about these discussions is that OP will get a feel for how to shop the various considered powerplants.
Next!






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[b454rat]

I don’t know where you guys are coming up with 454 are dogs. My 97 ECLB with 285s would smoke the tires from a stand still just hitting the gas. My father had a 98 ECLB lifted with 35s, wouldnt smoke the tires, but would friggin haul ass. The 8.1 shares the mounts with an LS and regular SB/BB, so mounting it won’t be any different. But if you want A/C you need the medium duty accessory brackets to mount A\C up higher. Those motors are rated 325-ish all the way up to 500 horses in boats, all by cam chance n tune. But dunno why they don’t last as long as a does. Stock motor not boats. And nothing interchanges. The blocks are tall deck, not an issue in our trucks, heads wont interchange, exhaust manifolds are the only directly interchangeable part. If anyone wants to read up on these motors I’ll link to the expert on these from CK5.

 

[LC2NLS6]

My cammed (208/214 .550/.550) and tuned 5.3 2009 burb (243 heads) even with 3.08 rear smokes my tbi 454 Suburban that has 4.10 gears, which is why the 454 is getting a cam, intake and sniper, but I'm sure it won't be able to hang with the 5.3 other than towing, which is the real goal. The LS is no joke with a cam, tune and exhaust upgrade. But, if a lifter is bad, slap a new bigger computer capable cam and lifters, and run the L29 as-is.

 

[b454rat]

Can’t really compare an LS with a TBI. I’ve had a bunch of TBI’s that ran very good, but engine mods n tuning can be a pain. LS’s have good power but no torque like a big block. And if your towing That’s what you need.

 

[LC2NLS6]

Cammed and tuned 5.3 has 350-400+ ft lbs everywhere in the useful rpm curve. Usually more than enough, its the suspension that limits towing more than power/torque.

https://www.hotrod.com/articles/big-gains-cam-swap-5-2l-ls-mill/

 

[Erik the Awful]

Option #1. Stick with the stock heads. Pony up for quality lifters. Call your preferred cam maker and ask what they're recommend for your application. Ask them if it would gain any real benefits from a roller cam - they might have a roller profile that crutches the TBI heads. Since it's a Suburban, I'll assume towing. There's not any real sense in building a high-rpm motor for it.

 

[Chris Westphalen]

Think of it as a racecar project, pick a budget, and see what you can do with that as a starting parameter. You can get a shortblock ready to go for 2200. Have the heads rebuilt and put them back on, L29 are I think 102cc chambers and with this https://www.jegs.com/i/ATK-Engines/059/SP06-HP/10002/-1 would be low 9's to 1 comp ratio? You can get a +22 but might be too much compression for pump 87 gas. Throw the stock cam back in or a mild comp 206/212 https://www.compcams.com/94-801-10.html
Headers are gonna cause trouble, at least on my 93 with rear heat and rear a/c the lines are in the way. Could do what I'm doing, cam, intake and holley sniper efi. Let the stock computer control the 4L80E by hooking the sensors back up like stock.

I've thought of doing what you are. Have you done it already and got it running? How does it work?

 

[LC2NLS6]

Working on it still, waiting on gaskets and balancer installer. https://www.gmt400.com/threads/93-k2500-suburban-454-holley-sniper-upgrade.50223/

 

[L29Sub]

Option #1. Stick with the stock heads. Pony up for quality lifters. Call your preferred cam maker and ask what they're recommend for your application. Ask them if it would gain any real benefits from a roller cam - they might have a roller profile that crutches the TBI heads. Since it's a Suburban, I'll assume towing. There's not any real sense in building a high-rpm motor for it.

He already has roller cam. '99s have decent heads too. Nothing like the '95 and down peanuts.
The rockers can be converted to adjustable. One thing to be aware of is final height of valve train. If the OEM throttle body is retained (factory FI components) the low profile valve covers are required. Throttle body interferes with tall covers. There are low profile roller rockers that can be used.
Comp Cams offers a couple of good roller L29 street cams with good enough idle and good torque beginning around 1800. With a 4:10, 245/16s, about 60 MPH in 5th will give about 2000-2100 R's. Any moderately radical cam will require the manual or a torque converter. Rad cam = heating issues with auto trans.
I went with a Scat stroker for a 489. Very pleased with outcome. I was able to tow in 5th pretty much on any interstate, there were exceptions. I-40 and I-26 heading into Asheville would be in 1/1.
I towed 6500 lb TT for several years. Great for that. Bought a 12k toy hauler and truck would pull it OK, the chassis was not up to the tongue weight. The clutch didn't like 12k either. Had low range for easy close work.

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