Head Swap Options For 5.7L 350 TBI Engine

[Majoraslayer]

I noticed over the weekend that my truck has developed a head gasket leak (coolant in the exhaust, hard cold starts, and engine compression shooting pressure into the cooling system). Since I'm going to have everything apart anyway, I'm considering options for possible upgrades to get a little more HP out of my engine. My truck is a 1988 K1500 and uses all of the sensors/accessories for that year, but the engine block itself was pulled from a 1995 truck. There's not a LOT of difference there, but I want to mention it since some of the electronics had minor changes in 1994/1995 and the blocks were supposedly cast without provisions for a roller cam.

For reference, I'm looking at possibly following this guide for suggestions, and it's where some of my info I'll reference came from. --> https://harristuning.com/Tbi/recommended-350-tbi-mods/
I noticed they offer custom tune chips as well, so I thought I might work backwards from setups they use since I don't have a tuner shop anywhere near me for customization.

In the article above, the author recommends either swapping to Vortec heads or using a set of Summit Racing aluminum heads for better flow. I've already skimmed through the thread in this forum on swapping Vortec heads onto a TBI block, and it sounds like a pretty big headache (no pun intended) that I'd prefer not to deal with. Since Vortec heads are also prone to cracking, I'm moving them to the bottom of my list for options. I want a boost in power, but this will be a street truck and I'd prefer to make it as reliable as possible. Reliability may be a pipe dream if experience with this truck is anything to go by, but I'll do what I can anyway.

That brings me to the Summit Racing aluminum heads, which sound like a direct swap. The problem is that the Summit site lists them as Not Available, which leads me to wonder if they've been discontinued completely.

I know there are a lot of options to take here, including custom fuel systems or carb swaps, but I'm hoping to work within the confines of retaining a TBI setup. I'd prefer to keep my factory 700R4 happy without having to pull the transmission and do valve body modifications, since the TBI ECM controls TCC lockup in 3rd and 4th gear on these trucks.

I guess my opening questions are:

1) The Summit Racing heads sound perfect for what I want to do. Does anyone make a comparable alternative to the SUM-162108 heads that could accomplish the same or similar result?

2) Are there any other factory GM heads that would make for a good upgrade, without needing major block modifications to run TBI?

3) If I go the Vortec route, I may cut out the middle man and just get a complete Vortec engine instead of just swapping heads, then install one of the aftermarket TBI intakes. I know this would require swapping my chip (obviously) and my exhaust headers. What other modifications would I need to do? Will the rest of my accessories be able to work around the Vortec water pump, or would I need to run all Vortec accessories and brackets?

 

[98 Nitro]

Well the other GM heads that are an easy swap are the TPI ones, but stock wise it is not much of an upgrade, but they have more potential.

 

[Majoraslayer]

Well the other GM heads that are an easy swap are the TPI ones, but stock wise it is not much of an upgrade, but they have more potential.

If I do upgrade the heads, I intend to upgrade the cam as well. I'm just starting at the heads first, since the consensus is that the TBI heads are the worst bottelneck.

 

[Schurkey]

Far as I know, the Summit TBI heads are "done". Edelbrock also made TBI heads, and they're discontinued, too. If there's another supplier of direct-fit heads, I don't know about 'em.

Another option, depending on your skill level and courage, is to buy heads with the older 6-bolt intake pattern. Put aluminum bolts with Loctite thread-locker and "activator" so the thread-locker actually hardens, or epoxy, or Superglue, or whatever into the center two holes. Re-drill and tap those two holes at the proper angle and spacing to fit the TBI manifold. Overall, this is going to be the easiest solution.

Biggest nightmare on the Vortec heads is the lack of an exhaust-gas crossover port, which means the EGR won't work without major modification. Second issue is the insane amount of money GM wants for a TBI-to-Vortec-cylinder-head intake manifold.

There's a whole thread on Vortec-to-TBI swaps. Recommended.

When it was my '88 K1500, I installed ancient Trick Flow aluminum heads, an old-bolt-pattern ZZ4 intake manifold, and a TBI adapter plate. Again, the EGR was a royal pain, and numerous other issues needed rework or fabrication. The thing could really use a computer-tune, but runs acceptably well 95% of the time. Main issue is cold weather, engine-not-fully-warmed-up stumbling/misfire/hesitation. Completely cold is OK, completely warm is OK, but it doesn't like to be warming-up.

 

[L31MaxExpress]

The TBI heads are way down the list as far as the bottle neck goes in power. I have made 330 hp with a set of stock heads. I ran a 12520270 Goodwrench L05 years ago. The 8.75:1 compression version rated at 180 hp and 300 tq. With some basic airflow modification and tuning it made 204 whp and 306 wtq. Small 203/210 @ 0.050 GM roller cam bumped it to 250 whp and 320 wtq.

When I bolted that engine in, I put tri-y headers on that I swapped over from the 305 that was in it. I kept the 2.5" GM true duals that were already installed on my 83 G-van, but had previously added a Dr Gas X-pipe to them. Basically cut the pipes behind the trans crossmember, welded the X-pipe to them, then had a local exhaust shop bend up pipes to connect the Thorleys to the X-pipe, leaving the OE mufflers. When I first ran the thing it had an OEM TBI manifold and 350 throttle body. That manifold developed a coolant passageway leak from its previous life and neglect. I bought a 3704 and had it bored to 2". Put a 1" tall open oval center 454 spacer on it with a 2" bore 350 Marine TB and a 454 air cleaner and duct. The 454 aircleaner had a built in power bowl. Then I put 1.6 full roller rockers on it. When I first put the engine in it made 177 whp and 262 wtq with the headers, older OE dual exhaust and X-pipe. After the manifold/TBI/air cleaner swap and 1.6 rockers it made 204 whp and 306 wtq. Then I swapped a 1996 LT4 roller camshaft into it. Cam swap pushed it to 250 whp and 320 wtq.

Also for reference a stone stock light duty 210 hp crank rated L05 350 TBI does not make 160 whp.

 

[Moofus02]

The 2 95 motors I've had apart were both cast and drilled for roller cam

 

[L31MaxExpress]

The 2 95 motors I've had apart were both cast and drilled for roller cam

I have pulled a couple apart that were not. The 638 and 880 castings I have opened all had the roller provisions. There is another casting that ends in like 427 that does not have the bosses nor are the lifter bores machined down.

 

[L31MaxExpress]

This is the casting number that I have never seen as a roller cam block. It was used throughout the TBI years. I have seen them even in 1995s. Alot of the 95s had transitioned to the 880 blocks though. GM was building the L31 short blocks prior to Vortec engines. The 95 I opened had PM rods, vortec pistons and the vortec windage tray. Also had the vortec oil pan stiffening rails.

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[Erik the Awful]

If I were going to spend money on heads, I'd go with the AFRs. They're assembled and ready to go for $1250. Unless you're building a full-on race motor they're all the head you'll need. They were my plan on my $150 350 until my budget disappeared.

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[Majoraslayer]

The TBI heads are way down the list as far as the bottle neck goes in power. I have made 330 hp with a set of stock heads. I ran a 12520270 Goodwrench L05 years ago. The 8.75:1 compression version rated at 180 hp and 300 tq. With some basic airflow modification and tuning it made 204 whp and 306 wtq. Small 203/210 @ 0.050 GM roller cam bumped it to 250 whp and 320 wtq.

When I bolted that engine in, I put tri-y headers on that I swapped over from the 305 that was in it. I kept the 2.5" GM true duals that were already installed on my 83 G-van, but had previously added a Dr Gas X-pipe to them. Basically cut the pipes behind the trans crossmember, welded the X-pipe to them, then had a local exhaust shop bend up pipes to connect the Thorleys to the X-pipe, leaving the OE mufflers. When I first ran the thing it had an OEM TBI manifold and 350 throttle body. That manifold developed a coolant passageway leak from its previous life and neglect. I bought a 3704 and had it bored to 2". Put a 1" tall open oval center 454 spacer on it with a 2" bore 350 Marine TB and a 454 air cleaner and duct. The 454 aircleaner had a built in power bowl. Then I put 1.6 full roller rockers on it. When I first put the engine in it made 177 whp and 262 wtq with the headers, older OE dual exhaust and X-pipe. After the manifold/TBI/air cleaner swap and 1.6 rockers it made 204 whp and 306 wtq. Then I swapped a 1996 LT4 roller camshaft into it. Cam swap pushed it to 250 whp and 320 wtq.

Also for reference a stone stock light duty 210 hp crank rated L05 350 TBI does not make 160 whp.

I'll be honest, I don't really have experience building and modifying engines internally. Most of what I know comes from reading online and watching YouTube teardown videos. This whole thing will be a learning experience for me. That being said, I may need somewhat of a simplified explanation of some things.

I already have a couple of the "budget" TBI mods with debated gains: the quarter mod in the fuel pressure regulator, a TBI spacer, and an aftermarket carb-style open breather. Additionally I'm running tube headers to a dual exhaust with a crossover pipe and dual Flowmaster 40s. I read somewhere that the stock 700R4 is rated for up to 300-350 HP, but supposedly in practice it can start struggling to survive at 300 HP. Ideally I'd like to avoid the cost and work of upgrading the transmission. If I set a target goal of about 280-290 HP to preserve the stock 700R4, what kind of modifications would you recommend for my setup with the factory TBI heads?