Head Swap Options For 5.7L 350 TBI Engine

Sean Buick 76 said:

I vote for re using the stock heads as well. In my opinion the strength of the TBI is reliability in stock form. Yes there are some modifications that can increase the Performance however the mail order tune chips are not ideal.

I would look at one of the following two options:

1. Find another Chevy 350 to build, just ensure it’s a roller cam version and do a complete rebuild on it and swap it in with a carb or a self tuning EFI kit.

2. Find a 99-06 LM-7 5.3 and regasket it and drop it in with a modified wiring and computer package. The LS engine is light years ahead of the TBI for performance and fuel economy.

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People want to claim the LS is superior in fuel mileage but I have NEVER seen that in any vehicle. I have also never seen the LS engines top end oriented HP curve account to much in the way of acceleration without deep gears and a lot of converter stall speed, which acts directly against fuel mileage.

L31MaxExpress said:

People want to claim the LS is superior in fuel mileage but I have NEVER seen that in any vehicle. I have also never seen the LS engines top end oriented HP curve account to much in the way of acceleration without deep gears and a lot of converter stall speed, which acts directly against fuel mileage.

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So if a TBI 350 gets 17 mpg and a 5.3 also gets 17 mpg but one is 160 wheel HP and the other is 280 HP which would you prefer?

I do understand the advantages of the SBC, and I’m agreeing about the low rpm torque.

To the OP: if you're someone with little to no experience modifying engines I stand by my previous statement. Fix what ya got. Having a vehicle down unexpectedly is not the time to be saying "while i'm here I might as well do XYZ". Especially if this is your primary driver. XYZ needs to be planned with a budget in mind, funds saved, tools bought, etc. Taking on a project like this will bring heartache especially if you get to the point of tuning and the mail order chips don't work, and you discover there is only a small handful in the continent that still tune this era professionally if you can even find them. YES there are some great options out there (EBL, etc) but you will not learn this or have it running like a top in a weekend if you never have tuned before. I have seen dozens of people over the years give up on projects because they thought it wouldn't be too hard or they "read it on the internet". The worst thing is having a vehicle down for months (or years) because you are trying to get it "perfect" the first time.

EDIT: I don't think LS swap is the answer either. I read and see all these people that get complete drivetrains for $500 and do LS swaps for $2000. This just isn't a reality for me. The average LS engine is $3500 where I am (Canada), usually just the engine. If you are lucky it will come with the harness and PCM. If you are buying everything because you don't have skill/tools/shop space/etc this swap can get VERY expensive and I don't think the cost is worth it. This swap will "nickle and dime" you to death.

If you REALLY want to modify your engine, I would stay SBC and buy a crate engine (short or long block) with a warranty and modify that with the heads/cam/intake you want. While saving up for that do small projects on your truck, like upgrading the fuel pump, exhaust, start messing around with the ECU, That way when you go to swap the new engine in you are not taxed with having to do EVERYTHING at once.

Sean Buick 76 said:

So if a TBI 350 gets 17 mpg and a 5.3 also gets 17 mpg but one is 160 wheel HP and the other is 280 HP which would you prefer?

I do understand the advantages of the SBC, and I’m agreeing about the low rpm torque.

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Given the way my driving style has evolved over the years, whichever one has more average torque from Idle to 3,000 or perhaps if I am pushing it 4,000 rpm. That is not the LS.

That being said a stock basic Gen3 is not making 280 whp. More like 220 if it is a 5.3L and 240-250 if it is a 6.0L. Both a 350 and 6.0L make around 300 ft/lbs at the tires on an optimized tune with headers and a good air intake. The 6.0L makes its torque higher at about 4,000 rpm where the 350 makes it lower at 2,800-3,400. I am going with the 350.

This is a comparison of one of the most basic L31 350s against the hottest 5.3L made the Gen V direct injected version. Give me the 350. No high pressure fuel pump, VVT, or DOD lifter crap to deal with. The DI version of the 5.3L makes a solid 50 ft/lbs more than the Gen 3 port injected non VVT version. The 350 has as much grunt down at 1,500 rpm as the new 5.3L has at 2,500. The 350 kills the 5.3L everywhere under ~3,600 rpm.

This was from a datalog on a more than 100 mile trip. I did not run over ~2,500 rpm at any point. The 383 makes loads of grunt and moves the van even loaded down to 7,500 lbs easily at low rpm. As I said before, give me the low-speed grunt over the gutless, dyno queen LS that only runs hard over ~4K RPM.

L31MaxExpress said:

Given the way my driving style has evolved over the years, whichever one has more average torque from Idle to 3,000 or perhaps if I am pushing it 4,000 rpm. That is not the LS.

That being said a stock basic Gen3 is not making 280 whp. More like 220 if it is a 5.3L and 240-250 if it is a 6.0L. Both a 350 and 6.0L make around 300 ft/lbs at the tires on an optimized tune with headers and a good air intake. The 6.0L makes its torque higher at about 4,000 rpm where the 350 makes it lower at 2,800-3,400. I am going with the 350.

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All good points I agree.

But the 20 year old me wanted the high rpm power. I’m old now so I want both lol.

I’m building my 92 2500 4x4 with a 3.73 14 bolt with an added limited slip, NV-4500 and 60 over 350 with vortec heads, 2500-6000 cam, GT-45 turbo and Holley fuel injection

Sean Buick 76 said:

All good points I agree.

But the 20 year old me wanted the high rpm power. I’m old now so I want both lol.

I’m building my 92 2500 4x4 with a 3.73 14 bolt with an added limited slip, NV-4500 and 60 over 350 with vortec heads, 2500-6000 cam, GT-45 turbo and Holley fuel injection

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Just did a similar build. Cam is more like 1,500-5,500 in the one I did and I used a ProFlow 4 injection. No turbo on it because it is just a budget cruiser. I doubt that engine will see the high side of 4,500 rpm much if any. The Proflow 4 is an experiment to me even, the stock injection would have been enough.

tayto said:

To the OP: if you're someone with little to no experience modifying engines I stand by my previous statement. Fix what ya got. Having a vehicle down unexpectedly is not the time to be saying "while i'm here I might as well do XYZ". Especially if this is your primary driver. XYZ needs to be planned with a budget in mind, funds saved, tools bought, etc. Taking on a project like this will bring heartache especially if you get to the point of tuning and the mail order chips don't work, and you discover there is only a small handful in the continent that still tune this era professionally if you can even find them. YES there are some great options out there (EBL, etc) but you will not learn this or have it running like a top in a weekend if you never have tuned before. I have seen dozens of people over the years give up on projects because they thought it wouldn't be too hard or they "read it on the internet". The worst thing is having a vehicle down for months (or years) because you are trying to get it "perfect" the first time.

EDIT: I don't think LS swap is the answer either. I read and see all these people that get complete drivetrains for $500 and do LS swaps for $2000. This just isn't a reality for me. The average LS engine is $3500 where I am (Canada), usually just the engine. If you are lucky it will come with the harness and PCM. If you are buying everything because you don't have skill/tools/shop space/etc this swap can get VERY expensive and I don't think the cost is worth it. This swap will "nickle and dime" you to death.

If you REALLY want to modify your engine, I would stay SBC and buy a crate engine (short or long block) with a warranty and modify that with the heads/cam/intake you want. While saving up for that do small projects on your truck, like upgrading the fuel pump, exhaust, start messing around with the ECU, That way when you go to swap the new engine in you are not taxed with having to do EVERYTHING at once.

Click to expand...

I should point out, this is NOT my daily driver. It's been a project vehicle for the past 17 years for sentimental reasons. I've done a 2WD to 4x4 conversion on it with a full frame swap, it's on it's 4th engine, and it's 3rd transmission. I call it the Truck of Theseus. My dad bought it when I was a kid to pull his boat with, we went on fishing trips in it, and it was the first vehicle I learned to drive in. Pretty much only the body is original at this point, because that's where the memories were made. I say all that to explain why I'm constantly doing financially unreasonable things to it, including keeping it around as a project in the first place.

That being said, that's why I want to use it to take on the challenge of a mild build. There's no need to rush or anything like that, but at the same time I'm not looking to do anything extreme.

I was in a similar spot a month or 2 ago. '88 k1500 5.7 with coolant issues around the intake or head gaskets. I did some research with the same thoughts- 'if I've got to pull the heads, might was well upgrade them.' From there it is a slippery slope. "New heads? Might as well do the cam while its apart..." Next thing you know a $1,000 repair turned into $3,500 in parts and at least 50 hours of labor (at my speed).

I talked to my machine shop guys about the heads before I tore down the engine. They've been around 25+ years. What they said is the factory castings on these heads aren't great. They're too thin in spots and are prone to cracking. They offered to vat them and pressure test them for cracks. They said there are replacements for these for about $300/per that fix the casting problems and said if I'm not going with an aluminum head its better to replace them with the upgraded cast ones than rework the originals. They said they'd source the replacement heads, test them etc... before I put them it, which makes sense to me. I asked about porting and polishing. Not a bad idea but no one around me does it anymore and it doesn't add that much performance wise. Plus it bills per hour and the time it takes ends up making aluminum heads a better option price wise.

I looked at the summit heads which are no longer being made. I believe they were produced for Summit by someone else that does have TBI heads in stock which flow better with bigger valves. I'll edit this comment when I find my link to those heads. I found a few articles comparing performance of different aftermarket heads on these engines. Although the Edlebrock performer TBI heads are still in production for around $1,100 each, they didn't rate as well as the others in those articles that cost half as much or less. Seems like some of the other performance houses have their own heads too, Jegs and Speedway maybe, and they did well in the test. I didn't get as far as checking those.

In the end, it turned out to be my intake gasket and valve seals. My truck now runs great, has plenty of power for everything I do with it. I'm still planning what I'll do for performance. It'll be heads and a roller cam & rockers, larger injectors, factory intake and a chip I can tune. Mine isn't a daily driver so I can fiddle with it for as long as it takes to get it running right. If you are going to keep the original intake, I suggest replacing the heater quick connect on the intake with either the Dorman stainless one or eliminating it and putting in a nipple. I put in the $12 Dorman steelie rather than replacing the hard pipe and was thankful the pot metal OEM one came out easily.

There is a thread here on performance upgrades which talks about both the TBI and Vortec that is worth a read. Basically for the TBI's it says the first stop has to be the exhaust. It is too restrictive for the CFM produced by the factory engine and any upgrade to the heads and cam produce more CFM. Shorties, a mandrel bent Y-pipe and a high flow cat; or, shorties, dual pipes to a single cat and single muffler (or two cats and two mufflers), all help. It seems like with just shorties, y pipe and cat someone got an extra 50 ponies.


Tranny wise, I put in a corvette servo in the 700R4 and noticed a difference especially in the 2-3 flaring which is all but gone now. For about $50 and some fluid, it was an hour well spent. I'll eventually add the Sonnax 4th gear super hold servo. Next time I'll just get both the 2nd and 4th gear servos from Sonnax and use the factory pin. The 700R4 has some issues that can be fixed with some parts in the valve body. I'm not a tranny guy so I asked here and got some good info that I haven't followed up on yet. I live in the mountains and do some towing so I want to be able to hold gears going downhill to engine brake and am leaning towards the command shift kit plus the stuff to resolve the known issues. https://www.gmt400.com/threads/700r4-4x4-advice.63915/#post-1346505 My tranny only has 60k miles on it. Otherwise I'd have it rebuilt and get the upgrades done then.