TBI Heads, how do they flow compared to Vortec Heads

[NavyCPO]

So I plan to build a 350 for my sons 90 Chevy Truck which currently has TBI heads and TBI intake and throttle body.  I told him to buy a set of Vortec Heads that I found cheap and they'd flow better for him.  That was before I realized that the TBI intake would not work with the Vortec Heads.  Shame on me.  The TBI to Vortec head intake from GM is like $650 you guys pointed me to and with shipping I figure a $700 Bill.  So now I'm wondering just how good are the stock TBI heads?  Did the TBI heads get and upgrade from the low intake volume of the stock Gen 1 SBC Heads (I think they only run about 160-170cc of intake runners and with 1.94/1.5 valves flow OK but not great.  Anyone have knowledge about the TBI Heads?  Should I just stick with his TBI heads and a good valve job or garage porting/gasket matching maybe?  I know the Vortec heads are much superior to the Gen I heads but how are the TBI heads?  I"m tempted to just switch him over to carbureted and use the Vortec heads but kind of like to keep his Stock TBI Fuel Injection setup so he can keep his stock fuel tank fuel pump etc.  Another thing I am curious about is the TBI only has like a 2bbl setup but I'm assuming because it's fuel injected it would get as much fuel as a 4 bbl carburetor would send because of the big injectors. (and of course he could get larger injectors for his TB I assume if we needed to and it all still goes into the plenum chambers) Did I make any sense there?  You guys following me?  Original question is TBI vs Gen1 Stock vs Vortec, then I babbled a bit...............LOL

[Jason72]

Flow of the tbi heads nothing worth talking about. If you look down the runners, you will see the casting has, let’s call it a “swirl generator “ in it that takes up a tone of space and is a huge obstruction as far as airflow goes. 
 

the tbi unit is only rated at ~500 cfm. You have them big injectors hanging in the way. 
 

as far as fuel delivery, you can switch over to a carburetor and keep the stock tank and pump. Just put a fuel pressure regulator before the carb. The tbi system only uses 15 psi or so if I recall correctly (the pump can generate around 45psi) . The steel lines can be rebent or replaced or spliced the same way you do brake lines with the exception the ends that connect to the fuel filter. Also, not all of the tbi engines have the hole drilled for a fuel pump push rod but that shouldn’t matter if you use the in tank pump. 
 

if you keep the tbi heads, the center bolts on each side are at a different angle than the classic small block so you need an intake for tbi heads. 
 

these engines were the first to be injected and meet emissions. They were meant to be fuel efficient and produce torque. And they failed at both lol. 

[NavyCPO]

On 5/21/2025 at 7:50 AM, Jason72 said:

Flow of the tbi heads nothing worth talking about. If you look down the runners, you will see the casting has, let’s call it a “swirl generator “ in it that takes up a tone of space and is a huge obstruction as far as airflow goes. 
 

the tbi unit is only rated at ~500 cfm. You have them big injectors hanging in the way. 
 

as far as fuel delivery, you can switch over to a carburetor and keep the stock tank and pump. Just put a fuel pressure regulator before the carb. The tbi system only uses 15 psi or so if I recall correctly (the pump can generate around 45psi) . The steel lines can be rebent or replaced or spliced the same way you do brake lines with the exception the ends that connect to the fuel filter. Also, not all of the tbi engines have the hole drilled for a fuel pump push rod but that shouldn’t matter if you use the in tank pump. 
 

if you keep the tbi heads, the center bolts on each side are at a different angle than the classic small block so you need an intake for tbi heads. 
 

these engines were the first to be injected and meet emissions. They were meant to be fuel efficient and produce torque. And they failed at both lol. 

That's a buttload of useful information Jason.  Thank you.  So it sounds to me like him keeping his TBI is actually just a waste of time.  Sounds like he'd be much better off going carbureted.  I thought they ran a much higher psi fuel pressure like 30-40 psi or so.  Isn't that about how much the TPI and Direct injection systems use?  I didn't think of just using a regulator to control the fuel pressure with the stock in tank pump.  As far as the fuel pump push rod, that wouldn't matter because I've picked him up a good Gen 1 block we were going to try to build when he gets ready.  Thanks very much for the helpful info.  Cheers!

[Jason72]

I do not recall the pressure for tuned port. 
 

[420ponies]

Just my $.02, You have the Vortec heads, buy a performer air gap intake and 600 edelbrock carburetor, a set of 3/4 length headers, and maybe a good torque style cam(low lift,RV style), would be a perfect 300hp small block. A great friend to us here, passed member (Robyn), had built one with his sbc back in the day, and was a great build and raced it also.

Edited May 25 by 420ponies
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