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ALL vortecs lose torque to a TBI head under ~4K. I have worked on numerous dozens of examples of both the TBIs and L31s both stock and modified. On just about any combo the TBI heads will have better torque to 4,000-4,500, then the vortecs pull ahead. The TBI heads burn the air/fuel much more quickly.
Except it took GM a better flowing intake manifold, better exhaust system, dual monolithic cats in place of the pellet box, sequential fuel injection and a roller cam, giving a higher dynamic compression ratio to get to those factory ratings. That is not even close to an apples to apples comparison of the cylinder heads themself. Compare changing only the heads and it is a vastly differenr story. The Vortec roller cam alone is worth probably 20-30 ft/lbs over the flat tappet in the TBI. In fact I have run a L31 bottom end with TBI heads and still made right at 300 hp and close to 400 ft/lbs with headers, factory GM dual plane manifold and a Q-Jet.
Except I have done the actual testing numerous times with the same result. The Vortec heads were not where the added torque came from, they actually cost peak torque. Plain and simple. ALL of the torque improvement is the intake, exhaust and cam. Even stock L98 heads made more torque than the Vortecs.
sounds like you need to put a serious number on budget and see how far that will get you. 15+ years ago finding a set of somewhat decent vortecs was a non-issue, good luck now. you are better off going aftermarket and that's a whole new rabbit hole. L31MaxVortec has done ALOT more of this stuff than me, but I can tell you i have done a full 360* over the last 19 years of modifying this stuff. You are better off working with what you got. it will be more enjoyable than trying to make some "perfect" combination.this is not a cheap hobby and the "while i'm here" mentality will bite you hard financially & cause heartache.
I wrote an article 10/12/2006 on TGO about building a budget TBI. At that time it was not uncommon to be able to buy the whole L31 350 vortec for under $500 that had less than 100K miles on it. GM still offered the 1996 LT4 production cam for $182 new. The LT4 springs and retainers were also dirt cheap new from GM. At that time it was the best budget way to get over 300 hp out of a TBI engine build and still be able to pass emissions in most areas. I swapped several lower mileage L31 spring sets and cams without even unbolting the heads. Just yanked the valve train, put air on the cylinder, pulled the springs and retainers, swapped the LT4 units on after fully seating the valve seals, swapped the cam and bolted it all back together. Those times have come and gone. Good luck even finding a pair of OE Vortecs that are not cracked. I had a buddy go through 3 or 4 pairs before he found 2 that were not cracked. He got them done and within a year or two both had cracked. Ended up buying a pair of Etec170s that I tried to talk him into in the 1st place. He had the money and budget but was stubbornly into trying to run the Vortecs because the internet said they were the best thing since sliced bread and butter. FWIW his truck is the one that gained 15 hp @ 5,000 rpm from Vortecs after all that work. I had already told him multiple times he was not going to see anywhere near the 40+ HP people were claiming from swapping to them. 15 hp was a swift kick in the you know what to him. When the heads cracked, he got input from me yet again on how to get more power, he actuslly listened the 2md time. Went with Etec170s, a Comp XM270HR, bored out the GM TBI manifold to 2" and put a 454 TBI on it. It gained 70 rwhp over the factory cam/vortec head configuration and 40 ft/lbs at peak with gains from the load in at 1,500 rpm. That setup made a little over 300 whp and 340 wtq. The GM manifold was holding it back atleast 30 hp compared to a victor 2bbl single plane but at the time the truck had to go through smog tests and pass a visual inspection.
