They seem to flow really well, better than every head made prior apparently (never really looked at as-cast camel humps vs. Vortecs flow numbers) but MOST people simply look at "it makes X more HP" and not the whole picture.
I've never run TBI heads. I've got TPI which already makes very good low end torque, I'm running long tube headers, and I've got a really mild roller cam that also is designed with torque in mind. So I'm not coming from a place of experience with TBI heads, just Vortecs, and I dumped all those parts into the motor at the same time. It does seem the Vortecs have little if any benefit over the TBI heads down low. If you don't need higher RPM, I'd think long and hard about the swap.
I'd take the heads regardless. Even if you don't use them, they could be resold later. Racing classes that spec stock heads often allow them, and they are thin castings, so they tend to use them up pretty quick. That transitions well into the thin casting part though...they often crack in the chamber IIRC, so be very careful if you do decide to get into them. Can't go wrong with free, but you'd want to ensure they aren't cracked before investing in the swap.
IME they need a LOT less timing than what previous heads needed. That becomes a bit of a pain with TBI.
Vortecs are often touted as being the end all, and the issues with them often are just kind of glossed over, but they are real. The valve springs are extremely weak, the valve guides are only good for about .450" lift without clearancing, they still have press in studs, they require guided rockers, they require a special intake, they may raise compression (depending on what your present head CC is), might have issues with TV cable geometry, and they benefit from a PROM tune. So that's a lot of money and time to invest in them, and I've not yet been convinced they are *better* than the TBI heads in terms of low-end.
If you google the specs of the L31 motor, which has a very mild cam, and whatever the truck TBI motor was, and look at the numbers, the L31 moved the power band into a higher RPM range, and at least with HP, the difference seems to solely come from the heads (oft-quoted/tested at +25HP over earlier heads) not from the induction setup...so if the Vortec heads make more power, but at a higher RPM range, are they REALLY any better if higher RPM isn't where you need it?
