First off what is the difference if any between the "late model" heads on a set of 91 LO3 and a set of vortec heads?

also will these heads work on a pre 80 block so long as I use them with the FI intake and what not?

 

...surely one of you guys knows the answer to one of theses...

 

91 LO3 heads should have 58cc chambers which give 9.5:1 on a LO3. Vortecs will have a minimum of 64 stock and will lower your compression ratio. Vortecs also have 1.94 intake valves and will flow much better than a set of LO3 heads wchich have 1.74 intake valves or something like that. I know they are smaller and the port design allows for more flow on the vortec heads. Both of which should blot up to an 80's block without any problem. Vortec heads will requrie some sort of cvortec intake although the standard third gen fuel injection may or may not fit, I don't have much experience with either. Hope that helps.

Gilley's86

 

ok that's useful information, what I have is a 30 over 400sb that I'm trying to build and an LO3 with a thrown rod, I'm hoping to get my hands on a 350 out of a fullsize 90's pickup which might or might not be a vortec motor. regardless of which set of heads I use on the 406 I'm going to have them machined for 1.94 onepeice valves bronze guides and studs, and port and polish them myself.
So, from what you're saying I might as well salvage the entire topend and computer out of the truck if I have access to that motor for parts?

 

No, more research required.

To correct some of the provided info: LO3 heads have 1.84"/1.50" valves. But, that's not the problem. The problem is they have "swirl" intake ports, which flow very poorly - they work fine on an LO3, but that's their limit.

L31 is the 350 "Vortec" version. There are also 305 "Vortec" engines out there, so beware. They have the same size chambers and valves as your LO3 heads, and flow a lot better than LO3 heads, but not as good as L31 heads. 1996 was the first model year for the L31, so "90's pickup" doesn't cut it. Most 90's pickups with a 350 will have the LO5, which is the 350 version of the LO3 - with the same poor-flowing swirlport type heads. They would be bad news on a 400.

Yes, the heads will bolt to an early block. You will need to drill steam holes in non-400 heads, including Vortecs.

The L31 induction was pretty poor. Don't do it. The LO5 induction is a better choice with a Vortec TBI intake manifold on a 400.

 

ok, I'm startin to get the general idea, so let's say I get stuck using the LO3 heads, it seems like they should be pretty much the same as the 350 heads considering the fact I'm not just gonna put any of the three choices on as is, regardless of what I start with I'm having them machined for larger valves and everything I mention in my previous post.

now let's say I do get my hands on the 350 and it actually IS a vortec motor those heads would perform better than the LO3 or LO5 heads with the same modification. correct.

so correct me if I'm wrong after doing the machining, porting and polishing, the lo5 andlo3 heads are gonna be identical and the vortecheads will be better than those but I have to have the intake from the vortec and not the LO3 or LO5.

 

Both the LO3 and the LO5 use swirlport heads - same "type". However, they are not the same heads. The LO3 uses 58cc chambers, LO5 64cc. LO3 has 1.84" intake valves, LO5 1.94". Both use 1.50" exhaust valves. Neither would work well on a 400. L31 Vortec heads would work well on a 400 if steam holes are drilled and proper planning for compression ratio is carried out.

The L31 intake is a unique design. You can't use one of those with a TBI unit. However, the aftermarket supplies an intake manifold that mounts to Vortec heads and mounts a TBI unit to it.

 

I'm not sure about the L31's but I know the 94 s10 I use as my daily driver has a 4.3 v6 with vortec heads and it's a tbi set up, are the v8's not tbi? even if not couldn't I just salvage the computer and the rest of the top end of the motor(intake, efi unit, and heads)

 

I forget exactly what it's called, but the L31 induction has a spider of fuel lines under the intake. From what I understand, it is finicky and difficult to modify for performance. The computer et al is designed for that particular system, so unless you take the whole thing, none of the parts will do you any good.

The TBI forum has more details in a sticky about a budget 350 build-up. Uses a Vortec 350 as the base.