Finally got my engine running good got all the bugs worked out now i want to change out my heads. i currently have a rebuilt 350 vortec roller block with 4bolt mains and i still have my 305 tbi heads on them cause i couldnt afford new heads at the time my engine died. now i have a set of vortecs but it turns out they are the 520 casting so 305 truck vortecs. will these work on my engine or will the compression just be way too high?

The compression won't be any higher than it is with the 305 TBI heads.

i thought that the 305 vortecs had a smaller cumbustion chamber?

Smaller than the 350 Vortec, but not smaller than the age-old 305 chambers.

sweet that puts me at ease. guess im strapping on some vortecs when i get the manifold...

You do realize that the only thing the 305 Vortecs share with the 350 Vortecs is the intake manifold mounting style. The ports themselves and chambers aren't like the "famous" 350 Vortecs.

yea just saw that when i was looking at the picture... so looks like i got a nice new set of paperweights. guess i can just resell them.

Do us all a favor, and post pic of them (chambers, intake flange, and exh flange); so that when other people ask about those heads, there's something to look at. Also post the casting #s.

this is what the combustion chamber looks like. notice it doesnt have the heart shape to it. man im still pissed about that... casting number is 520 listed as 305 vortec truck heads from 97 up.

anyone happen to have the flow numbers on these heads i cant find anything else on them.

The 305 vortecs have the same raise ports, the same intake and exhaust ports, and the same basic chamber shape. The ONLY thing missing is the little peak that sticks out between the intake and exhaust valves. The chamber in the 305 head is nothing like the older carbed heads. The 305 probably did not need the added swirl on the back side of the chamber with its smaller bore, therefore engineers obmitted the little vane. The flow is slightly less on the 520 heads, but it is more than the 081 TPI heads on both the intake and exhaust.

Keep in mind that the 305 vortec was rated at 230 HP/290 TQ and had a single catalytic converter. The 350 was rated at 245 HP/335 TQ and had dual catalytic converters. I installed a LT1 cammed 305 vortec in place of a 350 vortec and could barely tell the difference in power.

The heads I see in that pic don't look too terribly different from the older 305 heads such as 416 or 081, although the pic is such poor resolution it's hard to tell. Typical bathtub sort of thing with the boss around the plug. Maybe I'm missing something? Wouldn't be the first time.

Show us the intake flange. Put a known gasket of some sort next to it or on it, so we can compare them to a standard. Use a 1204, or a 90316, or whatever; just tell us which one it is.

here are the ports i dont have the heads yet i can take better pictures when i get them so this is just what the guy sent me.

got them today they look good have a little bit of surface rust on them but valve's look almost new the guy said they had 2800 miles on a rebuild. they just need to be cleaned and hit them with a nice coat of paint. ill get some pictures later i still need to get the gaskets for it so right now thier is really nothing i can compair it to...

Hmmm... those ports aren't in the "Vortec" location (raised). Looks like a set of 081s with the Vortec bolt pattern drilled on them instead of the early-model. Not that 081s are "bad"; but they sure aren't "Vortecs".

Those don't have the swirl-port "ramp" obstructions in the intake ports, do they? If they do, they'd REALLY be pitiful. WAY WAY less potential than 081s, without spending a whole day or more grinding those out.

they are 520 castings 305 vortec heads from 97 and up trucks.

does nayone have any pics of the "059" 305 vortec castings?
12558059

Agreed.
I was told by a very reputable head builder along with the head guy at the machine shop I worked at and he said the same thing, 305 vortecs will still be an improvement over the older heads, but not as much as 350 vortecs.

I was very much in the same situation as you were in. Build a mild lower end (350 roller) and rebuilt the old heads. Later, I got a pair of cheap 305 vortecs from my buddy, got my head guy to rebuild them with 1.94 valves, and yes, there was a definite difference.

I do somewhere on my laptop, I will see if I can't dig them up out of the 1000s of engine pictures I have on it. The 059s were on the 2000-2002 Express IIRC.

well i got the heads and the ports are the exact same as the 350's only diffrence is the combustion camber. here are som pics after i cleaned them up. for $200 shipped i think it was a good buy

Those don't look like "Vortec" intake ports (raised) to me. They look like the runners are in the "classic" SBC location. No matter what buzzword came along with them.

They are however just like the 906 castings that I have on my crusty carboned 1997 350 Vortec core in my garage.

Ummmm, I don't think so...

Looks to me like the 305 "Vortec" ports are about 1/8" - 3/16" lower at the top than the 906s. Compare the top of the port to the bolt hole.

I think so, take the intake gasket, intake, etc for example. They fit equally well on both. 3/16" is alot of mis-match. If I have to I will take my dial calipers to both, take pictures, just to show you they are the same. Atleast on the 059s they are the same. Port height and port width are the same, port shape is the same, etc.

Compare the top of the port, to just below the valve cover rail. Maybe I need to go scrub the head down for a clearer picture, then lay the 305 head on top for reference..

I didn't use dial calipers; I just drew a line on them straight across.

Looked like about half the bolt hole diameter or just a little less.

I know what you mean, but having both of them side by side is ALOT different than looking at two pictures, from two angles, from two different cameras, you get the idea.

I don't know for sure on the 520 castings, but the 059s ports are identical to the 062s.

Thanks for posting the pics. Never actually eyeballed these castings.

Looks like a head casting I could make something out of.

Bigger valves, porting, mods.

I guess some see the glass as half full, others see it half empty.

Here is a pic comparing the 305 vortec head 520 casting to a bowtie vortec chamber.

unfortunately they dont have the same chamber design but with a smaller chamber i doubt it was needed. i think the boosted compression would make up for the fact that it doesnt have the fast burn design. ill let you know what happens when i strap them on. im still waiting for my new intake to come in.

That Vortec 305 chamber is still a hell of alot better than anything you could get through the mid 80s.

The single cat 305 Vortec is only down 15 HP from the dual cat 350 Vortec.

huh... are you guys sure that the vortec 305 heads have smaller (58cc) chambers? They look smaller around the plugs, but I wonder if the open area where the 350 heads have the vein might make up for it

they are 58cc chambers anything bigger and the compression ratio would have been too low for the 305. i know its hard to tell from the picture but if you look at the outside edge of the chamber the 350 vortec is bigger. look at the distance between the coolant holes and the edge of the combustion chamber you can see the diffrence.

anyone know how big of a lift you can put on these heads? and what the cam specs for a 96 vortec 350 are?

nevermind i found it.
(with 1.5 rocker arms): @ .050 191in 196exh, lobe separation 110
lift .414 in .429 exh

Don't get too hung up on the subtle differences in the chamber shapes between Vortec 305 (L30)and Vortec 350 (L31). The keys to making them both fast burn are:

1. swirl imparted by the intake port bias and good intake airflow at all lifts;

2. projected position of the spark plug as close to the chamber center as possible;

3. Good squish/quench areas (helps keep the CR up, and it helps fast burn by concentrating the mixture close to the plug, AND finally the squish helps promote turbulence in the chamber as the piston rises to TDC).

The chambers themselves don't look that much different than the 081/083 (TPI) or 187/191/193/810 (TBI) chambers because GM had already made the chambers closed for smallest-linear-distance burn path and boosted CR during the mid 1980s. So when the LT1/L31/L30 heads came out in the early 1990s, the chamber shape changed very little from what it already was; the so-called heart-shape is not the major feature that makes the LT1/Vortec heads so good. The airflow into the head, while maintaining a fast burn, is what made it so good.

The big changes that raised the airflow happened at the valve (back cut for low lift flow gain) and in the intake port (flow gain everywhere).

great write up man. im looking forward to installing these heads just need to find a good intake combo for it.

[quote=kdrolt;3114417]

1. swirl imparted by the intake port bias

What exactly does that mean?
I am porting a set of 416's and what to know more about swirl.

[QUOTE=85z28iroc;3116767]Swirl = rotating flow, in this case of fuel+air. Think "toilet flush" and a picture of swirl will occur.

The intake port bias is a term to describe the way the fuel+air move in the intake runner and past the intake valve. A biased port has more flow (because the flow speed is faster) on one side of the runner than on the other (where it is slower), like water moving through a river. When the flow enters the chamber, because it flows faster on one side of the runner than the other, then the flow tends to swirl after it enters the chamber.

A runner than is unbiased has even flow across the runner, so it's more balanced (which might seem good for cylinder filling) but the penalty occurs when you try to burn the mixture. With poor swirl the burn speed is fairly slow, so the power conversion isn't optimum (think about burn speed, and the consequence of burning too slow at high rpms.... the burn will still be happening when the exhaust valve opens -- so some of the heat never helps do any work).

For the record, swirl is fluid rotation parallel to the piston top; tumble is fluid rotation perpendicular to the piston crown. Both are helpful to increase burn speed, and deciding on how much of each is part of the skill in designing an intake tract and combustion chamber shape.

Pictures would help a lot here, but the best ones are in Vizard's SBC Cylinder Head porting book. HTH.

Great explanation, thanks.
Would it help if I added a couple of swirled valleys through the port?

I don't suggest that because you'd be experimenting on something you have no experience with.

OTOH I do suggest that you get a copy of Vizard's book, as well as reading the DIY head porting threads here. There have been several that are very useful to read through.

I wouldnt recomend it per the design of these heads pretty much the only thing they would benefit from is a good bowl blend and port matching. if you do any internal grinding you would gain volume but reduce velocity these heads are so great because of the speed at wich they move the air and the way that they swirl it.

does anyone have flow numbers for the 305 vortec's? i cant find them anywhere and i need to see what lift they flow the best at so i can pick a cam. the l31's flow best at about .500 to .530 on the intake after that they start to loose velocity but i cant find any solid data on the 305's.

just got this from fast355 aparently he flow tested a set of 305 vortecs a while back and figured i should publish the info so its actually availible. over 2 months worth or researching these heads and i finally found what i was looking for so here it is.

These are for a set of 059s off of a 2002 Chevy Express with the 305 Vortec. The 059s have the same intake and exhaust ports as the 062s for the 350 and feature 1.84/1.50" valves with 56cc chambers.

The flow bench was operating at 28 in/h20 pressure drop

Lift----Intake---Exhaust
.050-----36-------28
.100-----68-------47
.200-----128------103
.300-----179------138
.400-----205------152
.500-----221------163
.600-----225------165

So upgrade the intake valve to a 1.94" with a new valve job and you got a rocking head for cheap.

I would do a little bowl work to them too. They flow very well as is, especially for a 305 head. (But that is a give based on the HP/TQ of a 305 Vortec, the same HP as a G92 305 TPI with a smaller cam and more restrictive intake/exhaust setup) On a 305/350 with 1.94/1.60 valves they should run very strong. I have a pair of ported 081s with that valve combo on a 350 and it runs VERY strong with a ZZ4 cam in it. I have plans to work over the 059s and install larger valves in them, some porting, and a .018" shim style gasket will really pick up my 18cc dished piston 350 over even the ported 081s.

Who makes a .018” shim gasket that works with late model heads? FelPro makes a .015” coated shim. GM uses something around .020” but I haven’t found an actual PN for them, and MRG and a few others make shim gaskets in that range but say that they won’t work for late model light weight head castings.

My mistake, they are actually .016s, steel shim. It is even shaped for the lightweight heads. My 1983 305 with the lightweight 601 heads even happened to come from GM with this steel shim style gasket on it.

I have found that NEW HEADBOLTS are almost a a manditory thing if you are considering the steel shim gaskets. It is also best to have to accurate and freshly machined surfaces.

http://store.summitracing.com/partde...5&autoview=sku

Damn, I’ve never noticed that they listed the .015” gasket as having a compressed thickness of .016”… you didn’t happen to see my email froma couple of days ago, did you?

You mean the one to my Yahoo account? I read over it but didn't have the time to respond at the time and it somehow got swamped with new email so to speak. I will look over it again and get back with you. 601s are a nice snag.

well i decided to do a little p&p work to the heads just basic stuff im not gonna hog them out or anything. i was thinking with portmatching, bowl blending, smoothing the top and bottem on the runners. smoothing the radius a bit and polishing the chamber and exhaust ports should be able to net a little higher on the flow bench.