BronYrAur

iTrader: (1)

Hey, I'm guessing this has probably been brought up in the past, but I've seen some 305 Vortec heads go for pretty cheap and I'd like to know if anyone has a final word on how good of a head they are.

I've done searches and everyone has a different opinion. Are they anything like L31 vortec heads? I've heard some people say that the combustion chamber isn't the heart shape on the 305 heads; yet others have said that it is.

Can some of you guys that have experience with these heads please speak up. I'm contemplating buying a set and would like to see some flow numbers, but I can't find any. Thanks a lot guys, I hope this topic can bring up good points and factual evidence about these heads.

Oh yeah, and I've seen two different casting #'s for these heads '059's and '520's. Differences? Similarities?

BronYrAur

iTrader: (1)

ttt

BronYrAur

iTrader: (1)

guess i'll let this die if nobody knows anything about them.

RB83L69

The chamber shape is about 10%, maybe less, of what really matters about "Vortec" heads.

"Vortec" is GM's tradename for "we moved the intake ports". Specifically, they raised them, toward the valve cover rails, which gives the intake gases a much straighter shot at the valve and into the chamber. That's what's really important about them; not the chamber shape.

The 305 heads have much poorer flowing intake ports than the 350 ones; and are therefore not suitable for performance usage. Ignore the buzzword attached to them.

BronYrAur

iTrader: (1)

Thanks a lot for the post! What makes the intake ports flow worse than the 350 versions? I've heard they are 150cc ports instead of the 170cc 350's, is that true?

RB83L69

I don't know the exact numbers; hopefully somebody else that does will help out.

But, a 150cc port vs a 170cc port, is pretty easy to see what the problem is..... if that's accurate.

BronYrAur

iTrader: (1)

Yeah, I agree, this is just one thing I heard though. I'd say more of an educated guess from someone else; nothing to bet the house on.

Sitting Bull

For some reason I recall there was some controversy over the L30 305 Vortec heads and it turned out that they were essentially the same as the L31s but the intake valve was 1.84" instead of 1.94".

So enlarging the intake valve gave you L31s.

The problems with Vortecs in general was that they didn't stand up to rebuilding, they tended to crack and ended up in the recycle bin

Sitting Bull

ttt

BronYrAur

iTrader: (1)

Thanks for the input Sittin Bull, that could brighten my hopes with these heads. I hope that is the case, but it seems like everyone has heard different stories about them. Let's see if others chime in here too.

IHI

iTrader: (1)

Speaking from personal experience:

I ordered a set of "vortec" heads from a shop in arizona to doa cheap freshen up on my old 355. Once the heads got here I noticed the casting number was not either of the two that are sought after, so I looked them up and found out they were 305 "vortec" heads of a truck. 2.02/1.60 valves were installed, screw in studs, good to .550 lift etc...anyways; I took them to our head shop and had them flow tested-put simply:garbage. Most noticably the chamber shape of the 305 head is not like the 350 head so you lose effeceincy with that right there, but they flowed 30cfm less than my friends pair of 062's on the intake side and I cant remember what the difference was on the exhaust side. Stay away from they for any "performance" application and go with the 350 vortecs.

On a side note I already had all my components purchased to completely change the top end(heads, cam, gaskets,intake,timing chain,lifters, pushrods, etc... but after seeing the terrible flow I e-bayed the whole set-up. Fella that purchased everything stuck it on a 383 shortblock he had for his 66 Chevy II. When I checked back in, his first trip to the track netted a 12.10 and said the streetibility was great. So in a light car (2800lbs) they did okay, but nothing like what a better head would do.

My advise after seeing the actual flow sheets in person from the 305 vortecs that I had to the 350 my buddy had...STAY AWAY!!

BronYrAur

iTrader: (1)

Good information! Thanks for the report of your experience with them. I think you're the first person I've seen report real experience with these heads. I guess they aren't such a great option. Or at least not a good enough option that's worth buying a new vortec specific intake manifold for them. Thanks IHI

IHI

iTrader: (1)

No problem, I just pulled my flow sheet out from them and happened to have the real vortec numbers written above mine for comparison, I'll scan and post them, hopefully after shrinking the numbers will be large enough to read.

numbers on TOP are the 062 casting flow numbers
numbers on BOT are the 305 vortec head flow numbers

Keep in mind too that my 305 heads had 2.02/1.60 valves and the 062 castings were bone stock 1.94/1.50 valve!! I think the bigger valves I had may have be a victim of shrouding, but I've heard stories both ways on the "real" vortecs getting better with increased valve size or getting worse since velocity is slowed down, quench is changed, shrouding, etc... pick your posion in that descion

BronYrAur

iTrader: (1)

VERY nice information, thank you. It looks like they're fairly close on teh exhaust side but the intake side they're really hurting. I'll steer clear of those, especially when 350 Vortecs are still really cheap.