I know the compression drop, what are the other problems? I'm thinking of saving down time over porting my own current 305 heads.

I don't want anything like it's pointless, they won't make more power etc. Will the valves fit w/o problems seems like my only concern (total lift ~.500")?

I'm thinking dirt cheap stock iron heads ~$40, home porting ~$50, valve springs(must for cam change anyways), 1.6 roller rockers(also doing anyways), and valve seals(already have), Maybe milling them to not loose too much compression(~$60). Also head gasket(have to/going to anyways). So basically it looks like $100-150 extra(heads/milling) assuming i can find a cheap set of stock heads and then I will have much less down time on my head/cam swap and a little saftey buffer if I somehow really *** up porting my self( I doubt it though).

Also, I'm not too worried about a small drop in compression, being I have a nitrous kit right now and these heads aren't totally permanent, maybe 6-8 months or less. Then it's either supercharger or more likely New Heads(like AFR).

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14.62@96mph headers, muffler, chip, ghetto stuff, duct tape
89 GTA 305 TPI 5 speed 3.42 gears

 

if the heads have 1.94/1.50s you won't have any bore interference issues.
Beyond that they could be worth some performance over small valve 305 heads. How much would be pure specualtion, but a couple of tenths from a mildly cleaned up set would be pretty realistic. If you have the means to port, i highly reccomend you spedn as much time with your base as you can. The stock TPI base is a huge bottleneck in itself.

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Ed Maher - Moderator @ The TPI & Carb Boards
92 Z28 Convertible - Quasar blue / Tan top
305 TPI A4 2.73 - 14.7 @ 93.6
Stock except ported plenum and dual cats
-=ICON Motorsports=-

- Definitely prototypes, high powered mutants of some kind. Too weird to live, too cool to die

 

Yeah, I have a spare base that will see some sort of siamesing and porting. It would've been done already, but the guy who runs the machine shop at school, is a bit **** and wouldn't let me just wing it with the mill(everything has to be perfect for him). I'll probably end up using a die grinder unfortunetly. I understand that I shouldn't gain more than 10-20 hp at most vs. the stock heads, but for $100-250 it's worth the learning experience to me. I was more concerned with the 350 heads having spread out valves or something stupid like that causing interference issues.

 

Oh no, they will definitely bolt on and run no problem (1.94/1.50s that is), people have been doing it for years to get a little bigger head on a budget 305. Seems to always be worth a little unless it was in the hands of someone who had a knack for slowing there car down every time they turn a bolt.
Between cleaned up 350 heads and a well ported stock base a few tenths to a half second would be a reasonable guess.
hints on the stock base: raise the roof at the intake port into the injector boss area to give the air a better transition to the head. If you look at it as cast you'll see the runner comes in way too low and flat to effectvley let the head work. Then smooth and straighten it out as much as physically possible.

 

This area around the injector boss.. Does that bottom lip create a seal? Doesn't look like there is much material to play with there, but maybe it will be clearer when compared to a set of heads.

 

I believe the base i have is off an 88 and there are 2 differrent bases, so maybe yours is different.
On mine There is a lot of meat in the boss area right above the port that you can take out to contour the entry into the head. There is a lot of space between the bottom of the o-ring boss and the port. You wouldn't have to cut into it that high because the real limiting factor is the runner itself. They are relatively thin so only port enough out of the boss area to shape it proportionally. Imagine it as just being an extension of the angle of the entry into the head to smooth the transition.

 

I gotcha, this base is an older one modified for later bolt pattern. I'll need to look at the set of heads going on the car before I touch that part then. Thanks.