michealleger

So i got a 1986 iroc with the 5.0ho and 5 speed. The motor is junk(intake cracked filled everything with water). So assuming the motor is indeed the H.O still im wondering if you can take the cam/heads off and put them on another 305 which I have. I also got a 350 here and I'm wondering what the best thing would be to swap into the car. The 350 is from the SMOG years so Its not the greatest years for a 350. I have read about putting the 305 stock or 305 H.0 heads and or cam into the 350. What would this work like?

Any help is appreciated.

Am in the process of putting mostly all new floors in this car so i have a few weeks to figure something out for the motor

dmccain

iTrader: (2)

Well, anything is better on a 350 I guess. Even those 305 HO heads. Ive heard porting those heads and maybe putting better valves and such can make them pretty decent. I would save my coin and find some vortecs though.. Do not re-use a flat tappet cam and lifters though. Buy a cheap setup from Summit K1103 maybe $100.

midias

I would not reuse the cam and the heads I would not use unless a machine shop check them and magnafluxes them.

What are the casting numbers on the 350 heads?
What is factory compression the 305 heads will most likely raise them up.

michealleger

i will try and look into the casting numbers.

AlkyIROC

It's not just about the size of the combustion chamber to bump up compression. A larger engine needs to breath. If the heads don't flow enough, they'll choke the larger engine. Port sizes vary a lot from casting to casting. Smaller engine don't need as much air so they generally have heads with smaller sized ports along with the smaller valves.

1.94/1.50 valves in a 350 is minimum. Not sure what your 305 heads have in them. 2.02/1.60 in a 4" bore engine makes a big difference but 2.02/1.60 won't fit in the bore of a 305 engine.

By the time you work over the 305 heads, put in bigger valves etc, it can be a lot cheaper to just buy some aftermarket heads that will have the work already done plus will be better castings right out of the box. Aftermarket iron heads are inexpensive but the cost of aluminum heads is much lower than they were 20-30+ years ago.

five7kid

iTrader: (14)

First, an '86 did not have an "HO" engine. Often claimed, but it never existed.

Second, the lo-po LG4, "HO" L69, and higher-HP (higher than LG4) LB9 TPI up through '86, all used exactly the same heads, the 416 casting. They all had 1.84"/1.50" valve, and they all had 58cc (roughly - we're talking GM production here) chambers. The difference between the LG4 and L69 was due to the cam, pistons (dished vs. flat-top - but '85-'86 LG4s had flat tops as well), and exhaust. The LB9 got all of the "good stuff" the L69 had.

So, having said all that; yes, you can do a porting job on the 416s, put in larger valves (1.94"/1.50" or 1.94"/1.60" - by the way, this is a machine-shop-only job), and they will raise compression on a 350. But, you don't really want to do this if the 350 has flat top pistons and the car is street driven. If it has dished pistons, that's a different story, and they will work okay.

If you do the porting yourself, you can probably get as much power out of the 416s for the same money or less than cheap aftermarket heads. But, to pay a shop to port 416s, you might as well go for aftermarket heads.

Do post the casting #s from the 350 head. In all likelihood, they are junk. Get the casting number from the block while you're at it.

I also would not reuse the 305 cam. It's flat tappet, which don't do as well as roller lifters & cam when changing them to another engine. A flat tappet cam & lifter set is relatively cheap, and it isn't hard to get one that's better than the factory cam, anyway.