will someone tell me FOR SURE if i can get 350 heads on a 89 tbi 305? people tell me i can, people tell me i cant. i checked the board archives and i found alot of mixed responses i.e. loss in compression, valve slapping piston or cylinder wall. Details, details, details, tell me everything i need to look for to do this swap if possible. THANKS EVERYONE FOR LOOKING!!!

 

You will be fine fitment wise, everything will bolt up. Depending on what casting you choose, you will lose compression. The larger chambers found in the earlier 350 heads will do that, especially the smogger heads.

350 heads are usually 1.94/1.5" valves, so no problems on clearance.

The camshaft is what effects the valve-piston clearnance, so you will have pretty much the same, assuming you don't swap the cam. Good to go on cyl. wall clearance as well.

 

thanks man. now how much compression will i drop. say with a pair of heads off of a 350 tpi? if i do this should i find ones with 1.94/1.50 valves? if i do this swap, honestly, will i notice any positive gains? is it worth it, is what im trying to figure out.

 

You would be better off to get the heads off of a 305 TPI; and have the larger valves installed in them, if you want larger valves. Frankly on a L03, without significant other mods, the larger valves won't accomplish much.

The casting # to look for is 081. Those flow roughly the same as the 350 TPI heads (083) but have the smaller chambers which will avoid lowering the compression.

 

thanks guys i was going nuts because a buddy of mine who's career is working on cars told me that a 350 head swap would be a walk in the park. i questioned him about the possible loss in compression, and he called me an idiot. im glad i didnt get those heads off ebay.........
thanks for your help

 

Sounds like your buddy is the idiot.

If you want to step up the power on your 305 TBI motor by changing the heads then start with a non tbi head with small combustion chanbers so you'll at least maintain the same compression ratio.

A head for a 350will have a larger combustion chamber than a 305 head. A 305TPI head would be a good logical choice. Other posibilitys are a set of 64cc 350 heads that have been milled to reduce the combustion chamber volume.
A set of 305TPI heads that have been improved with home porting and larger valves would be a nice upgrade.
Keep your friend away from it and you'll be fine.

 

I second this statement. Keep your friend as far away from your engine compartment as possible. While you are at it, get online and show him a compression calculator. Show him the difference, then give him a good ol' fashioned .

 

what would i do without thirdgen.org! the only reason i was even thinking about doing the head swap is because "it was going to be a walk in the park" kinda thing. im not even going to keep the 305. Im in the process of saving to put a motor and drivetrain in. the heads were an "easy/cheap" mod that would have kept me quiet for awhile, or so i was told. thanks again guys, ill be sure to keep him away from my car!

 

If you use the casting I told you, and then build your "next" motor in accordance with that, you can use them now to advantage; and continue to use them later as well.