A few years ago with the help from several of you on the boards, i built a very healty 350 +.030, middle of the road cam (specs. escape me right now), 5.7 inch rods, flat top hyper pistons with 4 valve reliefs and vortec (350) heads. This motor made great power and It currently resides in my 1985 Firebird. Fast foreward 2 years.... I bought a 1987 formula with a 305 TPI, 3.23 posi, all power options, t-tops, WS6 etc. To make a long story short I have to get rid of one of my cars. I am going to sell my 85 to a friend who's car was flooded last year minus my 355 and trans. I really don't want to part with my 355 because the engine probably has almost 400 miles since i built it and I put a good bit of money into it. What I want to do because i'm in a pinch right now is to take the 305 out of the formula, have the heads freshened up and install them on my 355. I would then install the 355 into the formula and shelve my vortec heads. Unfortunately, the $400 SDPC Vortec TPI base is just not in my budget right now or else i would not be asking this question.
So here it is, will my 355 be compatible with the 305 TPI heads for the time being until i can afford the SDPC base? (I know all about the 305-350 TPI swap, injectors/knock sensor/PROM/etc) I understand that i will be taking a step backwards, by using inferior heads, but I am stuck between a rock and a hard place on this one. More or less I don't want any detonation/internal clearance issues. Will this combo be mechanically sound? Can someone with more experience on this subject lend me some insight on this one? All insight, advise is appreciated. -Bob

 

The only issue is the 350's pistons. If they are flat tops with 4 valve reliefs, that is typically around 5cc volume. If the block wasn't decked, and the pistons are the typical down-in-the-hole rebuild pistons, and you use a .04" thick composite gasket, you'll have plenty of volume to keep the static compression ratio down. Of course, the quench distance is going to be above ideal, so you might get a little pinging anyway. You can either burn more expensive gas, or back the timing off a little, if that turns out to be the case. Or, while you have the heads off, unshroud the valves a little and increase the chamber volume as well to reduce CR even more. Performance will suffer, of course.

How much is the head refreshing going to cost you? Between machine shop costs & gaskets, you'll probably be close to $400. Have you checked sources for used Vortec TPI bases? Seems sad to shelve good heads for a band aid solution.

 

I agree that it is a band-aid solution as you put it. Performance as in racing is not the whole idea here, performance in terms of driveability is. The block is at the stock deck and you are right about the valve reliefs being about 5cc. I considered running more expensive gas and adjusting the timing accordingly. I can probably get both heads machined for about $180 plus gaskets. It seems that the Vortec TPI bases usually don't stay long in the classifieds due to the high demand and I always seem to miss them. I will try to look around here to find a used one, although though highly unlikely. Thanks. -Bob