I own a shop, and have seen this done. The intakes are different as in how they bolt on, so you will have to get an aftermarket intake. Compare the bolt patterns of each, and you will see what I mean. If it was me, I wouldn't do it. A lot of people think the 305 heads will make more power on a 350 because the cc of the combustion chambers are smaller. It will get your compression up higher, but they have smaller valves, and don't flow good on a 350 due to the quench area of them. There is good Vortec heads, and there is some not so good Vortec heads. The 305 Vortec heads are great on a 305, but will slow your 350 down because your timing will have to come down to keep the detonation down to a tolorable level. If you will measure the bore of the 350 cylinder, and then measure the bore area on the 305 heads, you will see there will be an overhang of quite a bit on the 305 heads. Carbon tends to build up on this overhang, and the detonation will get worse and worse as time progresses. You will keep backing the timing down to make it go away or risk damage to the pistions. You would be much more ahead of the game to just find a set of 350 Vortec heads, and use them. You may be suprised at how cheap a new set is from the dealer. You can get a set complete for under $500, and a used set for a couple of hundred dollars, but the used set would need to be serviced with new seats, seals, guides, and grinding the valves. This would be a couple of hundred bucks in machine shop work, so as you can see it just wouldn't be worth it. Besides the runners on the 305 heads are smaller and won't flow the air the 350 runners will. You would be better off having your 350 heads redone, and machine the surface to get the compression up. Do a mild port grind, and you got some good heads that will make plenty of power. I know this, been there and done it before.
If you will go to www.chevyhiperformance.com and look up the cylinder head bench flow tests they have done (and continue to do) you will find every head GM made. You will also find that I'm correct in telling you these heads may even slow your car down. Also; check out www.gmperformanceparts.com or
You will find you can buy a complete set of the good Vortec heads for under $500 for the pair. Don't waste your time, or money on the heads you have now. I don't know if they made a "92" Vortec head or not, but some vortec heads are crap, as not all those are the good one's. The 305 heads that most people go for have the big valves, and are called the "Torquer" heads. The one's you have don't, and won't work.
Glad to help out, Good Luck!!!
Certified Master Mechanic, Shop Owner, 40 yrs. experience.
· 1 decade ago