Hey y’all so I’m building a 305 I bought for $200 and I’m putting 350 heads on it which I know will lower my compression but get a higher revin motor out of it. But I need to know a way to up my compression back up so it doesn’t run terribly. Any suggestions for cheap?

 

You paid too much for the motor, the 305 is a very weak motor. They tend to spin rod bearings in the TPI engines. At the dealer I worked at we could see 2 a month and I have seen them with 7 of the 8 rod bearings spun and that was on stock engines under warranty. If I had to guess I have scrapped 2 dozen 305's back in the day for people upgrading to 350s. In the 80's you could not sell a 305 even with low miles. On the other hand the L98 350 had way more torque and I never saw one with a spun bearing. If you get much more than 250 HP on a 305 it will have a short life unless you baby it. Everyone I knew that tried to make a 305 fast ended up with a scrapped motor. At one point I asked a GM engineer how to fix the 305, He said the issue was the block flexing. The 305 was designed to be as light as possible to improve MPG and there is no fix.

On the other hand you could go buy a 4.8 with high miles for around $300, pull it apart clean it and put in a new oil pump and you have a motor that can handle 600-700 HP.

 

 

It's still a 305. I wouldn't give a nickel for one. You can find 350s every where for a few hundred more and you're money ahead at that point.

If you're dead set on using the 305 with the 350 heads, easiest way to raise compression is to have the heads shaved and/or dome pistons and/or thinner head gasket. In either case, you have to check piston to valve clearance. You also have to make sure you don't go too nuts or you may end requiring to use 93 or better fuel...especially if you use steel heads.

 

Ditto! Sell that boat anchor to someone who needs a motor and get a 350.

 

 

Just a FYI the 305 casting design is the same start to finish. There is no "better" 305. This block was designed in the early to mid 70's with one goal, be light as possible so GM could save MPG. The original motors only had 140 HP so the light weight did not matter. The failures started in high volume as GM used that same block on their 220 HP TPI engine. So don't think that the lower HP blocks are better think of it as the TPI engines showing you the limit of the 305 block.

Also keep in mind there are a lot of variations in castings. While some TPI engine did not make it out of warranty many are still running today. But as I said before, everyone that I know that tried to go fast in a 305 broke or spun a rod. I am sorry to say that include myself and a 1984 305 HO Camaro