February 2013 Chevy High Performance Q&A

Kevin McClelland Mar 6, 2013 0 Comment(s)

This is where the issue begins. We had a stock set of 882 heads that had been worked on, sitting on a shelf in our shed, so we disassembled the engine and purchased a new head gasket set. We put the car back together. When we started it up, we noticed quite a bit of blow-by and thought maybe this was oil burning off the heads, or maybe some oil had gotten on the headers. Well, it got worse. We told a friend what we had done, and he recommended we check the part number on the head gaskets to make sure we had the right ones. He seemed to think we had the wrong head gaskets and the compression was getting under them, therefore causing the blow-by. We pulled out our receipt and they had sold us head gaskets for a 305. We called the parts house and told them of this mistake and they agreed they had given us the wrong ones and replaced them. So we tore it back down and installed the new head gaskets for the 350 bore; however, now we still have a massive amount of blow-by. I asked my friend again, and he feels that since the head gaskets were for a smaller-bore engine, it caused the fire rings to hang over into the cylinder walls, and this increase of compression caused the compression rings to collapse. Would the smaller-bore head gaskets cause this problem?

Al Roofer

Via email

Your friend has his thinking cap on! He’s had some great suggestions and got it right on the 305 head gaskets. Unfortunately, the difference in bore size on the head gaskets makes very little difference in compression ratio. Most replacement head gaskets on the market for the small 3.736-inch bore size of the 305 is in the 3.800-inch range. The replacement gaskets for the 350’s 4.00-inch bore is 4.100 inches. The compression difference between these two gaskets is in the 0.1 to 0.02 of compression ratio. For example, you probably went from 9.0 to 9.2:1. This small change wouldn’t have hurt the ring lands.

Now, what would have easily cracked the ring lands of your rebuilder, cast pistons would be if the pistons came out of the deck any amount. If the engine had been decked when it was rebuilt and the pistons had a tall compression height, the pistons could be coming slightly out off the bore. It wouldn’t take much to crack the ring lands of the pistons if they came in contact with the fire rings of the 305 head gaskets. You would see witness marks on the heads of the pistons on teardown where the gasket was coming in contact.

With the engine fully assembled, the best way to test the integrity of the pistons and the rings is to perform a leakdown test. This is where you put the cylinder you’re testing at top dead center on the firing stroke. You then apply air pressure to that cylinder with a special leakage tester. When you apply air pressure to the cylinder you’ll have some amount of leakage. With racing engines we shoot for the least possible leakage. On street engines it’s not uncommon to see the cylinder leakage in the 8-15 percent range when the engine is cold. On really sealed-up street engines we’ve seen the leakage in the 2 percent racing engine territory. Maybe your friend with the great answers can help you with a leakdown test. You can pick up a tester from most any tool truck, Sears, or online. In a quick search we found low-dollar testers out there in the $70-$80 range. Remember, you do get what you pay for, but if this is a one-time diagnosis you may want to go this route. Maybe you can find one to borrow. Good luck finding your leaky rings.

305 vs. 302

I have a 305 small-block out of a ’92 Caprice with engine code E. Why can’t you build respectable power out of a 305 like you can a 302 out of a (gag) Ford. I’m putting it in a ’91 S-10 and don’t need a lot of power, just want the sound of a V-8. I just have never understood why they are so unbuildable. Thanks.

Mike Moriarty

Via email

For anyone who has spent any time trying to build decent power from a 305, “unbuildable” is perfect! First of all, we don’t have to compare the 305 Chevy to a (gag) 302 Ford. We can take the same architecture of the small-block Chevy 302 versus 305. The 302 bore/stroke is much more desirable for performance with its 4.00-inch bore versus the small 3.736-inch 305 bore. The performance aftermarket hasn’t really built a small-bore Gen I small-block cylinder head for performance, so you’re stuck with replacement heads and what GM offered. Also, with the 302’s large bore combined with its relatively short 3.00-inch stroke compared to the 3.48-inch 305 stroke, the 302 loves to rev! Enough said.

Back to your S-10 build. Your E engine code 305 is an L-03 TBI engine. These are great workhorses but will build no power, as the cylinder heads have a swirl vane in the intake port to create mixture motion. They work great at building slow-speed torque and helping fuel economy, but they kill top end horsepower by killing the airflow potential of the heads. If we were building your engine, we would swap out for a set of the 416-casting GM cylinder heads, then step up the intake valves to 1.94 inches and pocket-port the intake and the exhaust bowls. This will give you the best chance in building decent performance from GM heads.

Next, you’ll need to kick the TBI to the curb. This system is very reliable, but not very performance orientated. We’d recommend an Edelbrock Performer PN 2101 intake manifold with either a Rochester Q-jet or the Edelbrock 600-cfm Performer carburetor PN 1405. This package, with your upgraded GM cylinder heads, will give your 305 a fresh breath of air. If you wish to stick with a throttle-type EFI, look into the FAST EZ-EFI, the MSD Atomic, or the Professional Products Powerjection III. Any of these auto-learn EFI systems are a snap to install and enjoy.

Finally, to continue with the theme of conservative torque-producing components, go with a relatively small hydraulic roller camshaft. Check out the Crane hydraulic roller (PN 104225), which specs out at 208/214 degrees of duration at 0.050-inch tappet lift, 0.438/0.452-inch max lift, and is ground on 112 centers. This cam will give you a slightly noticeable idle, but makes outstanding torque and horsepower to 5,500 rpm where all your components are matched to top out. This package will produce somewhere around 325 lb-ft of torque with headers, and 275 peak horsepower. For a mild 305 this isn’t bad when the base engine you’re starting with was rated at a whopping 170 hp! This might not sound like a ton of power, but it will pull your S-10 around nicely. Good luck with your swap.

Sources: cranecams.com, edelbrock.com, fuelairspark.com, msdignition.com, professional-products.com

It’s only a Name

I read CHP each month and see many articles mentioning LS-type engines. I hope you’ll excuse my ignorance, but what exactly does LS mean? I sort of get cubic-inch numbers, but LS? No clue. Can you help me out?


Erial, NJ


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