Chevy Car Questions & Answers - Performance Q&A

Kevin McClelland May 1, 2009 0 Comment(s)

Another interesting set of numbers is stamped on the right front deck of the block. First is the partial VIN, and the engine ID, which is T1111DC. The crankshaft is from a '77 casting date and is from a 350. The block is also a two-bolt main.

A couple bits of advice I've gotten so far is that since the block was cast in 1968, Chevy might have used the same forms for this block that it used to cast the 327s, so the cylinder walls would have the same thickness as a stock 327. The other advice I got was from the machinist who did the actual hot-tanking of the block for me. He told me the casting number on the block was used for both 307s and 327s. However, my research didn't show that anywhere.

So in all reality, the engine was a 350. It ran very well and did not run hot before I tore it down. My plans are to just do a stock rebuild to have an extra engine. I just wanted to get a few opinions about this engine to see if it's a safe gamble to use, or am I wasting my time and should find another block? Thanks for your advice.
Darrin Las Vegas, NV

A First, you must be careful getting advice and opinions-everyone has one, and only some will be correct. Some of the theories are quite plausible. Let's get down to facts.

Your block is a '68-73 307-only block. The 373 casting number is specific to this model-year range. This casting number wasn't used for late, large-journal 327 blocks. Yes, if they would have used 327 water cores, the bore thickness would be the same as the 327. The "DC" engine code is specific to a '69 200hp, two-barrel 307, which could have been installed in any '69 Nova, Camaro, or Chevelle.

Should you give up on this block? The only way to be sure this block is sound is to have the cylinder walls sonic-tested, in which the thickness of the finished cylinder walls is measured. Most well-equipped machine shops will have this test equipment. What you will be looking for is an absolute minimum wall thickness of 0.200 inch on the thrust side of the cylinder wall. You can run about 0.020 inch less on the nonthrust side. Any less than this and you'll run into ring sealing issues from bore flex and will risk overheating and splitting (cracking) the cylinder wall. If the block comes in above these ranges, slap it back together. If not, get a new block. This test will take all opinion out of the decision.

Z Bar Baby
Q I need the years or casting numbers for a four-bolt-main Chevy small-block with the clutch-linkage boss cast into the block. The '65 Impala SS I found has no engine and needs this connection to operate the bell crank (Z-bar) clutch linkage. Could I be so lucky that even an '87 (or a little earlier) still has this, or was it eliminated in later castings?
Mike Weil Adel, IA

A It's your lucky day. GM did play with removing and reinstalling clutch cross-shaft bosses on the Gen V and Gen VI big-blocks but left the small-blocks alone. This goes for (real) small-blocks, Gen I and Gen II. This gives you a year range of '55-96 in passenger cars and up to '99 in some truck applications. Pick up an '87-and-later four-bolt and enjoy the one-piece rear seal and roller camshaft block for your early Imp. They are very cool cars.

I'm Causing Trouble
Q I have an '87 Corvette with an L98 engine bored 0.030 over, hypereutectic Mahle flat-top pistons, 128-casting aluminum heads, a ZZ4 cam, and LT4 valvesprings with 1.5:1 ZZ4 rockers. I'm looking to add torque (hard launch) and excellent low- to midrange power. I was told to add 1.5:1 roller rockers for the exhaust and 1.6:1 roller rockers for the intake.

Some members told me that in your Q&A years ago you said the ZZ4 camshaft does not work well with 1.6 rockers. Is this true? Why?

What's the best way to add more torque to my engine? I already have a 2400 B&M Holeshot converter, a B&M Shift kit, and Bosch III injectors, and I'm planning to add Hedman Elite Headers and the rockers. I'm currently stuck because of the rockers. Thanks a lot!
Sammy Calderone Via email


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