December 2011 Chevy High Performance Q&A

Kevin McClelland Oct 24, 2011 0 Comment(s)
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With the stock 400 small-block rod, you had a stroke to rod ratio of 1.484. By using a 5.7-inch rod on a 3.75-inch stroke you yield a ratio of 1.52. If you bump the rod length up to 6.0 inches, the ratio increases to 1.60:1. None of these ratios are optimum for accelerating engines. A good number for accelerating engines is in the 1.8:1 range. With long stroke engines and stock deck heights, it’s impossible to achieve this type of ratio without the wristpin getting too high in the piston. It’s not uncommon to push the wristpin up into the oil ring and you have to run spacers to support the lower segment of the oil ring. On the street, this type of design can cause oil consumption issues. Keeping the pin out of the oil ring on a street-driven engine is preferred.

If you’re building a street performance engine, we’d recommend going with the more common 5.7-inch-long rod in your build. If it’s a race-only package, you can afford to push the envelope and go with a 6.0-inch-long rod. Hope this has answered your question and given you some background as to why. Good luck.


Q. I’m hoping you guys can help me out. I bought an ’80 Corvette basket case. After rebuilding my engine in 2009 I have been using oil. I suspected valveguides, as I only had the valves ground at that time due to budget restraints. Since then I bought a ’78 Camaro, and with that purchase I got an extra set of heads that I sent out and had completely redone. My old casting numbers were for 74-80 350. The ones I had done are for an 80-85 305 HO. The temperature-sending hole on the new heads is a 3/8-inch pipe thread and my old heads had a 1/2-inch pipe thread. I went to the auto parts store, and when they looked it up and pulled the part, it was 3/8-inch pipe thread. I thought, “cool!” Well, what happened next is I was “overheating” on the gauge. After monkeying around with thermostats, changing from a 180 to a 160, my gauge is reading around 200 [205-plus sitting]. I checked the intake with a digital temperature gauge and I really am only running around 180 on the manifold below thermostat, and on the upper hose, 160-ish. Is there a sender that is calibrated to my gauge, or is the sender just faulty? Any information would be greatly appreciated.

Dan Evans
Lisbon, NY

A. You’ve got a couple of options. First, you could move the factory 1/2-inch sending unit up to the intake manifold water crossover. If you don’t have a port available in the manifold, pick up a thermostat housing with a 1/2-inch hole that was used for thermo vacuum switch for emissions control devices. This is the easiest way to handle your original temperature sender.

The 3/8-inch later-model sending units have a different resistance to temperature range compared with the earlier-model 1/2-inch sender. This is why you are registering a higher than normal reading on your temperature gauge. Now, we have two other options you can try if you wish to keep the sender in the cylinder head. We’ve taken the early-model 1/2-inch pipe threaded sender and turned it down in a lathe and re-tapped the sender to 3/8-inch pipe thread. Over the years we’ve done this trick three times and have never broken through the sender.

Finally, we’ve used what is called a bell reducer, in which the male thread is 3/8-inch pipe, and the female is 1/2-inch pipe. These bell reducers are used for plumbing and natural gas in your home. They won’t have a hex on the outside to tighten them up and you usually need to use a pipe wrench to tighten the fitting into your cylinder head. You must take your sending unit to the home improvement store to make sure it will clear the inside of the bell reducer and not bottom out before tightening. Also, after installing the reducer in the cylinder head, you must bleed the air out of the fitting so there is water touching the sender to have an accurate gauge reading.


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