October 2010 Chevy High Performance Q&A

Kevin McClelland Aug 30, 2010 0 Comment(s)
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A: Tight quench area is always a good thing. It gives you mixture motion that promotes more efficient combustion. Is this always the case? In our LT4 small-block we had cut the block down to achieve 0.040-inches of deck clearance with a 0.026-inch GM composition head gasket. Well, if you remember our washer story (we're not going to repeat it!), we had to take the LT4 apart and replace the pistons, and we clipped the deck for a cleanup. After cutting several thousandths of material off the deck we had a set of Cometic MLS head gaskets made up at 0.030-inch to maintain our 0.040-inch of deck clearance. To make a long story short, the head gaskets came in as a Gen I design, and my LT4 is a Gen II with reverse-flow cooling. No fault of Cometic! We found this error on a Saturday and had to get the engine back together for a points race the next weekend. We ran down to the local auto parts store and bought a Fel-Pro Head Set with Perma-Torque head gaskets. These gaskets were the standard production thickness of 0.051-inch. So the deck clearance went from 0.040- to 0.061-inch. The next weekend we expected to lose a ton of on-track performance. Guess what, it didn't lose even a hundredth!

What happened here? Well, we believe the LT4 heads have a really good combustion chamber, and the intake port gives the air/fuel mixture a good ride into the combustion space. The increased deck clearance didn't affect the burn. This is not always true. With poor combustion chamber designs, like early iron heads and smog designed heads, they need all the help they can get. This is where you see gains from tight deck clearances.

Now, for your RPM heads and your specific application. We think the performance we've seen out of these cylinder heads shows that they have an active combustion chamber and good intake ports. Also, you already have 10.3:1 compression. If you reduce your deck clearance down to, let's say, 0.040-inch, you will reduce your cc's by 4.44. This will raise your compression up another 0.3 to 0.4 CR. This, with your relatively short camshaft and high rearend gears, is just looking for a spark knock issues.

If I were you I would leave your deck clearance alone and enjoy your lightweight street rod. The torque that this engine will make will give you quite a thrill when you stand on the throttle. Cutting the deck for a few extra horsepower really isn't necessary for the use of the engine. Enjoy your cruiser.
Source: cometic.com

H2O By Volts
Q: I've been looking at putting an electric water pump in my '64 Corvette. They appear to have several advantages over a mechanical pump: water flow at low rpm, freeing up horsepower, and no cavitation at high rpm. I am just concerned about reliability and suitability for the street. I drive this car daily, weather permitting, and it's hard to knock a mechanical pump for reliability, since it's been doing the job since day one. I have a 377 small-block in the car, with no air, and a flex fan backed up by an electric fan for sitting in traffic. I'd appreciate your help, as these pumps are pricey and there is not a great deal of info out there I have been able to find.
Tony Bassignani
Charlottesville, VA


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