Performance Q&A

Hi-Tech Engine Swap

Kevin McClelland Mar 1, 2008 0 Comment(s)
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What was your first engine swap? Did you rop a small-block in place of a six-cylinder? Or was that a big-block into a small-block Camaro's engine bay? Any of those swaps are very straightforward, even back in the '70s. No, what I'm talking about is when you started with nothing but a sheet of cardboard, scissors, scrap steel, and a stick welder!

My very first engine swap was dropping a 396 into my good friend Ron Kober's '55 Chevy. We were in our senior year of high school (back when dinosaurs roamed the planet) and he bought a pearl-white, glass-tilt-frontend, early-Oldsrearend, small-block-powered '55. My dad and I were running his injected big-block Fiat race car at the time, and Ron and I scored all the used parts from the Fiat. We built a handgrenade 396 from an Impala and used a Hurst front mount for the engine, along with a set of Horsepower Engineering in-frame headers. That car was a blast with its 4.88:1 gears and Muncie four-speed. I'm truly amazed that either of us is still here to talk about it.

Now for the real swap. While attending Los Angles Trade Tech, I was working for Norm Sappenfield at NCP Motors. This was a shop in L.A. that had been in the business since the early '50s. Norm was famous for working on the "stars' cars" from Hollywood and building some very odd creations. His personal car was a '70 Maserati Ghibli with an aluminumheaded L-88 crate engine and a TH400 that he had swapped into it. This car was an absolute blast to drive, and it could spin the wheels all day long. One afternoon, there was a '52 XK-120 Jaguar in the shop for a small-block Chevy engine swap. He looked to me and said, "There is your next job." I had never done anything like that! I credit Norm with giving me the vision that anything can be built. Needless to say, I'll never forget my first real swap.

Today, there are many very popular engine swaps out there. With the availability of the LS engine family and the six-speed trannies attached to them, they are finding their way into many engine bays. The first one that comes to mind is the Gen III small-blocks going into Mazda RX-7s. They are showing up at dragstrips all over the country. These cars are cheap and very easy to come by with blown rotary engines. Drop in a 400hp LS6, a six-speed, and a mild camshaft, and you're knocking on the 10s! If you search YouTube for LS1 swaps, you will find some outstanding, well-documented engine conversions. The common theme of these videos is the cars being thrown out of dragstrips for running too fast without a rollbar.

Step back and look around for a lightweight donor car. Many willing hot rods are laying around, just looking for some serious horsepower. Remember, anything can be done, but we never said it would be easy.

Why More Flow?
QMy question runs to the airflow requirements of your typical 23-degree 350ci small-block Chevy. In summary, a 350 that peaks at 6,500 rpm and operates at 100 percent volumetric efficiency would need airflow of approximately 658 cfm (which, by the way, is the same amount calculated on various Web sites dedicated to determining carburetor sizing requirements). Therefore, each cylinder requires approximately 83 cfm.

However, when reviewing the flow capabilities of several high-performance 23 degree small-block cylinder heads of 180cc intake port size, I noticed that, on average, the intake port flowed at least 100 cfm at 0.200 inch lift and as much as 250 cfm at 0.600 inch lift. I realize it's not appropriate to focus on peak numbers, but the flow rates at the lowest lift seem to be more than adequate to service the engine. If this is the case, why does the quest for cylinder heads that flow more air go on, and how does the engine benefit from it?Frank LanutoVia e-mail