This latest Tony Matthews cutaway at Mac’s Motor City Garage is a very special one: the Chevy Ilmor 265B Indy car engine. 

It’s special on several counts. First, this was a rather unusual engine on the Ilmor family tree. It was used for only one season in Indy car racing, 1992, and by only one team, Penske Racing, as team owner Roger Penske was also a significant investor in Ilmor.  

Next, the rendering was never completed, for reasons to be explained shortly, so we get to see Tony’s fascinating work while it is still in progress. In their pencil stage, Tony’s renderings have a wonderful, Leonardo-like quality. He also takes this opportunity to explain a bit of his technical process. Here’s Tony. 

The Chevy Ilmor 265B

by Tony Matthews

There are two ways of making a cutaway illustration of an engine—from the inside out, or from the outside in.

If an engine exists and is available, a drawing can be started from an overall photograph, the outline and the salient external features giving a good clue to where internal features are. It also helps to know the extent of the complete engine, as it is tedious to start a drawing, then find after several days’ work that the engine projects beyond the art board.

However, there are times when an engine, or at least a nearly complete engine, does not exist. Before I drew the Ilmor 265A all I saw was a cylinder head casting that had been sawn apart along its width and length to check the water passages. All the other detail came from engineering drawings and photographs of any available parts. It was only after the cutaway was almost finished that I saw an engine, and it was with a mix of interest and relief that I was able to study it.

With the 265B I never saw a complete engine, before or after, but there is something very satisfying about starting with a clean, white board and drawing a line that represents the centreline of the crankshaft, and constructing everything on this—the cylinders, the camshafts, the timing gears, and all the casting. Seeing it gradually appear is mesmerising in a rather slow-motion way.

I used to draw a little “armature” first, to establish the angle of the crankshaft, the centreline of the cylinders and their relative angles, the angles of the valves and the position of the camshafts. This way I could ensure that no vital components were directly superimposed. A camshaft directly over a crankshaft looks confusing, as does the centreline of a cylinder—everything needs to be seperate, if only by a small amount.

The 265A and 265B Ilmor engines were drawn from the rear, as this where the timing gears were situated, and at a fairly low viewpoint so that the camshafts, valves, and combustion chamber were separated from the crankshaft and pumps. The only slight drawback with this view is that the dry sump casting tapers upward toward the rear of the engine, and this gave a slightly odd look to the illustration, as if the perspective was wrong. I countered this with the 265A by adding a heavy shadow under the sump to restore the perspective.

Having drawn the 265A I was delighted to have the opportunity of drawing the B. Showing progress in design has always been a great interest of mine, even if the changes from one model to the next were small. Unfortunately, with the working drawing nearly finished, Paul Morgan called to ask me to stop. The B specification was deemed insufficient to meet the demands of the series, especially with a vigorous challenge from the other engine builders. “We’ve decided to go straight to the C,” he said.

For some reason I was not asked to draw the C, and the only other methanol-burning Champ Car/Indy Ilmor I drew was the magnificent 265E, otherwise known as the 500I, the pushrod engine. I would have loved to have drawn more, and in particular, the Ian Watson-designed IC108E.

The cutaway image below is high resolution. Left-click to open and left-click again to open to full size.