[Ron Sutton]

This is a cool thread ...

IMHO, the I think the key goals are:
A. Wide powerband ... to reduce or eliminate shifting
B. Smooth, non-peaky powerband ... to eliminate surprises to the tires
C. As much power as we can actually use

Concerns:
* The problem with big stroke engines is they build so much torque ... right at the corner exit rpms ... it's hard to not blow the tires away.
* The problem with short stroke engines is often ... not always ... they low end lack torque for optimum acceleration off the corners ... and with the wrong cam, can have a useless, narrow, peaky, high rpm power band.

From my racing experience, if you are in a series with no cubic inch limits, what is both fastest ... and EASIEST TO DRIVE ... is a big bore/medium stroke engine ... designed for a wide, smooth powerband. When I raced in West Coast NASCAR Modifieds, there was no cubic inch limit ... just a carb & tire limit. So we saw every combo including 355"/358", 372/377", 383"/388", 400"/406" & 434" engines. The story went a lot like the 3 bears & porridge.

While the 434" engines made the most power ... torque & horsepower ... they were too hard to drive fast. With 4" of stroke, the drivers were always struggling to get them off the corner optimally. They had to drive them with the proverbial egg under the throttle. That's doable occasionally ... but not consistently lap after lap when your adrenaline is up. The 355"-377" engines had way less tire spin challenges ... but just didn't make enough torque to accelerate the car off the corner optimally. The 383"/388" engines came of the corners hard, but laid over on the straights.

The engines that were "just right" were big bore (4.125"-4.185") & medium stroke (3.750-ish). These 400"-410" engines were dominant. They had optimum torque for the best corner exit on the narrow slick we ran. With the right wide lobe centerline camshaft, they had a wide, smooth powerband that was easy to drive fast & consistently. And the top end power was awesome ... pulling all the way down the straights. In my experience, the 383" & 434" combos are just two different sizes of the same long stroke strategy. Both build their torque down low & run out of stem too early. The 377" & 410" combos are also two different sizes of the same big bore/medium stroke strategy. The 410" just builds more power throughout the entire curve.

For road courses, this is even more critical, as the 10-12 corners are all different. Making the need for a wide, smooth powerband even more critical. I built all of our winning road race engines the same way ... big bore/medium stroke. Getting this strategy right will be even more critical for autocross on TW200 tires.

As over simplified as this sounds ... determining the stroke length you want/need for just the right amount of torque ... is a good starting point. Then design the whole engine around that. I have several versions of a 409" LS engine in development currently. The "tame" versions build 750 hp & the "mean" version will make 900hp. All very drivable on track with a smooth, flat, wide powerband. So that tells you my preference.