They have a good following in Nebraska and West/Central Iowa. A couple tracks in eastern Iowa tried to switch to SLMR sanction and just couldn't get a good enough following.
The rules allow different engine packages to be competitive with each other. For example an IMCA Spec engine is unrestricted, Wissota motor has certain restrictors, a small cubic inch open motor has certain restrictors and a big cubic inch open motor has certain restrictors.
Bookmarks