The 8987 Triple Remote Reservoir style damper gives you preload, ride height, rebound and High/Low Speed Compression. When comparing the 8983 and the 8987 the difference is in the reservoirs, where compression damping adjustment takes place. The compression adjuster on the 8983 is a high speed compression adjuster. High speed refers to the velocity of the wheel moving up and down, not how fast the bike is moving around the track. To clarify, low speed compression is "firmness" or "feel". High speed compression is "bumps". So what does all of this mean in the real world? With ordinary racing shocks, you have to use the compression adjuster to make the bike feel firm. This works acceptably at smooth racetracks. The problems arise when you get to a bumpy track. In order to get the shock to soak bumps, you have to soften the compression damping. The result is a bike that soaks bumps, but some squat will result under acceleration. You need to be able to "dial in low speed compression" to restore chassis feel, but you won't be able to since you only have a high-speed adjuster. You are forced to compromise. This is where the triple-adjustable Penske becomes a critical component for professional racers. You are able to adjust for bumps and feel independently, and there is no compromise. The most interesting effect of this shock is that once your bike is set up to have a firm feel and be compliant over bumps, you will be able to return a smooth track and change little or nothing. The bike will not need to soak as many bumps, and it will still feel firm. It is state-of-the-art!
Since Penske shocks are built to order please allow 2-3 weeks for delivery.