Engine Change between 90 and 91?

What changed on the 4.0 between 90 and 91? I've noticed that Chips, INtakes, and headers, and throttle spacers are available only for the 91 and not the 90. Whats the difference and what will still fit? :huh:

The '90 still uses the older Renix engine management computer, while the '91 is the newer 'High Output' model. HO engines have a different cam and computer which is why you can't use the same chips; additionally the head has been modified slightly although the Strokers group in Modified can give you a better sense of the difference. I know the Renix also incorporated a knock sensor so it's more desirable to some of the builders around here.

The cam is the same in the '91-'95 models as the '87-'90 but the HO cylinder head is higher-flowing, the HO has different intake/exhaust manifolds, a larger TB, Chrysler SBEC engine management. The HO also produces 13hp/1lbft more than the Renix 4.0.