i have a 2 year old engine with about 27 1/8 mile runs on it! e.t. 5.90 it made 690 hp on chassis dyno with nitrous an engine built by lme.most recent mods is computer pin swap 98 2002 an weight loss an the car went to the dyno an runs an sounds fine but it used to make 690 at6900 rpm then flat lines from there but now the engine flat lines at 5700 an fall straight down with 70hp power loss.you cant tell it by sound only by dyno graphs. my question is do you think that its weak valve springs or what. car pull a 3 ft wheelie out of the hole an then feels lazy on top end! who builds the best race nitrous convetor?

 

2 year old engine with that many passes on it, I'd say it's valve springs.