Cranking Compression change>>>HP drop

[8secbusa]

Question for all>>

My 1441 spun a bearing, took out the crank.. So had the crank and rods replaced.. Back to the track, performance was down .2 and 4MPH..The weather has gotten worse, but the change seems more than that...

So went to the dyno, HP was down 17, TQ down 9.. We started trying to track it down, only thing I found so far is a significant change in cranking compression. Prior was 280-282, current is 248-250. Is this where my performance went?

What we have checked so far: Cam timing, exactly the same, same fuel, we checked the crank throw, still 65mm... Any thoughts????? Engine builder used the same dimension gaskets..

[gazza414]

Just a few to consider

-leak down test conducted?
battery condition?
butterfly's fully open?
engine hot or cold?

[8secbusa]

It was the battery. I fully charged it and the cranking comp was the same. Still clueless about the dyno HP lloss. Leakdown was 2-3%.

[Johnnnycheese]

don't worry about dyno numbers just MPH at the track and convert for the weather change

[8secbusa]

Thanks. Prior was 159 on average, now I am 156 on average, difference, corrected air density 1400 ft vs 2900 ft. Does that seem consistent?

[Johnnnycheese]

I am not anywhere with access but someone will chime in

[moparict]

Thanks. Prior was 159 on average, now I am 156 on average, difference, corrected air density 1400 ft vs 2900 ft. Does that seem consistent?

Yep, that sounds about right.  The higher the DA gets, the worse your bike will run.  In short, there just isn't as much air to burn.