As above mycar is down 6hp on the same dyno from before.
First time was 178bhp on a stock header and full system. Oil used was 10W40 on irridium tipped plugs.

Now its got 172 on a J's header(should increase power) and full system. Plugs were changed to new NGK platinum plugs and oil used was 15W50.


Any ideas. The dyno was the same one. And runs were about 3 months apart.

 

Did you try a compression test at 178 and at 172?

 

Quick update
Anyway changed back to 10W40 today and timing was adjusted as it was off I was told. Also compression was 160-165-160-160.
Car feels better now.
2 questions, what would cause the timing to be off and would resetting the ECU harm the adjustment made to the dizzy position??. and secondly are the comp test figures good?