Today we baselined my 2008 AWD Sierra Denali. Kooks catted 1.75" long tube headers. We then took those off and installed a set of American Racing headers catted 1.875" and re-dynoed it. The results are surprising.



Jeff

LMT

 

Wow, so no power difference. I assume the graph with the lost low end is with the bigger primaries.

 

It makes more power down low with the 1-7/8 and basically the same up top.

 

WOW thats crazy

 

This proves again more exhaust is not always better.

 

You positive? I would have thought the smaller diameter would have kept velocity up and improved scavenging at lower rpms. I lost a good amount of low end going from manifolds to LT's.

 

That is crazy, I have seen so many different dyno sheets between the battle of 1.75 vs 1.875" primaries its not even funny....every single vehicle responds so differently. Nevertheless, thanks for reporting the results!

 

Very easy to say yes I'm positive on the results. I made the Dyno pulls on my Dyno. I'm quite positive on the 4 pulls I made with both sets of headers. The proof is in the graphs. I gain nothing by posting the results. We took my kooks headers off. Installed the ARH headers. And reinstalled my kooks for the soul purpose to see the difference.

Jeff

 

Looks to me the 1 7/8 made more power in the midrange.... And this is with out any adjustments to the VVT

 

No this in my truck. It's tuned. Zero changes made. Only change between pulls is the headers only