New Best in 1/4 but slower MPH. Questions

[jlsnsw]

Well,
Ran at California Speedway today and got a new best, and on street tires to boot.

60' - 1.925 (sweet on street tires full pressure)
1/8 - 8.150
1/8 MPH - 89.35
1/4 - 12.63
1/4 - 110.24

Here is my question, and I think that I know the answer but want to get opinion. Why is my MPH so low with the following mods:

RPM Outlet CAI
2.8 Pulley
Predator Custom Pulley Tune (5 % rich)

Previously, with the 3.10 pulley I ran 12.8 at 112.5 with a 2.25 60 '.

My suspicion is tons of belt slippage above 3500 or 4000 rpms. I know that I got way more boost at lower RPMs compared to my 3.10 and that can account for the lower ET, but the slippage probably killed my MPH. Right?

Just wanted to see what everyone thought.

EDIT : Also, I am not getting anymore boost on my gauge then I did with my 3.10 pulley. I gets to about where 12lbs should be and sits there. I got the same amount with my 3.10. That is why I think I am getting tons of slip.

Thanks.

 

[Venomized281]

It could be due to traction since you have more torque now. With no traction, you don't have mph since you're just spinning. Correct me if I'm wrong.

 

[HAVEIGHT 13R]

Better 60 ft generally lower MPH, generally. I don't think with that setup you are having belt slip and belt slip isn't all bad, really if it were perfectly tight you would go through belts like no tomorrow I know!
Great pass and congrats on a new best!:rockon:

 

[jlsnsw]

ttt

 

[stevenscamaross]

Something is up. I trapped 112 with intake and exhaust on street tires at 2100 ft. :shrug: