Car down power 6 mph help please

[white.t/a.96]

Put my old motor in my brother car.. Down 6 mph.

Motor went 7.237 @93 11.475@114 in my car at 3400. Put motor ,trans, stall ,headers, y pipe and tune in brother car been 7. 85@86 12.46@ 107. His weighs 3570.

My car had 3.73 his has 4.10. Which should help the diffence in weight.
We been fighting this a year now seem.
We have swap stall and trans 3600 to 4500 no help just 60' better. Checked fuel pressure 43 psi at wot. Changed plug wires. Running tr6 which are clean. I have changed tunes locked out timing etc no help. added/ pulled timing no help.changed map and tps. Which they look good in Logs. Nothing in logs coming up odd. Did leak down test come back normal. Compression test was good. We have swapped out opti few times. Valve lash is at 1/2 turn. Swap different Cold air intake no help


Oh motor info is
Ported head flow 260
Cam Le 228/236
Ported intake
Other normal stuff


In my car at same weight with cam only cc305 that motor went 7.79@ 87.

This car has made roughly 60 pass and stay the same.

Any help.. Please!! My brother so upset. I thought he was gonna cry other night he was so pissed at car.


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[blackbirdws6]

MPH is down quite a bit but couple thoughts are if you confirmed A/F and no leaks in the system (exhaust, headers,etc). I see you checked plugs and those looked clean but perhaps the tune is just oddly off between both cars.

[BALLSS]

what are the comparable 60' times between the 2 cars with that motor?

same rear tire type/size for both cars?