Roush 427r only made 400whp :(

[ssqpolo]

I have the 14" oval. I'll have to check exact specs. Per backdraft website it's a 14" with k&n filter

[itstock]

You should be fine with that filter.

I would definitely make sure your carb is going wot. It's the easiest thing to check and is a proven problem on the backdrafts.

[ha_pe_1968]

Hi!
Have the same engine like you in a SPF.
Roush rated it at 548 HP (flywheel) with dual plane intake and 870 Avenger.
On a Mustang dynameter the result was more or less 450 RW HP. Take
a look at my Gallery the sheet is there. It is with stock SPF pipes and headers.
Have changed some years later to a Quickfuel cause i had Problems with my Holley.
I feel no difference in max. Power, but the Response is faster. Timing and Timing curve is optimized too. This Sumer i will investigate
additional time for carb Tuning.
If there are missing 50 HP i do not believe that a carb swap will bring the result - if the
Avenger is tuned right it will be not a miserable one - and believe me without Tuning a new carb will not work correct.
So in any case i would first check the Timing, the Timing curve...then optimize the existing carb and then you will have a solid base.

Wish you a great day!
Peter