Modified seat position

[Classy]

I am deep in the planning stages of my V2 setup and one of the changes I am looking to make is to lower the roof line (yes cut up the chassis).

I am trying to find out how much head height to the bottom of the roof (wearing a helmet) and how much room is behind the seat for someone who is 6’1” or close to it.

I am looking at running a seat like this to have more of a F1 position in the car and allow me to hopefully chop off about 1 foot from the roof.

https://www.summitracing.com/parts/kir-32150kit

 

[Desert Sasqwatch]

That seat looks like it has more recline than most seats installed by builders. Obviously, with your upper torso being further back so are your shoulders too and your legs will extend further forward, so steering wheel position and pedal reach are something to include in your design.

But, to get to your question. At 6'3" with these seats installed, using about 1.5 inch butt padding (uncompressed):

https://www.jegs.com/i/JEGS/555/702266/10002/-1

On seat mounts at 2.0 inches above the frame rails with a 20ish degree layback, I have about a 1/2ish inch to the bottom of the halo - no helmet. The top of the seat just touches the X-brace at the b-pillar with a comfortable reach to the pedals.