EXCLUSIVE

Paul Walker's entire body was charred through the skin it was burned so badly ... this according to the autopsy ... burned so bad none of his organs were suitable for donation.

According to the report ... obtained by TMZ ... Walker's body was laying supine in the passenger seat in a "pugilistic stance" -- that's a defensive position, as if he were bracing himself for impact.

He had multiple fractures throughout his body, including his jaw, collarbone, and left upper arm. There were also various ribs and pelvic fractures.

The report concludes Walker died from "combined effects of traumatic and thermal injuries" sustained from the Nov. 30 crash in Santa Clarita, CA.

According to the report, the L.A. County Coroner is preserving portions of Paul's organs in a jar -- sources tell us tissues are kept for a certain period of time in case of lawsuits.

Roger Rodas -- the driver -- suffered major head trauma with the top portion of his skull fractured and his brain exposed.

No alcohol or drug traces were found in either body.

The report also says there was "scant soot in Walker's trachea" -- suggesting he took a few breaths after impact. Sources close to the investigation, however, tell TMZ, they believe both men died almost immediately.

And the report goes on ... Paul had 14% carbon monoxide saturation in his blood stream ... the normal level is 2%. Roger had 10%.

According to the report ... after impact the car spun 180 degrees, struck a tree and nearly tore in half before exploding in flames.