RIP

The sports car Paul Walker died in was so gnarly to drive ... Porsche WARNED its dealers, in writing, about letting just anyone drive the vehicle ... because it's hyper sensitive to road conditions.

TMZ obtained a copy of a memo sent from Porsche HQ to multiple dealers in the Midwest back in 2004 ... right before the $500K Carrera GT went on sale -- and it explains how ridiculously powerful the car is, but also that ... "this vehicle cannot drive over a Foster Beer can that is lying on its side."

In the doc, a Porsche exec says, "You need to be aware of what type of road surface you are on (dips; pot holes, seam heights, etc.)"

It's worth noting ... the road where Paul and Roger Rodas crashed is covered with reflective dots -- y'know, the ones you've probably driven over harmlessly thousands of times. Of course, you probably weren't driving the GT ... which some pro drivers have called "brutal and savage" and difficult to control.

Police are still investigating the exact cause of the accident, and, so far, have only said speed was a factor.

The exec's memo explains the GT is damn close to being a real deal racecar, but adds ... "This car has all the disadvantages of a racecar."

10:45 PM PT -- Vin Diesel just spoke to fans at the crash site. Right after the private memorial ended, fans were allowed back to the area ... and Walker's co-star and friend got on a patrol car loudspeaker to say, "Thank you for coming down here and showing that angel up in heaven how much you appreciated him."

Cops just cleared Paul Walker's fans and all media from the crash site ... in order to prepare for a private family memorial ... TMZ has learned.

Thousands of Walker's fans have been gathering on the site since Saturday afternoon to pay their respects -- but moments ago sheriff's deputies dispersed the crowd ... as well as all reporters and photographers.

A source close to Paul and Roger Rodas tells us the families just wanted some private time to mourn while visiting the site of the tragedy.

The high speed crash that killed Paul Walker and Roger Rodas caused a huge explosion and fireball that could be seen for miles ... and it was all recorded on a security camera that captured the precise moment of impact.

The footage was recorded from a rooftop camera in an industrial park next to the crash site. It shows the initial collision (on the right of the screen) which caused the Porsche to explode in flames ... moments before another, larger blast sends a fireball high into the sky.

What's also interesting -- there appears to be no other cars either immediately in front of or behind the Porsche at the time of the crash.

Paul Walker liked his cars fast fast fast -- in fact, he once boasted about hitting a top speed of 185 MPH -- and it wasn't on a racetrack ... it was on a freeway.

"The Fast & The Furious" star -- who died in a fiery car crash on Saturday -- made the revelation on GTChannel back in 2011 ... while taking a Nissan GT-R out for a test spin in Japan.

"The fastest I've ever gone is 184 to 186," Walker says on the video .... and then he reveals how fast he was clocked on an actual racetrack.

Paul Walker's father Paul Walker Sr. could barely keep himself together today in L.A., claiming the entire Walker family has been struggling to cope with the actor's sudden death.

Paul addressed the media outside his home, saying he's never experienced anything like this in his life. "It's hard ... every now and then I'll really break down."

And the rest of the Walker family isn't any better -- Paul's dad says the actor's 15-year-old daughter Meadow has been taking it really hard, but thankfully ... she's surrounded by family and friends who love her.

RZA -- the leader of the Wu-Tang Clan -- paid tribute to his friend and former movie co-star Paul Walker with a new song ... and it's incredibly emotional.

RZA -- who worked with Paul on a film called "Brick Mansion" -- posted the tribute song called "Destiny Bends" online Sunday night ... and says he wrote it with singer Will Wells after hearing the tragic death news.

In the song, performed by Wells, RZA reflects on the time they shared together and thanks Paul for his friendship.

"On that highway to Heaven, you will drive in the wind and surf in the seas .. oh how can this be?"

RZA says he made the tribute because, "Millions of people get to know an artist or movie star through their work, but few are allowed to cross each others' paths and see through the veil of stardom and find the common denominator that we share."

The site where Paul Walker died has become a danger zone ... with some fans paying tribute to the actor by doing dangerous burn-outs, donuts and other high speed stunts -- and now cops tell us they're cracking down before someone else gets hurt.

In fact, one our of own TMZ producers personally witnessed the exhibitions of speed at the crash site -- people roll up, burn rubber, and peel out in an effort to pay tribute to the late "Fast and the Furious" star.

The producer of the movie Paul Walker was shooting when he died says production is on hold right now ... telling TMZ there are more important things to worry about.

Neal Moritz -- who's produced all the "Fast & Furious" movies -- is currently shooting "F&F7" and, as TMZ reported, the film was scheduled to resume shooting key scenes with Walker this week in Atlanta.

This is the dramatic moment when a cop had to physically wrestle one of Paul Walker's friends away from the crash scene ... seconds after it became clear Paul could not be saved.

TMZ broke the story ... Paul's friends rushed to the scene -- one even grabbed a fire extinguisher and desperately tried to extinguish the flames.

When the fire dept. arrived they tried to pull Paul's friends away. One of Paul's longtime friends, a guy named Nute, was so overwrought with emotion, he punched a firefighter. We're told Sheriff's deputies put Nute -- and several other of Paul's friends -- in custody, but let them go when they realized the circumstances.

Cops now believe Paul and the driver of the Porsche may have been in a street race with another car at the time of the crash and are looking for footage and witnesses.

Cops are investigating the possibility that Paul Walker was in the middle of a high-speed street race with another car at the time he crashed and died this weekend ... TMZ has learned.

Law enforcement sources tell us ... investigators have received tips that Walker and the man driving the Porsche, Roger Rodas, had been racing prior to the crash ... and the high speed may have contributed to the wreck that killed both men.

Sources say ... the area where the crash occurred has a history of being a popular street racing location.

We're told cops are on the hunt for video and witnesses that could prove another car was involved.

The exotic sports car in which Paul Walker violently died, crashed as a result of mechanical failure -- very possibly a steering fluid leak ... this according to sources closely tied to the auto shop where the vehicle was stored and maintained.

Sources connected to Always Evolving -- the shop co-owned by Walker and the Porsche driver Roger Rodas -- tell TMZ they saw evidence of a fluid burst and subsequent fluid trail before the skid marks at the accident scene.

The AE sources point to the fact there is a noticeable absence of skid marks until just before the point of impact. They say if Roger had lost control the skid marks would show swerving, but instead the marks were in a straight line. They feel this cements the theory the driver didn't have steering control.

Also suspicious -- the fire spreading so quickly in the front of the car. The sources say flames would be expected in the rear where the engine is ... but fire in the front reinforces their theory of a fluid leak of some sort.

We're told the $500,000 Carrera GT was NOT modified and was driven rarely so they believe any failure must be a factory defect.

Paul Walker fans have been heading to Valencia, CA in droves ... building out a massive vigil for the actor on the spot where he died.

Fans began to gather literally hours after the fatal crash on Saturday evening ... and by Sunday night, the memorial had grown exponentially ... with hundreds of flowers, candles, photos trinkets and letters.

As we previously reported, Walker's "Fast and the Furious" co-star Tyrese Gibson visited the crash scene yesterday ... and broke down crying when he arrived.

Matt Damon finally said what everyone in Hollywood has been thinking -- Paul Walker's death is "f**king horrible."

Damon was arriving at LAX with his wife yesterday when he was asked about the tragedy involving the "Fast and the Furious" actor ... and was as brutally honest as he could be.

Damon said the two knew each other -- though it's unclear how well. It doesn't appear the two ever worked together.

Still, Damon's words couldn't ring more true -- Walker was known around town as one of the nicest guys in the biz ... and was attending a charity event at the time of the fatal crash.

Paul Walker may not have ever gotten into the car that took him to his death if it hadn't been acting up moments before the crash ... TMZ has learned.

Paul showed up Saturday for a fundraiser at Always Evolving -- Roger Rodas' high end auto shop that specializes in exotic cars. Paul had a stake in the shop.

Sources connected to Roger tell TMZ when Paul arrived ... Roger was watching one of his employees try in vain to back the Carrera GT into the shop, but it kept stalling. Roger decided to take matters into his own hands ... told the worker to get out and took the wheel himself.

As Roger began to back into the garage ... Paul came up and said he hadn't driven in the Porsche yet -- so he jumped in the passenger seat and they took a 20 minute drive.

The fatal accident happened on the way back from that drive -- just 500 yards from the shop.

Paul's best friend from childhood, Nute, grabbed a fire extinguisher and was among the first to arrive on scene. We're told Nute frantically tried to extinguish the flames ... even though it appeared to him both men were already dead.

Tyrese Gibson was overcome with grief Sunday afternoon when he showed up to the crash site where his "Fast and Furious" co-star Paul Walker died less than 24 hours before.

Tyrese paid tribute to Walker during a quick stop at the Santa Clarita crash spot moments ago ... the same place fans are leaving tons of flowers and various tokens in honor of Walker.

Gibson is clearly falling apart while visiting the death site ... and everyone around him is completely silent while he mourns.

3:00 PM PST -- Tyrese took a piece of the crash wreckage home with him and posted a pic of it online afterward.

Paul Walker's daughter does NOT have a public social media page ... and his reps have already shut down one site run by an impostor.

Multiple news outlets posted stories Sunday morning saying Paul's 15-year-old Meadow Walker -- pictured above with her dad back in June -- paid tribute the actor on her Facebook page after the crash ... only problem, it's run by a fake.