I used the Jansen P12 Track Package.
Learn to drift the car slightly as you corner, as it helps conserve your boost. Also the art of Blipping your boost at the right time, will length the time you can go between stunts.
Starting at the Stunt run in the intersection of South Bay Expressway and S. Mountain Drive. Head North and hang a right onto Casey Pass, hit the jump that is under the right side of the Crane. This will drive you through a few jumps and crash your first Billboard. Keep blipping the Boost as you go. As you cross Casey Pass, boost over the Super Jump (Dam), and head towards the right. Come up onto Manners Ave, and head right (East).
Coming up on your right is a Bill Board. You won't be able to get it from this direction. Take the Shortcut (Tunnel) under the Bill Board and blip the Boost through the tunnel. At the End, pull a 180, and blip the Boost back through the tunnel, hitting the Boost at the end to catch the Billboard. Pull another 180 and head back through the tunnel. When you hit S. Rouse Drive, pull a 180 and head West towards the South Bay Expressway Bridge. Blip the Boost up the hill , and hit the frst Super Jump on the Bridge. Skip the next jump (the Billboards) and hit the Second Super Jump. Pull a 180 (you'll be back at the starting point) and head back across the Bridge, hitting the Middle Jump set and picking up the Two Billboards above the bridge. At the end of the bridge, there is a shortcut to your right that has two choices. Take the left choice across the top of the shipping containers. It has two drops, and you get a ramp to hit a billboard. Land from that Billboard, and pull a 180. Blip the boost up the hill back towards the bridge.
Pull a 180 as you hit the top of the hill, (just before entering the birdge again) and aim for the right side of that shortcut across the top of the Containers. There is one drop, then a ramp through a billboard. A Super Jump and then two ramp jumps. At the end of this, you land back on road level, and immediately on your right is a ramp up to a billboard. From that billboard, you'll head through the Aircraft carrier. Keep blipping the boost, as you shoot by the gas tanks. And over a few small jumps. This is a super Jump across the bay. As you pop up from this shortcut, you'll see a shortcut on your right, this leads you back to Manners Ave.
There is a Billboard on your left, up a ramp. I didn't grab this one, as I've often screwed the jump up trying to get it. I went right, and headed towards the billboard on the right in the Wharf building. Hit that billboard, slip through the building on your right and hang (drift!) a right onto Harber Street. As you pass Fry Ave. there is a set of stairs on your left. Take these, and hit the Billboard at the end, dropping you back down onto Harber st.
Careful use of the Boost blipping, will bring you around to Webster Ave. You'll shoot right by a billboard in the middle of the street. Pull a 180 after it, and boost up the ramp to get it on the median. Pull another 180 and head North on Webster. Using the Median jumps and judicious use of the Boost blipping, you can pick up the two billboards in the median of Webster ave. Immediately after hitting the second one, hang a right onto 4th st. headed East. Drift the intersection onto Angus Wharf, and head through the Fuel stop.
Blip the throttle, and as soon as you go over the Green Arched steel bridge, head right into a shortcut, picking up two more billboards over two jumps. The shortcut splits, so take the one on the left, as it has two jumps that help conserve and increase boost. This dumps you out at the Coast Guard station, on E. Crawford Drive. Blip the boost through there and head right, dropping down onto the boardwalk. Take this jump and you land on Big Surf Beach. If you're confident, hit the Barrel Roll and then the next jumps getting you back up onto E. Crawford Drive. Skip the Super jump into the building under construction in the Middle of E. Crawford Drive, as you won't have enough speed. Go right around the building and take the ramp on your right through the billboard, dropping you down onto the boardwalk. Hit the Super Jump over the building, and then hit the next jump on your left to pop back up onto E. Crawford Drive. Immediately, take a left onto Hamilton Ave. Go immediately right into a shortcut and skip the short jump, instead aiming for the super jump up onto I-88.
Pull a 180 in front of the toll booth and head back East on the correct side of the highway. You'll be able to pick up a super jump immediately on your left, which will drop you into oncoming traffic. The edge of I-88 (on the left) has sawhorses on it, and you can hit a billboard right there, dropping you back down under the highway. Pull a 180 and head south on the railroad tracks. As you blip the boost, take the middle of the tracks jump and pick up the billboard right there. You can hit the next set of jumps and increase boost. There is another ump where you land onto of a few railroad cars, and hit another billboard. Boost through that, and hit the next Super Jump in the middle of the Tracks.
I ended here, as I was over 5,000,000 points. Total was 5,050,920 points. If I recall correctly, it was 49x bonus at that time.
morning edit
Blip the throttle, and as soon as you go over the Green Arched steel bridge, head right into a shortcut, CRASH picking up two more billboards over two jumps. The shortcut splits, so take the one on the left, as it has two jumps that help conserve and increase boost. This dumps you out at the Coast Guard station, on E. Crawford Drive.
I gave a test run last night, and I crashed entering the first jump. At this point, I was at 37x multiplier. I'll have a look at another Stunt run later tonight and post another run, if I have the time.
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. Is the DLC region free? Or there's no hope for me to get the legendary cars (why oh why didn't Sony put Indonesia as one of the countrys in PSN 👎)?
, the game seems to decide to always stop chaining after 18 chains 
) with the SI-7, works a treat with stunt runs in the city, but with ones in White Mt. I can't get to the I-88 quick enough. Any tips/suggestions?
...Keep the window open guys 👍.
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. What a difference a car makes to showtime! I used the WTR like you said and I never have to restart more than twice to beat the records. I even reached a 13x multiplier once 
. To get the 40x multiplier in Stunt Run I also used the P12 Track Package. I got the award after 3 tries 👍. I combined a few of your stunt runs write up with my own route and that gives me enough multipliers 
. Contrary to what you're saying though, I don't find them twitchy or nervous at all. They have lots of grip, yes, but still manageable. I find the normal WTR to be twitchier than all of the toys personally. The Legendary Cars are less impressive to be honest, I was expecting more from them. The P12 88 is by far my favourite (just because it can hover), followed by the Nighthawk (because of its retractable spoiler) then the Bootlegger (the horn is one of the most iconic sounds ever). The Manhattan Spirit is pointless IMO. I've also downloaded the Boost Specials. They're good, but still not better than the Toys. The Hawker Mech allows you to switch between Stunt, Speed and Aggression boost types, but I don't find it that useful because I always stick to Stunt boost most of the time (the Stunt boost bar is shorter also, dunno why). And the Extreme Hot Rod, once you engage the boost, will continue to boost until you wreck, which makes it completely useless except in straights. I also downloaded the Party Pack, but I haven't tried it yet. Should be fun though, from the looks of it.
