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Exhaust Flex Joint required?


jaredperry

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Hello All,

 

I would like some feedback regarding an exhaust setup and what you would do about it.

 

Current set up is a CA18DET and I have a 3" v-band down pipe that goes into a 2 1/2" slip joint under the vehicle.  The exhaust then goes back into another slip joint (right before the rear subframe) and up into the rear subframe then out the rear.  There is a hanger on the rear portion for stability and flex or whatever. Currently there is no flex joint and only slip joint / exhaust clamps installed.

 

The car is lowered quite a bit and the suspension is pretty stiff, but I am still wondering if I should put in a flex joint...

 

Would you install a flex joint?

 

If you were to install a flex joint, where would you place it? Front? Rear?

 

Thanks, for your opinions!

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A flex joint is meant to eliminate vibration from the motor to the exhaust. It goes between the down pipe and the beginning of the exhaust pipe. If you have poly motor mounts dont bother, but if you're running stock rubber mounts I'd do it. The motor moves around a lot when it gets all wound up.

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An alternate would be to add rubber shock isolaters to the spot where the exhaust passes under the first chassis cross member.  This is the scheme that the RL411 uses to isolate its rigid piping from the exhaust manifold to the rear bumper.  A clamp and 2 rubber isolators between the clamp ends to suspend the pipe from the chassis

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I used one years back but after it internally came apart I simply removed it and hooked up the exhaust via flange. The difference is,,,well I haven't felt any. They were originally used for fwd cars to absorb the engine torque keeping the exhaust from clanking against anything. I don't really think you need one but like what StoffregenMotorspots said makes sense but just so you know they do create a lot of exhaust turbulance because of the ID ribbing/flex design make sure you get a stainless unit.

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You want to use a high quality stainless steel connector that should be smooth with no ID transition at all. no short cuts here. Mine works great, I have a rigid mounted 3" exhaust all the way back that is tight to the floor. Sounds awesome 

 

flexVband.jpg

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For me this harkens back to my childhood. I had a friend with a 59, Ford 4X4 that had the duel exhaust turned down just before the rear axle. Supposedly it broke up the sound wave so it wasn't as loud, but it also looked sick. Especially when he revved it and clouds of dust and leaves shot out from under the truck. Mine is just a nod to John Lupton's Big Red Brick and those memories.

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For mrethis harkens back to my childhood. I had a friend with a 59, Ford 4X4 that had the duel exhaust turned down just before the rear axle. Supposedly it broke up the sound wave so it wasn't as loud, but it also looked sick. Especially when he revved it and clouds of dust and leaves shot out from under the truck. Mine is just a nod to John Lupton's Bid Red Brick and those memories.

I turn the exit a bit as a nod to Laguna Seca. We'd have to beat the sound meter so we'd point the exhaust away from the side of the track that had the sound meter.

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What Mike means is: if you want flexible exhaust with the volume of large pipe, just use small pipes. I figure (4) 3/4" pipes per cylinder should be equivalent to a 3" exhaust. And it would look boss having 16 exhaust pipes out the ass of a Datsun.

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You would think so but not really. If you double the pipe diameter it will flow 4X as much not double. Four 3/4" pipes have a combined cross section of 1.7 square inches. A 3" diameter pipe has just over 7 square inches. A three inch pipe is way overkill even on a CA18DET. 

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I like the way you think Tr8er.

 

Actually 3/4" Pi r2 = 1.17 Sq in. The doubling factor for the area of a circle is a logarithm of multiplying the diameter by a factor of 1.4 So 3/4" pipe X 1.4 = 1.05 x1.4 = 1.47 X 1.4 = 2.058" Pi r2 = 4.7 Sq in. 4.7 divided by 4 = 1.17

A CA18DET needs no back pressure, so unless it's too small, size is irrelevant. With a turbo you want to minimize the pressure downstream of the turbine in order to get the most out of the pressure generated upstream. This upstream pressure is what drives the turbine. Everything passed that you want to get it TFO. There is no such thing as too big, because it has no effect on performance, but does make for a louder exhaust note.

Calculating the appropriate exhaust diameter for a turbo motor has nothing to do with displacement, rather it is the HP being produced that dictates what size. At 250 hp, 2.5" is fine, 300 hp and you're definitely suboptimal with 2.5"

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Picasa, Jacob turned me on to them, they are easy to use on Ratsun, at least easy to use on my desktop with Chrome.

I have had Picasa for a few years now, I do a lot of photos, well at least I used to, I have used about 25 percent of my storage, and I have never even seen a bandwidth warning from them, but before I quit loading photos into Photolame, I was getting bandwidth warnings all the time, but I was at only 10 percent storage capacity, but I was at 75 percent plus bandwidth capacity.

I did not close Photolame, I just quit loading and posting photos from them, about once a month I log on and I post a photo from them to keep it active, even though that might not be how that works, it might have something to do with how many views it has, once you get no views for a certain amount of time, it may automatically close the account.

I just upgraded 5 minutes ago. They had me, I had to do it. Bastards.

 

What do you use?

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All kidding aside I actually use Photofuckit. I know it gets a bad rap, but It's been my go to for years. I can find an image on Google, upload it to PhoBuk and have it up on the Rat Trap in seconds. That being said I'm using a fast Mac, running OSX 10.95 and navigating with Chrome. Knock on wood, it's always been stable for me.

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